Two or three different Lithium Battery Banks

[Lance Glogowsky]

I will be upgrading from 4 to 6 100 amp lithium batteries in the near future. We boondock up to 15 days at a time. I have the Victron Multi Plus II installed with 1200 watts of solar and possibly going to 1600 watts. My current 4 battery setup is in the normal parallel arrangement. Like some, room to best connect the batteries individually to a busbar, with same length cables, etc, would be a little tough. The current arrangement of the Multi Plus II would also make this very tough. Can I wire the batteries in 3 banks of 2 each, or possibly 2 banks of 3, to my busbar, with same cable lengths, etc. and achieve a better setup then the normal parallel configuration with all the batteries?

Thanks for the input.

 

[Soundsailor]

While I'm not an electrician, I believe that as long as the total cable length from your charger to each battery is the same, you should be fine. Cables add resistance, if the resistance is the same, the batteries will charge evenly.

 

[TimtheToolMan]

Even with two very equal length systems (parallel), the batteries (even within a group) likely will discharge at different rates with LFP--sometimes very dramatically. So each battery will have different SOC (at least with LiTime). Is this OK, maybe? It will not be seen unless each battery has its own BT display. This is not so much the case for LA but is a BMS LFP (LiTime?) issue. In just one night use I have seen 30-40% difference (and increasing) between the two. Both batteries were purchased at the same time and on the surface seemed exactly the same. Each battery wiring set has the same resistance wi .1 ohm display, that most meters can display.

Most users never know this because they do not have SOC BT (or a shunt) for each battery. This surprised me and there are some discussions on various sites specifically about this. What "should be" based on LA experience may not be if LFP.

I do not see remotely even charging or discharging (5A light loads at least) between two 100Ah LiTime with BT BMS when charging with my LPF solar charger). Charging is pretty even when slow charged with bench top power supply wired in a perfect symmetrical loop. They eventually will both charge to 100% just fine using any charge method that I have available. This is partly why the number of batteries in a group is limited by manufacture and it is common to try to go with larger capacity batteries so there are fewer batteries. Current limits going through each battery is also a limitation. I now wish I had gone with a single 200/230Ah but my system works OK for my use. One battery will get much more use/cycle (BT displayed) unless I intervene by turning one battery off--a bit of a hassle but is fine with my no inverter system.

If all batteries are above 0% SOC, this likely is not an issue when trying to pull a lot of amps for the system--when a high amp load is required for the set and one battery can't safely pull the full current.

I have no answers and can't provide more information...still digging.

I possibly could improve how it is wired a very small amount but have read it will not make any difference. I will play with it more this summer but if what I am seeing and reading, it is a waste of time.

 

[TimtheToolMan]

My wiring has each battery with a set of Anderson connector pairs so batteries can easily be removed independently. The positive from each then goes to on off switch—1 on or 2 on or 1&2 on or all all. So wiring is not in a perfect loop where one battery has positive out and other has negative out (12V parallel wires between). Each wire is the same length with the same connectors. I know this matters and is not ideal but will run tests later.

 

[Lance Glogowsky]

If I had to do it over again I would probably go with higher amp batteries. With the different configurations when it comes to battery efficiency, away from the standard setup that I currently have, I want to make sure I’m doing what is felt to be the latest and greatest to what Im able to do since I’m adding to my power supply. The two or three bank of batteries connected with same length cables to the buss bar seemed to be an upgrade from my current connections. I always want the thoughts of those who know more than I do.

 

[Riverbug]

Here's the answer in a nutshell. Yes, cables should be the same length from batteries to buss bars or between batteries if not using buss bars. However, the lengths of cables on the positive side can differ from the lengths on the negative side. And the cable lengths from the buss bars (or battery bank if not using buss bars) to the main fuse/cutoff switch (+) can be different than the negative cable to the shunt/distribution block. This is best practice, but of course you will find people that say it doesn't matter.

 

[Butcher]

I have 4 sets of DIY 304ah batteries. All are attached to a common buss bar. Cable length differs due to how far the batteries are to the buss bars. Some as short as 18" and others as long as 3'. I have one common shunt. I can see the SOC on each battery separately through the BMS and see a common SOC with the shunt.

Here is my take......It just does not matter what so ever. The entire rig runs on the buss bar voltage. When it needs 12v, it gets it from there. The buss bar provides that voltage from all the batteries connected to it. If there is a large draw [A/C on] all of the batteries are supplying current. Some higher than others, but they are all very close to each other [within a couple amps]. I suspect if one battery is slacking, the other will pick up the demand, but the demand is met by all of them as a team.

When I charge the batteries [I have a 125A converter] they all take about the same current. When the batteries are close to being full, there is a noticeable difference that each battery is charging at, but they are all fairly close to being full. That is because with Lithium batteries, they absorb less current as they reach a full charge.

We all have LA on the brain and we all keep forgetting that the LiFePo4 batteries are just different. There will always be a voltage differential between batteries. Just not like the differences of LA batteries. The very slight differences in battery voltages is not as big of an issue because there are too slight. Especially when they are all attached to a common buss bar.

That said, if I have a really low charge on one of my batteries and another one that is fully charge, they will equalize and I can see that using Bluetooth on my phone. That large difference would never ever happen if you got good cables/connections from your batteries to your buss bars.

That is my take, in theory, I know I am not correct, but in practice, I know it works for me.

 

[Lance Glogowsky]

Thanks for the thoughts and chiming in to help guide my thoughts. I know there are different opinions out there and we or I learned from all of them. That’s why I appreciate this forum so much.
With everything I’m gathering and able to do, I plan on hooking up two banks of three 100 amp batteries each. I will attempt to make the cables all the same length going to the bus bar. The two banks of batteries is the best route I can go to make them fit. I’d rather do the 3 bank route though. Again, I feel I’m upgrading from the way I had my four batteries with each of them connected to each other.

