power supply max current

"Warren Thai"

** 1. Read the labelling.

1. Ask the makers.

BTW

Kindly only post questions with the relevant context included in future - dickwad .

...... Phil

Load it little by little until the voltage drops. Then back off about 10% for a safety margin.

OH SO SORRY!!!! YOUR MAJESTY! so power supplies don't apply to electronics huh? why be so rude for? everyone should ignore this guy

current

Everyone does ignore him.

"Friday"

** FUCK OFF - WOG TROLL.

....... Phil

What sort of power supply? More details would help, otherwise Lord Garth's reply is about the best you'll get. For instance, is it linear or switching?

... Johnny

Find the output power in watts and divide it by the output voltage.

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

"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

On Fri, 20 Oct 2006 19:15:59 +1000, "Warren Thai" 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

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