The original plan was to have all of the batteries in the rear of the car in a single battery box. The very compact A123’s would have made this possible. The CALB CA60FI’s that will be going in the rear aren’t as compact. The battery box that would have held 96S3P worth of A123’s will only hold 74 of the CALB 60’s. Since my goals include a cell count in the 90’s I needed room for some more cells. The “engine” compartment was never designed to hold a battery box, however there was a space in front of the motor that remained unused. After some quick measurements I found enough space for the battery box that I built in the previous update.
Now it’s time to figure out how to mount it. I raised the front of the car on jack stands so that the battery box can be installed from the bottom. There is no room to fit it in from the top because of the hood latch and pop up headlight mechanism. Because of some careful measuring before building the box it fit the space exactly, I did get lucky as to where the top of the box sits though.
The top edge of the box is basically level with the “frame rails” of the car, it’s a unibody car but there are distinct frame rails front and rear. The box is also basically centered below the mounting position of the pop up headlight mechanism. By inserting a plate between the frame and the mechanism it allows me to suspend the battery box from the frame rails very easily.
I sketched a bracket design on a post-it turned that into a CAD drawing and milled a pair of them. The CNC router is one of those tools that I simply couldn’t live without now.
The bracket fits nicely under the pop up headlight mechanism using the factory hardware and mounting holes.
Both sides test fit, and everything lines up as it should. The top of the battery box will get a plate with 3 studs on each side that will align with the 3 holes in the aluminium bracket. Raising the box up from the bottom with some guidance should put the studs in the holes, with some lock washers and nuts the top will be secure. I’ll paint the brackets black for the final install.
The bottom of the box aligns with the bottom of the old radiator mount so a small bracket between those two points will ensure the box can’t move. Although the box is fairly far forward it sits very low and should help even out the front/rear weight balance.
The whole reason for the front battery box is to hold the displaced A123’s from the arrival of 72 CALB cells that recently arrived (plus two I already had). The cells were well packed arriving in two small crates, from CALIB Power out of the USA. Thanks to Don Blazer for being the retailer in this transaction and providing a very good price. You can find Don on the Diyelectriccar.com forum here.
I just hit the half way point in my testing, much faster than the A123’s since there are far less individual cells to test. I’m testing two at a time using a pair of PL6’s with similar settings to the A123’s except charge/discharge at 40A and a CC-CV discharge instead of just a CC. Using the CV portion on the discharge is providing the bulk of the work in bottom balancing. Shown below is one of the only good uses for Lead, I borrowed a group of gel’s that use to power Wade’s Solectria Force since his EV got the upgrade to 56 of the CALB 60’s recently.
I really like the form factor of these cells they are tall and slim giving them a small footprint and making the best use of a deeper battery box. They also match the height of the A123’s very closely making them fairly interchangeable.
As shown in the above picture I am now using kapton tape on the edges of the A123 cells. This should help eliminate the chance of the edges shorting which seems to be related to the electrolyte leakage I was experience in many cells previously. The aluminium heat spreaders in the bottom of the battery boxes also has a very tough 3M film on the top to give another layer of protection. Anyone who still wants to use A123’s must tape all of the edges of all of the cells, this is not a suggestion it’s a requirement. Kapton tape is available on ebay or from some soldering supply places.
I created a simple gland plate for the high current positive and negative wires along with a multi pin connector for the heater wiring and power for the Cell Log 8 Breakout Module. The studs that align with the mounting plates are also in place, the last step is creating a watertight lid to seal the box, I’m deciding between a simple aluminium plate or plexiglass lid.