# Motor/inverter cooling system design



## Tremelune (Dec 8, 2009)

I've got a Nissan Leaf motor and inverter in my Mini and I need some way to cool them. It seems like the cooling needs of this powertrain are _very_ modest without the batteries or charging involved, so I'm trying to figure out something small and cheap. Basically, I'm trying to design a system without a traditional radiator. The Leaf ports are 3/4" OD, so it would be nice if other parts of the system were, too. I doubt that'll be possible, though, so maybe I'll just figure out some adapters...

Here's what I'm thinking:










Small heater core (~7" x 8") with an inlet/outlet, but no filler cap. The smallest radiator I could find with a filler cap was too large. They should fit nicely behind the Mini grill without interfering with the motor.










Any ol' 12v waterpump...I'd use the Leaf pump, but it seems to want some kind of PWM, and I'd rather just buy something than figure that out.










Expansion tank. This gives me a place to fill and burp the system, since my radiator won't have one.










Clear tubing. No reason, except that it might look cool. 150°F seems like plenty of headroom.

I haven't done much math, but it sure seems like this is overkill for me needs. My other thought was to just use the Mini radiator (which is much larger), and put it sideways in the engine bay, near the fender (with no expansion tank). There wouldn't be much airflow through it, and I don't want to bother with a fan unless it's necessary—electric motors don't heat up when the car is stationary.

I'm guessing that this solution would also be overkill due to sheer size alone, so maybe I'm just creating work for myself with the heater core solution...I sold my Mini radiator, so any tiny OEM radiator would probably do...What's the smallest they've made in the US? Miata? Geo metro?










Routing would be pump -> inverter -> motor -> tank (maybe) -> radiator top

Are my assumptions correct? Can anyone think of a simpler/cheaper system? I don't think I need any of the traditional, pressurized elements, because I can't see how the coolant would ever get near boiling.


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## Tremelune (Dec 8, 2009)

Ooo, it's looking like adapting a hybrid system might be the way to go...Inverter coolers are small, cheap, and easy to find, and the EV/hybrid coolant reservoirs are designed with low pressure and similar hose diameters.


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## brian_ (Feb 7, 2017)

A radiator from a motorcycle, ATV, etc might be suitable... and would likely have a matching fan available if needed.


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## Duncan (Dec 8, 2008)

I suggest that in the British climate you will need the cooling system to avoid internal hot spots and that the overall heat load will be removed by the outside air flowing over the various bits!

I use a liquid cooling system for my battery - but I really just use the coolant to cool my controller and then flow around the battery - I don't have any type of actual radiator - the highest temperature I have seen so far on a hot day at the Drag racing is 27C - for max performance I should really be heating my batteries


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## MattsAwesomeStuff (Aug 10, 2017)

This is good basic stuff that - because I don't know anything about cars - is great information for me to see you troubleshoot through.

Please keep it up!

Do most vehicles have a 12v water/coolant pump? Black magic under the hood, I've never looked.

Expansion tank? Hmm, also something present on vehicles?

I was going to suggest if you need really minimal radiator, to use something like a transmission cooler, they're about the size of a paperback, but, I don't know what they have for cap or fill, if anything, since it'll have trans fluid it in not coolant. Brian's ideas are better.


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## Duncan (Dec 8, 2008)

I'm using a power steering tank as my coolant container - you don't need to pressurise the coolant as you are going to be using it a low temperatures - more important to make sure you have anti-freeze - and a little 12v solar water heater pump


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## brian_ (Feb 7, 2017)

MattsAwesomeStuff said:


> Do most vehicles have a 12v water/coolant pump? Black magic under the hood, I've never looked.


Only in some rare cases. Originally electric coolant pumps were only found on racing vehicles (to avoid cavitation in the engine-driven pump at high engine speeds), but there are some in production cars now (to reduce parasitic drag, or to allow cooling system operation when the engine is not running such as in a hybrid). Because the use in drag racers, electric coolant pumps are readily available aftermarket, typically as conversions of the existing pump from belt drive (which is not useful when you don't have the engine and thus don't have that pump).

An electric coolant pump intended for an engine would typically have more capacity than desired for an EV application.



MattsAwesomeStuff said:


> Expansion tank? Hmm, also something present on vehicles?


Yes, there are two approaches...

