Motor Over Heating Problems

PARADOXICLES

100 mW
Joined
Dec 24, 2012
Messages
38
i realized my post was in the wrong section, so im reposting it here and deleting the other, sorry

if youve seen my other posts, you know ive been having alot of trouble with the ebike im building. This is what i have...and whats currently happening with it...

Bike- Shimano Breakpoint duel shocks, 21speed ( now 7 speed with ebike kit)
Motors - GNG Ebike 48v 900w mid mount ebike kit ( 450 w motors x 2)
battery - Ping 48v 15 am LiFePO4

one of my 2 motors burned out at the beginning of summer ( after 40-60 miles total use), after about 3 weeks of debating with "Jon Chan" at gng, and taking motors apart per his request, i proved to them( him) that it had burned out, and that it was because magnet came lose and jammed up the coils, causing them to burn out...... finally they replaced my motor ( for 75$ despite the fact that it was under warranty and that it said " we will pay shipping" ( and when i got it the paid shipping on my package was half of what they charged me...geeerrr).... to install this new motor i had to do a bit of rewiring, the old motors were wired end to end ( black wires soldered together), i figured that this was putting extra stress on the front motor ( first in line, and the one that burnt out), so i decided to wire them up side by side so the second motor dosnt have to draw its energy through the first one, this also gave me an opportunity to give them plugs to disconnect rather then soldered wire, so i can disconcert them as needed for maintenance.

. Today was the first time i test rode it with the replacement motor, and it seamed to be even better then before, was running smother and noticeably faster( closer to the speeds advertised by GNG). After about 1/4 to 1/3 of a mile, i stopped to check things out and make sure every thing was ok.... they wernt.... right away i noticed my motors were very hot, and my brand new one had a some smoke coming out of one of the extra unused screw holes in it. needless to say i rode it back home using only the peddles.... then at home i realized my connector for my battery was slightly melted to its other half ( this is an EC3 plug rated to 60 amps).

im still new to the ebike world, but i think i know why this happened, and what i can possibly do to fix it. i have 2 ideas, and i was hoping some one with more experience could tell me if they will help, or suggest other possible fixes. the 2 motors are connected to one 900w controller, and i think its feeding them too much energy despite the fact that 450+450=900, the same rating as my controller. my idea is to replace the one 900w controller with two 450w controllers, each motor wired to their own controller. this should make each motor 100% independent of the other and reduce extra stress, right? my second idea is to add a circut breaker or fuse in between the motors so when they try to draw, or are given too much energy, the circut breaker/ fuse will pop and protect them. i think circut breakers would be better sense they are not destroyed when used like fuses are.

ive been looking into a 3rd option of rigging up a small radiator to liquid cool the motors, but so far it seams like it will be too big, and expensive, of a set up, plus i shouldnt need something so extreme for an Ebike, especially if it didnt come with the kit.

in the words of Freddie Mercury " i want to ride my bicycle"

any and all help you guys can give me would be greatly appreciated. thanks.
 
When you switched them to parallel operation (they were series before), you mentioned that they spun faster. It's possible that they are now running at a higher RPM than they are rated for, and are now experiencing eddy-current losses.

Best of luck, please post what works after you get it sorted out...
 
yes, they defiantly were getting higher RPMs, which was allowing me to reach speed closer to what was advertised by gng, (26mphin 4th gear, wasnt able to try the higher ones due to the over heating) but clearly something is wrong. i am not familiar with "eddy current loss" but i did just find this definition

" eddy current loss A phenomenon caused by the rate of change in an induced magnetic field. The relative motion causes a circulating flow of electrons or current within the conductor, leading to efficiency loss."

i still dunno what it means, but it sounds like it means energy is being held back? i dunno... what is a possible solution? would my 2 controller idea help?

ps, spinningmagnets, you seam to be a regular on here,and always reply to my posts, thank you.
 
When your controller says 900w, that is the rating for continuous use. Usually a controller can output maybe double the power of its rating. The best way to understand what your controller's maximum output is to look at its maximum amps. It should say on the controller the maximum amps. For example, I have a 48v controller that's rated at 500w, and it can output a maximum of 28 amps. That means that it can continuously output about 11 amps without overheating, but its true maximum is 28 amps:

48v X 11amps = 528 watts
48v X 28amps = 1344 watts

Perhaps you're using too large of a controller?

It would be helpful if you posted all the info on you kit including pictures. I like pictures.

Best,
Eric
 
beagle, thanks too, but sadly the only info on my controller is " 48v 900w" and then a brand name in Chinese... nothing more, so i have no way to tell you any more info about it. sorry. and its the motors overheating, not the controller.

but do you think splitting my single 900w controller into duel 450w controllers will help prevent the motors from getting too much power?

which reminds me,i have another question, my motors are brushed... the controllers im looking at say they are for brushless ( the only ones on ebay right now) is there really a difference between controllers for brushed and brushless motors, if so, what is the difference?... it also says "universal" so im a bit confused.

ill try to get pics soon, sun is setting so it would be best to wait.
 
I've recently begun learning about eddy-currents (along with other motor phenomenon). Each motor design has it's strengths and weaknesses, the two big things that affect eddy-current losses is the pole-count of the motor and the thickness of the stator laminations.

More poles costs more to make, but they also run better at low RPMs with a sensorless controller. Their downside is that if it was designed to run continuously at 1,000-RPMs, and you decide to up the voltage (or run the motors in parallel) in order to get higher RPM's, the higher pole-count means that the stray currents that are magnetically induced in the stator steel: they will reverse direction more often. Running a motor prototype slowly up through rising RPMs while it's on data-collecting instruments will identify how efficient the motor is at every part of the power curve.

