It’s been some time since my blogpost about redesigning the cooling system, high voltage diagram and battery box. This blogpost is about exactly the same items, but “Keeping It Simple”. My approach got a bit too advanced looking to much at how Tesla solved things. However I am building a completely different kind of car, so time for some simplification.
Since the front battery box is almost finished I started designing the contactor box. This is the central high voltage distribution and I am drawing it including wiring to be able to determine the positioning of the gland nuts.
To meet the EMC requirements it needs to be a metal box. I am going to try and find a suitable standard box or otherwise I’ll have it fabricated using my 3D drawing.
Rear battery box
A while ago I started 3D drawing of the rear battery box. The dimensions of the tow bar were not exact so I redraw that.
And constructed the box “in context”.
That allowed me to digitally test fit the Tesla modules and I indeed do have enough room.
Where to mount the chargers?
Another important question is where to position the chargers. Within the battery box does not fit.
Outside the box does not work either.
Perhaps above the rear axle would be an option. There is enough space, but how about the IP rating.
I cannot add another. According to Thunderstruck they are IP66. the second 6 means:
Water projected in powerful jets (12.5 mm nozzle) against the enclosure from any direction shall have no harmful effects.
But in the manual they mention:
Don’t place the charger where it can get wet, this may cause damage to the charger as well as electric shock to the operator.
But even if the charger itself is IP66, the connectors are not so I’ll have to fabricate some kind of enclosure. Not ideal. Digitally test fitted them underneath the rear seat Either through the floor:
Both not very convenient and difficult to build. I ended up with my initial idea: left and right in the back.
The charger itself exactly fits behind the panel but I’ll have to add a cage to ensure the minimum required room for ventilation of 50 mm. They will be visible in the trunk but they remain accessible and I’m having the connections where I need them.
Simplification of the cooling system
Furthermore I’ve been working on simplification of the cooling system. Like Anne from New Electric mentioned “every connection is a possible source of an error”. Having that in mind, I reviewed the need for a heat exchanger.
At cruise speed the motor used 10 to 16 kW at an efficiency of about 90%. 10% loss is approximately 1000 to 1600W. Of course it would be nice to make use of that but before that heat is used to heat up the batteries a lot will be lost already. If we assume this is 50% the usable amount of energy is 500 to 800W.
I’ve done some calculations of the heat capacity of my battery system and I need 55 Wh to increase the temperature with 1 degree. So after 30 minutes of driving the increase in temperature is 5 to 6 degrees. Given the increased complexity my conclusion is that it’s not worth it. While discharging the batteries will heat up as well. I do intent to keep the possibility to heat up the battery pack once the car has been plugged in. While heating up the batteries to their ideal temperature of 25 degrees is a nice to have, charging below zero is a no go. The simplified diagram will be:
I intend to install the battery heater and the radiator in the back. I updated the coolant distribution block and added the temperature sensor.
To be continued….