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Old 20th October 2004, 11:15 AM   #11
Eva is offline Eva  Spain
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Winding dissipation is equal to I^2*R and output power is equal to I*V [rms values]

The current the windings can whitstand without overheating is independent of applied voltage so operating a 240V winding at 120V the power rating is halved, altough the minimum allowed frequency is also halved [ie: a 240V 50Hz winding works also as a 480V 100Hz winding and a 120V 25hz winding]

The current rating remains constant so theoretically the power rating is doubled for 480V 100Hz, and doubled again for 960V 200Hz, etc... But leakage inductances, core losses, wire skin effect and wire isolation put limits on the highest practical operating frequency [50Hz toroids are usually usable up to 200..400Hz]. Anyway, I think this fact explains why designing and operating transformers at 50Khz is so advantageous in comparison to ancient 50Hz operation

15 years ago I belived 50Hz transformers were beautiful things, but then I learnt in detail how transformers work and realized how wrong I was

PD: I'm interested in cheap mains isolation transformers
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Old 20th October 2004, 01:12 PM   #12
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Default Eva and all friends, i may have twice your age

And i remember very well that no television failled because of supply, old times the transformer was there, working hard years long without any signal, they were so reliable that we forgot the existence of power supply.

Now a days, i always remembering switching supplies, always burning component as a "serial killer"..all parts burning and going to out space... sometimes burning IF circuits, Chrominance going to hell, and audio ICs burning together.

We cannot use those switching supplies with audio, have electro-magnetic flowing, and if you use the "high speed" transistors, some of that is detected and amplified.

Also to Radio frequency it is not adequated, in Multi Band receivers you will capture a lot of signals from the main oscilator frequency and harmonics too.

My car when faill, cannot move, even not touch in the damn thing, full of computers, cannot even disconnect batteries, cannot push to make it work..... if stoped, have to call some truck to send it to Volkswagen.... the old ones, i used to polish the contacts with some sand paper, or woman nail sand material....some modern things are creating more problems than solutions. And people call this evolution, have no sense to me.

I think, the switching, pulse width, or those kind of supplies are terrible, evaluating by the several problems created on television sets..... thousands each month going to repair shops...in brazil we use to repair, till the repair price reach one third of some new television price.... when repair price goes up...junk!

Our Television models are the same you have in your country, wide world models, starting from Sony last models.

90 percent of damages are supply damages, here 30 degrees celsius.

In the past, supply never reached 10 percent of the failure reasons.

But it is beeing improved, and i i think someday i will trust in those things, for a while i am repairing a lot of them...poor customers, good to my pockets, but i fell this is a dirty work.... he will return,and sometimes i do not charge them, we cannot trust those things now a days.

Yes, you can say that this is ignorance, i really ignore the circuit, i cannot follow the electrons as i do with audio....i cannot see a "mind movie" of the operation, as a animated cartoon...i am a changeneer, engineer of changes, replacement enginneer.... when damage, we do not loose time thinking, as that exercise is not possible, and, if possible, spend too much time.... we go pulling out and changing the supply parts.... sometimes we check each one to reduce price to people you see cannot pay for that king of changeener work... sometimes we do not spend time.... all supply replaced in a matter of 18 minutes and television goes out and we charge 50 dollares. People beeing recognized as poor, we go checking parts, we delay more than one ours and we charge only 25 dollares.

But the values here are different....one dolar here you have 2 good meat pounds, first bull meat..... repair prices lower, because income lower, and food prices and all stuff lower too...another reality proportion... to send one receiver to brazil, you will paid 35 dolares in US, and will wait 3 monthes by sea travell...here i can pay 5 dollares, and will be in your hand in a matter of 8 days.


Sometimes i am thinking what is first, second or third world....hehe, confused things


regards,

Carlos
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Old 20th October 2004, 01:54 PM   #13
Eva is offline Eva  Spain
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Do you remember old B/W tube TV sets with no SMPS? I remember some of them from my early childhood. I only remember distorted jumping images, lost synchronisms, distorted sound, destroyed tubes, burnt resistors and random loss of station tuning, allways due to too low or too high mains voltages or just distorted mains waveform

I was never able to see a decent quality picture and to hear decent sound in a TV set until I got one with a regulated SMPS

My computer SMPS is 10 years old now, working almost 24hrs/day since I bought it and still no failures, it has survived lighting, short circuit and overload several times [in my early audio days, I used it to power a 4x15W car amplifier and the computer at the same time]

My 14" monitor is also 10 years old, uses SMPS and has no potentiometers, only digital controls (it was pretty advanced whem I bought it). It's only failure in 10 years was a blown IRF840 MOSFET on the SMPS due to lighting 5 years ago. I replaced it by an old IRF833 [discontinued] from a old junk computer SMPS made in 1985 and it's still working

I also own several ATARI ST computers that use SMPS and are 15 years old now, still no failures

