Water Cooling Mass Flow Rate?

[GrandeDan]

Hi All,

I am working on using the liquid cooled 5kW BLDC motor to run my boat. I am having trouble with cooling though. I have a 5kWh battery and am trying to run wide open for that hour. There doesn't seem to be enough cooling and the motor overheats. Does anybody know the mass flow rate of water that needs to be running through the cooling passage to cool the motor?

Side note: I am using sea water and not a heat exchanger.

[GrandeDan]

I should add that the controller model is EZ-A48500

[Ziper1221]

Check the outlet temperature of the water cooling. If the delta T is large, then you would benefit from moving more water. If the delta T is small, then you wouldn't, and the limitation is somewhere else.

[GrandeDan]

Check the outlet temperature of the water cooling. If the delta T is large, then you would benefit from moving more water. If the delta T is small, then you wouldn't, and the limitation is somewhere else.

The temperature difference between inlet and outlet is roughly 3 degrees F. It is not a large difference but with cooling, the more mass that flows through, the more heat will be exchanged. My issue though is that when I run the 5kW motor at 140 amps for an hour on a 52V setup, it still overheats. I would agree there is enough water cooling it but I should be able to run this hard for an hour. This is the only thing I can think of that would be fixable.

[Bikemad]

I have no experience with the EZ Bluetooth App so I don't know what temperatures it actually monitors and displays. Are you sure that it's the motor that's overheating or could it be the controller?

Does your coolant flow in series through the motor first and then through the controller?

What rpm is the motor running at when it's drawing the 140 Amps?
If the motor speed is considerably lower than its rated 3,500 rpm it might be running too hot because the motor is being overloaded, in which case a smaller pitch/diameter prop (or possibly a gear reduction on the propshaft) may be required to reduce the load on the motor to allow it to operate at a more efficient rpm, which should then generate less heat in the stator windings.

Alan
 

[GrandeDan]

I have no experience with the EZ Bluetooth App so I don't know what temperatures it actually monitors and displays. Are you sure that it's the motor that's overheating or could it be the controller?
 

I am positive it is the motor overheating. Through the GM monitoring app on WeChat, I can see them temp limit is 150degC for an alarm and 155degC for it to depower. 160 degC is Shutoff. I watch the live motor temp reading say 155degC. The controller also has temp limits to it, but I am reaching the motor temp limits before the controller.

Does your coolant flow in series through the motor first and then through the controller?

Coolant flows from controller to motor but with a small temperature differential between the inlet and outlet temp of the coolant, I don't believe switching the order of this will help very much. Especially because the motor temp is far hotter than the coolant. a 3 deg temp differential will not cause a huge difference in heat transfer between motor and coolant.

What rpm is the motor running at when it's drawing the 140 Amps?
If the motor speed is considerably lower than its rated 3,500 rpm it might be running too hot because the motor is being overloaded, in which case a smaller pitch/diameter prop (or possibly a gear reduction on the propshaft) may be required to reduce the load on the motor to allow it to operate at a more efficient rpm, which should then generate less heat in the stator windings.

Motor is running at roughly 3600 underload.

I would like to note that the cooling loop on top of the motor (where ALL the cooling is located) does stay cool. Cool enough I can touch it. But  moving down to the middle of the motor, it gets so hot on the outside casing that it could burn skin. I am wondering if GM just has an inadequate cooling system for their motor to run at full power for any extended period of time.