| ChocoHolic |
Hi Guys and Ladies!
Somehow I am not getting lucky with my PSU concept for my subs.
I planned to design a SMPS which would allow universal AC input and additional 12V car battery supply.
The part which makes me thinking is the line SMPS.
First I planned a PFC-Boost + Halfbridge Forward Converter.
With my lower power requirements (600W max. / 150W average), I started thinking about an Flyback, which would allow a simple single stage design.
BUT :
No matter which topology I choose there are several drawbacks already in theory.
-The safety standard EN 60065 (Table 11) would require enormous creepage distances for reinforced isolation. Safety class II is a must for me as I do not want to have a mandatory earth connection.
In case of a flyback I would end up in a minimum creepage of
12.6mm and in case of PFC-Boost + Halfbridge around 10mm.
...values which make a suitful small sized transformer difficult...
The leakage inductance for the flyback is critical anyway.
BTW: I found some cut core material, which can handle high
flux and HF operation (pic...).
-EMI filtering:
a) I would need massive X-Filtering.
b) To avoid HF-noise on audio signal ground, there would probably the need of screening layers in the trafo in order to catch the capacitive leaking currents from the fast switched high voltages.
Size and weight of all this will be at least the same like a 250VA torroid. :bawling:
I will need large caps ( 2F ) for the 12V battery supply anyway.
Coming from this it looks quite reasonable to use a simple 120V/240V ==> 10V torroid and a rectifyer instead of all the trouble above.
2F caps will lead to an acceptable low rippled 12V supply and
a traditional regulated push pull SMPS should then give stable
+/- 50V rails for the amp itself (or any other desired voltage).
So in my application the only remaining advantage of the
line-SMPS seems to be the possibility to draw sinusodial currents from the mains.... hm, who cares at such low power !!
What do you think?
:xeye: :xeye: :xeye: :xeye: |
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| Eva |
Don't let outrageous safety regulations pi$$ you off. They were written just for that purpose, in order to help big companies to monopolize SMPS development (and EMC actually states for 'Eliminate Minor Competitors').
Have you ever seen a 50Hz standard toroid with three layers of mylar tape between primary and secondary windings? or even with a faraday shield? No! Most of them use a single layer of a low quality non-adhesive tape with some overlapping, that melts at approx 90ºC. Furthermore, they suffer from high primary to secondary leakage currents due to thin insulation and huge capacitance, so earthing is always required. They don't met any leakage specification, most brand-new big toroids will shock you if you touch any wire from the 'isolated' secondary windings with your feet wet on the floor.
Have you ever seen a 50Hz 'EI' transformer witn 16mm or 10mm primary to secondary creepages? No! They use no creepages at all!
Everybody is using these 50Hz transformers without trouble and nobody is messing with their manufacturers.
I hope you got what I'm trying to explain.
PD: I use just 5mm creepages (2.5mm per layer) and some plastic tubing for my SMPS transformers, and this already makes them *far safer* than most 50Hz ones. Earthing is a must anyway. |
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| Danko |
| What connect you to the wall socket's earth on the SMPS? Where do you connect it? To the heatsink? |
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| ChocoHolic |
Hi Eva!
Thanks for the clear words. And I believe that there are
many 50Hz trafos out in the field that have poor isolation, even
if you pick a certified one.
Sometimes it seems to be sufficient that the trafo just passes the
4kV isolation test, to get a safety certification.
I only wound off one E-core-trafo, 15 years back. And that one had triple isolation layers between primary and secondary. The creepages would have been to small from what I would expect, even when I take into account that for a 230V standard transformer 5mm should be sufficient. But that transformer also had a shielding layer to be connected to ground and with this I expect that basis isolation would do in that particular case and so half of the creepage would be OK.
The inconvinient high requirements for the creepage in my SMPS are resulting from the fact that the RMS and/or DC values (that's the criteria according EN60065) in my boost converter would be 480V compared to 230V in a standard 50Hz torroid....
With regard to EMI, I feel that a shielding layer in a 50Hz trafo is less important than in a SMPS. The SMPS has high voltages and excessive du/dt typically ranging between 100V/µs .... 10kV/µs, while a 50Hz trafo operates with 0.1V/µs .
Do you really always ground all components?
One of the earliest reasons for humm that I discovered were ground
loops between the power plug and antenna...
In the beginning I simply decoupled the antenna shield.
Since some years I decided to change to class II designs for my DIY projects... ...and up to now I am quite lucky with that...
Many HiFi manufacturers have done this step, too.
Just N & L at the mains plug, no earth.
Danko, I guess your question is also answered above.
For my shieldings I planned a pseudo EMI-earth formed by
two Y-caps between L&N. The center tap of these both
would have been connected to the shielding. Shielding
would be inside the SMPS trafo, between primary & secondary.
And around the entire SMPS unit .
Attached a picture of my first winding trial for the flyback solution. 6mm margin tape on each side ==> with the additional
thickness of the isolation between prim/sec, I would get around
13mm creepage... The wires are isolated with a shrinking sleeve, which gives 0.6mm isolating wall thickness.
This design did not have interleafed prim/sec and the leakage
inductance was around 7µH. Not funny if you go for a flyback with
20A peak in case of 120V/AC.....
Even with interleafed construction, I guess still half of it will remain.
And I would have to consider the inductance of the rectifier loop on the secondary. Let's guess around 10nH, resulting on reflected 2µH on the primary side (Trafo: 15 turns : 1 turn).
BTW:
Now I am between the seats. Yesterday I was tending more
to the simple way.
Now .... :xeye: |
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| ChocoHolic |
...uhps, I forgot to say, that the pic only shows the primary and the
zero-detection-winding.
