Mystery tranny current capacity question

[macula56]

I recently found a box of trannies that i bought off of ebay a few years back. I don't remember what they came out of and while i can easily measure their voltage output i have no idea how to figure out how much current capacity they have. Can anyone suggest a way to find this out? Any help greatly appreciated. JMac

[panhead]

I don't think there's any non-destructive test that can give you that information. Unless you can ID the tranny or the equipment it came out of and look up the info, I think you're out of luck. Physical size can give a rough indication of not-much to more current capacity, but no hard numbers.

[jojokeo]

I've read where suggestions were to guesstimate by comparing the unknown tranny's size w/ a similar sized one that is known and you can figure a reasonable "closeness" of the two. It will pretty hard to get any exact rating w/out a way to look up a serial number or something more definite. Another way I believe you could go is to try putting an increasing load on whichever tap you use until you get the voltage to drop to some reasonable level below it's un-loaded condition. Like somewhere between 10% or 15%. So for ~10% if you measure 6.9v un-loaded how many amps does it take to get down to 6.3v? And for ~15% if you measured 7.3v how many amps does it take to get to 6.3v? This would handle the heater current availability and then do the same on your HT (that would be mA's of course). Then you could leave the tranny loaded like this for say an hour and see how hot it gets. If you can keep your hand on it then you should be good to go w/ what you're using/measuring.

[kagliostro]

May be you can find something of your interest here

http://www.el34world.com/Forum/index.php?topic=11841.0

Kagliostro

[DummyLoad]

I recently found a box of trannies that i bought off of ebay a few years back. I don't remember what they came out of and while i can easily measure their voltage output i have no idea how to figure out how much current capacity they have. Can anyone suggest a way to find this out? Any help greatly appreciated. JMac

any markings? part #'s etc?

[RicharD]

Download Duncan's PSU Designer II.  It does have a bit of a learning curve.  Take the parameters of a couple of known power supplies and plug them in to get to know the software.  Once you have it figured out, you can measure:
The unloaded AC output voltage
The AC input voltage
The primary DC resistance &
The secondary DC resistance
Plug these values into PSUD II and run a simple model where you can increase the load.  Once you're dropping about 10% DC, you at the transformer's limit.

You can do about the same thang in real world if you have the junk part resistors laying around.  Build a little rectifier circuit and start with like a 100k load and measure DC output.  Start dropping the resistance until your voltage goes down about 10%.  That's easily a safe limit for most transformers.  Be mindful of resistor wattage.  If they're big ol trannies, you'll end up pulling a lot of current and therefore need high wattage resistors.

[macula56]

Thanks for all the replies gentlemen. I'll see what i can do with this info.