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View Full Version : Motor repair of inrunner with broken winding


Bill G
12-28-2008, 01:28 AM
First, I'll start by saying that I'm convinced most thin wire inrunners can probably handle much more power than rated for. I've only blown 2 in my time, and they both were in the same setup where they were ran hard. Interestingly what I found was the both blew at spots where the windings had been nicked. I would bet that many inrunners fail due to nicked wires during the mfg process. The GWS 4600 long can had a number of nicked wires which blew, where I assume they packed them in to make the endbell fit. Sloppy work creating nicks.

The motor that I repaired for this thread had nicks caused by an idiot:D who hit them with too long of a mounting screw. The motor still ran afterwards, and it was so long ago, that I only remembered doing it after taking the motor apart and noticing the damaged spot from the screw end.

The repair:

I carefully moved the broken wire ends slightly away from the other windings to allow for a pen tip solder iron repair. In the first pic one can be seen broken, but a second was nicked so bad that I pulled it away from the "dented" area caused by the screw, and the wire broke also at the nicked spot. Next, you have to carefully scrape insulation from the winding ends with a sharp exacto knife tip, while using a small flat blade screwdriver to support the wire end while scraping. This may have not been necessary, as the solder gun seemed just capable of vaporizing the varnish right at the wire end, when touched to it. Still it's probably a good idea to try to scrape away as much varnish as possible before soldering.

Bridging the broken ends was done by twisting several strands of small gauge copper stranded wire, and tinning them. Next, hold this tinned wire across the broken motor wire ends and bridge them together with the pen tip solder iron. Finally, carefully cut away the excess wire repair, leaving nothing but the small bride repair, with fine cutters.

With this motor, there was reasonable clearance between the windings and the endbell, so there was no worry of shoring the repair out, when re-installing the endbell. I pushed them back in place as much as possible, without shorting together, or against any other windings, since the area below had been scraped a bit by the screw that caused the initial damage.

During the first test, it didn't work, so I lightly manipulated the repairs with a knife tip and noticed that one had probably been a cold joint, as it came apart easily. You want to try to test the repair for strength to determine if the solder job is sufficient, but the windings are so weak that you really can't do this sufficiently. Best to get a magnifying glass and examine the quality of the solder bridge. Soldered again, reassembled the motor, and voila, it works fine. Ran at 7A load with a GWS 5030 prop on the wattmeter.

While I wouldn't trust my life :Q with this motor now, I will use it on a plane that glides well, and go from there. Hopefully a good useable motor.

Rolling Thunder
12-28-2008, 02:17 AM
does it have to be revarnished in some way as well?

Bill G
12-28-2008, 03:01 AM
does it have to be revarnished in some way as well?Not unless it would touch anything. Fortunatley there was enough space between the windings and the endbell that I was able to leave the repair areas postioned away from each other, and the other windings. I doubt varnish would work, since the solder job leaves some sharp points that would not insulate with a thin coating. If I had to insulate, I'd probably think of trying to do it with a bit of thick CA, applied with a small tool, in a few layers. Hopefully it would take the heat. I imagine the motor people may chime in with a temp proof coating for these types of repairs, if insulating was necessary?

One nice thing is that I now again have 2 of each kv version of this motor. If it holds up this will be nice, as I will still have 2 matched sets of motors.