Wednesday, June 27, 2012

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.


Electric said...

Not bad only one cell is way below 2.5V. Cell 30 should be higher than 2.4V because of the voltage drop on the cable.
Your new cells look good. They appear to be on par with my CALB cells.

Peter Taggart said...

Wonderful job you're doing here! Thanks for sharing!

I stumbled over your blog while looking for help with battery leakage in my s2000. I must say, what you've done here is very tempting.

As a EV-Novice I have some questions:

1) In the first version you compared the power your car was able to deliver with a Civic. Now that you've added more batteries, tweaked the controller and replaced the motor, what would you compare your car to now? How fast can you achieve 60mph/100kmh? What's the top-speed and for how long can you sustain it?

2) As there's a huge amount of current flowing, do you know how strong the magnetic fields inside the cabin are when accelerating or maintaining speed (at legs, torso, head)? I assume there's DC current from the batteries and AC current from the controller to the motor - if so, then there should be a mixture of static fields and variable fields - both interesting regarding magnetic storage (hard disks), signal transmission and the human body.

3) Is it already possible that while breaking or driving downhill that your system recuperates the energy and charges your batteries (or a short-term storage)? Would the charging current be too high or the system be too inefficient?

Keep up the good work and "may the cells stay with you!" ;)

Brian said...

Now it's probably clos to a Civic si. I still need to test the 0-60. I still plan to get it faster yet. I want it to compare to the car stock.

The car uses around 150 amps cruising down the road. I have no idea how strong the magnetic field is or it's effects on the human body.

The is DC so you typically won't find any form of regenerative breaking. I'd like to move to AC motor in which case it's pretty hard to find one that doesn't have that support.

alke said...

Thanks for sharing!