Beginners Guide to Processing 18650 Cells | Cell Database

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Opus BT-C3100 v2.2 Issues?
Ah. Good point. 10% does seem high.

Now I'm really hanging out for the new Batlab to see how that compares.

When charging with the Skilhunt M4D it gives 10-20% less capacity than what's previously discharged by the BT-C3100, % depending mostly of capacity and chemistry.
For exemple:
-Two identical cells will have the same capacity drop and the more high cap they are the more they drop most of the time, like 10% until 2000mah, 20% on some 2600+.
-Two 2200 mah discharged on the BT-C3100 but different brand/model can result one 2100 and the other 1950 charge on M4D.

So both my bt-C3100 give false capacity, but I will keep them as discharger, if all my cells are tested the same way it should be ok for a powerwall but I have to keep in mind they can't be trusted for small packs of different cells.
Current setup: 21x 215wc poly, 7.5kWh 7s 18650, PIP 2424msxe.
You can test the same cell in the same charger twice and it won't give you the same exact capacity. Just go with the one you feel is most accurate. Also, what is the discharge voltage of the BT-C3100? Most of them including the iMax, are 3.0v. I use the DigitalCharger 4s since it goes down to 2.8v.
Yes, I know, and it's pretty close when I re-run a test, the problem is they always give too much capacity, a 5-10 year's old Samsung 26F can't give 2700-2800Mah at 1Amp.
BT-C3100 V2.2 stop discharge at 2.8v but capacity between 3V and 2.8V is almost null and most batteries fall from 3.1 to 2.8 in less than a couple of minutes.

Imax is one cell at the time so I need the two bt-c3100 to have 8 channels to test capacity.
Current setup: 21x 215wc poly, 7.5kWh 7s 18650, PIP 2424msxe.
Hi I had my Opus BT-C3100 blow up on me last night while discharging my current collection of batteries; then did that mad dash around the room while 50+ plus batteries are charging because I can smell 'magic smoke', then waving my IR thermometer around like a mad man. Only to find smoke pouring out of of the back of the opus where to DC connector plugs in. I unplugged and took the back off and found the PCB sparking and the display flashing (indicating a buggered PSU) and possible an arcing track on the power in track. Needless to say it's about 2 weeks old, and I've contacted the ebay seller.
Wow!!!  that's nuts!!   Umm, you didn't get it on video, did you?   Rolleyes  I would of loved to see you running around like a madman  Tongue

It sucks that the opus died. However, it's better the opus than the cells, imho. Cells could cause lots of fires as they like to explode and fling across the room and land in a place you absolutely can't get to as it found the 'only' too small to get into and can it before it runs rampant. And no, not from experience. Just thinking of what "could" of happened.
Glad nothing major happened, just a little excitement
Proceed with caution. Knowledge is Power! Literally! Cool 
Knowledge is Power; Absolute Knowledge is Absolutely Shocking!
Dollar Shave Club. Best Razor I've ever used
Certified 18650 Cell Reclamation Technician
Use the number from the charger as a number. Ie just stating in what bin you should throw them. If that number is 10% to much or 100% to much its a way to tell at what state the cell is in. We all know that it is 10-20% higher than some other but it also depends on what charger you do compare to and more importantly what voltages. First of all the opus tend to go a bit high and then it also goes very very low. Compare to some others that stop rather early at both ends Smile (If you want to compare full capacity)

The last cells i got new for testing they all had their capacity measured between 4.2 and 2.5V and at 0.2C... Thats quite a difference to what most of us will be running in real life Smile
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The reason these chargers eat power supplies is because (electrically speaking) it uses the power supply as a hammer to beat the batteries to death with. There are some detailed reviews around, which show they draw peak currents between 6 and 9 amps from a 3 amp supply.

When charging, even at 200mA, they are blasting pulses of 2.4 amps into the battery.
When discharging, irrespective of the current selected, they are drawing pulses of 3.5 amps from the battery.

I think this is also why they give wildly inaccurate discharge currents - they're not discharging at a constant current. and the formula used to convert the peak current to RMS current changes with the pulse width. Either the algorithms aren't up to the job or the pulsing is messing with the battery chemistry. At 1 amp charge, I measured 950mA DC and 1.2amps AC. I'm no expert on charging lithium but I know that kind of ripple on a thonking great 12v AGM lead acid will void your warranty. It can't be healthy for a little old 18650.

I know that lithium is supposed to be charged at a constant current and then constant voltage - this charger produces neither and is about as constant as a hammer banging in a nail.

My other 3 chargers produce reasonably comparable discharge figures. This one is a bit of a rouge and is always optimistic by 20-40%. It's not so bad if this is your only model and you are only grading batteries, but you just can't use this one in combination with any other brands.

If you haven't already bought one of these, I'd recommend giving this model a miss. It is a shame because they are almost a brilliant charger - the physical construction is nice, the features are good, but who ever designed the electronics needs to go back to school and needs to calibrate their multimeter.
Do you have a site that has more information about this?
Proceed with caution. Knowledge is Power! Literally! Cool 
Knowledge is Power; Absolute Knowledge is Absolutely Shocking!
Dollar Shave Club. Best Razor I've ever used
Certified 18650 Cell Reclamation Technician
I recently witnessed something strange while charging cells with my MC3000s. This is a possible explanation.

I have three of them and used their original power supplies at first. These are rated for 50W and got surprisingly warm when charging four cells at 1A each. I then modded the MC3000s a bit and power them from an ATX PSU now. Because I had some excess solar power I connected the PSU to my Inverter where I always have a wattmeter at its output. Turns out the PSU peaks at over 70W at its input while three MC3000s charge four cells each at 1A max. I thought that this is a bit too much really given the known effciency of charging cells and the known efficiency of the PSU which is well over 85%
However, this wasn't the only thing. power consumption was also very unsteady. Over one or two hours I saw all kinds of numbers on the meter, most of which made no sense to me whatsoever. They do now, maybe the MC3000 does exactly the same thing as the Opus while charging.

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