openinverter forum

Hi, I'm converting a gs450h to EV (hopefully).
I'd intended to keep the orignal engine rad and AC/rad and use the engine rad to cool the inverter/motor coolant.

However the battery I'm looking at buying will be too long and will protrude through that area, so id have to get inventive with some smaller side mount radiators to cool them.

Does anybody have an idea of how much cooling the inverter and motor will need when running around 150kw?

Is the original engine rad overkill or about right?

Sorry I know it's a bit of an abstract question, but any info from somebody with experience is helpful.

Thanks
Dan

Well, the original radiator is meant for the ICE engine. Lets say hard or fast driving you will get 100kW of usable engine power out of it. At 20% efficiency this is about 400kW of waste heat. Or take something more in the realm of regular usage, cruising at 120 km/h you need about 20-25kW of power, again at 20% efficiency this is 80-100kW of waste heat that the radiator needs to take care of.

For electric only: 150kW continuous motor power is what, like 200-240 km/h say you add all inverter and motor inefficiencies together you get to about 85%+ efficiency. Which means you need to get rid of 22kW of waste heat. In a more regular application at the same 120km/h speed you need to get rid of 4kW.

So the conclusion is that your original radiator is way overkill and probably a lot of dead weight.

OK thanks for breaking it down, that was the answer I was of course hoping for!

jnsaff wrote: ↑Sun Oct 24, 2021 5:40 pmAt 20% efficiency this is about 400kW of waste heat. Or take something more in the realm of regular usage, cruising at 120 km/h you need about 20-25kW of power, again at 20% efficiency this is 80-100kW of waste heat that the radiator needs to take care of.

I used to do the same math to explain this to people.

... and then someone pointed out that not all the waste heat is dissipated by the radiator. A lot of it goes out the tailpipe as exhaust.

What percentage of the heat is lost by the radiator, and what percentage is lost as exhaust? Very roughly, around half.

So, take those rad numbers and chop them in half.

Also, consider that you will quickly overwhelm the cooling system of a vehicle if you're using anything even close to a full load.

... That said... it's still probably close to an order of magnitude overkill to keep the original rad.

Let's put this another way:

At those power levels, you'll run out of battery so quickly you won't have time to build up enough heat to worry about. You're running at 150kw... that means with a 75kWh pack you'll be dead empty in 30 minutes. And, you'll be travelling at speed, which is going to provide it's own not-insignificant cooling.

It's not that simple. The electric drivetrain has to be kept at lower temperature than the ICE, which in turn requires a larger radiator per kW dissipated.

Outside temperature has a large effect there, as in some places around the world that can almost reach the target temperature of the drivetrain, in effect requiring an infinitely sized radiator or more reasonably a heat pump.

But let's say originally the radiator was able to dissipate 200kW continuous at 20degC outside temperature, at 80degC coolant temperature. Now you need to keep the coolant at 40degC, which is third of the temperatuee difference, so the original radiator can do that at third of the power which is 67kW. That's still 3x the required 22kW, so you can do with a radiator 1/3 of the size of the original.

Of course you then have set yourself a maximum outside air temperature for maximum performance. The original radiator would likely give enough cooling in basically any weather.

Yeah very good point, the temperature differential between the coolant and ambient is much lower and therefore cooling potential per area of radiator will also be lower.

Thanks for the replies, great to have a base of experience!
Refreshing compared to the usual car forums!

In the end I've decided to go for a different battery pack design allowing me to keep the original cooling pack. But this has been a good learning point for me, thanks for everyone's input!

On a separate related note - the two wires coming out of each resolver on the transmission, pins 4 and 8 - is there a way to hook those to a separate device like a Arduino or something and have a screen displaying the temps?