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Old 18th March 2004, 10:25 PM   #31
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Hi there.....Sweaty fingers with HV,EHT, then stay with Low Voltage..........Is one....risky ventured and confident ?....Read on.. .

No-one has yet mentioned the hazards with Switch Mode Power Supplies (SMPS)......As an avid user of this technology in my power amps (400W upwards at 550V B+) .....Iíve discussed this on other posters......it offers incredible performance advantages in B+ power amp management and some shockers if one doesnít get it right......... The golden rules regarding dangers of HV apply even more so as the terminal impedances are considerably lower than DC originated from standard mains L/C input power supply. ....problems with switchmode failure often result in a dramatic semiconductor device destruction for TO220 style and other hard plastic type devices that can explode on intantaneous unlimited current supply... These can act as downsized handgrenades to unprotected eyes and ears...Study and observe peak circuit currents and device specifications........ USE eye and ear protection when prototyping off-line equipment is a serious must.....Always make sure that the voltage feedback loop is connected in the layout and has been volts calculated... Hard advice otherwise......a 500uF cap charged at 400V+ and dumped into a duff switching diode and mosfet on switching shortcircuit conditions will literally explode the devices with a cosmic bang..... no Hi Fi can hull out .......ears donĎt like this slam tactic....and never forget it. ....However, IF you get the design near right and it works...........itís a sweet go-er... getting the ElectroMagnetic Interference under wraps is often the greatest challenge even for experts to sort out. In my amps, the only solution with the power (850W) is to use feedthough caps and the biscuit tin to EMI screen. Thereís also piles of safety thrown in to save those precious o/p tubes.

Working with HV or SMPS, organise the work bench discipline i.e equipment prototyping wiring Vin and outís; meters and trannies in the right place and donít work in bird nested wiring. Normally i like the mains isolation equipment on the LH side with osciíscope in centre back with test equip and soldering iron on right side away from cabling. Same discipline for steam trains, the coal goes in the centre with driver and fireman religiously not getting in each others way.

To fast discharge a stack of hi value caps/volts I nearly always use a chain of domestic light bulbs (230V) or two/three in series to discharge..and then recheck with a multimeter. Power resistors can often fuse open cct on peak V&A without symptoms of smoke or discolouration so I avoid using them....

If the DMM has separate current terminals; then purchase another and use one exclusively for in-circuit current measurements and the other for voltage and donít change.......thatís the golden rule for SMPS work.....it avoids the risk of inadvertently S/C the B+ when on the current setting ! (Yes Iíve done this a few times......)

I use SMPS technology in my amps....it may be more component pricy and require more technology but... the punch it can give out with circuits using fixed bias.......brilliant bass and mid range transient handling & B+ holdup on full load far exceeds the floppy conventional PSU capabilities, but I also needed to create a design file, just in case something goes wrong with mine.

..I donĎt want to put off anyoneís confidence venturing into H.V power switchmode technology, itís a brilliant and challenging multi-facetted technology; but those unfamiliar.... start with smallV project, and get the hang of the topologies and magnetics.

Enclosed photo of 130+130W amp innards using SMPS.

ViVa the SMPS Rat....

rich
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Old 18th March 2004, 10:39 PM   #32
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Default Re: Move Back to Tubes for Awhile?

Quote:
Originally posted by DrDeville

Anyone tell to care me what the difference is, if any, between an isolation transformer and a Ground Fault Interrupt outlet?
An isolation transformer completely breaks the continuity between the incoming electricity of your house from the AC voltage on the secondary of the transformer..an isolation transformer has a 1:1 ratio, but the secondary is floating with respect to everything...it eliminates the hazard of a voltage with respect to ground, and opens ground loops.

A GFI is NOT an isolator, but instead, monitors the current that is going through both the neutral and the hot wires of an outlet. If the difference exceeds a preset limit (10 to 15 mA typically), the GFI has a relay that disconnects the line. The usual way it is tripped is if current flows from the hot side to something that is taking that current to ground, like a person who inadvertantly puts themself into the current path.

The GFI's I saw have a toroid inside, and both hot and neutral together do a coupla turns in the toroid..there is a secondary also wound around that toroid, and the difference between the two wires shows up as a voltage across the secondary.

W/R to the thread name...WHERE'S THE ULTRA HIGH VOLTAGE STUFF????

We have a pair of tandem van de grafs here, and each runs 10 to 15 megaVolts....now that's ultra high...

