openinverter forum

Hello all

I am currently planning and designing my cooling/heating system for the engine, inverter and batteries. I am using the EM57 motor with inverter.

I would like some feedback regarding what coolant temperatures you other Leaf motor/inverter users get during different driving scenarios. Any and all data is helpful!

I am hoping to be able to combine the coolant & heating loop for the motor/inverter with the battery loop. Of course this is only realistically possible if "engine" coolant temperatures never exceed say 30-35 deg C in a worst case scenario, so as to not overheat the batteries. Otherwise I will have to have two separate systems, one for the drive unit and one for the batteries, each with separate cooling (and for the batteries, separate heating which I will incorporate regardless of solution, to be able to pre-heat the battery pack in cold weather). Since the deltaT of coolant/environment is probably going to be quite low compared to an ICE, shedding heat will be inefficient without large single-row radiators and/or high flow rates.

The data I have been able to find so far suggests that EM57 motor/inverter efficiency is always going to be >90% in a motorway cruise situation, so somewhere between 1-2 kW of waste heat that has to be dealt with by the radiator in that scenario. A post in the Nissan leaf owners forum mentions max temp of 59 deg C which would of course be way too hot for the batteries https://mynissanleaf.com/viewtopic.php?t=23353

I have seen similar temperatures when driving fast, like 70°C or so.
In winter its good to heat the batteries but of course in summer you would rather have the batteries as the first device after radiator.

The highest battery temperature I saw was 52° on a hot day after 4 50 kW fast charging sessions.

Well i have Leaf motor and Volt inverter temperatures at some 35°C. In summer it went to 40°C and i could actually feel inverter getting a little warm after a long drive. I actually needed to put paralell resistance to my coolant gauge sensor since car would start to raise error if temp sensor wouldnt move to 90°C after some minutes into the drive. Protection from coolant leak i guess. And that sensor now stays at 90deg and wont budge! I tried to calibrate it so fans would come on, but i cant get enough dT to move the needle...
My coolant line starts with a low but long engine cooler from Fiat Uno car, then pump, inverter, motor, Eltek charger and back to cooler. I dont use forward cooling fans generally, though i have a plan to implement automatic thermostat. I find Lebowski inverter surprisingly efficient, or my cooling system is really good at its job.
In future i intend to add 2x Outlander chargers into the loop. I belive there is enough coolant in the system so inverter temperature will never go above 50°C. Actually the highest I could observe from use i could see charger would actually drive temperature up to 45°C since cooler was not in the airflow. I think i will have to think about cooling fan switching thermostat when i add those chargers...

65°C is actually not that hot for batteries, since you need to think of how much kW is behind that heat. If you switch on additional dQ consumer (batteries) you will quickly ran out of dQ to feed to your system. Then you will actually have to add dQ or force motor to be less efficient.

You could also just use webasto fuel heater with separate coolant loop and have an ordinary household thermostat valve in your battery box to open coolant path to battery if temperature drops below 10°C and close if it is above. I have seen it done. If you want to be warm, so does the battery.

I'm using the original petrol engine radiator in my conversion, which is huge, and simply pump coolant into two loops from it, one through the inverter+motor+charger and one through the Tesla Model S modules.

On sunny summer days, let's say 25°C outside temperature, after a DC fast charge session the battery does cool down while driving, almost fast enough for a second full charge when it gets empty. I think I have a 50°C temperature limit when charging.

It could use some extra cooling. Maybe having a separate radiator for the inverter and motor would help for long trips, but just forcing more flow into the battery modules could also work.

I have no idea about coolant temperatures at any point in the loops, but in this setup coolant stays much cooler than what the internal inverter and motor temperatures get to.

Thanks for all the input!

My main goal is to keep the batteries at an optimal temperature while driving. I currently do not have plans for fast charging, but of course the cooling system will come in handy if/when I decide to implement fast charging. Battery heating while stationary will be done with an immersion heater for the battery cooling loop only.

Seems like temps can hit 60 deg C+ while driving, then. I will have to scale my system accordingly. Batteries will surely be first in the loop after the radiator. Good data on battery efficiency seems to be pretty scarce, I've found one study showing 96% efficiency at 5c discharge for LiFepo4 (not my chemistry).

With A couple valves you can very easily switch from a series coolent loop to a parallel loop.

I’m trying to maximize as much energy efficiency as possible. so any “waste” heat, I’d like to use if I need it. Ether heating the batteries, or the cabin.

A very crude but simple drawing of the basic loop.