Battery load testing

I've been using the CellLog8 units for monitoring my high and low voltage for awhile now. I've yet to use the logging feature of the CellLog8S. Sadly I saved some money and only bought one unit that does the logging. I had to run seven seperate tests and the graphs don't match up for a really good comparison but I think the results still show what I wanted to know, "Which cells have had a significant increase in internal resistance".

The tests main goal was to take the cells to 3C (480 amps) and check for cells that are sagging too much.

All cells are connected with busbars except (15-16, 30-31, 37-38, 42-43, 45-46) which are connected with 2/0 cable.

This is the legend for cells 1-8 of each graph.



Cells 1 - 8

Cell 5 appears the be the worst of them. It sagged below 2.0v at 3C

Cells 9 - 16

These cells were fairly spread out from about 2.6v-2.85v. The lowest was 16 so this might be from any voltage sag across the cable.

Cells 17-24

This group was mostly 2.8v-2.9v except cell 19 around 2.6v.

Cells 25-32

This group had cells in the range of 2.4v - 3.0v. The two that stand out are cells 30(2.4v) and 32(2.6v). 30-31 seperate the from and rear packs and would be the area to show the most voltage sag so I don't think this cell is as bad as it looks.

Cells 33-40

This group had a wide voltage range as well. Cell 33 was the worst at about 2.5v.

Cells 41-47

Nothing too bad here, worst cell being 47 at 2.8v.

Cells 48-54

By far the best group (these are all newer cells). All cells were around 3.05v-3.1v.

I'm frequently getting low voltage alerts (<2.5v) while driving and was curious how many cells were meeting this criteria. First I'll recheck the torque on the batteries, but assuming thtat is fine, it looks like I can replace the one cell and fix this. My normal driving never reaches 3C range unless I'm really needing to pass somebody. Replacing this one cell should remove the low voltage alerts most of the time. I have an extra cell sitting around that I've tested at 160Ah capacity. I'll replace cell 5 with it and hope the voltage sag on it is closer to the averages seen here.

Heatsink replaced

I got some time yesterday and installed a new heat sink that I think will be more efficient while driving. I mentioned before the old heat sink below has the fins parallel with the controller, but the air while driving is perpendicular to the fins.

Here is the new heat sink attached to the controller. You can see the mill work done so the bolts are recessed now and touch the thicker base of the heat sink. This allows for more consistent torquing than before and should allow for better heat transfer. Don't forget your thermal compound when installing any heat sink. Thermal compound greatly increases the heat transfer



I wanted a better way to attach my temperature sensor for the controller. I made a little L bracket that attaches to one of the bolts.

Here is another shot with the sensor attached. I'll try to do some temperature comparisons next week, but with the increase in temperature just over the weekend it may be hard to get any reliable results.





This is cool!

Awhile back when I was still running the ADC 9", I had installed the air conditioner around Fall time or so. Before summer hit, the ADC motor went out. Replacing with a Netgain Warp 9 I soon found out that only the transmission bolt patterns matched. The accessory side did not. The accessory output shaft was larger, the motor diameter, slightly larger. A few little things that made my existing AC setup worthless.

Now that I'm driving to work again, and the heat is coming, I figured it was time to rebuild the AC system. There was quite a bit of machine work needed, so luckily my uncle Duane had some time yesterday. The main pulley was bored out to 7/8" and a new key way made. A thin bushing was made that went on the shaft first. This slid to the furthest inward point on the shaft and allowed us to tighten against that and not allow anything to slowly walk in and rub on the housing. Next, I reinstalled the Netgain RPM sensor and finally the main pulley went back on. A 3/8" bolt, custom washer, and some Loctite then went on to keep everything in place. The mounting brackets base had to be cut and slid outwards about 1/4" to account for the new position of the main pulley.

Here are some pictures of the final system. You can see I reused the auto tension pulley from the original serpentine belt system. I reused the same belt I purchased the first time I did the AC. Luckily it was still the right length even after the positioning of the components shifted a bit.

I took it out for a drive today after I finished. It was about 92F outside, so not too bad but hot enough when the top is up to make you start sweating pretty quick. I turned on the AC and instantly the temperature dropped to a very comfortable level and remained there for a quick 10 mile test. Too cool! No more hot days driving home.

The heat from the condenser now passes right by my motor controller and that heat sink. I'm now noticing the temperature of my motor controlling running much hotter. I'll be replacing that heat sink next with one where fins run parallel with the wind, compared to perpendicular as they do now. More on that later.

Back to work

I drove the S2K to work all last week and things are looking pretty good. I'm using 100Ah to get from home to work and 65Ah to get back home. This gives a pretty idea of what a 2,000 ft elevation climb will do to your range. Since my weakest cell is still delivering nearly 140Ah, I should be in good shape for quite some time.

Air Conditioning:
The weather is going to start heating up. Later this week I have plans to meet up with my uncle and get some machine work done. Afterwards, I can rebuild the brackets to mount the compressor and I should have a comfortable commute home in the afternoon. I'll post some pictures of the AC system when completed.

My worst cell

I was curious to see how much my cells have degraded so I took the car out for a test drive. I forgot how much I missed this car until I dropped the top and drove through the hills. What a blast!

I drove 65 miles and brought it home using 137 Ah. At this point my check engine light was coming up with only about 1C draw so I new at least one cell was getting low. I saw that my voltages were fairly well scattered around which was expected considering how scattered the self discharge seems to be.

Below are the photos of each cells voltage starting from the back of the car and working forward. There is one cell at 2.7v. This cell is basically dead and my worst cell. I'll probably yank or replace at least it. I have two more cells at 2.9 which means there is maybe another 5Ah in them tops. Most of the remainder of the pack is around 3.1. I'm guessing there is at most 10Ah in these cells. On the last two pictures you'll see sequentially 10 cells which are all 3.25v. These are the additional cells I added about 1.5 years go which have almost no miles on them compared to the others. They are still happy and have at least 20-25Ah left in them I'm guessing.

So this means that my worst cell is still giving me just over 85% capacity after four years. If I hadn't over charged some cells slightly, and over discharged multiple times, and never went over the 3C rating, I would be a bit upset. Considering the abuse I'm guessing this is right on par with what's to be expected.

So now I'm debating what to do. Ultimately I'm thinking I'd like to go with a much higher pack, say 350v using 100Ah CALB cells. These cells are now rated at 4-5C with 10 second bursts of 8C! This would require multiple changes. First and obviously the pack needs to be completely replaced which isn't cheap. Second the motor controller would need to be replaced with something like the Netgain or Soliton1 which allows high input voltage but you can regulate the motor side voltage to keep it safe. This also equates to even lower cell side amperage draws which should be easier on the cells. I'd also need to replace the charger. No hard feeling here though. The Thundersky charger is twice the size of say the Manzanita Micro charger for the same output (did I mention is weighs twice as much too?).

My other thought is to slowly replace the TS 160Ah cells as they wear out with CALB 180Ah cells. Physically they are identical so no mods would be required. These cells are also 4-5C rated so they can handle the amps my modified Curtis is demanding. I've got some thinking to do.

Either way, before I get back on the road any time soon, the AC needs to be redone. I'll need to engineer the mounting bracket (again) and machine some parts for the pulley. It's a shame it wasn't a direct bolt on replacement from the ADC 9".

It's suppose to cool off next week, so despite no AC, I think I'll drive it to work and see how the batteries hold up before investing any further time.