For instance, going from 500-RPMs to 1,000-RPMs, the power may double, and also heat may increase 20F-degrees. Then, when you increase the RPM's to 1,500...and you expect the heat to go up another 20F-degrees (just like it did before), you are surprised to see the heat went up 60F-degrees.

In the engineers point of view, there is no benefit to raising the cost of the motor in order to reduce the heat at 1,500-RPMs, when the motor is sold in an application where it should be run at 1,000-RPMs.

A motor could work if the stator had teeth that were a solid chunk of steel, but if the loose electrons are magnetically pulled from one side all the way to the other, that long travel makes a lot of heat, due to the resistance of the electrons to being forced to move away from where they start out. So, stators are made from a stack of thin steel layers that are insulated, and electrons in the steel can only be pushed and pulled back and forth a short distance.

So, what is the optimum thickness of lamination? Twice as many laminations that are half as thick is more expensive. The old MAC had the common 0.50mm thick lams, because it was advertised to run at 36V, but...more people were using them at 48V and even up to 72V (more volts makes a motor spin faster). The new MACs use the less-common and thinner 0.35mm lams, for a small extra price.

The similar BPM motor still uses the thicker lams (@ 0.50mm), but it has half the number of poles compared to the MAC. The well-known BPM and the new MAC can both be run up to 2,000 motor-RPMs without eddy-currents being an issue.

I think your motors were specified to run at a specific max RPM, and they were designed to be as cheap as possible, while still performing well at that RPM.

Another motor characteristic that has a big effect on a motors performance is the kV, which is how many RPMs it provides per volt applied. If you take two identical motors, there is a certain amount of airspace around each stator tooth (wrapping wire around a steel core makes an on/off electromagnet). You can fill that airspace with many turns of thin wire, or a few turns of thick wire. Many turns will run slower, and fewer turn will run faster (if both motors are given the same voltage).

Since many motors of interest here are purchased with only one kV available, there are threads about stripping the old wire out and re-wiring the motor to a different kV.

There is no single perfect motor, each choice or change in the design seems to affect everything else. Run your bike as-is for a little while longer, but keep the RPMs down, and see if they still get hot. If they only get hot at high RPMs, I'd bet a dollar its eddy-currents because those motors were selected to run at a specific RPM with two motors run in series.

edit: the motors are brushed, they can only be run with a brushed controller.
 
WIth brushed motors, if you switch the leads, the motor will run in reverse. Is it possible that the wires were switched so the motors were running against each other? (Longshot guess.)

If you run two controllers, you will need to use smaller controllers or it will make the problem worse. Your problem is that too much current is being run to the motor(s).
 
I would start with buying a watt meter for $15 on ebay. Or a more quality one if funds allow.

That way you can see what power you're actually using as you ride around and may help diagnose if the motors/controller/gearing are the issue.
 
One thing I've noticed about through the gears stuff. It makes it possible to run in too high a gear and murder batteries.

Probably easy to murder motors that way too. Not that that was your original problem. I think you need to put that thing back the way it was supposed to be wired now.

You will definitely make more motor heat if you romp on the throttle from a start in the highest gear. But again, I think now you may have other problems related to your rewiring.

Brushed stuff, eww. Brushed always runs hotter. Little arc lamps inside, called brushes.
 
wow thanks for all the replies guys...

spinning magnets...wow... i dont even know what to say to that much in info.... the motor i burnt out i still have, i did not have to return it, so ive been considering experimenting with re wrapping the coils ( i tried it years ago for an rc car motor and it didnt go well) i have an old vacuum motor i will probably use for the replacement wire, simply cuz its what i have, and there should be 2 or 3 times the wire i need sense its soo big, so i know ill have enough, i dunno how well it will turn out, but if it works, i will share the results.

Gregory... can you tell me more about this watt meter, where id install it, and whatnot, my budget is pretty much nothing (thats why its taken me so long to get this far), but think i could get that, seams like it could help...

beagle.... yes, id split my 900w controller to two 450w .... but i need to know if the fact that the only available 450w controllers on ebay saying they are for brushless, will make a difference if hooked to my brushed motors.... i know the difference between the motors, but i dont know the differences between the controlers.

dogman ... yeah ive dicked around withit in different gears ( before this new motor) just to se what it can do, it has the power to start in 7th, but i know thats nto good for the motors so i only did it as a test, 1st is a 34t gear so its just instantly maxed out, ( if going up hill i can wheelie it in 1st)... it also maxes out 2nd pretty much instantly, so i tend to use 3rd ad my 1st, and usually use up to 5th as my main drive gears, 6 and 7th i usually only use when i have a good clear straight away, other wise i just have to downshift again when i get to a corner..... and yeah if gng offered brushless, i would of chosen them instead,



so i was doing more thinking, what if i added a resistor with the same power ratings as my motors, right before the motors that way regardless of what the controller tries to give them, or what they try to draw from the controller, the resistor should prevent them from going over their max safe limit.... this would also be a cheeper solution to my problem then replacing controller(s)
 
Once you wired the motors in Parrallel, you doubled their speed. Tha means you need to double the gearing reduction to get the same RPM from the motors. Othwerwise, they will over heat. Or wire them back the way they were, in series.

There isn't going to be an issue with the "first" motor getting more power than the second when in series. Electricity doesn't work that way. You need both wires in order to run.
 
drunk skunk, yeah im considering just doing the rewiring the way it was, i thought htis would help but i guess not...
 
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