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Re: power supply max current
Its a ac plug pack, the ones you use to power electronic keyboards or
computer speakers etc. The label has been removed a long time ago. I know
the voltage by measuring with a multimeter. I'm after an experimental way of
determining its maximum output current.

current

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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