How to wire 8 lithium 12 volt batteries for a 12 volt system?

[jarett906]

I need help with wiring multiple 12v lithium batteries in parallel!
I have the following setup for my RV:
Magnum PT-100 Solar Cell Charge Controller
Xantrex freedom SW 2012 (100amp charge)
(8-11??)- 280watt solar panels
8- lifepoe lithium (k2B12VG27-3)100amp/hr batteries
RV QG 5500 generator with 20/30 dual breaker

I did not install this at the time and have been trying to learn since. I have Xantrex controller setup for (manually programed) lithium charging and use the gen to top of the batteries. However I can never seem to get them all fully charged with the wiring setup there currently in (all 8 in the same parallel string). Most of the info i see states that u should only put 2 lithium batteries in parallel. Does that mean i should do 4 sets of 2 lithium's in parallel, with all 4 positives from each set wired to one +lug to Xantrex and all 4 negatives from each set wired to the - lug to Xantrex? or all 8 separately? Anyone with experience in this?

 

[chrisski]

Look in my signature block for an article on paralleling batteries.

 

[jarett906]

chrisski, that is the exact setup there in. However there not charging fully. I start with them all being fully charged and topped off every summer for the past 4 years. wire them exactly how ur diagram shows. But every year within a few days the first 2 batteries and 1 in the middle of the string go red and stay there, never fully getting charged. im wondering if there's a better way to wire them? Like running 8 separate negatives/8 separate positives to one centralized negative/positive lugs so each battery gets a better split of amps if thats such a thing?

 

[rmaddy]

For the amount of solar capacity and battery capacity you should consider a higher voltage setup.

8 280W panels is 2240W. At 12V that's 187A of charge current. You need 2 100A charge controllers for that. At 24V it becomes 93A which can be done with a single 100A charge controller.

 

[rmaddy]

that is the exact setup there in

The link in their signature shows 4 ways to wire batteries in parallel. Which of the 4 methods are you using? For 8 batteries the first two methods shown in that link are terrible ways to do it.

 

[jarett906]

rmaddy, my bad. im using the #2 option in that link and now that u pointed out there were 3 more options. which one of those 4 are the best? method 3?
Also I was told not to put these battries in series due to the electronics? not sure exactly why or if true for these batteries.

 

[rmaddy]

From that article I would use method 3 for 8 batteries. But I would use a pair of bus bars on each side for connecting all of the batteries together. As noted for that method, all of the negative wires from all 8 batteries must be the same length. All of the positive wires from all 8 batteries must be the same length. The whole idea is to ensure the same amount of resistance through every battery to help keep them balanced.

LiFePO₄ batteries can only be put in series if its BMS allows it to be. If the specs for the battery you have doesn't explicitly state that they can be put in series then they probably can't be put in series.

Note that your 100A solar charge controller is only good for about 1400W of solar on a 12V system. You have over 2200W. If you only want the one SCC then you should setup the panels so half face SE and the other half face SW. Then you can get good solar all day.

 

[jarett906]

rmaddy, Thank you! I was thinking #3 would be a better way! With it being ran the other way it was installed with 4 gauge jumpers. I'm thinking that is overkill and might cause issues/extra resistance using that size? What size gauge would be best and would i want thin stranded like kicker power amp wire, thick stranded like auto battery cables, or solid wire? Also where do i put the 2 heat sensors (one from pt-100 and other from xantrex) or does it really matter which neg on the batteries its connected to beings there all the last in the string? Also do u have a particular style buss bar u recommend for 8 batteries?

I also like your solar panel idea, not sure if i can thoe because there mounted on my rv roof but i will look into that and see if it is possible

 

[chrisski]

The only thing I will mention for #3 is it can take a lot of wire. You could use #4 and save wire. Not just for amount saved on wires and busbars but also for space.

I agree a 24 volt system could be better, but that could be $1.5k for a good inverter, 24 vDC to 12 vDc converter, and 120 VAC to 24 vdc chargers, plus wiring.

 

[rmaddy]

I was thinking #3 would be a better way! With it being ran the other way it was installed with 4 gauge jumpers. I'm thinking that is overkill and might cause issues/extra resistance using that size? What size gauge would be best and would i want thin stranded like kicker power amp wire, thick stranded like auto battery cables, or solid wire?

4AWG wires is far from overkill. It's barely big enough. The wire size for each parallel connection should be based on the max continuous discharge current rating of the BMS of your batteries. Let's say it's 100A (not to be confused with the 100Ah capacity of the battery - two very unrelated values). I would use 2AWG marine grade pure copper high-strand-count wire. Never use solid wire in a mobile application for any wire in the vehicle. Fuse each battery with a 125A fuse (all 8).

Also do u have a particular style buss bar u recommend for 8 batteries?

A copper bus bar with 9 attachment points - one for each battery plus one for the rest of the system. You might need to make your own out of copper bar stock if you can't find one with that many lugs.

I also like your solar panel idea, not sure if i can thoe because there mounted on my rv roof but i will look into that and see if it is possible

It can't be done on the RV roof. Though you will have lots of shading issues if the roof is like most big RVs. Between being flat mounted and shading issues, putting all 2200W of panels when your 100A SCC can only make use of 1400W may not be an issue since you may rarely get over 1600W (wild guess) out of those 2200W of panels.

 

[chrisski]

It can't be done on the RV roof. Though you will have lots of shading issues if the roof is like most big RVs. Between being flat mounted and shading issues, putting all 2200W of panels when your 100A SCC can only make use of 1400W may not be an issue since you may rarely get over 1600W (wild guess) out of those 2200W of panels.

I find this fairly accurate. I have 1650 watts on my roof flat mounted at times of the day shaded by 2 ACs, a TV antenna, and the vent pipes. That's about the proportion I get. I will add that after the equinox the numbers are like that, but in the shortest day of the year, it's a little less.

I do have portable panels that I point at the sun three times throughout the day and are angled to the sun that produce at real close or above the rated power for hours each day. Its a pain setting them up, avoiding shade, moving them three times a day, and then tear them down before sunset so they don't blow away. The portable panels are worth the extra power to me.