Then a triple isolation followed, which can be seen in the pic of my first post. And the secondary for measuring the leakage inductance was a
copper foil, full winding width and 0.3mm thickness. |
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| mzzj |
| quote: | Originally posted by Eva
Don't let outrageous safety regulations pi$$ you off. They were written just for that purpose, in order to help big companies to monopolize SMPS development (and EMC actually states for 'Eliminate Minor Competitors').
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Have you checked that you have right medication? :eek:
I have put couple of small E-trannies apart, and yes they seem to fullfill creepage distance requirements with rather clever structure. Not so much experience from toroids as they are pain in *** to rewind, but that one what i put in pieces was insulated with 15mm wide mylar strip, with 2/3 parts overlap so efectively 3 layers of insulation. Or check almost any chinese piece of sith ATX power supply to pieces, there is at least 6mm creepage distance(wich is enough if primary and secondary sides are grounded?)
Recently i tested all of my junkbox trafos with 5kV ac hipot, all passed without breaktrough. Some of bigger toroids were quite high on leakage, something like 10mA at 5kV, but thats ok. Some double insulated potted E-core was superior to anything else, 0.2mA . |
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| mzzj |
Forgot to mention that toroids are usually? only class-I approved so you need grounding of primary side also.
Edit: and with little extra money Class-II |
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| Lars Clausen |
EVA: I think you should be very careful to encourage people to ignore safety regulations. These voltages can be dangerous, so i think Chokoholic's respect for EN60022 (safety for IT equipment) is very well considered.
Chocoholic: Have you thought about a resonance mode push pull converter? IME they are suitable for high power jobs. But forget the 12 V input to the same converter, you will have too much copper on your main transformer. Make 2 separate converters and join them on the secondary side. |
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| jackinnj |
| quote: | Originally posted by Eva
Don't let outrageous safety regulations pi$$ you off. They were written just for that purpose, in order to help big companies to monopolize SMPS development (and EMC actually states for 'Eliminate Minor Competitors'). |
All you Greens should look at it this way -- any noise created by an SMPS is wasted energy.
I am sure that GE, Siemens and Phillips would recommend that their CAT scanners be situated near unshielded ATX power supplies. |
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| Eva |
Oh, it's always very healthy to have some safety regulations, but something is going terribly wrong when they are routinely ignored for certain classic applications and by big companies without nobody complaining. I have to go now but I will put some examples later.
Same goes for emission and susceptibility regulations, it's healthy to have regulations but something is going terribly wrong when no small company can afford costly though simple approval procedures and they are not allowed to certify equipment by its own, thus then can't develop and sell switching equipment, even though they may actually met regulations.
Anyway, I think that Chocoholic got the point. |
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| ChocoHolic |
| quote: | Originally posted by mzzj
Forgot to mention that toroids are usually? only class-I approved so you need grounding of primary side also.
Edit: and with little extra money Class-II |
I already had a look at the assortment from Buerklin,
they offer potted, magnetic shielded and class II suitable torroids
for around EUR 100,- for 250VA or 300VA.
But this does not look for me like a bargain and also their primary
is a single winding, suitable for 240V only....
| quote: | Originally posted by Lars Clausen
EVA: I think you should be very careful to encourage people to ignore safety regulations. These voltages can be dangerous, so i think Chokoholic's respect for EN60022 (safety for IT equipment) is very well considered.
Chocoholic: Have you thought about a resonance mode push pull converter? IME they are suitable for high power jobs. But forget the 12 V input to the same converter, you will have too much copper on your main transformer. Make 2 separate converters and join them on the secondary side. |
Is there a reason why you consider EN 60022? During my search I came to the conclusion that EN60065 would be the perfect match, its title is definitely adressing to Audio-, Video- and similar electronic gear.
Don't worry, not even EVA could convince me to ignore the safety standards. She's got the typical southern relaxed position in this regard, and please note: She also implements 5mm creepage her designs.
I am more the accurate German. I don't mind to work with non isolated kVs. But after closing the casing, it must be baby save.
..."...forget the 12V input..."
Uhps, you calculated that I would get current peaks of 300A on my
primary right?
I agree, that 500W PFC-flyback from 120V....274V/AC to 12V/DC is
is crazy. And honestly speaking in the moment this fact would be the only reason for me to try.
With respect to size, weight etc., my clear brain would indicate a
50Hz transformer as the heavy Electrolytic caps for 12V are necessary anyway....
Resonance push pull converter:
Honestly speaking: No, I did not consider this up to now.
I considered a traditional PFC-boost converter followed by an
halfbridge which is switching to an transformer with reasonable leakage inductance to allow regulation of the +/-50V output.
But it's an two stage design. Furtheron it does not use the existing 2F energy storage, so I would need about 200µF/500V at the output of the boost converter......
:scratch1: |
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| mzzj |
| quote: | Originally posted by Eva
Oh, it's always very healthy to have some safety regulations, but something is going terribly wrong when they are routinely ignored for certain classic applications and by big companies without nobody complaining. I have to go now but I will put some examples later.
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Hmm, I Am intrested to hear about these, at least here at Finland local authorities are withdraving hundreds of products from markets every year nowadays(mostly chinese CE-****). Quality of electrical products has dropped dramatically in here after harmonised european safety regulations, maybe thanks to southern europeans :D
With Chinese pieces of **** it is enough that some underage slaveworker is sticking CE-stickers to their products and nobody is checking it for real. Then in here TUKES is doing some supprise test for products in market and quite often ordering importer to withdraw their s*it.
