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Old 14th October 2007, 04:29 AM   #1
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Default way to estimate choke current rating?

Like the title says, is there a way to estimate the current rating of a filter choke? I have a bunch of old chokes and have measured the inductance and resistance but figuring out the current rating has me stumped. Maybe try and compare it to something in a vintage manual?
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Old 14th October 2007, 04:50 AM   #2
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Hi,

Wire size is the only true way to tell, unless you have a brand/model number someone might have data for.

Some manufacturers wind "hot", some "cold". New Hammond chokes for example are wound a lot hotter (higher DCR for current rating) than their old ones.

Do you have a list of brands or numbers? Throwing them out here is a good idea.

Cheers!
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Old 14th October 2007, 08:31 AM   #3
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When I had that problem I used a variable CCS to pass current through the chokes whilst simultaneously measuring their inductance. When the inductance fell even more (it always falls with current), I figured I'd found the current rating. Surprisingly, some quite small chokes turned out to be quite good.
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Old 14th October 2007, 03:24 PM   #4
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Geek: These chokes are second hand from scrapped tvs or hifi units. I suppose the tube compliment of the hifi could be an indication. Like a quad of 6V6 outputs.

EC8010: Sounds like a good plan. How were you measuring inductance under load? Using AC with a scope? Keeping an eye on the temp would be another low tech way.
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Old 14th October 2007, 04:05 PM   #5
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Quote:
Originally posted by astouffer
GHow were you measuring inductance under load? Using AC with a scope?
No, my Marconi TF2700 bridge allows me to apply external DC whilst measuring inductance.
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Old 14th October 2007, 04:32 PM   #6
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Would it be useful to wave a probe around while increasing current and see the current at which the choke starts spraying field?
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Old 14th October 2007, 05:16 PM   #7
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Quote:
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Would it be useful to wave a probe around while increasing current and see the current at which the choke starts spraying field?
Very probably. It would need to be a search coil probing the magnetic field rather than an oscilloscope probe probing the electrostatic field.
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Old 14th October 2007, 05:44 PM   #8
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Quote:
Originally posted by EC8010
When I had that problem I used a variable CCS to pass current through the chokes whilst simultaneously measuring their inductance. When the inductance fell even more (it always falls with current), I figured I'd found the current rating. Surprisingly, some quite small chokes turned out to be quite good.
D'OH! Of course!

That's how I test new choke designs.

Here's a DIY circuit that can help:
http://www.angelfire.com/electronic/..._Analyzer.html

I used similar only with a CCS as EC suggests. Make it a real HV transistor for the CCS though, well above the DC + peak, lest you have a room full of smoke

Cheers!
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Old 15th October 2007, 08:37 PM   #9
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Geek,
I was trying to build a similar jig, too. What kind of CCS are you using?
I have build a cascoded CCS with EC's help with an MJE350 and BC558.
Works well up to 100mA but can't apply more current.
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