Upgrading 15s Battery to 16s

boarder2k7 said:

Do you have a suggestion on where to purchase from? I had been planning on signature solar because I've heard good things about their support.

Edit: also not sure that I really need as much as 5k anyway, though if it was the same price as I'm looking at I would go for it. My plan is to use this to run my home server rack (about 350 watts peak), with the ability to provide backup power for my furnace (250 watts while running) and one refrigerator and one chest freezer (100 watts each running, though the refrigerator defrost cycle is approximately 600 watts for 30 minutes once a day).

It will be set up in such a way that I can use it to bolster my small generator by using it to load level while the generator is running, allowing the generator to provide a constant output (its about a 1200 watt unit) to charge the batteries and use the battery/inverter system to handle all the sudden load changes that my generator struggles with.

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boarder2k7 said:

Do you have a suggestion on where to purchase from? I had been planning on signature solar because I've heard good things about their support.

Edit: also not sure that I really need as much as 5k anyway, though if it was the same price as I'm looking at I would go for it. My plan is to use this to run my home server rack (about 350 watts peak), with the ability to provide backup power for my furnace (250 watts while running) and one refrigerator and one chest freezer (100 watts each running, though the refrigerator defrost cycle is approximately 600 watts for 30 minutes once a day).

It will be set up in such a way that I can use it to bolster my small generator by using it to load level while the generator is running, allowing the generator to provide a constant output (its about a 1200 watt unit) to charge the batteries and use the battery/inverter system to handle all the sudden load changes that my generator struggles with.

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SparkyJJO said:

Well be aware some of these units cannot charge the batteries and invert at the same time. Some inverters can pass through your generator power and supplement with battery, but not all. Additionally, some generators are too "dirty" for the inverter to even use.

I'd be tempted to hook your generator to a chargeverter (once back in stock) to directly charge batteries, and then use the inverter to run the loads. Granted that does cost more, but it may be worth it to do what it sounds like you're trying to do.

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sunshine_eggo said:

That is allegedly the actual JK BMS store.

That's the only way I would consider using AliExpress.

I would still prefer ordering from a North American source when possible.

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42OhmsPA said:

Note that one only has 0.6A of balancing current. The others have 1A or 2A.

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boarder2k7 said:

You're thinking I might benefit by going up to the 150 amp BMS to get up to 1 amp balance current? That's a $20 jump which isn't too bad, but the one with 2A balance is a $40 jump so that's getting a little large for my "cheap" project. (as if there's such a thing!)

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boarder2k7 said:

Can anyone with more balancing experience chime in on the merits of 0.6/1/2 amp balance current for this effort?

I'm keeping in mind that theoretically there will be 15 cells with identical capacity and then one with presumably higher capacity in series.

The current BMS appears to have 4.7 ohm resistors in line with the leads, so passive balancing I presume?

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sunshine_eggo said:

Ultimately, they hasten the top balancing process if using active balancing (vs. wiring cells in parallel) and can compensate for SLIGHTLY different cell characteristics. For normal operation with a healthy battery, even 0.05A passive balancing current is enough.

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sunshine_eggo said:

My only concern is the reliability of the 15S BMS. If it will cut off, great. If not... potentially cooked cells.

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boarder2k7 said:

I have my power supply set to 55V so that should safeguard against cooked cells assuming they stay in balance, so far so good on that front. Still only up to 51.3V while charging at 5 A presently. BMS is now up to 40% SOC so depending on how accurate that is I have about 12 hours of charge time left, if the current holds which of course it will slow down as it gets near the top.

I'm not charging unattended with this current setup, so maybe I'll have results on the first pack by the weekend.

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boarder2k7 said:

I have my power supply set to 55V so that should safeguard against cooked cells assuming they stay in balance

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boarder2k7 said:

so far so good on that front. Still only up to 51.3V while charging at 5 A presently. BMS is now up to 40% SOC so depending on how accurate that is I have about 12 hours of charge time left, if the current holds which of course it will slow down as it gets near the top.

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boarder2k7 said:

I'm not charging unattended with this current setup, so maybe I'll have results on the first pack by the weekend.

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boarder2k7 said:

do we think that the 1A balancing current in the BMS would be sufficient to balance in the 16th cell assuming I get the voltages as close to each other as possible first?

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boarder2k7 said:

@42OhmsPA @sunshine_eggo

Well you guys were right, the end went really fast and the crappy BMS could not be trusted. Unfortunately I didn't read your replies in time and half fell asleep on the couch so it went 2 hours past my post there.

Final cell voltages got higher than I intended in a couple places. Final numbers at me shutting it off were:
3.613, 3.703, 3.797, 3.758, 3.657, 3.618, 3.598, 3.647, 3.731, 3.659, 3.561, 3.666, 3.667, 3.673, 3.733

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boarder2k7 said:

This morning I didn't take pictures of the display but everything has settled back to that 3.4ish range within about 25 mV

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