How would you check amps on power supply?

[hammer0630]

I have a QJE-50 amp power supply and was wondering what is a good way to see how many amps it really is capable of? In other words how can I apply say 40 amps to it and see how it does. My diagnostic meter only reads to 10 amps so I would have to rely on the QJE meter that is built into the p/s. The p/s amp meter reads up to 63 amps and have heard their meters are reliable. I have read they run 48 amps and surge 52 amps.

 

[The Mad Scientist]

you would need to connect a device that is capable of running a little over the specified rating and install an ammeter inline with it that is capable of reading more than ten amps.

An inductive clamp on dc ammeter perhaps.

 

[Beetle]

A battery shop should have a carbon-pile load resistor for testing battery output, and one of these should handle 50 amps without breaking a sweat. Clamp on meters are perfect for this type of use, but if the meter's been mishandled, it could be pretty far off. Use Ohm's Law to determine what a reasonable current would be from the voltage and resistance values you have, and see how close the ammeter is.

 

[The DB]

40 amps at the rated 13.8 volts? 0.345 ohms of resistance between one terminal and the other will flow 40 amps of current. Make sure the resistor can handle the current or you will burn it up. That rules out the little ones.

For 50 amps 0.276 ohms of resistance should do the job nicely...

In both cases we are talking about very small resistance numbers, make sure the resistors used are accurate as if you get much lower than 0.276 ohms you will be out of the power supplies specifications.


The DB

 

[hammer0630]

A battery shop should have a carbon-pile load resistor for testing battery output, and one of these should handle 50 amps without breaking a sweat. Clamp on meters are perfect for this type of use, but if the meter's been mishandled, it could be pretty far off. Use Ohm's Law to determine what a reasonable current would be from the voltage and resistance values you have, and see how close the ammeter is.

I was thinking the same thing and I use to have a Schumer or something and I think they test at 50 amps only? I can't quite remember now but I do remember I never sold or gave it away! Another tool mysteriously gone.

 

[Captain Kilowatt]

40 amps at the rated 13.8 volts? 0.345 ohms of resistance between one terminal and the other will flow 40 amps of current. Make sure the resistor can handle the current or you will burn it up. That rules out the little ones.

For 50 amps 0.276 ohms of resistance should do the job nicely...

In both cases we are talking about very small resistance numbers, make sure the resistors used are accurate as if you get much lower than 0.276 ohms you will be out of the power supplies specifications.


The DB

50 amps at 13.8 volts is 690 watts of heat to get rid of. That would be some resistor. Better to use a parallel string of headlamp bulbs. I used to use the filaments of some 833C tubes. They are rated at 10 volts at 10 amps so short times on 13.8 were fine for testing a supply under load. At that voltage each tube would draw almost 14 amps.

 

[FuzzyTheBear]

A word of caution

Unless you do have access to very high power resistors it will end up in smoke. Think about it .. 13.8 volts 40 amps that's 552 watts ! That's the power of small electric heater baseboard. You need a 1000W resistor or so to make such a test. Using lower power rating resistors will end up in smoke and a failed test.

The test i DO recommend is to use headlights. Yup .. good old car type sealed beams. Find a bunch and connect them in parallel one by one . That is an easy test that is also safe for the average bear If they are all equal powered lights taking the current reading on one branch of the circuit * number of beams you have will give total current drawn.
That number can be then compared to the PSU meter and have a fair idea of the meter's accuracy

Again , i stress that safety should come first for any type of testing.
<gotproof>