Ever seen cheap 6-20 euro multimeter like this? :D
http://www.tukes.fi/kuvat/myyntikie...040210-04_y.jpg
Have only 3.5mm creepage distances on PCB, reguired is 20mm for 1000V classII meters. Will explode before reaching 1kV :D |
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| ChocoHolic |
| quote: | Originally posted by Eva
Anyway, I think that Chocoholic got the point. |
I think I got it. "No need to be cleaner than the pope".
But safety ... I am not afraid about my own safety, because
I know what I am handling with.
But friends? Children? Or if I decide to sell the stuff in some years?
mzzj:
Don't you know the Chinese interpretation of CE?
"China Export."
Or about copyright?
"Copy's right."
...somehow I like these guys *lol* |
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| Ultima Thule |
Chocoholic,
I don't know but quite sure it's the same in Germany as in some other Northern european countries, you are NOT allowed to sell or even give away or let it be operated by others a design you have made in private that is not approved with the electrical safety regulations if it's going to be connected to the mains, so you don't have to worry about your friends etc. ;)
Flyback for 500W, you will have huge currents through the secondary diode, maybe upto 200 A peak... the problem with Flyback and high power is switchng losses.
BTW I was a bit puzzled LC mentioned EN 60022(eg. CISPR 22) when talking about electrical safety, its an EMC standard dealing with radiated and conducted emissions.
I think Choco got it right, heres a note of the exact versions to be used:
The last date for evaluation and production to EN60065:1998 is 1st March 2007, when it too will be superseded by EN60065:2002 (which will apply until further notice.
In general:
BTW, talking about creepage and clearance distances, when designing transformers for SMPS one must leave a distance towards the sidewalls of the coilformer, which means one have to put yhe winding layers without support from surrounding walls.
This have made me wondering for many years how we can trust such winding will stay in place.
Distance are needed because it prevent dielectric breakdown between electrodes caused by the ionization of air. The dielectric breakdown level is further influenced by relative humidity, temperature, and degree of pollution in the environment, so one have to also take into account the pollution degree.
Well, but theres a solution, one can always pour the transformer in a plastic pot which will give much smaller creepage and clearance distances, and there wont be any problem with the pollution degree class as in such case its the lowest.
However at least 3 layers between primary and secondary with a good tape and preferably a suitable glue/silicone between primary and secondary at the peripheral "winding package" in the coilformer(not inbetween the winding layers) will do a lot for DIY:ers.
Michael |
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| Kenshin |
How did cellphone chargers pass safty standards? The whole transformer in them have a size only less than 20mm. Also...laptop adaptors are small.
Maybe use some special insulation wire / material?
| quote: | Originally posted by ChocoHolic
-The safety standard EN 60065 (Table 11) would require enormous creepage distances for reinforced isolation. Safety class II is a must for me as I do not want to have a mandatory earth connection.
In case of a flyback I would end up in a minimum creepage of
12.6mm and in case of PFC-Boost + Halfbridge around 10mm.
...values which make a suitful small sized transformer difficult...
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| mzzj |
| quote: | Originally posted by Kenshin
How did cellphone chargers pass safty standards? The whole transformer in them have a size only less than 20mm. Also...laptop adaptors are small.
Maybe use some special insulation wire / material?
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Vacuum potting helps with creepage distances as you dont need to care about creepage in trafo after it is vacuum impegrnated in epoxy |
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| ChocoHolic |
Yes, but it is sometimes hard to pass the certification with vaccuum potted designs.
Typically the certification institute cuts the transformer into thin slices and if they find any bubble, you can go home and try another improvement to manufacture it really perfect.... ...experienced this in my old company and our vaccum potting was definitely not a poor potting !!!
Aside potting there are special wires and special bobbins. |
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| ChocoHolic |
| quote: | Originally posted by Ultima Thule
Chocoholic,
I don't know but quite sure it's the same in Germany as in some other Northern european countries, you are NOT allowed to sell or even give away or let it be operated by others a design you have made in private that is not approved with the electrical safety regulations if it's going to be connected to the mains, so you don't have to worry about your friends etc. ;)
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I am not a lawyer, but I thought you are allowed to give away or sell. But you will be responsible with your life for anything that might happen. If you ignore safety standards and something happens, then you are in trouble.
| quote: | Originally posted by Ultima Thule
In general:
BTW, talking about creepage and clearance distances, when designing transformers for SMPS one must leave a distance towards the sidewalls of the coilformer, which means one have to put yhe winding layers without support from surrounding walls.
This have made me wondering for many years how we can trust such winding will stay in place.
Michael |
The unused volume is often filled with 'margin tape'.
It is simply wound at the side wall, or can substitute the side wall if fixed properly. The isolation between the layers must extend throughout this margin tape (See my pics above).
Instead of margin tape there a special creepage spacers, which can be clipped on the bobbin.
If you are able to wind without margin tape or spacers, you ensure
that the windings will stay in place by a simple impregnation with varnish. Varnish also helps to reduce noise and improves humidity properties. |
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| Eva |
These are some evidences showing that safety standards are usually ignored in the equipment we routinely use in real life.
Most AT and ATX PC power supplies doesn't include any creepages in their transformers, altough their labels are loaded of approval symbols:
This one has CE marking...
But no creepages at all...
This one has a bunch of seals...
But no creepage at all...
This other one had also a lot of seals...
But it not only lacked creepage but its common-mode EMI filter was also missing! Note the jupered common-mode choke and absent capacitors:
mzzj you should check the PSU of your computer(s), you may have been using a unit without creepages for years without even knowing it, like most of us.