And finally, I owned a big 28" TV set for 10 years that also used SMPS with no failures, until lighting almost destroyed it [UHF+VHF aerial mixer/amplifier and a circuit breaker were also destroyed]

So I'm not aware of any SMPS failure problem. It just happens that nodern ultra-cheap TV sets sold here are designed allowing components to heat up to 120ºC at 40ºC ambient temperature and manufactured in east-europe with negligible quality controls. The expected life of any electronic component is halved for each 10ºC increase in working temperature and this explains a lot... I think

So blame cost cutting and poor repair practices instead of SMPS technology. I've seen lots of people repairing TV sets without any knowledge about SMPS working principles. They replace resistors and capacitors randomly, and also switching transistors and diodes by anything they have at hand until they find some component that doesn't blow instantaneously at power up and kindly return the TV set to its owner and they sometimes charge more than 1/3 of the cost of the TV set for that
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Old 20th October 2004, 02:15 PM   #14
quasi is offline quasi  Australia
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Umm ...I suggest a soft turn circuit. This will allow you to use an input fuse that will help protect your amp but stay intact when you turn this sucker on.

Let me know if you can't find a circuit for it.

Still ....nice torroid.
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Old 20th October 2004, 02:19 PM   #15
quasi is offline quasi  Australia
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Oops sorry Zero Cool....didn't read your post that included the soft start ......disregard my last reply ....cheers
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Old 20th October 2004, 03:39 PM   #16
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Hi Quasi,


I would still be interested in looking at your soft start circuit. But most i have seen use banks of resistors and a relay for the soft start. this works well, but i know i have seen some that ramp up the voltage by controlling the on/off times of the incoming sine wave.

They make Solid state relays that do this but there very expensive. I would be interested in finding a DIY soft start that performs this same function. (always better to build your own right?).


Eva, I would love to find some SMPS power supplies that are large enougn for audio amplifiers! Many pro audio companies like QSC, Crown etc use them. But i have yet to figure out where there getting them from. Who makes a +/- 70VDC 800+ watt SMPS Power supply?


Zero
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Old 20th October 2004, 09:36 PM   #17
MikeB is offline MikeB  Germany
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EVA !!!! Where do you live ? I only read "destroyed by lightning"...
Sounds scary ! In my whole live i never had something damaged
due to lightning....

Mike
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Old 20th October 2004, 11:51 PM   #18
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Anyone that has ever lived in Florida Knows all about Lightining!!!



And here is a link to the Crydom Solid State Relay module i am interested in trying:

http://www.crydom.com/pdf/crydom_MCST.pdf

50 Amp rated, Adjustable ramp Soft start DC controlled.

BUT, i dont know how well these work with audio. I may want to build my own with a relay bypass once the Soft start has ramped all the way up. I dont know what detriment a device such as this will have? if it will produce any noise etc.


Zero
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Old 21st October 2004, 12:10 AM   #19
Eva is offline Eva  Spain
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I live in the North coast of Spain, near a cliff and the sea, in a place where lighting storms with lots of wind coming from the sea are common at the end of the summer and the beggining of the spring [August / September]. Sometimes lighting is so strong that everything shakes for a moment [like a small earthquake], but this happens no more than two or three times a year

In the last 10 years I've lost several equipment de to lighting, including two TV sets, a 19.2Kbps modem, a 33.6Kbps modem, an ADSL router, a couple of circuit breakers, UHF/VHF aerial mixers/amplifiers, a home alarm system, and a telephone. Also my SVGA monitor was damaged and I got blown PC PSU EMI filtering capacitors, etc..

The causes for most blown equipment are big common mode voltage transients appearing from mains line [both phase and neutral] to earth and from telephone line to earth. Connecting equipment to earth in lighting days is a very dangerous practice [lighting allways follows the lowest impedance path to earth]. I installed a switch to temporally disconnect the main earth of my house these days and it has helped a lot to prevent more disasters. TV sets were blown because TV aerial was unexpectedly earthed and part of lighting reached the aerial

My current ADSL router is protected by an external custom isolation transformer with a grounded copper sheet guard and 100mA fuses on the thelepone line. The guard discharges all leakage currents directly to power supply ground and prevents then from damaging ADSL transceiver chipset. Otherwise I would have already lost two or three more ADSL routers
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Old 21st October 2004, 12:30 AM   #20
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Here's a simple soft-start.

The resistor to the relay of course needs to be sized properly to feed the relay. The relay I use in this circuit is an Omron G8P SPST 24VDC with 30A contacts and a 660 ohm coil, available at Digikey, PN Z209-ND. The cap across the relay coil is just to slow it down a bit (the smaller the dropping resistor for the relay coil, the larger this cap must be...I like a delay of 1/3 to 1/2 a second. The .01µf caps across the relay contacts and power switch must be a saftey cap.
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