# How to measure Amp?

Could somebody explain in a very easy way (with a drawing of what goes to what) show how one measures how many amp a motor is taking?

Thanks!

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It is a 4.000 Amp motor!

I did this:

Turn the knob to the other 2000 (6 clicks left of "off". This is 2000 ohms (Or 2K.). Put the red lead in the leftmost socket. Attach the end of the red lead to one pole of the motor. Attach the black lead to the other pole of the motor. Write it down (call it "R").

Write down your battery voltage. (Call it "V".)

Get a calculator. Perform the operation V / R. (V and R are the numbers you wrote down above.)

The result is your stall current in Amps. (Stall current is when you have put such a heavy load on the motor that it can't turn and it starts to gethot and very soon the blue smoke will come out.)

V: 7,2
R: 0,0018

7,2 / 0,0018 = 4.000

Should I assume that is Microamps or something, so it is actually 4,0 Amps?

Happily, you have translated the Kohms into ohms before doig the division. 7.2/0.0018 is actually 4000 amps.

No wait a minute. You use "." as a thousands separator and "," as a adecimal point, don't you? I'm confused.

Is your battery seven point two volts and your resistance zero point zero zero one eight ohms?

Assuming your resistance measurement is correct, this does appear to be a 4A stall motor. Now, this information isn't all that relevant. The motor might only draw 1A when it's running normally. (Not stalled.)

Cheers :)
Do solution 1 but don't try to stall the motor.

Run it off a 2000ma battery. Use some of that hot melt glue you like so much and glue the shaft so it will just barely turn. Now hook it up to the battery and start a stopwatch. Now if it doesn't blow up, just wait for the battery to die and check the stop watch. Now simply devided 2000 by the time gone by and there you have amp-hours which can simply be converted to amps!

It looks like your meter will only measure up to 2amps, so pray the motor's not drawing 4A.

Turn the dial to 2000 (3rd setting to the right of "off"). This means 2000mA (= 2 Amps).

Put the black lead to -ve of battery. Put the red lead to one pole of motor. Put the other pole of motor to the -ve of battery. This is "series"and you are now measuring current. It is displayed in milliamps.

(If that doesn't work, move the red lead to the rightmost socket andtry again, but I think on your meter you only need that for currents <200mA.)

Bear in mind that this is the "no torque" current. The motor will draw more current if you try to "stall" it (grab it with your fingers and see the current go up). You need to measure teh "stall current" (what current it will draw if some muppet stands in front of it blocking its path).

Turn the knob to the other 2000 (6 clicks left of "off". This is 2000 ohms (Or 2K.). Put the red lead in the leftmost socket. Attach the end of the red lead to one pole of the motor. Attach the black lead to the other pole of the motor. Write it down (call it "R").

Write down your battery voltage. (Call it "V".)

Get a calculator. Perform the operation V / R. (V and R are the numbers you wrote down above.)

The result is your stall current in Amps. (Stall current is when you have put such a heavy load on the motor that it can't turn and it starts to gethot and very soon the blue smoke will come out.)

Tell me what toy the motor is from and if I have one, I'll measure it myself.

Ask the question on www.letsmakerobots.com, so your so-called "friends" can send you useless, humiliating replies.

(Note how I put number 4 last? It the LAST thing you should try.)

I recommend you do both 1 AND 2 and compare the results. They might be quite different as the chances are the coil resistance is quite low.

actually the maximum on his measure thingey (if i can see well on the photo) is 200ma. the one you're talking about (3rd setting to the right of off is something with the "micro" next to it...so just go for the second solution (right boa?)

Yeah, my analog multimeter can only read up to 250 mA current too. That seems surprisingly low. Aren't there meters that can read several amps? That don't cost hundreds of dollars?

Dan

Now here's a thing. My \$50 one and my \$10 one BOTH have a 10A scale.

I hardly ever use them I just guessed they were for people who couldn't be arsed to put in a series resistor and measure the PD across it.

Bother. Yes. I only read the first thing on the scale rather than looking at all the options. Bad BoA. I assumed it was mA then A. It looks like it's uA then mA.

Fritsey, dude your DMM will only measure up to 200mA. Need more details on the motor before you even THINK about hooking it up. You risk blowing a fuse inside the DMM if you hook it up to a 2A motor.

Go with solution 2, like the man says. It involves a floating point division, but that should only take you a few cycles. And then go and get a DMM that measures up to 10A.