But, no doubt, where creepage is always mising is in 50Hz E-I mains transformers. I have still never seen a 50Hz transformer with creepage in my whole life, and these are the ones used in most commercial audio equipment and in most DIY projects.
This one is from my preamplifier, I bought it brand new in an electronics store some time ago:
No creepage at all...
This other one is an isolation transformer from a 12V 50W halogen lamp:
And concerning these toroid transformers that everybody uses for audio assuming they are absolutely safe...
These two pictures are from a 1000VA unit that suffered from an intermittent short between adjacent turns in one of the secondary windings. I stripped the secondary windings to further investigate the effects of overheating on insulation.
Note how the plastic tape (not mylar, maybe PVC?) has melt badly leaving primary-side and secondary-side magnet wires in direct contact far before the wires had any chance to overheat (temperature probably never exceeded 90ºC):
Also note how the insulating tape (and magnet wire enamel) is always badly stretched on the corners of 50Hz toroids, leaving a very thin insulation layer and increasing leakage dramatically:
Why are we not dead? We are still alive because creepage requirements are outrageous. Magnet wire enamel has usually over 3KV dielectric strenght (more like 5 or 7KV) and mylar tape also whitstands more than 3KV per layer. Furthermore, in order to start an arc between two needle shaped electrodes placed 5mm apart, more than 5KV are required, and this is the worst case, since 50KV or so would be required in order to start an arc between insulated round electrodes placed 5mm apart (like magnet wires).
This means that even a transformer without any creepage will pass flawlessly all classic '3,750V for 1 minute' insulation tests, it may even pass a 10KV or even 20KV test depending on construction.
This also means that any multimeter with 3.5mm creepage between +V and -V PCB tracks is probably going to reliably measure 2KV or even 4KV without PCB arcing, altough resistors will suffer breakdown with such high voltages. So in case any government decides to whitdraw them from the market, it would be actually for any reason other than objective reliability, probably economics and company fights.
(check this out as a refference http://www.kronjaeger.com/hv/hv/msr/spk/ )
Chocoholic:
Now try to figure out how much voltage is required to get an arc between two insulated magnet wires placed 10mm apart :D
And even though, I'm sticking to 5mm creepage, and this already makes my transformers far safer than most ones everybody is using for audio. Then again, does tube gear dealing with 480V use 10mm creepage? No, it doesn't, and their chasis isn't even earthed!
Anyway, as Ultima Thule mentioned, even if you build equipment following all safety regulations, if anybody (other than you) uses that equipemt, it will be a violation of law and you may be lawsuited and jailed. It won't matter if your equipment is objectively safe or not, what matters is that you have to pay dozens of thousands of euros to certification agencies in order for your equipment to be lawful. Nowadays safety is a question of money, not creepages, you must buy it.
kenshin:
I've just opened the off-line battery charger from my old Nokia 3210 phone. It's a self-oscillating flyback. It uses a special magnet wire with a very thick insulation for the secondary winding and standard magnet wire for the rest. Creepage is 5mm (total) and it's certified as a double insulated product. It doesn't have a primary-to-secondary common-mode shunting capacitor.
Safety regulations should be dictated by objective physics, not by economics, politicians and convenience. That's why production and design is progressively shifting towards China: Safety regulations in USA and Europe are dictated and strongly biased by big companies and by the own safety certification companies (these ones that charge you 30.000 euro for each approval), with the only purpose of preventing small companies from growing in order to avoid competence.
On the other hand, Chinese companies are free to grow in their country, until they can afford approval costs in order to enter our market. Ironically, their electronics market is free while ours is under a strong dictatorship. |
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| Eva |
kenshin:
Sorry, creepage in that Nokia charger is actually 4mm, I've taken some pictures:
Note the thick secondary wire...
Also note that the secondary is shifted 4mm from the primary connections and a small flux band is used to reduce the stray field created. Standard wire is used in the primary side.
Overall PCB view showing a 4mm spark-gap.
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| ChocoHolic |
Hi Eva,
I guess you are seeing our world a little bit to negative.
And please do me one favour: Do not trust normal enamelled wire for 3...4kV. Their specified breakdown voltage depends on the wire gauge
and - yes thicker wires are specified with some kV.
BUT these breakdown voltages are specified as spot test with five probes.
Now :D :D :D
From these five probes one is allowed fail and the test is still passed.
...dont't touch, I would recommend... :angel: :angel:
Further on for thin the wires are not treated in a rough manufacturing site, but carefully wrapped around a 40mm ( if I remember right) cylinder. Thicker wires are twisted for the test and two times enamel is between the opposite potentials.
Even if some of your pics are not very promising, this is no reason
to damn all safety regulations.
Did you ever work with 10kV or 20kV to estimate that even this could be handled with poor isolation?
In fact I got some respect vs 10kV and more after I had
a 6 month practice in an internal isolation testing dept. for
generators at ABB.
Well, back to my PSU.
I did some simple simulation and came to the conclusion that I would need a 12V transformer, not 9V.
First the schematic of the simulation. |
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| ChocoHolic |
Already a load of around 15W...20W will let the DC not exceed 15V...16V, which is fine for my E-caps (20V rated).
When drawing 40A it will sag down below 8V....
Well, the regulated push pull will have to work a lot.... |
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| ChocoHolic |
| quote: | Originally posted by Eva
Why are we not dead? We are still alive because creepage requirements are outrageous. Magnet wire enamel has usually over 3KV dielectric strenght (more like 5 or 7KV) and mylar tape also whitstands more than 3KV per layer. Furthermore, in order to start an arc between two needle shaped electrodes placed 5mm apart, more than 5KV are required, and this is the worst case, since 50KV or so would be required in order to start an arc between insulated round electrodes placed 5mm apart (like magnet wires).
