Liquid Cooling for Nissan Leaf motor

by Ben N on May 24, 2020

I’m getting ready to bench test the Nissan Leaf motor, but both the motor and inverter use LIQUID COOLING! I doubt the motor and inverter will make much heat at all when bench testing. However, since I have to figure this out sometime anyways, I thought I would get it taken care of right now.

Leaf motor with radiator hoses connected.

The first thing to do was to get a pump.
I took a look through a number of 12V electric pumps currently available for the automotive market. One pump I thought might work well is a Prius inverter coolant pump. Surprisingly, they were more expensive than I thought on the used market!

I did find a Bosch brand pump that looked pretty good. The specs of the motor actually list it for use with electric vehicles and electronics cooling. I also posted it on a DIY Electric Car group, and another user said that he used the same pump, with good results, on his Nissan Leaf powered project.

Since I was mail-ordering the pump, I also ordered some 3/4″ radiator hose and stainless steel hose clamps at the same time.

Once I got the pump, the first thing I did was identify the input and output ports of the pump, and the polarity of the power connection. On black plastic, there is often raises lettering, but since it’s black on black, it’s ALWAYS hard to read! I marked them with a silver Sharpie pen.

The pump did NOT come with a wiring pig-tail, so I crimped 1/4″ solderless connections to a pair of wires. I could then run the wires to a small 12V battery through an automotive fuse. Unlike a bench power supply, the battery is very small and portable. Since I’m working with water, the battery also eliminates the AC shock hazard which would be possible with a power supply plugged into the wall.

I connected a short section of radiator hose to the input end of the pump, and filled a bucket with water. Placing the pump into the water, I plugged in the DC power. One thing I had to do was “Prime the Pump.” Many pumps need liquid IN the pump before it can work. I simply pushed the pump end (but not the electric motor) down below the water line to fill it.

Bosch pump moves water faster than my garden hose!

With water IN the pump, it started working, shooting a geyser of water from the outlet. I also wanted to check how much power the motor was using. I clamped on my DC Ammeter to one of the wires from the battery and found that the pump was drawing 0.8A. At 12V, that’s about 10 watts. Seems like a very reasonable amount of power.

The flow rate looked great, but I would need to do something to quantify that flow.

I brought out a bucket with measurements marked on it. I set my stopwatch and started pumping from the one bucket to the other. In 30 seconds, I had pumped 3 gallons of water. That translates to 6 gallons (about 23 liters) per minute.

After that, I wanted to actually hook the pump up to the electric motor. This was a pretty simple matter of cutting another section of hose and connecting it from the pump outlet to one of the ports on the motor. The other port of the motor used whatever was left from my roll of hose back to the bucket.

After priming the pump (I had to break the air-lock at the motor,) water easily flowed from the bucket, through the motor, and back to the bucket.

The flow looked just a little slower than it did when it was free-flowing in my first test. I was expecting that, as the water would meet more resistance going through a longer section of hose and the water jacket of the motor.
What I wasn’t expecting was that the current draw from the electric motor was slightly LESS than my first test. As best I can tell, it is probably from a siphon effect. On my first test, I did NOT have a hose on the outlet port. With the hose going from the Leaf motor back to the bucket, it’s likely that the water “pulls” and makes it easier for the pump to send water to the motor because of that.

I wasn’t expecting it to be difficult to add liquid-cooling to the motor. This is pretty straight-forward – standard size hoses, clamps, and basic 12V power. In the final installation, the system will include a radiator and fan, likely controlled by a thermal switch.

Next up? Wiring the Thunderstruck Vehicle Control Unit to bench test the motor!

Until next time, stay charged up!
-Ben Nelson

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