View Full Version : motor up in smoke, how to test it??

11-12-2009, 10:34 PM
I have a z20 brushless motor. when i connected to castle controller, the motor only made a slight jump. then the motor smoke "bummer" also sent speed controller back to castle as it was bad. so now I need to know in very, very lamen terms how to connect ohm meter. I am guessing from post i have read that it is broken wire inside. most of the posts are too much information for me. so anyone that can talk to me like i am 6 years old :blah: would be much appreciated..thanks Dan

11-13-2009, 04:22 AM
You should get a very small resistance value (0.05 or so) between any two motor wires. You should get very high resistance (infinity, over limit, or no connection) from any of the motor wires to the motor housing, shaft, or mount.

If there was smoke from the motor, chances are good that one or more wire windings have melted through their insulation and are shorted out. There's no simple repair to correct this issue. The motor can be rewound, which isn't nearly as hard as it sounds, but also takes some patience and practice.

11-13-2009, 01:08 PM
Dry testing electric motors:

Prettig weekend ;) Ron

11-13-2009, 09:58 PM
WEll i tried the dry method with a drill. spooled up and had the leads on all 3 wire configurations. each one (set to 20ma) read .03 then .02 then .01. Then ended in zero. So does that mean the motor is ok

11-14-2009, 05:08 AM
You'll get more useful results if you have the meter set to an AC voltage range rather than an amperage setting (and make sure the probes are plugged into COM and V/Ohm, as well). If your motor is good, you'll see anywhere between maybe 0.5 volts and 3 volts, depending on the speed of your drill.

11-14-2009, 06:14 AM
aram, i did actually have it set to ac. my drill says it is 1k rpm. I took the motor apart, blew with airgun and inspected. I dont really see any wires that look burnt. I did find however the positive wire had a huge gapping slice. so i repaired that. i am hoping it maybe just shorted on something and that caused the motor to smoke.

now, about the voltage readings. Should those numbers be constant? example if it reads .05, will it read that as long as drill is spinning. or will it fluctuate between there and 3?

11-14-2009, 07:04 AM
The numbers will be constant; they should not fluctuate or change very much. If this (http://www.rchobbiesandmore.com/Z_Power_Z20_1700kv_6S_Brushless_Motor__KV_1700-details.aspx) is your motor, with a 1000 RPM drill, the output voltage should be near 0.6 volts (not .06). If the motor is lower KV, the measured voltage will be higher.

Finally, you may have tested with an AC setting, but you didn't test with a voltage setting. That's equally important; 20 ma is a setting for measuring current, not voltage. Set the meter to AC Volts (VAC or ~V or something along those lines) and make sure the probes are plugged into the corresponding sockets. Again, the results should be near 0.6. If you're getting a value like the others you've posted, along the lines of .03 or whatever, you either have the meter set wrong or have a fried motor.

11-14-2009, 05:58 PM
Ok, re-tested today per your instructions I set my meter for ac and switched to 200. I get .4 from all leads consistent. I then put a smaller motor on park 400 980kv. I got .7 from it so i hoope this is good news. I am going to get an inline fuse today. put it between the speed controller and the motor (read somewhere this is a good way to keep your speed controller from blowing from a short.) I read 35amp fuse would be about right. then I will spool up really slowly so as not to overload the fuse too quickly.

Will post my results later today....thanks soo much for your expertise aramid!

11-14-2009, 06:28 PM
You're quite welcome for the help, but my expertise is nowhere near as complete as Ron's, up above. It sounds like your motor is probably safe, but you still might find it doesn't behave the way you expect. The first time you connect it to a speed controller, advance power slowly and be prepared to cut power in a hurry if something seems wrong.

I don't particularly like the fuse idea, though. You'd technically need at least two of the three motor wires to be fused, otherwise you could end up with a short across the two unfused leads and still fry something. A more appropriate location would be between the battery and speed controller, so you would only need one fuse, but only if you have a separate BEC which is not on the fuse (otherwise, you'd lose flight controls when the fuse blew). In either case, if you choose a slightly oversized slow-blow fuse, you shouldn't need any special precautions or slow spool-ups to prevent accidental failure.

Rather than adding failure points, weight, and complexity to your model, I think a much better idea would be to make an inline fuse system for bench-testing. A small length of wire with battery plugs on the ends and a fuse in the middle would allow you to easily plug a fuse in between the battery and speed controller to safely test new or questionable components. Once you'd made sure everything worked, and made sure the power draw was appropriate for the components, you could remove the fuse system before you actually flew. This gives you the best of all situations - safe component testing, with minimum weight and complexity in the air.

11-14-2009, 08:38 PM
Yes this definately is for bench testing the motor only. Its not installed in anything right now. here's what i read re the fuse. I guess this means the fuse goes in between the battery and speed controller right??? I thought it meant between controller and motor.....

And, lastly, before connecting the questionable motor to your ESC, you may want to put a temporary fast blow type instrument fuse in series with the battery and the ESC. Typical fuse size would be on the order of 10-15 Amps for an ESC of 40 Amp rating or higher, and 5-10 Amps for the back yard flier type.

Be certain to slowly :cool: wind up the motor without a prop with the small in line temporary fuse during testing, since quickly winding up the motor can blow the fuse due to high starting currents