way to estimate choke current rating?

[astouffer]

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?

 

[Geek]

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!

 

[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.

 

[astouffer]

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.

 

[EC8010]

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.

 

[SY]

Would it be useful to wave a probe around while increasing current and see the current at which the choke starts spraying field?

 

[EC8010]

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.

 

[Geek]

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/funwithtubes/Filter_Choke_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!

 

[resident]

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.