Imax b6 - 18650 capacity test

[B8rez 2g4]

What settings should I use to do a discharge test with the B6.
I have the B6 , B6AC , and the Hitec X1

LiPo 3.7
Discharge to 3.0
0.5 amps

I've charged my cells to 4.2 and let them sit for a few days

 

[Korishan]

A little more information about your cells would be helpful.

But generally speaking, you capacity test at the current you would be most likely peak be using. So if in heavy continuous load conditions you pull 100A from the battery, and they are arranged in 100p, then that'd be 1A per cell. If you only pull 50A from the battery and 100p, then that's 500mA (0.5A).
This will give you the lowest capacity you could expect to achieve from the cell if you had a sustained heavy load. You could also test with actual estimated load and that'll give you more real world active capacity you could expect on a daily basis.

 

[B8rez 2g4]

Thanks for your reply Korishan. This is for a marine application.

The trolling motor is rated at 24 lb thrust
I estimate it pulls approx 25 amps @ 12 VDC consuming approx 300 watts at full throttle (bursts)
Back EMF will reduce the load once the boat is planing and at max speed, as will running at lower speed settings.

The cells are repurposed 18650's from laptops LG's, Sanyos, Samsungs, Panasonics and Sonys.
My waterproof box can house 225 cells
I'd like to build a setup with many small 3s packs, so it's easier to disassemble, isolate and replace parasitic cells when necessary.
Any suggestions ?

 

[Wolf]

I'd like to build a setup with many small 3s packs, so it's easier to disassemble, isolate and replace parasitic cells when necessary.
Any suggestions ?

The best build is one you don't have to disassemble, isolate, and replace parasitic cells. How is this accomplished you say?
Suggestions, as you asked for them, would be to test every battery using proven methods to eliminate parasitic cells..
Flow charts are available to follow: https://secondlifestorage.com/index.php?threads/18650-harvesting-flow-charts.9714/#post-74868
There is also much discussion on how to test and verify cells for your build. I personally go overboard and test to the nth degree but then again after all the effort of harvesting/liberating a cell and building a pack I certainly don't want to have to do it again very soon.
See: https://secondlifestorage.com/index.php?threads/wolfs-powirwall.7804/post-72754

What settings should I use to do a discharge test with the B6.
I have the B6 , B6AC , and the Hitec X1
LiPo 3.7
Discharge to 3.0
0.5 amps

As far as your original question probably need to do a manual settings on the charger/discharger/analyzers as they are really designed for battery packs. Also the LiPo setting may not be ideal. Not sure if those units have a LiIo setting. I only have iChargers X6 and X8.
You can certainly use it/them to test each cell but you will be there forever. Once the packs and battery is built you can certainly use them to charge /test the battery and or test the individual packs if you choose to go a modular route.

The C/D/C testing or each cell would be, charge to 4.2V, discharge to ~2.8V, and recharge to 4.2V, all at a 1A setting, and recording the discharge mAh. Easier to get an OPUS that does it natively.

25 A max draw . If you have 50 cells in parallel per pack that would be 0,5A draw per cell quite acceptable with ≥ 2000mAh cells that would give you about 4 hrs. at full throttle. The more cells in parallel the less mA draw per cell the longer the battery will last.
I would build parallel modules and combine them into a 3s battery.
A 50A BMS should cover the amp draw.
Wolf

 

[ajw22]

it pulls approx 25 amps @ 12 VDC consuming approx 300 watts at full throttle (bursts)

Just FYI, a 3s lithium-ion configuration has a tad lower voltage than nominal 12V systems, so...
1. The motor may deliver the full advertised thrust / wattage only at the very beginning
2. The motor/controller may have a low-voltage cut-off that triggers even through the cells still have ~30% charge left in them.

 

[Wolf]

Just FYI, a 3s lithium-ion configuration has a tad lower voltage than nominal 12V systems, so...

Excellent point! At 12V is were the LiIo conundrum sets in, Voltage at 3s is kinda to low and 4s is kinda to high.
Wolf

 

[OffGridInTheCity]

I'd see if the troller moter can handle the higher voltage - it might. At 4s (instead of 3s) and reasonably full charge you be at the 16.4v level and it will go down (battery empty) to around 13.2v - e.g. more in the range of 80% of battery capacity.

Yes - in theory 4.2v * 4 = 16.8 but at 4.1v max charge (16.4v @ 4s) you'll have longer life + good power and the voltage will pull down a bit when load is applied.

 

[B8rez 2g4]

Thanks for the replies

The limitations of my chargers (Imax-B6) only allow a discharge of 4.2 V to 3.0 V
Using a 1A setting as suggested, most cells are testing well above 2000 mah.

Over the weekend, I quickly threw together a 3s10p pack and spent a day on the water.
The motor ran fine @ 12.6V , but struggled around the 10.5 V mark.
Still plenty of juice left ~ unused

Would it be safe to operate the motor @ 16.8 V in a 4S configuration? Maybe just charge the batteries to 4.0 V to get 16.0 V instead ?

The manufacture states "Lithium Ion batteries maintain higher voltages for longer periods of time than lead acid. Therefore, running a Minn Kota trolling motor at speeds higher than 85% for a prolonged period could cause permanent damage to the motor.... "

Sounds like they've had a history of heat related issues.
Over volting a a standard old school brushed motor, likely the brushes will wear prematurely, and the magnets will de-magnetize prematurely, increasing resistance , causing more even more heat until eventual failure .

 

[Wolf]

@B8rez 2g4
Maybe you can build a 4s or more and get a 30A buck/boost that way you will always have 12v and you can use the full spectrum of the Li pack.
Wolf

 

[ajw22]

The manufacture states "Lithium Ion batteries maintain higher voltages for longer periods of time than lead acid. Therefore, running a Minn Kota trolling motor at speeds higher than 85% for a prolonged period could cause permanent damage to the motor.... "

Any kind of conversion is going to introduce a 5%~20% loss due to inefficiencies in the converter, so it's 2 steps forward, one back.
The best solution is to exchange the motor with a 24V model and use a 7s lithium battery.
Another possibility is to use LiFePO4 batteries - they have voltages that perfectly match 12V systems. And use the Lithium-Ions for something else.

 

[B8rez 2g4]

You're absolutely right .

Ideally I'd want to get a 24V or a 36V motor and use a 7S or 9S configuration. They're more efficient and use a PWM controller for better efficiency at lower speeds (increased range)

When building a pack is it OK to mix capacities. I have cells ranging from 1800 to 2400 ish.

 

[Wolf]

When building a pack is it OK to mix capacities. I have cells ranging from 1800 to 2400 ish.

At higher discharge rates, capacity and IR matching becomes kinda important. You don't really want low capacity cells with high IR competing with high capacity low IR cells or vice versa. Preferably stick to ≈400mAh and ≈15mΩ difference and that IMHO is actually stretching it for a high demand application.
Wolf