power supply max current

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suppose you have a power supply but don't know what is the maximum current
it can deliver. how would you find out what the max current is?



Re: power supply max current



"Warren Thai"
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** 1. Read the labelling.

    2.  Ask the makers.

BTW

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




......   Phil




Re: power supply max current


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



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current



Re: power supply max current


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Everyone does ignore him.


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Re: power supply max current



"Friday"


** FUCK  OFF   -  WOG   TROLL.







.......  Phil



Re: power supply max current



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



Re: power supply max current



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    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



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.


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current



Re: power supply max current



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

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



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** 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



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



Re: power supply max current


put finger to keyboard and composed:

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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.

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