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power supply max current

W

Warren Thai

Jan 1, 1970
0
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?
 
P

Phil Allison

Jan 1, 1970
0
"Warren Thai"
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?


** 1. Read the labelling.

2. Ask the makers.

BTW

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




....... Phil
 
L

Lord Garth

Jan 1, 1970
0
Warren Thai said:
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?

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

jasen

Jan 1, 1970
0
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?

if the device it is was designed to power has published (or labeled) power
requirements you could assume that it atleast meets them.

Bye.
Jasen
 
W

Warren Thai

Jan 1, 1970
0
OH SO SORRY!!!! YOUR MAJESTY!
so power supplies don't apply to electronics huh?
why be so rude for?
everyone should ignore this guy
 
P

Phil Allison

Jan 1, 1970
0
"Warren Thai" = Top Posting Shithead


OH SO SORRY!!!! YOUR MAJESTY!


** **** YOU - Mr Smug Prick


so power supplies don't apply to electronics huh?


** Learn to bloody read - you FUCKING TENTH WIT.


why be so rude for?


** Just getting started with YOU - fuckhead.




......... Phil
 
F

Friday

Jan 1, 1970
0
Warren said:
OH SO SORRY!!!! YOUR MAJESTY!
so power supplies don't apply to electronics huh?
why be so rude for?
everyone should ignore this guy

Everyone does ignore him.
 
P

Phil Allison

Jan 1, 1970
0
"Friday"


** **** OFF - WOG TROLL.







........ Phil
 
J

Johnny Boy

Jan 1, 1970
0
Warren Thai said:
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?

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
 
D

Dac

Jan 1, 1970
0
Warren Thai said:
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?

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

Warren Thai

Jan 1, 1970
0
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.
 
P

Phil Allison

Jan 1, 1970
0
"Warren Thai"
Its a ac plug pack,


** 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 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.


** 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
 
F

Franc Zabkar

Jan 1, 1970
0
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?

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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