The title of my previous post was “Cooling system design final and developing radiators” but it wasn’t very final. I have decided to add active battery cooling in which one uses the airconditioning to cool. There are two main reasons for doing this:
- I already have airconditioning in the car so it is a relatively small step
- The ideal operating temperature of the batteries is 15 to 35 degrees.
On a hot day during the summer the difference between the environment temperature and the target temperature can be quite small. As a result there is no cooling capacity in particular with the small radiator I use. In case the batteries have already warmed up during for example a 1,5 hour drive and you want to fast charge the chances that they would be come too hot so the battery management system kicks in and stops the charging process. Proper thermal management is key in a long life span of the battery pack.
Battery cooling research
So I did some research on how Tesla, Volkswagen, Audi, Volvo and Opel do this.
To me it is important that it is possible to enable the cabin and battery cooling independently. Apparently there are multiple ways to achieve this. My way forward:
- Block valve with solenoid from a Tesla for the cabin evaporator
- Heat exchanger / chiller from a Tesla
- Block valve with solenoid from a Tesla for the chiller
Implications cooling system design
Adding active battery cooling does trigger some changes in the cooling system. I do need three routes as a result:
- Through radiator
- Through heater
- Through chiller
I’ll stick to my decision to use a 3-way valve even though a 4-way would be better since that would allow me to only use one valve. Instead I’m using a second 3-way valve.
Airconditioning system design
The cabin evaporator will be in parallel, each with a solenoid to be able to use them independently.So I got myself a block valve from a Tesla.
Unfortunately it does not directly fit onto the tubes of the Peugeot evaporator I’m using.
Reverse engineer Tesla part
From the Tesla wiring diagrams I could not tell whether it was a 5V or 12V solenoid so I just gave it a try.
It does engage at 5V but not very firm and it is close to the minimum voltage required. Thanks to Erik for suggesting that I can find out its rating by monitoring the temperature.
At 13,6V no measurable temperature increase after being on for a while. Via the DIY Electriccar forum someone suggested the possibility to use a chip that ensures a high engagement current and then reduces it to a lower hold current. I found the TI DRV103 as a suitable economiser but I have decided to keep it simple and take the 8W consumption for granted.
New engine bay layout
It came to my mind that it was better to move the Tesla battery heater to the left hand side of the motor. There are two advantages:
- The cooling hose does not need to go over the motor.
- Chances are that the upper control arms both remain accessible to have the car aligned with all components installed.
Disadvantage is that the cable and connector do not make it to the contactor box. This could be a possible position and then the chiller next to it.
Took me some searching but via the help of another Volvo enthusiast in the US (thanks Lee) I found the Tesla chiller I was looking for.
That’s good news. The bad news is that it’s a lot bulkier that I had anticipated based on the pictures. So just next to the heater isn’t possible. Will become something like this:
Installing heater and chiller
The only way to squeeze that in is to move the heater a bit more towards the firewall. I had already removed some excess adapter plate material to get it in in the first place but I’ll need to make some more space.
It is a genuine B20-M410 bell house so it does hurt a bit but I won’t be needing a starter anyway.
Made a temporary support.
Now the heater fits in with some room for the motor to move in its rubbers.
Moved it around slightly to also keep enough space for the clutch lever and made a final support.
And a support at the bottom as well.
So now the heater is in place and by using a 135 degrees silicone hose it fits together!
Now the cooling system design is final.