280ah Lifepo4 Leisure Battery - Build Thread

Im still going DIY individual cells, the valance was just for demonstration! Interesting point about fusing the BMS cabless, npt something ive read about before!

Mrdanielmh said:

Im still going DIY individual cells, the valance was just for demonstration! Interesting point about fusing the BMS cabless, npt something ive read about before!

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Yeah, I haven't heard of anyone fusing the individual BMS wires like that either, however I've seen multiple builds where two smaller wires are used in place of a single main battery cable, and both wires are fused separately at a level that protects the individual wires. Dhowman's design is one example, there is some discussion relevant to this on page 4

NEWYORKHILLBILLY said:

what are you using to draw these nice diagrams

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Ditto?

NEWYORKHILLBILLY said:

what are you using to draw these nice diagrams

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Looks like Draw.io

Honestly, I'm just using PowerPoint

i'm a bit confused by that diagram, as it doesn't look like the BMS is in between battery negative and input/output connection!

Updated Diagram (Zoomed Out of Battery setup):



Zoomed into Battery and BMS Configuration:

Dzl said:

......IDK what the best practice is or should be for protecting the multiple smaller wires going to and from the BMS. If one or more of those wires shorts or opens (and there are 6 individual pieces of wire and 12 total connections)

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My BMS has internal over current protection for the BMS sensing wires. In a large pack like my 17S 48 volt pack there is a risk of high voltage, the tradeoff of accuracy is important. A fuse will add unnecessary resistance to the sensing wires and result in incorrect voltage measurements. They do not even recommend cutting or extending the sensing wires.

Ampster said:

My BMS has internal over current protection for the BMS sensing wires. In a large pack like my 17S 48 volt pack there is a risk of high voltage, the tradeoff of accuracy is important. A fuse will add unnecessary resistance to the sensing wires and result in incorrect voltage measurements. They do not even recommend cutting or extending the sensing wires.

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Ampster beat me to it.
The BMS is already controlling the current and has its own protection. The microvolts of differential between the lines would only be complicated by adding 2 more connections per line with a fuse.
See the pic.
This is literally how long the wires are. If they were 6 FEET long, I would agree that there is a possibility of one wire failing, leaving more current to another. In fact, if additional length is needed, I recommend going to a bus and using a single heavier conductor simply due to the resistance of the wire..

Ampster said:

My BMS has internal over current protection for the BMS sensing wires. In a large pack like my 17S 48 volt pack there is a risk of high voltage, the tradeoff of accuracy is important. A fuse will add unnecessary resistance to the sensing wires and result in incorrect voltage measurements. They do not even recommend cutting or extending the sensing wires.

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Just to be clear, I'm not referring to the BMS sensing wires/balance leads, I'm referring to the main wires that pass current.

Adding a fuse would add some resistance and an extra point of failure (taking the total from 12 points of failure to 18).

Haugen said:

The BMS is already controlling the current and has its own protection.

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Your BMS has overcurrent protection, to protect itself, not to protect a 10AWG wire. Overcurrent for your BMS is >120A, but 10AWG can only handle half of that.

The microvolts of differential between the lines would only be complicated by adding 2 more connections per line with a fuse.

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I agree but this is one of the potential problem of going with multiple smaller wires in the first place as I understand it, without fuses there are already 12 connection points that could fail, or that could cause differences between the wires. With fuses you now have 18 points of connection but the wire is protected.

I recommend going to a bus and using a single heavier conductor simply due to the resistance of the wire..

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I agree


Y'all are probably right that the risk is very low, I don't contest that, but I'm still not totally satisfied with leaving those wires unprotected, maybe its a non-issue, but the rule I've heard many times in marine electrical to fuse every time you step down to a lower unprotected wire size has stuck with me and seems reasonable. But I've never considered a scenario like this before, so maybe I'm misapplying the rule, taking it to the extreme, or overlooking something (Or just being a nervous nelly ). In either case your system isn't going to spontaneously combust or be drastically less safe either way.

q

Dzl said:

Just to be clear, I'm not referring to the BMS sensing wires/balance leads, I'm referring to the main wires that pass current.

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Yes, I understand that. My comment was in response to the OP original question about the sensing wires, but the thread has diverge to talk about the current carrying wires and your point is a good one about changing wire size and the need for over current protection for the smaller wires. I wonder how short they would need to be before being joined to a large conductor and could to be considered safe, or at least a small risk?

Alrighty folks, a great update! I have just taken delivery of my battery cells. Im very impressed withcthe packaging. The batteries arenin fantastic condition andnall measuring 3.33v!



Next step is to hook these up in parralel and get a top balance completes!

nice
Looking good so far

Exciting! I've been following this thread with anticipation. You ordered the cells mid April, correct? I need to get mine ordered so I can build something in like... August. Haha!

Hi @Sipma02 ! I ordered beginning of May! So its taken about 5/6 weeks. So get that order in!

Mrdanielmh said:

Alrighty folks, a great update! I have just taken delivery of my battery cells. Im very impressed withcthe packaging. The batteries arenin fantastic condition andnall measuring 3.33v!

View attachment 14732View attachment 14733View attachment 14734View attachment 14735View attachment 14736View attachment 14737

Next step is to hook these up in parralel and get a top balance completes!

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package looks great

Really chuffed with the cells.

Update

Cells were hooked up in parralel overnight
TThis morning i connected them up to the power supply at 3.4v.

Im planning om doing the stepped approach. 3.4, 3.4 and finslly 3.6

Its moving very slowly. Ive been documenting lots over on instagram (harrisvanadventures) but ill post up on here too!

Alrighty!

Things were going very slow yesterday so ive taken a different tack, im now charging at 3.614v and putting out 3.5amps.

0607am

Cells: 3353, 3351, 3351, 3351

Adjusted terminal layout based on some research.

0640am

3.614v and 4.08amps showing at power supply
Cells: 3375, 3373, 3373, 3373

3375 across terminals