Cabin in the woods

[Hedges]

It was a first initial charge, and it just pissed me off that 2 cells wouldn't go higher than 3.5 while the other 2 were higher .

I'll confirm tomorrow . Thanks for the tip !

That simply means they are not top balanced at or above 3.5V
If you top balance to 3.65V they should do better.

Please take a video and post it to "Up in Smoke!" when the time comes.
We love to read stories about lithium packs destroyed by cell imbalance with no BMS to disconnect.
Although we do feel bad for the cabins and vans.

 

[Substrate]

Exactly. There isn't enough current to do the job adequately, so balance is waaay off.

Nerd-hat suggestion: Put the iMax B6 into single-cell or 1S config for LFP. Charge each one individually. Do a little discharge. Then recharge with the 4S config changing cables obviously.

The ol' college-try.

 

[909]

Update. After a few cycles they've charged up to 3.52. Dead even. Seems like they were sitting idle for a long time and just needed to be cycled. There is slight variation between a few of the cells "sometimes" of 0.01 but for the most part they're dead even.

The B6 is 6A. Thanks for the suggestion to upgrade to a 10A.

 

[909]

Mountain Lion. Time to buy a gun.

 

[Rednecktek]

Mountain Lion. Time to buy a gun.

 

[Sverige]

@909 I suggest reconsidering whether you need a BMS, if you ever plan to run your battery down to the low voltage cutoff point of the inverter and rely on that to protect your battery from over discharge. It cannot, as the inverter doesn’t see the individual cell voltages in the way the B6 charger can.

Based on below screenshots the low voltage cutoff on that Bestek inverter can be as low as 10V (designed with a lead acid battery in mind). Although you may imagine your Lithium cells to be 2.5/2.5/2.5/2.5V each when that happens, grab a multimeter or hook up your B6 charger in balance mode with a super low charging rate of 0.1A so you can see the cell voltages either during or immediately after a low voltage cutoff event and I bet you’re going to be shocked to see at least one of your cells under 2V, which will quickly ruin that cell over a few cycles as it will no longer stay in balance with the rest of the pack from the internal damage which starts to occur.

The reason is those lithium cells are never fully in balance and never identical in capacity and that small difference between cells becomes a big voltage difference when they run out of energy to provide because they’ve been run down below 2.75V, where they are basically empty.

A $50 80A BMS like a Daly or any other brand will watch the voltage of every cell and cut the power before your inverter over discharges one or more cells, ruining your expensive new battery. It’s up to you.

 

[909]

Thanks Sverige. Beside small peripherals, the main load is an upright freezer that's 53 W that surges for a few seconds with a traditional compressor. Typically with my old smaller lithium ion packs, they'd cut off around 10.9 V @ 3s which is acceptable because it's still close enough to nominal . There's still power. It just can't handle the surge.

Every morning when I disconnect the inverter to charge, it hovers around 3.24 V - 32.2 V depending on how much I've used the night before. When I eventually need more power , I'll simply add more cells to make a bigger battery . When I'm finished building this house , I'll build a separate house to hold my toys : Boats , ATVs, Snowmobiles and of course batteries , LOTS of panels , a controller , big inverter ect . And of course a BMS by then. For now , I'm putting on a metal roof. Windows and doors are already in. House is sealed. Insulated. Wired for electrical. Siding and drywall are next. And lighting.