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Re: power supply max current

"Warren Thai"

******So NOT a "power supply " at all - just a transformer.

Now, WHY was it Sooooooo hard to DRAG that tiny fact OUT of YOU ????

******The VA ratings of transformers are determined by temperature rise alone.

The primary side resistance is your guide to VA rating and temp rise.

6 VA = about 800 ohms at room temp.

10 VA = about 450 ohms at room temp.

15 VA = about 240 ohms, at room temp.

20 VA = about 140 ohms, at room temp.

Apply a load resistance that draws a VA in line with the above table, then

let the unit heat up - check it now and then.

The temp rise is OK if the primary resistance increases by no more than 30 %

of its room temp value after an hour or so - jut un-plug the unit and

quickly apply your DMM leads to the AC plug to measure ohms.

A 30 % increase corresponds to a rise of 76 degrees C, since the tempco of

copper is 0.39 % per C.

....... Phil

Re: power supply max current

put finger to keyboard and composed:

If it is linear, then it may have a current sense/limit circuit, in

which case you would find the value of the appropriate resistor and

consult the datasheet for the regulator. Otherwise, if the CL circuit

relies on turning on a PN junction, then use 0.6V as the limiting

voltage and do the arithmetic. You may need to do a little reverse

engineering if other arrangements are used. Alternatively you could

just keep loading the supply until it droops and hope nothing breaks.

If the supply is a switchmode type, then its absolute maximum rating

would be less than or equal to the rating of the diodes on the

secondary side. I suspect you may be able to estimate the max current

by measuring the switching frequency, allowing for a certain max

ripple, and then calculating the current draw that would produce this

amount of ripple in the output cap.

- Franc Zabkar

--

Please remove one 'i' from my address when replying by email.

Please remove one 'i' from my address when replying by email.

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