Controller & motor wiring gets very, very hot-help!

[comfybob]

I am new to the hobby. I know nothing about EV. I bought a hub motor from a Chinese EV supplier to mount on my 20" bike wheel to help me relieve arthritic knees pain.
The motor three (3) wires coming from the controller to the motor and the controller (2 photos attached)
get very, very hot in the first few minutes of riding. I am using a LiFePO4 24V 10Ah battery.
The supplier suggested to use lead acid or NIMH battery instead, but there was no difference. I want to avoid melting the wires.
Any suggestions are very welcome.

 

[comfybob]

Apology,
Photos attached.
View attachment 1

 

[Pete]

Are the short, heavy gauge phase wires from the controller getting hot as well, or is it just the portion of thinner wire after the bullet crimps ?

I can't read the gauge (AWG) number on the phase wires comming out of the controller. But at a guess I would suggest they are around 12 to 14 gauge ? If so then the motor side of the phase wires has to be something silly like 18 gauge ?

As the cross sectional area of the wire goes down, it's current carrying ability goes down and the heat dissapation goes up.

In short, the phase wires on the motor look way too small. I have no personal experience with hub motor's but my Cyclone (24v, 650w) has 12 gauge phase wires and the main feeders to the controller are 10 gauge. Suggest you replace the phase wires with something beefier. At least 14 gauge, but as big as you can squeeze in the axle. Teflon insulated aircraft wiring has seriously thin insulation compared to it's actual AWG.

 

[docnjoj]

I agree! Those phase wires (the 3 together) look anemic and should be replaced if they get too hot! Ask ur dealer to help!
otherDoc

 

[Pete]

To be brutally honest, selling a hub motor with phase wires that small is selling a product not fit for the purpose intended.

Don't get narky about it, but do go back to whoever you got it from and ask them nicely if they will rewire it with something a little less anemic.

 

[safe]

I'm upgrading everything I have to 10 gauge. But I'm pulling in excess of 1400 watts. A 24 volt 12 amp controller is only going to pull 300 watts at best, so I agree that 14 gauge should be enough. Those wires are probably 16 gauge which is right on the borderline of workable. If they are 18 guage then that's criminal. :x

 

[fechter]

Other than the wires getting hot does it seem to run OK?

Using a different type of battery will not change anything. The current is limited by the controller.

Yes, the size of those wires is a joke. Replacing them with larger wire will help, but it may not be possible to put larger wire through the axle and that would require taking the motor apart.

If the wire has high temperature insulation, you could cut the wires and splice on heavier wire as near to the axle as possible. I would highly recommend soldering the wires wherever possible, rather than using crimped connections. There is still a chance that the wires inside the axle could melt and short out, but keeping the skinny part of the wire as short as possible will minimize losses and heating.

 

[Pete]

Had another look at the the controller closeup pic.. I would keep an eye on the battery feeder wire temperature as well, they look just barely adequate.

I personally think that battery feeders should be at least one gauge and preferrably two gauges heaver than your phase wires. Your phase wires only have to deal with a 33% duty cycle.

About the second best wire (from an insulation thickness perspective) is teflon insulated wiring used in aircraft. Get chatting with the mechanics at your local light aircraft hangars and they can probably fix you up.

For the very thinnest wiring insulation check out Kapton. Note that I am NOT recommending using Kapton as it does some really ugly things when you do damage the insulation and create an arc.

 

[deardancer3]

If the vendor suggested you change your battery chemistry to resolve this issue, He is an idiot and criminaly incompetent..

The wire to your motor is too small. Read the wire gauge number written on the motor wires coming right out of the controller, that is what should be going to your motor.

http://www.powerstream.com/Wire_Size.htm

see wire gauge table above.

your controller is rated at 12 amps? that means 24 amps peak.

We could go into some detailed technical explanation, but basically too small a wire starves power to the motor windings. If the motor is loaded, it asks for more, but the small wire keeps starving the motor, but more means more current, over the resistance of the wire means more HEAT.

 

[Pete]

I would highly recommend soldering the wires wherever possible, rather than using crimped connections.

