The Boss Escapes!

More fun! We continued discharges in 5A increments are got up through 7C with a constant 70A discharge. The test cell gave up 9.4Ah in a hair over eight minutes before reaching the 2.1V cutoff. Cell temperature peaked at 52.6ºC (126.7ºF).

Here's a recap of 55A thru 70A:

While we were talking about the way the capacity slowly creeps downward with each increase in load, we heard familiar whining noises from the bosses office. We decided we had to get to a 10C discharge so we could stop delivering food to his office three times a day. Besides - he needs a shower...

The cell isn't rated for a continuous 10C discharge so we took advantage of the option on the 10X CBA amplifier to cycle amplifier power during a test. We cycled power/load in roughly 15 second intervals. First two 'spikes' are 15 seconds load, 15 seconds 'rest'. Then we walked it out to 30 seconds on, 15 off; then 45 seconds on and 30 seconds off. The test ran for nine minutes 50 seconds and the CBA reported a cell capacity of 16.4Ah.

Now..about the bosses office - Febreze or Lysol? Both!

More Power!

Here are the results from the last three discharge cycles on our test cell. This takes us to a 55A load. As you can see from the charts posted so far, power delivery and voltage drop is consistent and predictable.

We've varied charge between a single 2A charger up to 5x chargers for a 10A initial charge rate. The only difference was charge time.

One nice feature of the 500W CBA amplifier is that we can turn the amplifier off and on during a test. This will allow us to simulate 'pulse and glide' power delivery and show voltage recovery during the 'glide' times. It will also allow us to discharge a cell to 2.1V at higher rates without overheating the cell.

End of test cell temperature is staring to come up. We've gotten to 47ºC at the end of the 55A test. Cooling starts immediately once the load comes off and contunes to ambient - even when the warm cell is connected to a 10A charge.

Stay tuned while we decide if a 10C (100A) pulse is enough to get the boss out of the office...

Throttle Almost Half Way Open

It's been an interesting couple of days! The West Mountain CBA Amplifier arrived and it started to absorb electrons almost immediately after we ripped the box open. We started the higher rate discharges at 1C (10A) primarily because we've changed the test configuration from earlier tests.

The basic CBAII is fed by a pair of 12AWG silicone leads connected to the cell via Anderson Powerpole connectors. The amplifier requires connecting the cells to its 5/16 inch terminal bolts. We decided to wire the cell to the amplifier with 10AWG wires - two per pole - with crimp-on ring terminals. It's giving us very low resistance connections and should give us an open highway for electrons to flow from the test cell.

(Click the image for a readable chart.)

The first round of tests took us from 10A thru 40A (4C) in 5A steps. This chart covers discharge cycles 23 thru 31. 25 and 28 were aborted due to improper setup of the monitoring software. (The boss forgot to enable the amplifier at test start. He's exiled to his office until we test at 10C.)

Test environment is a 24º-25ºC (about 77ºF) air conditioned lab. A couple of the tests were conducted on a quick-turn from the chargers - we didn't let the cell sit to cool and stabilize. Starting cell temperature ranged from 25º to 27ºC. End of discharge temperatures from 20A to 40A ranged from 34º to 42ºC (93º to 108ºF). We're finally starting to see a bit of heat on discharge. There's no significant heating on a 10A charge (1º-2ºC above ambient) - same for discharge up to 15A. Max discharge heating noted so far is 17ºC.

Capacity is trending slightly lower as discharge rate increases. We're down to 9.91Ah at the 40A rate. We've noticed a slight variation in the cutoff setting for the Voltphreak 2A chargers and we expect this will intruduce some cell capacity variation. Overall, though, we're happy with the consistency of the data so far.

Stay tuned for the next installment - maybe we'll hit 10C and let the boss out of the office.

The End of the Break-In?

Break-in testing continues. We're up thru cycle 22 with the basic CBAII and it appears that cell capacity has stabilized. Capacity varies a bit with discharge rate. 5A discharge produces 10.36Ah. 20A provides a bit between 10.08 to 10.13 Ah. A 25A continues discharge provides 10.19 Ah.

Comparing 10A loads, we've gone from 9.63Ah at cycle 1 to 10.26 at cycle 16 for a 6.5% gain in capacity. The experienced cell provides more consistent power until end of charge as well.

This is the end of our break-in tests for now. We've also reached the end of our discharge tests with our current CBAII configuration - 25A is the upper limit for a single cell. 26A does interesting things to fuses ...






Discharge cycle 23 at 10A is the first cycle with West Mountain Radio's 500W add-on amplifier for the CBAII. We'll increase the load 5A each cycle and see how these cells perform at higher rates. The cells are rated at up to 10C (100A) peak discharge.

Testing to date has been limited by equipment. Let's see how these cells perform when we open the throttle!