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I guess 15kV would do the job for two round standard enamelled wires with 5mm distance.
| quote: | Originally posted by Eva
Chocoholic:
Now try to figure out how much voltage is required to get an arc between two insulated magnet wires placed 10mm apart :D
And even though, I'm sticking to 5mm creepage, and this already makes my transformers far safer than most ones everybody is using for audio. Then again, does tube gear dealing with 480V use 10mm creepage? No, it doesn't, and their chasis isn't even earthed!
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Yes, and some other chassis are connected to mains. Depending on the direction how you insert the mains plug, you can find pretty powerful stuff on your E-guitar, whenmodifying a old radio to an guitar amp.
But that's not my goal. |
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| ChocoHolic |
BTW:
...we should not mix up creepage and clearance...
Usually the required creepages are higher than the required clearances.
Creepage requirements depend very much on cleanness stepped in three categories. For my considerations I used category 2.
Furtheron creepages depend on the surface isolation properties of
the isolation material. For my considerations I assumed the lowest CTI.
Which means the poorest comparative tracking index. With the right material you would be allowed to go for half of the creepage.
So I could search for materials with CTI>600. |
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| Ultima Thule |
Who have mixed up between clearance and creepage distance, I dont think anybody have directly done so! | quote: | | Creepage requirements depend very much on cleanness stepped in three categories. For my considerations I used category 2. |
Category 2 of what? Material Group... Pollution Degree.... etc etc....
Where do you find out all CTI numbers for all materials you are going to use?
Eva:
Your Nokia phone charger, the first picture shows a "thick" yellowish wire, to me it looks like a "tripple insulated wire" which, if I got it right, use to be approved in acordance with the most common electrical safety standards, these type of wires is authorized as "Reinforced Insulation" and can be used directly on primary windings without any isolation.
For instance wire from Furukawa, (for a certain diameter and type as I have noticed), the dielectrical strength is upto around 25 kV.
About demanding electrical safety standards, creepage and clearance distances, it's normaly known in free air it takes 1 mm of distance to make 1 kV to flash-over(as Eva's link shows), the much greater distances specified in many standards are due to the air will be ionized, dust covering parts that will slowly convert to carbon when theres humidity and ionized air leading to creepage currrents, and by time there will be a flash-over or lead to creeping currents that will make the equipment malfunction.
My experiences are that these problems are existing when the equipment are working in harsh environments, some have failured due to dust and humidity/condense even if these demanding creepage and clerance distance have been fullfilled due to the convertion to carbon(not to forget some galvanic/electrolytic/chemical reactions happening when theres humidity and dust) leading to creepage currents.
Though, a quite seldom problem luckely.
However, the cost to get an approval are expensive for small players, unfortunately! :(
Michael |
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| Eva |
In my experience, that mix of ambient moisture and dust will end up creating a progressively conductive layer everywhere. No amount of clearance will solve that problem, it's only solved by properly protecting equipment against dust buildup.
| quote: |
However, the cost to get an approval are expensive for small players, unfortunately!
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Actually, approvals were invented to eliminate small players because they can grow and turn into competitors for old and well estabilished players. These costs are not fair at all but arbitrary.
That's why I'm puzzled everytime I see a 'small player' trusting and believing in approvals and safety regulations. It's like watching a small mouse heading directly to the mouth of a hungry cat (altough they are free to do that if they wish).
Chocoholic:
These regulations are not here to help you in any way or to improve safety (as the pictures show), they were made just to persuade you not to researsch, not to learn and not to develop switching equipment. And they appear to be doing their job quite well, I suppose. It's a pity, though. |
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| subwo1 |
| quote: | Originally posted by Ultima Thule
My experiences are that these problems are existing when the equipment are working in harsh environments, some have failured due to dust and humidity/condense even if these demanding creepage and clerance distance have been fullfilled due to the convertion to carbon(not to forget some galvanic/electrolytic/chemical reactions happening when theres humidity and dust) leading to creepage currents.
Though, a quite seldom problem luckely.
However, the cost to get an approval are expensive for small players, unfortunately! :(
Michael |
Indeed, arcing in television sets is a problem in dusty conditions where humidity is high. |
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| mzzj |
Eva, yeap, in here at finland we have those chinese pingpong atx power supplies also at market, TUKES(local authors) is withdrawing couple of models every year from market. Deer, IT-snälzth(IT-shcaisse) and Q-tec are worst **** of all time. I prefer brand names, namely Fortron-source. And yes, i have also opened my power supply, it is just fine as far as i can tell without hacksawing trafo to pieces. :D
Eva, I guess that your 5mm creepage is enough if your equipment is grounded, even according to some safety regulations. Double/reinforced insulation is much more demanding, as we saw from chokoholic.
Kenshin, I can confirm what others have said about those small smps units, triple insulated "abnormal looking" wire is used in them. |
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| Eva |
In my opinion, double insulation is a total overkill for high power applications. I think that power amplifiers are the piece in the audio chain that should be earthed.
On the other hand, double insulation (with as much creepages as desired) is very easy to implement in low power audio PSUs where size is not strongly limited. Any potential ground loop issue is easily solved by using differential inputs or outputs (or both) and star grounding (to force loop currents to follow a known path).
Also, I'm thinking about building my own insulation tester. I have some medium-size and big 50Hz iron-lamination cores that I can dismantle and rewind as 100:1, 200:1 or 500:1 step-up transformers (this time with gentle creepages and maybe some epoxy).
I could bet that those chinese transformers with no creepage doesn't break down until well above 5KV (there's no better way to know than testing).
