# How to run ammeter in low resistance?

I need to measure current in a small electromagnet powered off 3 x AAA batteries in series. This is the manual for my multimeter. When I run this multimeter in series and try to find the current, the electromagnet doesn't work anymore. I suspect the internal resistance of the multimeter to be too high compared to my electromagnet (just a few coils of 20AWG magnet wire) so the electromagnet isn't getting enough voltage anymore. Is there a cheap/free solution for me to find the current in the electromagnet?

• AAA batteries still pack quite a punch, so if you practically short them, I'd still expect a couple Ampere flowing. Maybe you just broke your multimeter's fuse? Jun 11 '16 at 13:31
• there's a fuse in line only in current, not in voltage measurement mode. So this is not an indication of functionality. Jun 11 '16 at 13:44
• @PeterZhu why should it? In voltmeter mode, the device has an enormous inner resistance, so no fuse will be needed. Jun 11 '16 at 13:51
• Then it is possible you have blown the 10A fuse too. Jun 11 '16 at 13:59
• well, $\frac{4.5\,\text V}{0.2\,\Omega}=22.5\,\text A$. Happily, the batteries won't allow this, because of their source impedance, which is what I asked you to measure by comparing voltage with and without load (see comments under answer). Also, 0.2 Ohm is something that requires very good contact when measuring. I'd guess that it should be lower if you had a proper measurement device and proper connectors for resistances of this order of magnitude. Jun 11 '16 at 14:06