Battery Box


Ooops. Overshot a bit. Hit 107.00kw today.

Lead acid battery’s are the most expensive technology in our vehicles on a $/mile basis. If a good lithium pack could be assembled, it would make for a lighter and far more efficient vehicle.

In the near term I’m building Lithium modules from ten A123 cells in parallel. That’s a 23ah module. Not much harder to make a 20 cell/46ah module. I’m guessing based on my records, that my truck could go 40 miles max on 23ah since the pack would be so much lighter than even the nicad that I currently have. 70-80% of 40 miles is 28-32 miles. That’s a reasonable range for my city driving needs. Each 10 cell module will run about $125 in just cell costs. That’s $3250 for 154lb bare pack. There still has to be a housing of some kind designed to hold the module. It will use up just one half of the battery box. Leaving the other half for another pack as funds allow. Factory packs weigh from 1400-2200lbs. Can you imagine the range and efficiency increases from loosing up to a ton of pack weight??

CAD model of 20 cell A123 module. Displaces 2 flooded BB600 nicads.

Right now the large format cells that most EV folks are using, have very poor regen capabilityof around 0.3C. On a 100ah cell, that’s only 30 amps of regen allowed. Our vehicles have up to 200a with stock settings. 250 amps with modified settings. A 10 cell module can handle 100 amps of charge/regen current for 15 minutes at a time. So I can easily see them handling 200 amps for 5-10 seconds when regen kicks in with modified software, under specific conditions. In other words they are very low impedance cells that can handle our regen needs nicely.

As for discharging, the A123 10 cell module can handle 700 amps of discharge continuously, and up to 1200 amps for 10 second bursts. Our vehicles can only discharge at 200 amps stock or 250 amps in a modified configuration. Here is the data sheet from A123 on this cell.

These cells have a very long cycle life. 1000 cycles at the max ratings listed. Double that with any care at all. The factory told Bill Dube that if a person can tolerate a loss of 50% capacity over time, then these cells can go 10,000 cycles. Most lead packs lose 50% capacity at 200-300 cycles.

For all of these reasons I’m building an industrial spot welder for making A123 modules. Not just for EV’s, but for the Combat Robotics crowd as well. They use these cells without a BMS and they still last a decent amount of time. Far less than they could, but those folks are happy with the performance and longevity.

Each bare 10 cell module will be 66mm wide x 260mm long. That’s 2.6″ x 10.24″. There has to be some kind of structure built to house the module and some stout connections designed so they can be connected together into a pack. I’m thinking of making the structure look a lot like a flooded nicad cell. In fact I wonder if a nicad cell housing could be adapted as the structure. These modules won’t need to be strapped tightly together like the large format cells require so they don’t over expand and die. These cells will never expand.

In theory, a 23ah pack would be 100 modules. This could fit into the Prizm battery tray. My truck holds 126 nicad cells in each half of the battery box. So it could hold 126 A123 modules per side, for a max of 252 modules per truck. The stock charger could not charge them up past 400v so only 100 modules would be fitted per side. A second 100 module pack could be added to the remaining side if desired, and wired in parallel.

I have a couple of dozen A123 cells and the 10,000 amp (5 ms) microprocessor controlled spot welder is under construction. I plan to make one 10 or 20 cell module to take the place of 1 or 2 nicads in my current pack, for testing.

Along with several others I’m on a spot welder project. This will be the tool I need to spot weld A123 cells together to make a nicad replacement module for my truck. I was in Merced a few weeks ago and got the chance to meet Fritz. Here is a video of the spot welder in action. It’s very sweet!!

This past Saturday I went to the EAA meeting expecting to plug in and charge.
Didn’t happen. The GFCI had tripped on the Dolphin. Different outlets and a few
resets were fruitless. Vehicle still ran fine, but the GFCI would fail.

Here are the steps I took:

-Plugging in at home. GFCI still failed.
-Swapped the GFCI out with another unit. GFCI still failed.
-Visually inspected inside Dolphin. Nothing unusual.
-Isolated ground on AC line with 2 prong outlet adapter. GFCI did not fail.
Charger still works.
-Removed J2, the largest connector on the Dolphin. GFCI did not fail!
-Reconnected J2. GFCI failed again.
-Started truck. Measured ISO in Dolcom. Was -130 points below pack voltage. Not
good. Oh look, the pack has all of 4 bolts holding the lid on and it rained for
2 weeks….
-Took the lid off. No puddles of water found. But had a high humidity feel/smell
to the pack. This backs up the -130 count found on ISO in Dolcom.
-Hung the 12″ fan from the bed and let it blow on the cells all night.
-Next morning GFCI stopped failing. Charges fine on 120vac and 240vac.
-ISO at -100 counts below pack voltage, but pack much dryer feeling/smelling.

Time to go ground fault hunting in the pack again.

Tom and his son bought the spare USE S10 battery box from me some time ago and installed it in their ’84 S10. At Saturday’s SJEAA meeting, I asked for input on how to get a BMS data cable into the #1 trucks’ battery box while keeping it water tight. Tom knew the answer because he knew the battery box better than I did. By removing the drive shaft, the wall of the box that holds the watertight connectors, is exposed clearly from under the truck. That way I can see if how hard it would be to drill a hole and add another watertight connector. The hole would need to be something like 5/8″ to 3/4″ in diameter. Someone talked me into using the water tight connectors that don’t need a threaded hole to be mounted. That translates into less work in a tight space under the truck. Thanks Tom!

