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Low cost DIY Lithium camper batteries.

Lithium LiFePO4 LFP DIY Batteries

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#11 rando

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Posted 23 October 2017 - 03:01 PM

Small update - went on a quick weekend trip with the new lithium batteries.   We used as power as we could to give the battery a test - about 40Ah overnight.   I noticed two things about the battery performance relative to the prior AGM battery

 

1. The batteries will accept the full power from my solar panels (about 9A this time of year) up until the charge controller decides they are full and shuts off.   This is very different from the AGMs which would get to ~85% state of charge pretty quickly, then take another 4 hours or so to reach 100%. 

 

2. You don't really get much charging from the alternator.   I think the tacoma has a 'smart' ECU controlled alternator, which puts out 13.9V for a few minutes on start up but then quickly drops down to ~ 13.6V.   With the solar panels going, 13.6V is actually lower than the house battery voltage, so the alternator does not really provide any charging current.   Without solar, you do get a little charge current (~5A) but not much.    So if you rely on alternator charging you would either need a DC-DC charger or figure out how to turn up the alternator voltage to ~14V. 


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#12 photohc

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Posted 24 October 2017 - 06:55 AM

Nice job Rando. I did something similar in 2016, with LiFePO from batteryspace.com, not like your DIY version but did install with a BMS/Charger from Electrodacus. Been running since then and enjoying the easy daily recharge and loss of weight.


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#13 K6ON

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Posted 25 October 2017 - 02:15 AM

Rando,  Thanks for posting this project as it got me off my butt starting to do a similar battery for the camper.  I ordered two cases of cells and played with them for a few days, and then ordered a third case.  My plan is to use 40 cells per bank for a little over 200AH. I have a couple nice 30 amp charger/controller boards already so that's taken care of. Two banks of 40 cells, stacked on top of each other fit nicely in a small group 24 battery box.  I'll be using two boxes and replace the huge battery boxes that already exist in the camper. I played around with 18650 cells for a radio project a year ago, and at that time bought a battery spot welder. It's going to make this project much easier than soldering.  I'll post a report when I get the project done.

 

 

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#14 rando

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Posted 25 October 2017 - 02:27 PM

Good luck in your project!   A spot welder should make it much faster.   One thought though, if you bought the BMS for use with you 18650 batteries (lithium cobalt) you may want to check the set points.   Most of the lithium cobalt BMS have higher overcharge protections as it is normal to charge 18650 to 4.1V/cell, whereas the LiFePO4 cells shouldn't be charged much above 3.6V/cell. 


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#15 K6ON

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Posted 26 October 2017 - 01:18 AM

I have BMS systems for both.  This isn't my first rodeo. Just took looking at yours to get me off my butt.  Thanks!


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#16 rruff

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Posted 02 November 2017 - 06:20 PM

Thanks for the info! Looks like something I might be able to handle with not so much $ risk.


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#17 BWSracing

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Posted 03 November 2017 - 12:26 AM

Hey guys I really appreciate all the input. As much as I wanted to figure out a lithium battery pack it just wasn't in the budget or time frame. I have ordered two of the lifeline batteries and hope they work as well as everyone says.
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#18 rruff

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Posted 03 November 2017 - 12:48 AM

Hi, rando or anyone else who knows, if I build a 12v 100+ah pack would it be able to easily start my truck? I'd like to ditch my starter battery and just use the "house" battery. I was originally planning on AGM which I know will work.


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#19 Vic Harder

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Posted 03 November 2017 - 08:15 PM

Hi, rando or anyone else who knows, if I build a 12v 100+ah pack would it be able to easily start my truck? I'd like to ditch my starter battery and just use the "house" battery. I was originally planning on AGM which I know will work.

 

That's an odd thing to want to do.  The battery characteristics are different for starting and long slow draining.  Plus you would need some serious fat wire running to your truck starter.  What is the reason for your idea?


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#20 rando

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Posted 04 November 2017 - 03:00 AM

There is no reason this couldn't start your truck, but you would need to build it a little differently.  I designed my battery to be a house battery, which for me means a maximum current draw of ~20A, and typically more like 5A.  If you used it for starting you could see draws more like 100A, so you would want to use heavier gauge bus wire between the cells, and much heavier wire between the packs.  You would also want a BMS/protection circuit rated for a higher current.    You would definitely want to put the battery under the hood and run wires back to your camper, as opposed to the other way around as you would need some seriously beefy wire.   

 

I would also agree with Vic, that this may not be a great idea.    I think using a smaller lead acid / agm battery for your starting battery and a large LiFePO4 battery for the house loads would be a better idea. 


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