Hmm, crimping Vs soldering. now there is one of those lovely religious arguments .
Crimps done with quality tools and quality crimps can have very nearly the same resistance as soldered joints. They can be done faster and easier with a lower skilled tradesman, especially on seriously heavy gauge wires (4 gauge and bigger). Also very vibration resistant. But the caveat is all the tools and consumables have to be top quality.

Having said that, if you do not have access to the good gear and you do have reasonable soldering skills, then I 100% agree that soldering is the way to go. Low quality crimps are a recipie for letting out lots of expensive smoke.

 

[Pete]

Dancer, that is a very useful table and really needs a link in the EV basics forum.... fechter??

 

[Link]

Odd...I've got similar sized wires on the Golden Motor, and they're not burning up even with my 40A controller. Even if they were a gauge down from mine, they should still be able to take a measly 12A controller.

They could still use upgrading, though. See what you can fit through the axle and go with that.

 

[Pete]

Be careful comparing physical size to AWG #. Cheap car jumper leads are a classic example of using really thick insulation to make the leads look like high amperage leads yet I have seen fat lead with 16 gauge conductors.

 

[Link]

True. The GM's wires look like they're around 16ga, but it feels like the insulation is very thin, so they might even be 14ga. It's hard to tell. I have to get off my lazy ass and see if I can replace them with beefier teflon wires...

 

[comfybob]

Many thanks to all for a very insightful info.
A question: Why then the controller gets also very, very hot?
Would replacing the wires with thicker ones alleviate this problem?
I have difficulty removing the motor cover to get to the wires.
The screws are very tight and I am concerned that I may damage them. Any suggestions?
Just for your interest, attached is my bike on which I would like to mount the hub motor.

 

[Pete]

The body of the controller is getting hot to the touch as well ? I find my controller runs basically cold when I use WOT. It only starts to develop any sort of heat when I run a partial throttle, high load and low speed. Do you have a Cycle Analyist yet ? It would be good to know what sort of current draw your controller i pulling. Something does not seem right for you to be generating so much heat.

What sort of fasteners hold the motor cover on ? If it is hex head bolts, use some penetrating oil, then a good quality 6 point socket. A 6 point ring spanner at a pinch. Do not do anywhere near it with an open ended spanner or shifter. I would not use any sort of heat as you may damage the magnets.

 

[Link]

Where do you have that controller? They tend to get hot if they can't get good airflow.

And I bet it has to do a crapload of current limiting to keep the motor at 12A max. Current limiting via PWM generates much more heat than when the FETs are fully open all the time (full throttle; controller not limiting current).

And they probably skimped on the FETs and have ones with relatively high resistance in them. Replacing them with a better model might help.

 

[Knuckles]

Well, that motor looks like a Bafang PMGR with typical wire harness. The controller is a stock (low end) BLDC controller. At 24V and 12 amps NOTHING should be getting very hot (just slightly warm).
I also noticed that all the phase (and hall) wire colors match up. Although this seems to make sense to most folks, it may not be correct.

I generally will go thru the first 12 possible wiring combinations just to be sure. That motor probably has an internal free-wheel so only 1 out of 12 of the combinations are correct.
Do your testing under no-load conditions also. I like to use this spreadsheet as a guide ...
Start with column 1 and row 1, then try C1R2, C1R3, etc. (just varying the phase wire combinations). Then, switch the halls for column 2 and try R1C2, R2C2, R3C2, etc.
You will know the "right" combination as the motor should run very smooth in the forward direction. This testing gaurantees the wires are connected correctly.
And yes, those phase wires are wimpy. But all the Chinese motors come the same way. There may be something more to your problem than just the wire gauge as a cause of excessive motor AND controller heating.

cheers

 

[johnb]

Comfybob,

Could you give us an idea about your ride. What speed do you go? Is it flat or uphill? Does it run smoothly and feel powerful? Is the controller in a bag?

It could be to do with the wire gauge but I suspect not. I'm thinking that the controller may not be limiting correctly and allowing too much current to flow.