When using Dolcom for looking at ground fault info, the standard nominal reading is about +20 counts above the pack voltage.

In my experience when the ground fault reading taken with Dolcom is higher than nominal then the ground fault is between the negative most battery in the string and mid pack. When the ground fault reading is lower than nominal then the ground fault is between the positive most battery in the pack and mid pack.

So far with mild rain exposure the #1 truck had only had a ground fault reading swing about +30 to about -20 from nominal. It looks like the new gum rubber weather stripping is working.

A fellow EV’er commented about using 40 foot long greenhouse soil heaters
to warm his battery packs. Liking his idea, here is what I wrote back.

The ACP cars use battery heaters. It only draws a few hundred
watts when it’s running. It takes a day or two to heat up a cold pack,
but holds it there nicely after it does. The lead packs I’ve worked on
in ACP cars put off heat for a whole day once they are in the 30-40C
range. When we pull a pack out to replace a weak battery you can feel
the heat in a big way.

The pack heaters are also one of two reasons the ACP vehicles get 30k
miles from a lead pack. Heating up a battery to 30-40C also increases
it’s capacity, making it less likely to reverse a cell. The second
reason for such great longevity is having a BMS.

The ACP battery heaters are powered from the pack itself I just
remembered. That’s why they don’t have to worry about what voltage
they are charging from. They do have a simple IGBT circuit that turns
on, off, or pulses the heaters to keep them at the same temp with a
thermal sensor.

A little math shows that the ACP heaters total about 450 watts. So on a
336v system that’s about 1.34 amps. So our packs would supply a little
less as our nominal voltage is 312v. So it’s not a huge drain when
it’s running.

Yesterday the truck failed an important test. It rained and it cause a ground fault. Even with all new seals on the lid and gasketed washers, it still ground faulted. So I got into the pack and checked for ground faults with the volt meter. The ground fault was floating around as it had on me earlier this year. So I tried the meter in low current mode set to milliamps. It showed the same location for a ground fault. Removing the cells showed some KOH streaking. Cleaning it up did not change where the ground fault was shown to be. So I went to the new process that I had figured out last Feb. I removed a cell interconnect at the lowest voltage reading relative to ground. I kept pulling one copper bar at a time until the voltage suddenly shot up. It ended up showing me that the ground fault was in the rear drivers corner of the pack. Removing the 8 cells in that area showed that there was water between the corner of the cell and the wall of the battery box. So I cleaned off the walls and cells with diluted vinegar and reassembled the pack. That took care of that ground fault!! This time I moved the mylar insulator into the corner to help isolate that corner cell from the box if it gets wet again. There is another smaller ground fault on the passenger side of the pack. I just vacuumed in that area and called it good for now.

The rear edge seal was a different material since I had run out. So I tore it off and installed the correct material. Since the two ground faults I found were right under that seal, this could help.

Also I adjusted the ground fault setting in the software to give it more tolerance since having 252 nicads or 504 terminals is almost 5 times the terminals that a regular lead acid pack would have. Between that and having flooded nicads, the pack is more prone to having ground faults. So I will see during the next rain how it all functions.

The #1 truck now has dual gas struts on each side of the bed. With my back trashed this week, it is very apparent that dual struts makes the bed easier to lift. It’s also a great benefit to not have to have a prop rod to hold the bed up. Ironically the bed now needs a rod to hold them from going too high up when I pull the truck in and out of the garage during repairs.

I also removed the class 3 trailer hitch to save weight. There is now a lot of room back there for an additional battery box. The roll pan is dented up from hitting the hitch when the bed tilted up. So I’ll have to smooth it out with an old cheap long flexible kitchen knife like I did with my first car about 30 years ago.

The battery box lid received new screws and sealed washers to hopefully help with making it more immune to water leakage and thus ground faults.

It’s been cold out. I am seriously thinking of taking the new upgraded heater out of the #2 truck and putting into the #1 truck. I suppose I could just buy a second new heater.

The nicads have been leaving a coating of KOH all over everything and really needed better ventilation. The holes for the fans were already there, but the vents were very small for this type of flooded battery pack. So I clamped the lid to the mill and CNC’d nice round 2 inch holes for the exit vents.

Here is the exit vent for the nicad pack. It uses a 3 inch plastic cap anchored with 4 screws and nyloc nuts to 2 inch plastic pipe adapters, sealed to the battery box lid with silicone.

Here is the exit vent for the nicad pack. It uses a 3 inch plastic cap anchored with 4 screws and nyloc nuts to 2 inch plastic pipe adapters, sealed to the battery box lid with silicone

This is the cover for the 80mm fans and the inlets on the Nicad pack. These covers are just simple sandwich boxes from Target. The fans were also sealed to the battery box lid with silicone.

This is the cover for the 80mm fans and the inlets on the Nicad pack. These covers are just simple sandwich boxes from Target. The fans were also sealed to the battery box lid with silicone.

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