Re: [electricboats] Parallel LiFePO4 Packs

Miles,

Thanks for the reply. I currently have 2 X 48V banks of golf cart batteries. Each bank has a Blue Sea 300A rated on/off switch that ties to a common 48V bus. I have ram in parallel, never one bank at a time. It is nice though to be able to take one bank out of service to clean connections, etc. without killing the whole system as the 48V is also my house bank feeding the inverter, DC-DC converters for 12V stuff and to a controller for my 24V windlass. Thoughts?

Chris

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On Nov 8, 2023, at 15:08, Chris Hudson <clh5_98@yahoo.com> wrote:

Reuben,

Thanks for the reply. I haven't given that much consideration yet. Seems like I've heard possible reliability issues with the larger cells, maybe not a concern. The other thing for me is the configuration of my battery boxes limits me some in the physical size of the cell I can work with. Also, I was thinking from a reliability standpoint. Having 2 independent banks with each having its own BMS, but that can run in parallel would be more fault tolerant. I have a fear, maybe not legitimate of a BMS leaving "dead in the water".

Chris

Chris 

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On Nov 8, 2023, at 14:59, Myles Twete <matwete@comcast.net> wrote:



Thought: Dangerous for the switch unless it's a break-before-make or other exclusive-or arrangement.

 

Why: You've been running for hours on one string, then decide to switch to the other.  If you thought that you'd just use a standard marine battery combiner switch, you could accidentally switch to "ALL" position, which would then put both strings in parallel thru the switch, quickly shorting it and possibly melting the housing.  Might also have a problem with that type of switch switching between each string.

 

With Lithium-Ion there's something to be said for having separate strings---ability to switch and get a higher pack voltage again for a time giving higher power/speed than if the strings were paralleled and slowly going down together.  But really, a slowly dropping voltage is better than one that drops much faster due to not paralleling.  Not as much of a big deal with LiFePo, but still, I'd tend to think paralleling is better.

 

Just a thought.

-MT

 

From: electricboats@groups.io [mailto:electricboats@groups.io] On Behalf Of ChristopherH via groups.io
Sent: Wednesday, November 8, 2023 11:49 AM
To: electricboats@groups.io
Subject: Re: [electricboats] Parallel LiFePO4 Packs

 

Bobkart,

Thanks for the reply. Actually I'm proposing to have 2 independent 16 cell strings with the ability to parallel them at the 48V level with switches, not at the cell level. Thoughts on that?

 

Chris 

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On Nov 8, 2023, at 14:40, bobkart <couch45@msn.com> wrote:



Connecting two 230Ah cells together in parallel (sixteen times) would allow you to treat the 32 cells as one large 16S 48V x 460Ah battery

BMS, load, charger, capacity monitoring would be none-the-wiser.

 

One concern of that configuration that wouldn't otherwise come up is if one cell in a two-cell pair were to fail.

If the failure is a short, it would bring the other cell with it.

 

---

From: electricboats@groups.io <electricboats@groups.io> on behalf of ChristopherH via groups.io <clh5_98=yahoo.com@groups.io>

Sent: Wednesday, November 8, 2023 10:34 AM
To: electricboats@groups.io <electricboats@groups.io>
Subject: [electricboats] Parallel LiFePO4 Packs

 

Hi Group,
My Morgan Out Island 41 is ready for new batteries. I'm ready to embrace LiFePO4. When I originally converted to electric I built and glassed in 2 battery boxes to hold 2 banks of 8 (16 batteries) golf cart batteries. I always run with both banks in parallel, but have the ability to run on just 1 and this has worked well. Unfortunately this size battery box doesn't make efficient use of most individual LiFePO4 cells. I would however be able to use 32 X 230Ah EVE cells in 1 battery box, leaving the other box for some other purpose. My questions: I'd like to be able to run the 2 X 16S strings in parallel. Is this possible with LiFePO4? Is it safe to do this? Any precautions? Would I have 2 separate BMS units? How about capacity monitoring for the 2 banks in parallel? I have a Victron 48V/5KVA Victron Quattro charger inverter. 
Thanks in advance for any assistance/suggestions.

Regards,
Chris Hudson

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