Yesterday I picked up the Ford Escape battery in Ogden Utah. This battery is composed of 250 cells in 50 5 cell subpacks. It is rated at 5.5 AH as opposed to our 6.5 AH Insight batteries. 24 subpacks are need for a 144v equivalent of our battery. 25 subpacks would result in a ~150 volt battery.
Total cost was $420 including tax. There was no detectable voltage on the outside of the case even with the rotary switch thingee in the on position. I call it a thingee, because it really isn't a switch. It is more like a plug with an really small 100 amp fuse. It bridges two plugs in the top of a switch. This unit also contains a hall current sensor.
The case screws were hard to deal with as they are star heads with a little pin in the center. Rather than deal with them I used a grinder with a cutting wheel and turned them into straight heads.
These pictures include what I think are the equivalents of the BCM and a master output relay. There were two computers, the master switch and what appears to be a master relay. It is rather solid and brick like and was the heaviest of the three components and has two external heavy duty prongs.
Once the blower cover was removed you can see that cooling is accomplished by two blowers.
After quite a bit of work the case was finally open. Once split open you can see the temp sensors of which there appears to be 12 total, 6 per layer. There is also a loop that goes around the entire perimeter of the batteries. It has what appears to either be additional temp sensors or some catastrophic temperature device like our PTC strips. There are also voltage taps up the entire middle bus.
At this point I could take voltage measurements and read ~152 volts for the short side. Each subpack shows ~6.3 volts. I left one subpack testing overnight.
It tested at 5.7AH discharged (rated at 5.5AH). Load testing with 28 amps resulted in a drop from 6.94 volts to 6.7 volts or equivalent of a 120 cell pack at 166 volts dropping to 160.8 volts. So based on one subpack it is likely the pack is healthy.
The subpacks are slightly different than the Honda counterparts. Besides the 5.5 AH rating and 5 subpacks vs 6, they use a short keyed bus bar as each end. The battery tray is also keyed so the battery can't easily be put in backwards. The battery string crosses the entire tray from left to right then connects to the next row via bus bar on the side. This repeats until the string is complete at the top of the tray. The rotary switch thingee splits the two trays. One tray has 24 subpacks and the other has 26 for a total of 50.
Each tray measures approximately 27" wide by 20" high which is roughly smaller than the entire IPU compartment in the Insight. It is also noted that the battery case is only 4.5" thick. So as is it is impossible to fit it in the IPU compartment. This leaves the wheel well as a potential location. Another option would be to split each tray and double up each subpack. This would result in a single (110 lb pack) that is 15" wide by 20" high and would be roughly 7" deep. This could fit in the stock location, but only if the motor controller ducting is rerouted. Battery ducting might also be an issue to ensure the batteries stay cool.
On the idea of stacking each 5 cell subpack. Will the is be an issue when charging? The last thing I want to see is a battery fire, but this would be the easiest way to fit the entire case into the IPU. With the way each layer is setup the plastic case can easily be cut. making it half as wide. The half without the center bus mounts would be discarded. Copper tubing could be used as a spacer between the connected subpacks. With the way the trays are designed they fit snug over the battery, so all that is needed are bolts that will sandwich the extra thick layers. The stock switch can still be uses on the split. and I think a resistor splitting network can be used so the BCM voltage taps still have some functionality vs just being spoofed.
There is no stock PTC functionality unless the strips from the stock pack are transplanted. Temp sensors are the easy part as there are 12 in the Ford pack. These are really cool as the insert in the case and sqeeze between two subpacks. A much cleaner design than the Honda equivalents.
The most simple explanation. Imagine a 120 cell string, in this case 24 subpacks. Now, for each of those 24 subpacks there is an additional subpack permanently mounted in parallel or stacked at the subpack level.
Most parallel charging issues seem to result in one cell reaching peak prior to another in parallel, then dumping its charge to its counterpart. There are a few examples online related to battery fires or exploding packs such as:
Now, my theory was that longer strings aren't susceptible to this as the string becomes longer a fluctuation in one or two cells makes very little difference in the total voltage. What I am considering is 5 cells directly in parallel with 5 cells or one pair of subpacks. Those 24 pairs will then make up the entire pack.
As an additional option, but it would be more tricky, arrange the connections so they are electrically the same as my current parallel setup. Each full pack is isolated by a limiting resistor and is engaged when the HV relay turns on.
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Ford Escape Battery Project
