Hi.
I have bought a 30A PSU but I have trouble in testing it . Because my multimeter can only measure up to 10A . But can I test it's voltage with my multimeter , won't my multimeter burn ? (because it's 30A) ?
Thanks in advance .
Arman5592:
Hi.
I have bought a 30A PSU but I have trouble in testing it . Because my multimeter can only measure up to 10A . But can I test it's voltage with my multimeter , won't my multimeter burn ? (because it's 30A) ?
Thanks in advance .
You can test the voltage, since the meter won't draw 30A, and nor will the supply force 30A on it so you're safe.
If that wasn't how it works, we would never be able to test mains voltage since the national supply could provide basically infinite current....
Depends, do you want to know the current the connected circuit draws? Or the voltage of the PSU?
For the first, 30A is A LOT. Know what you do.
Second, yes, just connect the multimeter to the PSU in voltage mode. The 30A rating only tells you the maximum current the PSU can deliver, not what is actual delivers. Its a voltage source, not a current source. So voltage is constant and current depends on the connected circuit.
But because of your question I think it's wise to do some reading up on electronics...
thanks .
I have bought a 30A PSU but I have trouble in testing it . Because my multimeter can only measure up to 10A . But can I test it's voltage with my multimeter , won't my multimeter burn ? (because it's 30A) ?
If you want to calculate the current thru a device, you might measure the resistance of the device and the voltage drop across the device when being powered, then calculate the current.
Only if it's a resistive load...
Sacha22:
Only if it's a resistive load...
If the person is just testing the power supply then he probably use a resistive load for the testing.
You can probably get a shunt resistor for your multimeter, something like 1.0 milliohm
would give 30mV for 30A (at the loss of only 0.9W).
Alternatively hall-effect current sensors in the 50A range are available like the ACS756 (if I remember the
part # correctly)
Because my multimeter can only measure up to 10A . But can I test it's voltage with my multimeter
Just a little comment or two- It's actually quite rare to directly measure current with a multimeter. It's tricky because you have the break the circuit to insert the meter and there's always a danger of touching the probe to the wrong thing, or having unknown-excessive current and blowing the fuse in your meter. Or worse, touching the wrong thing with your meter probe and damaging your circuit. (The meter is essentially a short-circuit in current mode.)
I work in electronics and I measure voltage and resistance every day. But, I measure current less than once a year. I don't remember if I've ever measured current at home on a hobby project.
But, I do "cheat" a bit because my bench power supply at work displays both voltage and current.
Any half-way decent meter has is a separate connection for measuring current so you don't accidentally set it to read current and short-out your circuit. It will also have a fuse so you don't permanently damage your meter, and the fuse is only in the current-measuring circuit so your meter will still function and measure voltage and resistance with a blown current-fuse.
I think OP just wants to know if the supply he has is really able to deliver 30A.
But OP has not stated the voltage of the supply, and if it's fixed or variable.
I think in general it's best to just measure the output voltage, and start loading the supply with known resistors untill the voltage drops or cuts out.
It could be a problem to sink 30A.
If your supply is 12volts, you need a combination of resistors that total 0.4ohm/360watt.
Take care. 30A is some serious current. It could weld things together and start fires.
Leo..
Hi,
Can you post a picture of your supply and the specifications if possible?
Or where you purchased it?
Thanks Tom... 
I usually keep a partly burned out auto head light around to act as a dummy load. 30A is a pretty heavy load. Possible loads might be electric heater elements, stove/oven elements and similar.
Hi,
Zoomkat, I have half burnt out H4 globes.
Bore a couple of holes in a big Milo tin, so the globes point in and the tin acts as a lamp shade, more holes around base to ventilate air. Works well and self supporting.
But it would be nice to have more information on the power supply.
Tom......
Another way to easily get a high current load is to place 2 metal plates or foil sheets wraped around cardboard panels into a large plastic tub or bucket filled with water. Keep the plates as far seperated as possible to start. Connect positave to one plate and negative to the other. Stir in some baking soda or salt and the water will become conductive and draw current. Now you can move the plates closer to each other (DO NOT let them touch) to increase current load or more soda/salt to a point will do the same. The water will het hot after a time and also it will bubble which is hydrogen gas so only do this in a ventalated area to avoid fire/explosion risk. You will need some method to measure the current and voltage to get useable information, a current shunt works very well for high currents. I have used this method to measure dc current at low voltages (48 VDC) in excess of 10,000 amps by using a kids wadeing pool and screen mesh in layers seperated with pvc pipe for spacers. I had the pool to 180 degrees F in less than 5 minutes starting with cold water. It took a dozen short welding cables to hook it all up. The battery bank quickly showed the bad cells :).
R
That's good for the load but how did you measure the 10,000A?
I guess it was not the good old Fluke multimeter! ;))
Weedpharma
Weed,
It was indeed a Fluke 87 meter. The current shunt was a machined block of copper calibrated at the test points to .001 ohm. The output was 1 volt for 1000 amps.
R
Interesting, if true. What sort of 48V DC supply has a suifficiently low internal resistance, to deliver 10000 A ?
For how long?
Your house probably only has 200A, maybe even 100A, service, likely 2-phase power.
So say 220V, 200A, = 44,000VA of power.
Now you want to deliver 50x that amount of current?
48 x 10000 = 480,000VA (and I know I'm mixing AC and DC here).
You could take the 220V, run it through one big tranformer to knock it down, rectify it to get DC, and with the losses in the transformer and the rectifier you won't get 48V and 10,000A, since the power wasn't there to start with.
You're going to have to store up a lot of charge in batteries or capacitors to be able just to get bursts of 10,000A.
This page shows better what I am saying.
http://www.trans-tronic.co.uk/rectifier/?circuit=Full+wave+bridge+-+capacitor&dc=1&voltage=34¤t=1294&calculate=
With an ideal transformer, power in = power out.
So if 220V and 200A are available in, then
220/34 = ~6.5, so approx 6.5 x 200A = 1300A AC
Rectify & smooth the 34VAC into ~ 48V, and a DC current of 800A.
So you're a few thousand amps short of available power at steady state conditions.
He did say battery bank so talk of mains is irrelevant in this case.
Weedpharma