Re: power supply?
- From: Ray Carlsen <rr0cc@xxxxxxxxx>
- Date: Tue, 26 Feb 2008 09:21:49 -0800
Hey Glenn, have you tried testing the leads with a multimeter to see what the
amperage is on it yet? If the PSU is putting out 9 VAC on 2 pins and 5 VDC on
1 pin, and the ground on 1 pin then your ok there. THEN secondly, switch the
multimeter to the Amps setting and redo the test again on each and every pin
the same way you did the first test. You should get a "MINIMUM" of 1A on all
the leads. Most likely the 9 VAC leads will be 1.0-1.5 and the 5 VDC will be
around 2.75-3.5A typically.. Either way, it should work fine.
That's -not- the way to check a power supply... if I'm reading you correctly.
Your procedure for checking voltage levels is correct, but it sounds like you
suggest putting the ammeter directly across the supply to verify how much
current it can supply. Such a test will likely burn out the meter and/or damage
the supply. You can connect an ammeter in series with a load to measure current
draw, but -never- across the supply.
Look inside the supply for a fuse (if it has one) on the 5V output. Fuses
are normally rated at 1.5 times or so of the maximum rated output current so
they open on an overload. So, if the fuse is rated 1.5 Amps, the supply is good
for 1 Amp. If you overload it, the fuse will blow. Seems like I remember seeing
one of those after-market CPS10 supplies before, and it cannot handle the extra
load of a super CPU or RAM expander. It was only a replacement for the C64 brick.
If the supply has no fuses or the only one is in the AC line (most supplies
have only that one), the correct test for maximum output current would be to try
the PS on varying fixed loads and measure the voltage to see if it "sags". For
example, a 5 ohm resistor across a 5 volt output would draw 1 Amp. If you put a
2.5 ohm resistor on the same 5 volt line, it would draw 2 Amps if the supply can
handle it. If the voltage drops off, the load is too much for it. The resistor
would have to be rated to handle the current and should be a 20 Watt at least.
It will get hot if left on very long... that's normal. Momentary overloads with
a test resistor shouldn't hurt the supply but may blow a fuse if too much of an
overload. Run the test only as long as it takes to get a voltage reading with
the load connected.
I do routine power supply tests with automobile lamps (such as a dual
filament tail light) of known current draw. Testing a supply on good equipment
such as a computer or drive is not good practice. What happens if the supply
fails and outputs too much voltage? Zap! That's why an artificial load is the
only safe way to run PS tests.
Ray
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