Per-Cell BMS Cost?

What are people generally paying, per-cell, for a system which includes:

• Charging
• Protections (overcurrent, under-voltage, etc)
• Active balancing

I'm curious about off-the-shelf systems vs DIY.

For systems based on 18650's or 26650's.

Not counting the cost of the cells, cell enclosures, wiring, etc. Just the circuitry.

I think this post might be about different kinds of cells, and it includes the cost of the cells, housing, etc.

boom said:

For systems based on 18650's or 26650's.

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You won't find a lot of people here using these cells. Most builds are prismatic LiFePO4 cells.

Interesting question but i'd be surprised if anybody worked this out. Mostly because cost per cell is very low on MY list compared to other things like reliability, ease of use and efficiency.

If you're looking for lower overall cost, 18650s and 26650s are not very cost effective compared to other types of cells. If you munge it into cost per cell, then yea, 100's of tiny cells are cheaper per cell than a few 280Ah cells.

What are you looking to do? (and how big is your haul of free 18650s?)

MisterSandals said:

If you munge it into cost per cell, then yea, 100's of tiny cells are cheaper per cell than a few 280Ah cells.

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Ha, I had not thought of it this way. Yes, on a per cell basis LFP prismatic BMS's cost a fortune! On a per-energy-stored basis, not so much.

MisterSandals said:

Interesting question but i'd be surprised if anybody worked this out. Mostly because cost per cell is very low on MY list compared to other things like reliability, ease of use and efficiency.

If you're looking for lower overall cost, 18650s and 26650s are not very cost effective compared to other types of cells.

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I didn't say i'm looking for lower cost. I do care about reliability, ease of use and efficiency. Just wondering what typical costs are. Also, i'm just seeking cost of the BMS, not counting the cost of the cells.

boom said:

Also, i'm just seeking cost of the BMS, not counting the cost of the cells.

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A good 8-20S JBD BMS bought direct with 150A ability will be about $80. Buying from US reseller will be about $150.

If you get into more than 20S, the number of solutions get slim and spendy.

MisterSandals said:

A good 8-20S JBD BMS bought direct with 150A ability will be about $80. Buying from US reseller will be about $150.

If you get into more than 20S, the number of solutions get slim and spendy.

Click to expand...

I can't tell if these systems include all charging, balancing, and protection circuitry, including power supply?

boom said:

I can't tell if these systems include all charging, balancing, and protection circuitry, including power supply?

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Think of a BMS as a cutoff switch (to the battery negative) to protect the cells from under voltage, over voltage and over current. A moderate amount of balancing functionality.

A charger is a completely different item. How do you plan to charge? Grid? Solar? Alternator?

MisterSandals said:

Think of a BMS as a cutoff switch (to the battery negative) to protect the cells from under voltage, over voltage and over current. A moderate amount of balancing functionality.

A charger is a completely different item. How do you plan to charge? Grid? Solar? Alternator?

Click to expand...

Grid.

LakeHouse said:

You won't find a lot of people here using these cells. Most builds are prismatic LiFePO4 cells.

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What's the typical parallel-series configuration with prismatic cells in operation?

boom said:

What's the typical parallel-series configuration with prismatic cells in operation?

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I think it depends on the use case. For my stationary home pack I went with 3P16S using one BMS. I have the grid as backup. In an EV or Boat some people prefer redundant 16S packs with separate BMSs. In those situations on the water or in a remote camping spot there is no grid and having redundant packs might allow starting an engine to generate power. Also space may be limited and several smaller packs in parallel may be easier to fit in confined spaces.

These are just my best guess based on recollection. I also built this system a few years ago, so prices might have changed.

-For a 2p4s (8 cell) 12 volt system-

-My BMS was about $100
-10 gauge silicone copper wire was about $50 for the amount I needed (I used multiple conductors run in parallel for some portions of the battery). That being said, the company I ordered from screwed up the order and sent me some extra wire for free, so it could have been a little bit more than that.
-A crimping tool, good adhesive heat shrink, and connectors were about $50.
-I used two pieces of flat copper bar to make bus bars, they were about $20 total.
-The battery housing was made with scrap wood and a few bolts, maybe $15 in total if I were to pay for it. (This does not include the case that holds everything, just the pieces that hold the battery cells together)
-40 amp DC-DC charger was about $150 (allows me to charge from just about any source)
-I use used server rack power supply's as chargers, they were about $30 for two 70 amp units at 12-15v, but required some easy to do modifications.
-A good quality MPPT controller was about $125, I got it open box.
-I had an active balancer, it was about $20, but it's no longer on the system because my cells are pretty well-matched.
-Class T fuses we're all purchased used, for between $5-$30. There's probably about $80 of fuses in there.
-Small automotive power distribution box was about $15.
-Shunt was under $20.

My guesstimate is about $675 for a 12v system, not including the batteries themselves or the case and inverter. You can add an extra few hundred dollars for parts that I tried to cheap out on, and now live in a box, and ended up just buying a better quality component.

Sorry the numbers aren't exact, but it's been quite a while since I put it together, and I purchased a lot of items on sale or used.

All of that being said, every part is user replaceable, and can be upgraded or downgraded at will.