Low inductance pulse resistors that don't blow up?
Low inductance pulse resistors that don't blow up?
(OP)
I suddenly needed to compare a small three-phase transformer winding's reaction to a fast voltage front, similar to a Baker test but on a budget.
HV - no problem. A rectifier cascade built from PFC capacitors and standard 1N4007 diodes outputs 1.3 kV but the series resistors needed to get a reading on the scope is a problem.
Total energy in the capacitors is 1.3 Ws and I thought that ten 1 W 4.7 ohm resistors should divide the energy between them so each would see around .13 Ws. No sweat for a 1 W resistor was my reasoning.
The resistors flashed over on the first try. Same thing on second and third try. Then, there wasn't much left of the resistors and no hope to make it work either.
Obviously, the short discharge time takes momentary power up to tens of kilowatts in each little resistor and that power concentration is way too much for them.
I am sure there are standard methods and standard components for this. But I haven't found them. Isabellenhütte? No data given for this kind of operation.
HV - no problem. A rectifier cascade built from PFC capacitors and standard 1N4007 diodes outputs 1.3 kV but the series resistors needed to get a reading on the scope is a problem.
Total energy in the capacitors is 1.3 Ws and I thought that ten 1 W 4.7 ohm resistors should divide the energy between them so each would see around .13 Ws. No sweat for a 1 W resistor was my reasoning.
The resistors flashed over on the first try. Same thing on second and third try. Then, there wasn't much left of the resistors and no hope to make it work either.
Obviously, the short discharge time takes momentary power up to tens of kilowatts in each little resistor and that power concentration is way too much for them.
I am sure there are standard methods and standard components for this. But I haven't found them. Isabellenhütte? No data given for this kind of operation.
Gunnar Englund
www.gke.org
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Half full - Half empty? I don't mind. It's what in it that counts.





RE: Low inductance pulse resistors that don't blow up?
http://www.welwyn-tt.com/pdf/datasheet/WDBR.PDF
Disclaimer: I used to work for them, although not in the resistor plant (I was in thick film hybrids).
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If we learn from our mistakes I'm getting a great education!
RE: Low inductance pulse resistors that don't blow up?
Pot the whole thing?
Submerge it in Fluorinert?
I dunno.
Mike Halloran
Pembroke Pines, FL, USA
RE: Low inductance pulse resistors that don't blow up?
Scotty: I mailed Welwyn. Waiting for an answer.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Low inductance pulse resistors that don't blow up?
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Low inductance pulse resistors that don't blow up?
Were you using metal-film resistors on the first go around? I.e. something with lowest possible tempco?
Tungsten, by the way, has a huge, 10:1 or more, change in resistivity from room temp. to operating temp at 3000+ Kelvin. The inrush at start of a tungsten filament is the most likely cause of all failures (ok, weakened filament from 1000 hours of use also contributes).
I like the idea of spreading the load, but think you went the wrong direction, i.e. the did the leading resistor in the chain take the brunt of damage? Would ten 470-ohm resistors in parallel work, I wonder?
RE: Low inductance pulse resistors that don't blow up?
PS Diodes also bad. It all happened when I tested 400 V input instead of nominal 230 V.
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Low inductance pulse resistors that don't blow up?
These are famous in the radio industry and are often used in high power dummy loads for transmitter testing. They're indestructable.
RE: Low inductance pulse resistors that don't blow up?
RE: Low inductance pulse resistors that don't blow up?
RE: Low inductance pulse resistors that don't blow up?
I have some spare time. So why not make something out of it?
I blew some capacitors and diodes. h
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Low inductance pulse resistors that don't blow up?
RE: Low inductance pulse resistors that don't blow up?
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Low inductance pulse resistors that don't blow up?
RE: Low inductance pulse resistors that don't blow up?
You know what? I tried lead mines for architecht's pencils. They can take the high-powered pulse. But they only have around 7 ohms each (HB). But still..
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Low inductance pulse resistors that don't blow up?
A young gentleman that enjoys blowing things up with massive amounts of electricity.
RE: Low inductance pulse resistors that don't blow up?
my favorite choice for resistors with pulse power capability is the following series:
http://www.welwyn-tt.com/pdf/datasheet/PWC.pdf
However, I'm more interested in repetitive pulse rating for operation in IGBT driver circuits.