Cheers, John
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Old 19th March 2004, 04:24 AM   #33
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SY said:
Quote:
I left a "forwarding address" in the Tubes section. It may have slid out of sight just because there were no new postings.
Problem solved--thanks!

Rich Walters--
Your suggestions are absolute gems. I learned a lot--thanks for sharing them.

Dr Neutron--
Thanks for educating me on isolation transformers.

To see if I understand, may I ask you the outcome of a couple of thought experiments?
(Kids, don't try this at home )

1. My isolation transformer is sitting on my workbench, which is made of a perfect insulator. I however, through some horrid twist of fate, am standing barefoot on a wet ground. I reach out and grab *one* of the isolation transformer's output leads. What happens, besides SY slapping me silly?

2. My isolation transformer is powering my new 1000V power supply, and both are sitting on my perfectly insulated workbench.
Still standing barefoot on wet ground, I very carefully reach over and, touching nothing else in the amplifier, put my finger on the B+ terminal. Besides SY's beating, what happens to me?

Professor Neutron typed:
Quote:
WHERE'S THE ULTRA HIGH VOLTAGE STUFF????
We have a pair of tandem van de grafs here, and each runs 10 to 15 megaVolts....now that's ultra high...
Agreed!
What safety precautions do you use?

Thanks again, all.

Best,

George Ferguson
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Old 19th March 2004, 03:05 PM   #34
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Quote:
Originally posted by DrDeville

Dr Neutron--
Thanks for educating me on isolation transformers.

To see if I understand, may I ask you the outcome of a couple of thought experiments?
(Kids, don't try this at home )

1. My isolation transformer is sitting on my workbench, which is made of a perfect insulator. I however, through some horrid twist of fate, am standing barefoot on a wet ground. I reach out and grab *one* of the isolation transformer's output leads. What happens, besides SY slapping me silly?

2. My isolation transformer is powering my new 1000V power supply, and both are sitting on my perfectly insulated workbench.
Still standing barefoot on wet ground, I very carefully reach over and, touching nothing else in the amplifier, put my finger on the B+ terminal. Besides SY's beating, what happens to me?


What safety precautions do you use?
First..thanks for the promotion...but I am neither a professor nor a PhD. I build superconducting magnets at a national lab, and am just a lowly degreed engineer..

For both your scenarios, the current you draw will depend on the degree of isolation in the transformer assembly. There will be capacitance between windings, so the isolation is actually just a resistive isolation. Current is still possible, but with a good transformer, it will be greatly reduced with respect to what would happen if you did the same without it. And don't forget, as little as 2 milliamps, properly routed, can kill. The scenario's you describe can kill if the isolation is not 100% effective....and very few things are 100% effective

I certainly recommend that isolation transformers not be used as protection from electrocution. There are so many possible errors that can render the isolation ineffective, so should never be a substitute for good safety practices. The same applies to GFI's...yah, they work well, but should never be a substitute for common sense, only for protection from accidents.

Oh..btw..transient supression devices are designed around a 6 Kv standard...that is the transient potential that can exist at a US 120 volt outlet, and is actually the flashover voltage there. If you have an isolation transformer on an outlet, and a transient of that size hits the line, there is a possibility that the transient can arc primary to secondary, and if it makes a carbon track, isolation is gone..how many people can guarantee that scenario has not, will not, or won't happen. And, who tests the isolation of their device, to see that it makes spec?


Safety precautions for 15 megavolts?

The generator is a structure made of 1 inch thick or so steel walls. The voltage is inside, with some kind of insulating gas, hexaflouride stuff, I think (I have escorted tours there, but I work in another facility)

For that thing, distance is what I use..quarter mile or more suits me just fine.

From what I recall, the machines are in a radiation controlled area, and nobody can get near it during operation. But, they say that when an arc occurs in the machine, it sounds like lightning hit the building..

Cheers, John
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Old 19th March 2004, 03:47 PM   #35
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Quote:
The voltage is inside, with some kind of insulating gas, hexaflouride stuff
That would be sulfur hexafluoride. Sounds nasty, but it's quite non-toxic, albeit quite dense. Dayton-Wright used it in their electrostatic speakers to allow a greater stator-diaphragm potential without arcing. It has much better dielectric withstand than air, but the density mass-loaded the diaphragm enough to require the use of a separate tweeter.

As a side note, the high density of SF6 causes it to have an effect on the human voice opposite of helium. When I breathed the stuff during some experiments (mixed with oxygen, of course), I sounded like Paul Robeson.

