Does running brushed motor w/o controller harm motor?

While I have enough prismatic cells to make a 36v pack, ea are 30ah so bulky. I ended up making a 27v x 30ah pack that worked out fine except with regards to a controller; 24v would cutoff a bit early (but in retrospect, and I'm not great figuring this stuff out but seems cutoff would be 2.7v instead of my bms' which actually is lower than I like a 2v.) Originally I burned a couple controllers out, but maybe that was due to my faulty wiring as I had just started my e-bike project and was all new to me.
So, forward 3 years later, while I had built it to do 15 mile straight country runs, very little stop and go, charge before coming back, I stopped doing that and have been using it for in town rides, max 3 miles but a lot of stop and go. Motor pulls 35a dead stop, 15-20a while accelerating and evens out at 10a. Lately I've started hearing a rattling sound that I've been advised and agree is most likely a detached magnet/s. Do you think this would have happened anyway, or is the sudden hit of 35a having an adverse effect? I use 2 toggle switches; one by handlebars to turn on or off as I ride, and a second one in rear to shut power down (also as a backup if front toggle ever stopped working, I can reach back and turn off master switch.) Thanks.

With a controller, you normally have current limiting which kicks in during startup and high loads. Without limiting, the motor can get much higher than normal current peaks which translates into higher peak torque output. Most brushed motors won't have any problem with this as long as the temperature doesn't get too hot. I can think of lots of applications where the motor is just switched on/off.

I've also run motors designed for 20A maximum at levels closer to 100A and never had any problem other than heating.

I've had magnets come loose before. Usually it makes a horrible noise and it's obvious something is very screwed up. Nothing a little epoxy couldn't fix.

Most brushed motors come apart fairly easily. Dealing with the brushes is the tricky part. Some designs let you remove the brushes before you take the end off. Others you just have to let the brushes fly out of the holders and use some method to hold them in when re-assembling.

I normally use cotton thread to tie each brush back into the holder. One the brush plate is in place on the commutator (a little flat bladed screwdriver pushing in each brush in turn can help here) cut the cotton and pull it out.

The lack of current limiting will probably give you a little extra wear but not usually anything to worry about.

A vehicle alternator is a brushed motor when you apply voltage to the field and take out the regulator, could work without a sensorless controller then, just be on or off. I even read that could even make alternator into a brushless motor by adding hall sensors. I have purchased a used alternator from the junk yard, but I am waiting on having a larger order in place to get sensorless cont from greentime.

fechter said:

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Well that's good to hear as my toggle switch/27v system works pretty good for me. Any suggestions on what kind of epoxy would be best for reglueing magnets? I've read some threads mentioning jbweld, pc11, dp420. Is there something else that'd be well suited for this job? Thanks.

Look for some high temperature stuff. There is a topic about it somewhere, but I can't seem to find it.

It's also really important to clean the surfaces first. Use fine sandpaper first, then wipe with alcohol.
I've had good luck with whatever stuff I got from the hardware store. I would also recommend avoiding the 5-10min fast curing types. The slow 2 hour kind will give you enough time to align things before it starts to set up and seems to be stronger when it's cured. Also try to keep the parts pretty warm once it's all lined up to help the epoxy cure. Somewhere around 40C (100F) is good. Just sitting in the sun will do it around here.

Hmm, so you've just used regular off the shelf high temp' epoxy with good results? Any of the magnets ever come back off afterwards?

alpharalpha said:

Hmm, so you've just used regular off the shelf high temp' epoxy with good results? Any of the magnets ever come back off afterwards?

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Stayed on through lots of abuse.

The only failure I had was a long time ago when I failed to properly clean the surfaces and there was probably some residual oil.
Sand paper followed by alcohol worked well.