Chocoholic:
I don't like your idea of stepping down mains to 12V through a conventional transformer and then stepping it up back to the voltages required by your amplifiers. It sounds bulky and quite inefficient to me.
I would prefer stepping up 12V (10..15V) to 300V (250..375V) in an unregulated way (simple, smaller and more efficient). That +300V bus may be also powered from rectified mains (skipping PFC stage since you seem not likely to enjoy the added complexity and you can't sell your equipment anyway). Bulk storage capacitors should be placed on that +300V bus (they are required for mains rectification anyway, and this already requires a lot of capacitance, furthermore 400V capacitors store more joules per euro in less space, and peak currents when using 12V power are dramatically reduced). And then, a full or half bridge regulated converter powered from the +300V bus would follow (preferably using IGBTs since their losses doesn't increase proportionally to I^2 like in MOSFETs but to I). |
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| mzzj |
| quote: | Originally posted by Eva
Also, I'm thinking about building my own insulation tester. I have some medium-size and big 50Hz iron-lamination cores that I can dismantle and rewind as 100:1, 200:1 or 500:1 step-up transformers (this time with gentle creepages and maybe some epoxy).
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Hint: look for used oil burner ignition transformers, 10kV (+-5kV center-tapped). Or neon light transformers. |
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| subwo1 |
| quote: | Originally posted by mzzj
Hint: look for used oil burner ignition transformers, 10kV (+-5kV center-tapped). Or neon light transformers. |
Could a flyback transformer work if the primary drive were adjusted to lower the voltage as needed? |
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| Eva |
| It would work but I want 50Hz AC. Anyway, I have remembered that someone gave me an old neon lighting transformer some time ago and I have just found it (under a pile of other scrap stuff). Should it be in good condition most of the work would be already done :) |
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| subwo1 |
| Sometimes things in those piles of old parts come in handy. I have numerous previously wound toroids, e-cores, etc. and various and sundry parts which I have accumulated. It is nice being able to maintain as much momentum as possible and not be delayed when trying out design ideas.:) |
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| mzzj |
Chocoholic, what do you use for "operating voltage" for half-bridge or flyback?
"— the actual r.m.s. or d.c. value shall be used;
— if the d.c. value is used, any superimposed ripple shall not be taken into account;"
Rms voltage of waveform at transformer primary?
And what pollution degree you use/assume? |
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| ChocoHolic |
| quote: | Originally posted by mzzj
Chocoholic, what do you use for "operating voltage" for half-bridge or flyback?
"— the actual r.m.s. or d.c. value shall be used;
— if the d.c. value is used, any superimposed ripple shall not be taken into account;"
Rms voltage of waveform at transformer primary?
And what pollution degree you use/assume? |
You are right.
For the flyback it would be sufficient to calculate the RMS value.
Even with the reflected voltage and leakage peak going up around 750V peak in worst case... the RMS value would remain around 450V, instead 600V that I had assumed.
For a boost topology I calculated 500V DC, as
my plans were considering a 480V DC rail.
So the isolation requirements would be pretty much the same in both topolgies .
My pollution degree was 2. Isn't that the common assumption for
non sealed indoor electronic equipment? |
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| ChocoHolic |
| quote: | Originally posted by Eva
Chocoholic:
I don't like your idea of stepping down mains to 12V through a conventional transformer and then stepping it up back to the voltages required by your amplifiers. It sounds bulky and quite inefficient to me.
I would prefer stepping up 12V (10..15V) to 300V (250..375V) in an unregulated way (simple, smaller and more efficient). That +300V bus may be also powered from rectified mains (skipping PFC stage since you seem not likely to enjoy the added complexity and you can't sell your equipment anyway). Bulk storage capacitors should be placed on that +300V bus (they are required for mains rectification anyway, and this already requires a lot of capacitance, furthermore 400V capacitors store more joules per euro in less space, and peak currents when using 12V power are dramatically reduced). And then, a full or half bridge regulated converter powered from the +300V bus would follow (preferably using IGBTs since their losses doesn't increase proportionally to I^2 like in MOSFETs but to I). |
I also do not really get a state of the art feeling....
:whazzat: :whazzat: :whazzat:
But it is perfectly simple and as the heavy 12V caps are existing anyway, because of the car supply option.... A single torroid + rectifier seems to come not heavier, not bulkier... , than my set up
with boost + halfbridge + proper filtering.
I could skip the boost, you are right. And go for a halfbridge converter only. But this solution would not be perfectly simple and also not perfectly state of the art. ... and less fortunate for 120V/230V... Somewhere inbetween.... hm....
Currently none of the solutions is really giving me the kick.
:sad: :sad:
From technical side the boost+halfbridge would be the best.
BTW: I already finished the stepped gap choke for the PFC. |
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| mzzj |
| quote: | Originally posted by ChocoHolic
My pollution degree was 2. Isn't that the common assumption for
non sealed indoor electronic equipment? |
Umm, guess so. Just got this standard to my hands today so I am not any sorta expert.
How about epoxy potting your trafo, then you could use pollution class 1 creepages and best CTI values?? No need for vacuum-potting tough as its only for against pollution
btw, I dont have any clue about different material CTI values because I dont have access to that xxxx standard where they are specified. Do you have this standard? I would be intrested to hear some examples.
:devilr: arrgh, would need tons of publications to cover just en60065 and its references |
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| ChocoHolic |
Sorry... I also don't have the CTI details. That's why I considered the worst. From what I know some FR4 PCB material offer CTI above 600.
May be also coated FR1 or CEM1? I don't know.
