I have a digital multimeter and the manual only talks about the fused DC 10 Amp measuring, with a seporate 10Amp setting, but it does have a DC amp range from 200u, 2000u, 20m, 200m, and 2000m range, what would I use to test up to a 25amp circuit?
You can’t measure 25 amps with a digital meter. It can only measure up to 10 amps. If you want to measure higher than 10 amps you’ll need an ammeter.
Another meter, one that can measure up to and over 25 Amps. Usually, in that current range it will have a clamp on type probe.
Here’s one of many such possibilities.
His digital meter will only measure to 2 A, with a 10 A safety fuse. Some digital meters will go well over 10A. My bench meter does 20 A, and other do go higher. Somewhere near the 25A range it does get more practical to get a clamp-on style meter, but those come in digital too.
One way to measure higher amps than the meter is internal capable is to get a calibrated shunt the has a multiplication factor of amps per millivolts. Use the DVM to measure the millivolts generated across the shunt and multiply by the factor. That is basically how the DVM measures amps internally. The DVM has internal shunts that are introduced and the reading from millivolt section of the DVM is corrected by the appropriate factor.
If you can find a 0.1 ohm high wattage resistor, place it in the circuit to be measured and measure the voltage drop across it. At 25 amp the voltage drop would be 2.5 volts, and a 0.01 ohm wire wound would give a 0.250 volt drop. Try to keep the rated wattage a lot higher than the in circuit wattage dissipated so that heating effects do not change the resistance.
Hope this helps.
If the meter has a seperate 10 amps max lead input, it can read up to 10 amps AC/DC.
The OP indicated only a maximum range of 2A. I know of meters that are fused higher than their maximum range, but I don’t know what meter the OP has, so it could be either way.
In any event, it won’t read a 25 A load without an external shunt, and I’m not too fond of those. It would be better to get the correct tool for the job…
As Researcher says, you need a shunt. You can make one using an appropriate length of heavy duty wire wound around a dowel. You can look up how long a wire of what gauge to use for the shunt. Here’s one link. http://www.downloadingfiles.co.uk/teleflexfiles/library/instructionmanuals/External Shunt Type Ammeter.pdf
There are probably a zillion others to be found with any search engine.
If you don’t need a lot of precision and just need to make some relative measurements, you may be able to measure the voltage drop across the car wiring involved. It’ll be small, but it is proportional to the current flowing in the wire. That is to say that if you measure 0.1 volts with some device turned off and 0.2 with it turned on, you don’t know what the current flow is, but you know you have doubled it.
BTW, I think that a cheap analog meter is better for most (not all, but most) routine automotive troubleshooting than a digital meter because you get a reading immediately and don’t have to deal with jitter in the values read out. If you have an analog meter around and find using the digital meter to be annoying, dig out the analog meter and try it. Newer doesn’t always mean better.
What are you trying to determine? If your worried about a 25 AMP fuse that keeps blowing, use your multimeter to read the resistance in ohms between the load side of the fuse and a good ground with the power off. Then use Ohm’s law to determine the load, V=IxR, or I=V/R, with V = 13.5V, R=ohms, and I will be in amps.
That’s fine for resistive loads. It won’t work correctly for inductive loads (like a motor) or for electronic loads.
I want to thank you all for trying to help, I now understand my digital multimeter better, and tryed it this morning and found two circuits that read .90 and 1.30 in the unfused setting. Thank you all again, jotheuser