Keeping Our Cool

Recall from the post on fitting the Tesla batteries, the cells are made of a nickel cobalt manganese aluminum oxide cathode with a graphite silicon anode. The cathode chemistry of these cells is such that gives off free oxygen at a fairly low thermal temperature of perhaps 180C - very low by lithium battery standards.

The preliminary cooling setup with 3-port manifolds. Would not flow.

Without adequate monitoring, they can easily be driven to thermal runaway by overcharging or over discharging and can be explosive. The resulting fires are extremely hot and since they produce their own oxygen from cathode materials, extremely difficult to extinguish.

The individual batteries are interconnected by thin plates on top and bottom with holes at the cell terminals. Small wires are welded from the plates to the center of the cell terminals. These wires are designed to act as fuses in the event of the short failure of any particular battery cell.

Fuse wires on each cell in a Tesla battery module

Fortunately, Tesla provides a facility for managing battery temperature. A series of flat fluid conduits (see gold in photo) wind between the rows of battery cells. These are connected to two pipe fittings on the end of the module. To keep the batteries at a safe temperature, I need to run coolant through these fittings, along with a water pump and a radiator and fan for heat dissipation.

Coolant ports (oddly connected together via clear tubing in this photo) and gold coolant conduit in a Tesla battery module

In a perfect world each battery would be fed cool coolant equally (in parallel) but the orientation of my batteries (not all in a row, 10 in front, 4 in the rear) makes this complicated. I considered running a 10 port manifold up front and a 4 port in the rear but the number of hoses and fittings gets more complex than seems necessary. Instead, running up to 4 modules in series seemed a reasonable compromise between even cooling and simple configuration. I'd learn better later.

Using 10-port manifolds to run all 10 batteries in parallel. Fairly complex.

Using 3 port manifolds to cool batteries in three sets of up to 4 batteries in series. Not as fair to the 3rd and 4th batteries in a set but much simpler to plumb.

To implement the theory in the real world, I used the push-on fittings from EV West and some clear tubing with spring clamps to connect all the lines to the input and outlet manifolds (sourced from McMaster Carr).

Factory snap-on Tesla connectors, clear tubing, and sprint clip hose clamps allowed for initial layup of cooling hoses

One long run the top battery is required

Close up. The manifolds and the barbed fittings on them aren't complete yet -- just roughed in

Plenty of room in the front of the battery box for the hoses

The next step in the cooling system is a water pump, radiator, and fan.

I got a 16" Spal pusher fan that is quite thin. It is important to get everything as far forward as possible because there isn't much room between the front of the battery box and the car's radiator core support. I need to get a fan, A/C condensor, and radiator all into that area behind the grill. I already had a new, large parallel flow A/C condensor.

For a water pump I got two (more on that later) Bosch electric pumps. These are fairly small and oly pump about 5 gallons per minute but that's fine for my setup. Because the fittings on the water pumps, Tesla drive unit, and the onboard charger are all 5/8", it made sense to use a radiator with 5/8" heater hose sized fittings also but finding one is tough. I bought a 16" square radiator for a dragster that had threaded AN bungs for the hoses but it wouldn't quite fit into the opening in the core support on the car.

A Bosch electric water pump. Yet to be mounted.

In the end, I opted to use the same radiators I use on my shifter karts. They come with 5/8" fittings and are affordable but a bit small for trying to cool everything. That's not a problem, however, since I can run two parallel systems. In fact, it is better. The batteries like to run at about 80-100 degrees F while the Tesla Drive Unit's inverter runs quite a bit hotter at 130 degrees or so. Rather than have the drive unit adding heat to the batteries, I will run separate circuits for the batteries and everything else. Everything else is the Tesla drive unit and the onboard charger/DC-DC converter. Thus the need for two water pumps.

Two 3-row core shifter kart radiators mounted in front of the core support. The final brackets are not shown in this photo

Just enough room for the A/C condensor and fan in front of the radiators

Just enough room between the batter box and the radiators for hoses

In addition to cooling, it is very important that no charging of a Tesla Module S battery module be performed at an ambient temperature below freezing - 0C or 32F. Charging at cold temperatures leads to lithium dendrite formation on the anode and eventually failure of the plastic separator in the battery cell. If I want to charge these modules in extremely cold weather, I'd have to make provisions for heated fluid circulation through the modules. While this is possible (I have an electric heater element for cabin heating that I could use in a heat exchanger), I live in Southern California and it never gets that cold here so I'm ignoring this scenario.

When I finally went to test my system I had no leaks. Yeah! But no matter what I tried I could not get all the air out of the system. In frustration, I finally resorted to just testing the flow through a single battery module and was surprised/frustrated to find that the flow comes out as barely a tickle. There is no way one can run multiple batteries in series. I'll have to revert to 10-port manifolds and all in parallel.