The traditional method has a pressure-relief valve in the cap on the hot-side tank of the radiator - that's the cap they warn you to never open when the system is hot. When rising temperature expands the coolant enough to force the relief valve open, the excess coolant goes into an overflow tank where it cools down. When the coolant in the radiator get cool enough to drop the pressure below atmospheric, the vacuum pulls coolant back in through a siphon tube and the same valve. The overflow tank is normally partially full, and marked with "cold" and "hot" fluid levels. The cap needs to be at the high point of the cooling system.
In many vehicles the high point of the radiator only has a hose fitting, which goes to a remotely mounted tank. This tank is under the same pressure as the radiator, and is only partially full, just like the overflow tank. As the coolant temperature and pressure change, the level in this tank goes up and down. The fill cap is on this tank, and never vents in normal operation. This tank needs to be at the high point, which is easier to arrange despite the radiator being stuffed in the car's nose, because this tank is remotely mounted further back.



MattsAwesomeStuff said:


> I was going to suggest if you need really minimal radiator, to use something like a transmission cooler, they're about the size of a paperback, but, I don't know what they have for cap or fill, if anything, since it'll have trans fluid it in not coolant.


That makes sense. The transmission (or differential) cooler's tube size will be very small compared to an automotive radiator, but might be appropriate for this purpose. Engine oil coolers are usually built more like regular radiators, and have larger coolant passages. Any of these coolers have no expansion tank or fill cap, because the transmission case or engine sump handles those duties.


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## electro wrks (Mar 5, 2012)

For a coolant pump the 04-09 2 wire (runs on straight 12VDC) Prius inverter/motor coolant pumps seem to be a cheap, simple option: TOYOTA *OEM GENUINE* ELECTRIC INVERTER WATER PUMP PRIUS 04000-32528 G9020-47031 | eBay Never mind the rip-off expensive one in the posting! Scroll down to the more reasonably priced ones below it.

I've gotten them for as little as $10US at salvage yards. Beware: there are many, much cheaper knock-offs out there with reliability problems.


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## electro wrks (Mar 5, 2012)

The Prius plastic coolant reservoirs of different years come in various shapes to fit in tight engine compartments. Mostly they are mounted at a high point above the other parts of the cooling system. The ones I've used are pressurized to 108kPa (~16PSI). 5/8"(3/4"?) Diameter heater type hose seems to be the hose most commonly used to connect the parts together.


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## float_6969 (Jan 25, 2012)

I know this thread is a bit old, but if someone is searching and comes across this, I thought I'd throw in my $0.02. I'm a hobbiest ICE guy who recently bought a Leaf and now I have the EV bug and have been researching a conversion for my Nissan 240sx. I have a water to air intercooler system. The pump I use for all of my builds is this one;
Water to Air Pump 0392022002

There's also a bracket that makes mounting it simple here;
Bosch 044 Fuel Pump Mounting Bracket

It takes a simple 12VDC input and is designed for continuous operation. This is a Bosch pump that was spec'd for use in Ford vehicles for the intercooler circuit of their supercharged vehicles. I have one of these that's been on a car for close to 10 years and still works flawlessly. They're also pretty quiet as well.


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## Duncan (Dec 8, 2008)

float_6969 said:


> I know this thread is a bit old, but if someone is searching and comes across this, I thought I'd throw in my $0.02. I'm a hobbiest ICE guy who recently bought a Leaf and now I have the EV bug and have been researching a conversion for my Nissan 240sx. I have a water to air intercooler system. The pump I use for all of my builds is this one;
> Water to Air Pump 0392022002
> 
> There's also a bracket that makes mounting it simple here;
> ...


Massive HUGE overkill for an electric car system
About 10 times the cost and the power consumption of the pump I use


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## brian_ (Feb 7, 2017)

Duncan said:


> Massive HUGE overkill for an electric car system
> About 10 times the cost and the power consumption of the pump I use


Just to be clear, you're using an air-cooled motor, and even if your controller is liquid-cooled it is only used at high power for a few seconds at a time, right?

The power consumption will be lower with less pressure rise, but the flow rate is still more than needed in most cases. It might be more reasonable, if still oversized, for another conversion. It's good to know what's available, and to have perspective on the requirements.


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## Duncan (Dec 8, 2008)

brian_ said:


> Just to be clear, you're using an air-cooled motor, and even if your controller is liquid-cooled it is only used at high power for a few seconds at a time, right?
> 
> The power consumption will be lower with less pressure rise, but the flow rate is still more than needed in most cases. It might be more reasonable, if still oversized, for another conversion. It's good to know what's available, and to have perspective on the requirements.


The main thing that the "Liquid cooling of the battery" does is not actually "cooling" - its more "equalizing the temperatures" so that some cells do not continually run warmer than the other cells so the actual flow and heat rejection are minor - here (Southland NZ) battery warming would be more appropriate

Cooling the controller is more important - but there is much less heat generated than the IC engines - as in 4% of the motor power compared to 100% of the engine power in a dino burner


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