Also several high quality isolation tapes. But bobbins often are poor... |
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| ChocoHolic |
The stepped gap choke is a doubled EVD 36.
43 turns of 150x0.1 silk covered HF litz,
wound in three layers with interlayer isolation.
At low currents L=1.1mH.
At levels above 0.7A it changes to 330uH and remains stable
up to all area saturation at around 17A.
If heated to 100°C, this saturation may happen around 12A, which is
my worst case requirement at 120V.
...hm, somehow I am curious... |
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| ChocoHolic |
Sorry, I should mention:
White trace is the voltage across the choke: 100V/div
Coloured trace is the current through the choke: 5A/div |
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| ChocoHolic |
Eva:
Your Nokia phone charger, the first picture shows a "thick" yellowish wire, to me it looks like a "tripple insulated wire" which, if I got it right, use to be approved in acordance with the most common electrical safety standards, these type of wires is authorized as "Reinforced Insulation" and can be used directly on primary windings without any isolation.
For instance wire from Furukawa, (for a certain diameter and type as I have noticed), the dielectrical strength is upto around 25 kV.
Michael [/B][/QUOTE]
Yes, from my perception the pics of the Nokia charger did not look like poor isolation. Also they introduced cuts in the PCB to get the advantage of clearance vs. creepage.
The wire could definitely be the Furukawa TEX-E.
...25kV... well, the allowed dielectric strength is also a matter of frequency...
...coming poorer at higher frequencies. ...not only for the Furukawa wires, - this seems to affect most isolation materials. |
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| Eva |
This cut in the PCB of the battery charger was done on purpose. It has two small pointy electrodes (one on each side) spaced by 4mm, so an arc will jump if more than 5KV appear from primary to secondary side.
Nice choke, by the way. I have no access to litz wire nor triple insulated wire. Also, my core and bobbin selection is quite limited.
Actually, I had to look in German stores in order to find suitable stuff for my projects. I have bought cores and coils from Conrad Electronics, and heatsinks with mounting clips from Fischer.
I bet there is not much SMPS development in Spain. |
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| Kenshin |
50Hz transformers are not a good idea, too dangerous. A single transistor self-oscillating converter use old TV horizontal transformers (primary rewinded) could spark a several mm and output less than 1mA, powered by a single 1.2V battery.
The most easy way may be the spark thing in gas lighter, piezoelectric one could spark 5mm in free air, while big battery-powered one could achive more.
| quote: | Originally posted by Eva
Also, I'm thinking about building my own insulation tester. I have some medium-size and big 50Hz iron-lamination cores that I can dismantle and rewind as 100:1, 200:1 or 500:1 step-up transformers (this time with gentle creepages and maybe some epoxy).
I could bet that those chinese transformers with no creepage doesn't break down until well above 5KV (there's no better way to know than testing).
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| Eva |
kenshin:
I've been playing a bit with that neon lighting transformer that I found under a pile of stuff. It works fine and it's like new.
It sparks a bit more than 10mm between needles so no load voltage is probably between 10 and 15KV (obviously I can't use miltimeter here). Short-circuit current is 23mA. This is dangerous, it's just enough to shock somebody badly or kill him, but I'm pretty aware of the risks.
Note that these are special transformers with shunting rings on their cores that provide inherent current limiting, they work almost like current sources over a wide range of output voltages. I think that this feature is quite useful for insulation testing.
Bad news are that these units usually have their HV winding center-tapped to the chasis, but mine isnt :D , it's floating so I can referente one of the HV ends to ground in order to place a small resistor to measure leakage current.
I'll have to power it from lower voltages in order to get the desired no-load output voltage, though. Also I must get a high voltage probe. |
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| Kenshin |
About 50Hz transformers:
All small 50Hz EI transformers in my hand have primary & secondnary winded in seperated bobbin, "absolutly" safe creepage spacing. I have saw some big ones (>100W?) use unseperated bobbin with no side creepage, but they are very old things manufactured in 1970s.
I'm looking for seperated bobbin for SMPS but not found any, except common mode choke coils (something which is not for transformer use).
About PC SMPS:
I could see the wires in some PC SMPS main transformer from side, they have a distance ~ 2mm to the side of yellow tape. But PC is grounded equipment.
About phone charger & wires:
Some manufactures said on a Chinese SMPS design forum that their phone charger transformers passed 2.5KV hi-pot, the cost is 0.3 RMB (4 cents), it's a massive production price for >5 millions of products per year.
On the same forum I've heard some manufactures use triple insulation wire to wind their transformers. But it's relatively new things, not available to me. Could Teflon high temprature wire have the same safty voltage rating? These wires have more thicker plastic insulation layers. |
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| Eva |
'separated bobin' (split bobbin) transformers are not practical for SMPS since they show too high leakage inductances, neither they are practical for high VA 50Hz applications for the same reason.
Actually common-mode chokes are transformers, but leakage inductance is advantageous for these since it produces some degree of differential mode filtering. That's why split bobbins are employed. |
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| Kenshin |
I haven't begin any making work -- It's a project collaborating with my friend, he'll wind the transformer during vacation at home; and he could probably do vaccum potting in his father's factory.
I've bought two "100W" EI ferroite cores, my friend said that they are too small. He suggest to use a 200W core/bobin to wind a 100W transformer to leave enough spacing.
The secondnary will be winded with Teflon "high temprature" wires. The primary windings will be built thisway: put a layer of insulation tape per 2 to 3 layers of wires, leave 2mm creepage spacing on each side by folding the tapes back and block the wires (So the total creepage spacing is 4mm).
