BT-C3100 vs Battery Analyzer

I’m running a few cells through the capacity test on my new BT-C3100 charger and then running the same cells through my West Mountain Radio CBA2 battery analyzer.
The first cell is an NCR18650 laptop pull. I ran this test using a 1A rate in both devices. The BT-C3100 measured 2830mAh. The CBA2 measured 2723mAh. That’s a difference of less than 4%, which seems pretty darn good to me.
I’m running a few more cells and I’m going to test at the 2A rate.

Putting into consideration that the CBA2 is a high-precision device, <>4% variance is indeed impressive.

Wow, you have a CBA2? Even more impressive!

I just noticed that the BT-C3100 only discharges cells at a 1A rate. It will charge at 2A, but the capacity test is done during discharge at a 1A rate.

Many of the smaller chargers only use a resistor to discharge > heat produced. So they have to limit the rate to keep from getting too hot.

1A discharge rates are quite common even among hobby chargers. My iCharger 106B+ can do up to 7A, quite uncommon among hobby chargers costing below $90.

Yes, but you will have to mount an external bleeder resistor to reach 7 Amps. The 106B+ chargers internal discharge capacity is 20 W. At 4 Volt that is 5 Amp capacity.

I just tested the 5A discharge rate in my Panasonic NCR-PF and Soshine 2900mah protected, never tried the 7A:

Me neither, at 7A it should be good up to 3Volt without resistor (see manual for 106B), but I guess that the fan will be VERY busy.

Well, to just find out the discharge capacity and health of cells, a 1A discharge rate is good enough for most applications.

Tested two more NCR18650 cells.
Battery #2- BT-C3100 measured 2778, CBA2 measured 2687.
Battery #3- BT-C3100 measured 2828, CBA2 measured 2650. About 6% difference there, but I didn’t let the cell rest and cool between tests. I’m not looking for absolute precision, I just wanted to see if I could trust the BT-C3100 for decent capacity tests for all the laptop cells I got off eBay and it looks like it will work just fine for this.
My CBA2 is very precise and it can test up to 40A, but it only tests one cell at a time. I’ve got a box full of cells and now I can test 4 at a time on the BT-C3100.
I’m satisfied.

Edit- I saw a post in Chloe’s review thread where someone had problems with this charger running the 2A rate on 2 cells. Mine has no trouble charging 2 cells at 2A or 4 cells at 1A.
The only thing I’ve noticed is that the final charge voltage is not consistant. I’ve seen cells top off at 4.15 to 4.25 Vdc.

I don’t know if it was a mistake but the guy has listed his charger as the V1.0 version, and might already be malfunctioning, to quote:

Got BT-C3100 v1. issue or not ? In my unit bay 4 shows lower voltage readings, while other three bays indicating almost same value. So in slot 4 same cell has 3.55V while slots 1-3(DMM too) readings are 3,66V. As result each cell put in slot 4 is overcharged exactly up to 4,35V. LCD shows “4,20V” than “FULL” and after DMM measurements result is 4,35V. Other slots terminating at 4,21/4,22V(DMM mesurment). Maybe it’s a positive thing ? I can get 4,35V cells and use it only in slot 4. It will spear me case modification and i don’t have to use 4,35V switch inside charger.

If I measure the cell voltages on my batteries while they are charging, I read between.05 and .1V higher than what is shown on the charger display, but my final cell voltages after charging are OK, so I don’t worry about the display.

It is a bit difficult to measure the voltage on a pulsing charger, What is the correct value?

1) The voltage when current is turned on.

2) The voltage when current is off.

3) The average of the above two.

The charger will show 2) and you meter will show 3)

Especially in the early stages of the charging process, (when the cell is almost empty at 3.6) and much more if a high charging rate is used, (1.5A or more), I have observed this: try putting your DMM’s probe on the cell’s neg end and at the pos end, alternating between the cell’s pos end and at the charger’s pos end, and you will see a variance between the two by as much as .04V because it takes time for the electrical energy coming from the charger to be converted into chemical energy by the cell being charged. I have observed this both in my Pila IBC and in my iCharger. I see more variance during the process if I use 2.5A charging rate in the iCharger. As the cell is almost full and the charging rate goes down towards 10% of the initail rate of the charger, the variance will get smaller and smaller.

That’s why a low charging rate’s energy will be more absorbed by the cell and give out higher mah than a cell charged by a high charging rate.

Oh no, my C3100 has not arrived yet…