Thermal Management - Radiator, motor, battery

[bulletbug]

I'm looking for the right type of solution for thermal management in a conversion. I'm converting a 69 bug so it really presents a blank slate on the coolant movement/management since it had none originally.

My Assumptions:

• Cooling motor & inverter is required 100% of time while in use.

• Cooling battery is as needed to keep them at or below about 80 degrees Fahrenheit

• Heating Battery is only necessary when charging and battery temp is at or near freezing.

• Heating Cabin can be done with battery heater when coolant is diverted through a heater core with blower.

My questions:

• Are my assumption correct?

• What is an average temp range of water exiting the Motor/Inverter on a Tesla SDU while at cruising speeds?

• Is there a method of using mechanical valves and check valves to handle thermal management through one coolant loop or are 2 loops mandatory?

• If 2 coolant loops are required then is there a method that would allow us to still utilize waste heat from the motor/inverter loop to heat the cabin as requested?

My conclusions to this point is that 2 loops with solenoid valve might work, but quite complicated. 3 loops would work without valves but require duplication of other components.

For example, in a 3 loop system I would need - 2 Cabin Heat exchangers, 2 Battery heaters and 3 pumps

Loop 1 - Pump-->Motor/Inverter-->Cabin heat exchanger-->radiator--->back to pump. (cabin heat exchanger fan only comes on when sufficient heat is present and requested for cabin.)

Loop 2 - Pump-->Heater-->Battery-->radiator-->back to pump (battery heater is only used when appropriate during charging, otherwise just flows through)

Loop 3 - Pump-->Heater--->Cabin heat exchanger-->back to pump

I'd love to hear feedback and/or examples pointing to how others have handled these issues.

[Kevin Sharpe]

Can you tell us what components you're using and something about your plans for the conversion (racing, long distance cruising, town runabout, etc)?

[bulletbug]

Daily driver runabout is the primary goal for this one.

[arber333]

Daily driver runabout is the primary goal for this one.

Do you want to have a cabin heater AND battery heater from the same source? Then i would recommend you use webasto diesel heater and one thermostat valve in the battery box. This valve would open at some low value and pass the warm liquid to the battery. But when battery box would reach some 10deg it would shut off. Battery loop would be in paralel to the main heater loop but smaller diameter.

Heater would use one pump with two loops in paralel.

I will use another loop for motor and inverter cooling. Radiator - water pump - inverter - motor - charger - radiator. Charger is only active when motor is not working so heat source is offset. That way i only use one pump and system for two purposes.

I will wrap batteries in heating blanket 50W inside battery box and wire both of them to a single AC line just before charger. I think of using Arduino Due to interlock charger CAN signal to work only when battery temperature is more than 5deg. This way battery will be protected in case i leave my car out for some time.


I recommend you use inline 2kw dishwasher heater if you absolutely want electric heating. It is small and can be fitted on to 38mm hose. Very convenient.

Also for intermediate periods i use seat heaters and they work very nice.

[johu]

What sort of power are you looking into? In my first conversion I used a 18.5kW industrial induction motor overclocked to about 40kW. It has no active cooling at all, neither inverter nor motor. Even in these days hot summers (35°C or more) and going up the rather steep and prolonged hills in the region AND having the car fully loaded it never cut back power. Motor reached like 100°C in these conditions. In all other conditions it barely moves the gauge (starts at 60°C)

[joromy]

This is how I did it for battery heat/cool:
viewtopic.php?f=16&t=221

Maybe a little complicated, but less complicated than a heatpump.
The cabin heater is stock PTC heater.

Absolutely first on my list would be heated seats, and maybe heated steering wheel!

Sorry arber333, but diesel heater? Waste of money, not very environment friendly, and high failure rate.

[arber333]

This is how I did it for battery heat/cool:
viewtopic.php?f=16&t=221

Maybe a little complicated, but less complicated than a heatpump.
The cabin heater is stock PTC heater.

Absolutely first on my list would be heated seats, and maybe heated steering wheel!

Sorry arber333, but diesel heater? Waste of money, not very environment friendly, and high failure rate.

Well 2nd law of thermodynamics might change your opinion with -20deg outside, as it did for me. Old cars do not exactly have good insulation.
I think wasting traction electricity for heat is even greater waste than oil or alcohol fuel. Maybe AC reverse cycle would be more acceptable.
It is phylosophical debate anyways without good well to wheel calculation.

What is relevant with cold is how to keep them electrons running at sub 0deg. I think of putting electric blankets in my battery boxes 50W per box should keep the cells warm enough so they are able to accept charge at sub0. I will run them with 230Vac whenever i plug in. They will remain plugged in through whole night since i have to keep Mazda outside .
Also you want to be sure you use -40deg rated components for every piece of inverter! I had some inadvertend errors last week when full cells created sensor data as there was overvoltage. After some while into the drive things heat up enough everything wored.

I like your PTC system though. How much on the IN and how much temperature you estimate it can hold stable in cold?

A

[joromy]

I like your PTC system though. How much on the IN and how much temperature you estimate it can hold stable in cold?

A

If you mean the peltier (TEC) heater, you would get 1500W at any temperature, and the extra "heatpump" effect will decrease with lower outside temperature. The max temp difference is 70C, so you could get 50C in the battery if it's -20C outside (in theory, with no losses)
Also important in cold climate, would be good insulation of the battery pack.

[Roger]

I just found this on battery Short Circuit Self Heating which was interesting
https://curve.carleton.ca/system/files/ ... ystems.pdf

[arber333]

I just found this on battery Short Circuit Self Heating which was interesting
https://curve.carleton.ca/system/files/ ... ystems.pdf

Really nice implementation. I like the comparison with warm air transfer.
But really, this is done on a cell to cell basis. What we are discussing is more on par to one side of the pack VS the other side.
Or maybe 48V packs inside the battery. This would keep the component cost lower and circuit potential is non lethal.
Would that circuit be self sustained and present on the battery? Then we would have to consider some form of LVC to prevent discharging our cells.
Also i would prefer that to lizzard heaters and additional AC wiring going into battery boxes.

[johu]

Wow, the battery is actually short circuited
Do you think it would scale to a 400V pack?

[doobedoobedo]

Wow, the battery is actually short circuited
Do you think it would scale to a 400V pack?

Make sure you post the experiment on youtube .