Quote:
thanks for the promotion...but I am neither a professor nor a PhD. I build superconducting magnets at a national lab, and am just a lowly degreed engineer..
Everyone here is an honorary Doctor, much in the manner of the Black Widowers.
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Old 20th March 2004, 03:12 AM   #36
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First, I'll repeat some some warnings and disclaimers:
  • Any voltage can be deadly.
  • Electronic equipment is dangerous--each person (me included) is responsible for deciding if they are willing to risk their life, and for ensuring that whatever information they receive is correct.
  • This forum and its members accept no responsibility for any death, injury or property damage that result from any of these suggestions--your safety is your own responsibility.
Okay, with that out of the way...

The esteemed Sir Neutron wrote:
Quote:
For both your scenarios, the current you draw will depend on the degree of isolation in the transformer assembly, and very few things are 100% effective
Indeed, and that certainly bears repeating. I was just seeing if I understood the sort of situation in which an isolation transformer might be helpful.
Quote:
There are so many possible errors that can render the isolation ineffective, so it should never be a substitute for good safety practices.
Absolutely. At the same time, it seems to me that an isolation transformer is a must-have safety item, at least for me.

In aviation we think of safety practices as a series of nets or shields--each one might save one from a danger that makes it through the other layers.

Please tell me if you think this transformer is a good choice as an isolation transformer. The link is to a .pdf file showing its specifications and configuration. It seems to me that for isolation use, one would connect terminals 1 and 2 to mains hot and neutral, leave 3 disconnected, connect 5 to 6, and take the isolated power from 4 and 7. Does that make sense?

A bonus is that, wired differently, this transformer can be used to filter out power line noise before it reaches an audio system. Here's an article about how to do that. It seems to me that one could mount this transformer in a box with switching for the two modes, and use it for both purposes--use it as an audio power filter when not using it as an isolation transformer.

Comments?

SY wrote:
Quote:
Everyone here is an honorary Doctor, much in the manner of the Black Widowers.
Absolutely!

Thanks for all the help from all that posted. If I learn to follow them correctly, one of your suggestions might save my life someday.

Best,

George Ferguson
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Old 22nd March 2004, 02:31 PM   #37
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Default Hi George

The transformer looks good..

Questions I would raise.

1. Is the primary to secondary isolation capable of exceeding all safety requirements for an isolation transformer in the country it will be used in?

2. Is tying the e-sheild (pin 3) mandatory for an isolation setup, or is it required to be floating?

3. Is the primary to ground dielectric isolation good enough to meet safety requirements?

4. Are there specific layout requirements for the building of an isolation unit?

Electrically, it looks good. But, as that link to Secret points out, there's a lot of safety hazards associated with the voltages and application.. good luck..be careful.

Quote:
If I learn to follow them correctly, one of (your) suggestions might save my life someday.
I'm glad the thread is permanent now..

Cheers, John
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Old 23rd March 2004, 09:57 AM   #38
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Hi there...down to more rudimentary chassis stuff.....alot have asked me about correct mains input wiring sequence in equipment ....I take no ßß liability for this one........Mains switch is wired after input socket then comes fuse then equipment transformer.......That to me is correct or is it in 2004 incorrect.. can someone confirm IECC regs on this one ?

There's alot of equipment about with vice versa.........regulations in the old days seem ar**about face ........

rich
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Old 13th April 2004, 03:50 PM   #39
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Default misconceptions

Recent news article: this is actual text, with somebody's quote..

""A 34.5 kilovolt supply line went out for 10 seconds at 9:38 a.m., said city Department of Water and Power spokeswoman Carol Tucker. The line serves 26 industrial customers at the airport.

Apparently, a bird came in contact with the line and at the same time touched a cross-arm or some other grounded device, the DWP said in a statement. The line re-energized moments later.

"But we didn't find the bird on the ground, so it might have flown away,"""

Hmmmm...might have flown away...

Perhaps someone had a dustpan and brush available to remove the evidence..

Cheers, John
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Old 13th April 2004, 04:21 PM   #40
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A while back I was trying to finish/rush my project and avoid long waiting for new parts for a power toggle switch. But I have several single pole throw 15A switches at hand and I was going to install two of them per psu as a power switch. One switch for hot and one switch for nuetral. But I was lucky here that I mentioned it in this forum and got some quick messages from fellow members to warn me not to do it.
Do not do it this way, why? I don't recall now, but I trust my fellow members here so I just will not do such a thing and buy proper 2 poles power switches instead.


Chris
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