Solved! Controller phase bolts gets very hot

[jai134]

I don't know what the bolts where you connect the three pairs of cables from the motor are called but they where very hot when I came back home after a trip today. So hot so I burnt my hand when I touched them. I checked the controller temperature with my PC software and it said 54 degrees celsius.
I wonder if it can be to thin cables from controller to the motor? I use 50mm2 between battery, BMS and motor, but the motor comes with only 16 (or something close to 16).

 

[amberwolf]

I don't know what the bolts where you connect the three pairs of cables from the motor are called but they where very hot when I came back home after a trip today. So hot so I burnt my hand when I touched them. I checked the controller temperature with my PC software and it said 54 degrees celsius.
I wonder if it can be to thin cables from controller to the motor? I use 50mm2 between battery, BMS and motor, but the motor comes with only 16 (or something close to 16).

If only the bolts are hot, and not the whole length of the wires, it means they are not tightened sufficiently, and not forcing the lugs of the cables from motor to controller together hard enough to make a good connection. So there is too much resistance, and heat is created there.

Can you post a good, well-lit picture of the connections? We might be able to suggest changes you could make to fix this without replacing the entire connection setup.


If the wires themselves are getting hot, all along their length, then it could either be that they are too thin, or that the phase/hall combination is incorrect, causing higher-current operation than is normal.

 

[jai134]

I tightened the bolts before I went out for a ride. 40 minutes later the bolts are warm, not hot. It was a relaxed trip, mostly slow with half throttle. Yesterday I was pushing it harder so it is hard to tell if it's better or same. I had to lengthen the cables between motor and throttle if that can affect the temperature of the lugs and bolts? After what I can see the peak amps are low, a little over 200A, so it should not be a problem.

 

[4πr^2]

If truly the bolt generating the heat (and eyeballing those to be zinc plated steel bolts) - a brass bolt would have about half the resistance of steel, and a copper bolt would have about 1/6th, if memory serves.... maybe even less. So either of those two materials would create considerably less heating based on IR^2.

Though keep in mind that would be 'all else being equal' and assuming the heat isn't coming from loose / dirty / ill-fitting / poorly crimped connectors, too small of wires, internal controller heat, etc.

https://www.mcmaster.com/screws/material~brass

 

[jai134]

Thank You! For now it is ok. I'm taking it easy and has quite moderate settings so after tightening the bolts it is no problems at all. Lukewarm at most.

 

[amberwolf]

If truly the bolt generating the heat (and eyeballing those to be zinc plated steel bolts) - a brass bolt would have about half the resistance of steel, and a copper bolt would have about 1/6th, if memory serves.... maybe even less. So either of those two materials would create considerably less heating based on IR^2.

The bolt material's current conductivity is not relevant, because it only provides the clamping force between the actual conductors, which are the ring terminals on the wires and the top contact surface rings of the threaded tubes of the controller. The bolts don't conduct any current if everything is correctly installed. If the bolts have to conduct current then the wiring is not correctly installed.

Generally you'd want this order:
Bolt head
Lockwasher (to prevent loosening from thermal cycling, vibration)
Thick hard Flatwasher (to create even contact pressure all around the surface of the rings)
Ring Terminals of phase wires
Top Contact Surface Rings of the threaded tubes of the controller phase connections

Note that no or too thin/soft a flatwasher allows uneven contact of the phase terminal rings to the controller terminal rings, and creates higher resistance than it should. No washers at all means there is only pressure where the bolt head itself presses against the rings and potential loosening over time with thermal cycling and vibration. A lockwasher but no flatwasher means contact only where the lockwasher presses the rings together.

The faces of the ring terminals that contact each other and the top contact surface rings of the threaded tubes of controller are the conductive surfaces, and are what must contact as fully and tightly as possible. As long as they are very flat to each other and tightly pressed together, they will not generate heat from resistance between them.



Then the other source of resistance at that area is the crimp tube of the ring terminals where they connect to the wires themselves. If the crimp is insufficiently tight, there will be more resistance than there should be, and heat will be generated there.



If ring terminals and top contact surface rings of the threaded tubes of controller are in full contact, and the crimps are correctly done, then the other source of heat is the FETs in the controller itself, conducting thru the metal of the phase current paths out thru the threaded tubes of the controller connectors into the phase wires themselves. This is normal. If this heat is excessive, then it means the controller casing is unable to carry away the FET heat quickly enough (so the entire casing will also be hot), and a larger-surface-area heatsink needs to be attached to the controller casing, and/or greater airflow provided.

 

[jai134]

Great! Thank You so much. I will mark this as solved. The bolts a not hot any more. It was enough to tighten them.