He said 10mm creepage spacing is too much, the biggest insulation risk is not breakdown to the secondnaries (almost impossible), but breakdown between primaries (this would possibly hapen and burn the SMPS). Besides, another friend said the quality is depended on building techniques instead of spacing.
Is 4mm creepage spacing + Teflon "high temprature wires"secondnary enough for equipment without grounding?
:confused:
The transformer will be test under 10KV after building, use a spark igniter.
About SMPS debugging: He suggest power the design directly from the mains: Wire up all probes and oscillocope before start, and stand away from anything when the system is plugged to mains.
ps:
Rather strange that you order cores directly from big companies. I bought these things from small shops in my city, HEFEI. It's the center of "the poorest" province in central China, and electronic things are not aboudant. Nearby province centers (Nanjing, Wuhan, Zhengzhou) have far more devices to buy.
EVA:
It's only half true that "Chinese companies are free to grow in their country, until they can afford approval costs in order to enter our market." Electronic companies also have to pass safty recognitions in China to sell their products. |
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| ChocoHolic |
| quote: | Originally posted by Eva
This cut in the PCB of the battery charger was done on purpose. It has two small pointy electrodes (one on each side) spaced by 4mm, so an arc will jump if more than 5KV appear from primary to secondary side.
Nice choke, by the way. I have no access to litz wire nor triple insulated wire. Also, my core and bobbin selection is quite limited.
Actually, I had to look in German stores in order to find suitable stuff for my projects. I have bought cores and coils from Conrad Electronics, and heatsinks with mounting clips from Fischer.
I bet there is not much SMPS development in Spain. |
spark gap:
:bigeyes: :bigeyes:
I had a closer look to your pic and indeed it looks like spark gap with electrodes on purpose. But why? I seems to jump prim/sec, more or less parallel to the transformer isolation.
My choke will have to show if it is just nice looking or really nice.
In fact the litz wire was banned from the winding lab of my former company, because we decided to switch to 155°C-wires and that litz is listed for 130° only.
If you go shopping in Germany don't miss out:
http://www.buerklin.com/default.asp?l=e
Their ferrite assortment is one of the best here in Munich.
SMPS vs. torroid...
Design/R&D is the interesting part of DIY. The building work itself
is often a little bit boring & annoying. Well, I have started these two Sadhara Cubes and already with my old electronics they sound fxxxxx good. :spin: :yes: :emoticon:
I decided to go ahead with my SMPS at least for one them.
If it's getting boring, I still can simplify the second with an torroid. |
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| Kenshin |
Why there's a spark gap between prim/sec, isn't it dangerous creepage? Or the designer expext use recoverable spark discharge in air to prevent permanent insulation breakdown during high voltage spike (thunder induction, etc. )?
| quote: | Originally posted by ChocoHolic
spark gap:
I had a closer look to your pic and indeed it looks like spark gap with electrodes on purpose. But why? I seems to jump prim/sec, more or less parallel to the transformer isolation.
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| mzzj |
| quote: | Originally posted by Kenshin
Why there's a spark gap between prim/sec, isn't it dangerous creepage? Or the designer expext use recoverable spark discharge in air to prevent permanent insulation breakdown during high voltage spike (thunder induction, etc. )?
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Not creepage issue as there is hole in pcb. Clearance values apply.
I guess that if it really is desingned as sparkgap its purpose is to have controlled point of discharche, insulation break and surface flashover are much worser choices as the will/can lead to permanent degradiation in safety whereas airgap doesnt mind at all. |
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| ChocoHolic |
| quote: | Originally posted by mzzj
Not creepage issue as there is hole in pcb. Clearance values apply.
I guess that if it really is desingned as sparkgap its purpose is to have controlled point of discharche, insulation break and surface flashover are much worser choices as the will/can lead to permanent degradiation in safety whereas airgap doesnt mind at all. |
Hm, so it is preferred in case of an heavy spike on the mains to protect
transformer rather than the person? :hot:
: Ironic Mode OFF:
Or is the estimation as follows:
It is not probable that somebody touches the secondary right when
such critical event takes place. But surely somebody will touch sometimes after that and then it is better to have the isolation still working. ...would make sense for me... |
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| mzzj |
| quote: | Originally posted by ChocoHolic
Or is the estimation as follows:
It is not probable that somebody touches the secondary right when
such critical event takes place. But surely somebody will touch sometimes after that and then it is better to have the isolation still working. ...would make sense for me... |
Or really powerfull ESD from user. I remember when i was kid that we were playing in winter at school, 25mm sparks were quite easy to generate on lacquered wooden floor when sliding with wool socks.
:D It hurted like quite badly on fingers so we kept fork or similar in hand to spread current and shock others with fork/spoon whatever :D
Too bad that after couple of years of fun they re-laquered that floor with some more modern stuff that was generating 5mm sparks at best. :D |
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| Kenshin |
If use a spark generator to hit something on the mains, will the spark sustain and conduct mains electricity to the generator?
It's a problem I often worry while playing with gas lighter ignitor: The spark of it is safe, but what would happen if use it to shock something on the mains? |
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| subwo1 |
| I think it depends on where in a circuit you apply the spark. If there are components with sufficient dielectric strength or voltage rating in series with the sparker in the circuit, then the mains voltage should not flash over. |
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| Kenshin |
| quote: | Originally posted by subwo1
I think it depends on where in a circuit you apply the spark. If there are components with sufficient dielectric strength or voltage rating in series with the sparker in the circuit, then the mains voltage should not flash over. |
(suppose) spark to a naked wire, the spark is in the air. |
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| subwo1 |
| The output impedance of the sparker will offer protection is the answer that comes to me now. |
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