In the meantime, I have already made several design iterations with my cooling system and in March I bought a Defa PTC liquid heater for heating the batteries.
I also had a Defa parking heater in mind, also at 220V. So both put in the diagram in the front junction box.
However, that did raise the question, how do I ensure that 220V is available when the car is not charged. For example, because it is too cold to charge at all and you therefore want to heat first or when the batteries are full and you want to use the parking heater. Therefore, the EVCC (charge controller) studied more closely.
Because I do not want to interfere with the battery management system, I came to the conclusion that via the control pin and the EVCC was not preferred. In the end, I managed to design a correct and working circuit with an AVC2 as a secondary charging controller.
However, it is neither ideal nor universal. The moment you are at a charging station that is “out of session” and you have to give a payment order, it still does not work autonomously. After having had contact with New Motion and Allego, I started to look more broadly.
Change of plans: Tesla battery heater
After some more research and listing advantages and disadvantages, I ended up with a battery heater from a Tesla that works on the battery pack.
I will also use the already built-in PTC element for the parking heater.
The battery heater from a Tesla is in my case an LG Sheath heater and it delivers a power of up to 5 kW. That’s a bit much for my system so I want to be able to adjust it back. Because it is now about 350 to 400 volts, designing a PWM circuit analogous to controlling the heater is not an issue.
Now I learned on the diyelectriccar forum that in the front high-voltage junction box in a Tesla there is a piece of electronics that does that. So I went looking for both the heater and that junction box with a piece of cable.
It wasn’t a lot of cable, but I was mainly concerned with the connector.
It seems reasonably reusable if necessary.
Is probably mainly a matter of pressing a new HEX clamp to it.
Insight cooling system
I also had a number of ideas and insights for the cooling system itself during a weekend at the campsite. Initially, I had devised a heat exchanger for being able to heat the batteries with residual heat from the motor or controller during the time to get them to their ideal temperature working area. However, in a “keep it simple” battle last September, I left it out. I didn’t let go of the idea of using residual heat yet, so I took another look at how Tesla does it. They use a 4-way valve to run the motor/controller loop and batteries run as two separate circuits or as one circuit in series. That concept once applied to my situation.
And that later worked out digitally at home, in my case with the controller and batteries loop. The circuits as one system in series.
And parallel as two separate systems.
That should be able to work and adds relatively little complexity. So I got some of those Tesla valves.
And let’s fiddle around with finding out the control. That’s going to work fine.
And also know how to find and purchase the right and suitable connector. Tesla valve connector kit is now on sale at EVcreate.