 

[PeterInNH]

I will be upgrading from 4 to 6 100 amp lithium batteries in the near future. We boondock up to 15 days at a time. I have the Victron Multi Plus II installed with 1200 watts of solar and possibly going to 1600 watts. My current 4 battery setup is in the normal parallel arrangement. Like some, room to best connect the batteries individually to a busbar, with same length cables, etc, would be a little tough. The current arrangement of the Multi Plus II would also make this very tough. Can I wire the batteries in 3 banks of 2 each, or possibly 2 banks of 3, to my busbar, with same cable lengths, etc. and achieve a better setup then the normal parallel configuration with all the batteries?

Thanks for the input.

I thought there is an (potential) issue with battteries in a bank not being the same age ?

if so, if you're going to add 2 new batteries to an older bank, why not just upgrade to bigger batteries ? Your 4 batteries must be worth something on the open market ?

I just put together my system with 2 of these - haven't had them out for a test trip yet but in my driveway all is cool:

Amazon.com

I ran them each to a bus bar, then to a Victon shunt and then the shunt to another bus bar where all the Negs came in. So, I get 600ah and 400amps for about 130lbs worth of batteries.

Here's a (very rough - ignore notes !) diagram of what I did.

Good luck with whatever you decide !

P

 

[Butcher]

I thought there is an (potential) issue with battteries in a bank not being the same age ?

Old LA thinking.

It is really difficult to remove everything out of your head about lead acid batteries and download the newest lithium data. I know, I had to change my thinking a lot.

There was a time I was a factory trained BMW mechanic. When I went to Mercedes, I had a real tough time accepting a different way of doing things. I kept comparing the two products and getting upset because they were different. Once I accepted that comparing two different methods is a terrible way, life became so much easier.

Off grid garage has done a lot of actual testing with huge capacity differences with lifepo4 batteries and you should watch it. He also built a few mismatched capacity/age batteries and tested them. It's worth watching. I like that kind of data and the testing he does. It certainly puts a lot of opinions to rest.

The more you know, the more sense it makes.

Off-Grid Garage

Taking your house, shed or garage 'off-the-grid' is a very exciting thing to do. On this channel, I share my experience and thoughts of taking my garage offline, disconnecting it from the power supply and run it solely from solar and batteries (for teaching and testing purposes). We will do a...

www.youtube.com

 

[Lance Glogowsky]

I thought there is an (potential) issue with battteries in a bank not being the same age ?

if so, if you're going to add 2 new batteries to an older bank, why not just upgrade to bigger batteries ? Your 4 batteries must be worth something on the open market ?

I just put together my system with 2 of these - haven't had them out for a test trip yet but in my driveway all is cool:

Amazon.com

I ran them each to a bus bar, then to a Victon shunt and then the shunt to another bus bar where all the Negs came in. So, I get 600ah and 400amps for about 130lbs worth of batteries.

Here's a (very rough - ignore notes !) diagram of what I did.

Good luck with whatever you decide !

P
Thanks for the thoughts. My current four Safari lithium batteries are barely a year old and not that much use overall. I’ll kick around the two bigger batteries, but just keep thinking I already have the four, actually five, and just adding the two with a better connection.

 

[Lance Glogowsky]

If I learn adding two batteries to my current bank and then making them two banks of three is not efficient or a total bad idea I’ll change my plan of action and work out something else

 

[PeterInNH]

If I learn adding two batteries to my current bank and then making them two banks of three is not efficient or a total bad idea I’ll change my plan of action and work out something else

Oh, I'm pretty sure that if wired to bus bars (a common single one or multiple that end up at one) then your 'system' will see it as a single battery with some total of ah's and amps available. What you're comtemplating is really not much different than what I did with only 2 batteries.

My only concern was dealing with 6 (!) batteries is with all the space, weight, wiring considerations as opposed to just two that give you the same capacity. Although with 6 batteries you certainly have drastically better redundancy that I do with only 2.

Good luck with whatever you try.

Thanks,

P

 

[Lance Glogowsky]

Oh, I'm pretty sure that if wired to bus bars (a common single one or multiple that end up at one) then your 'system' will see it as a single battery with some total of ah's and amps available. What you're comtemplating is really not much different than what I did with only 2 batteries.

My only concern was dealing with 6 (!) batteries is with all the space, weight, wiring considerations as opposed to just two that give you the same capacity. Although with 6 batteries you certainly have drastically better redundancy that I do with only 2.

Good luck with whatever you try.

Thanks,

P

Yes, the disadvantage of my setup is taking up more space, a little more weight and a few more cables like you mentioned. I'd have to get rid of my current batteries to buy two bigger ones. Placing them 3 x 2 rows next to each other won't be to bad into two banks, which will be more efficient then all connected together. I do have some extra room in the front compartment.

 

[BoredWeasel]

unless you are drawing high currents. 100 plus amps for an extended period I wouldn't worry about cable lengths.

I have a mix bag of lithium iron battery's in my workshop totaling in the 1800 amp hour range now. they are a mix bag of manufactures and amphour ratings on a shelf hooked up with varying cable lengths to a buss bar. I power AC in the summer and the usual shop power tools.
the reason it works is each battery has its own bms. I have drawn 200 amps from the bank on more than a few occasions with no issues.

My point is don't get frozen by precision and close is often good enough.

 

[oubruceb]

I will be upgrading from 4 to 6 100 amp lithium batteries in the near future. We boondock up to 15 days at a time. I have the Victron Multi Plus II installed with 1200 watts of solar and possibly going to 1600 watts. My current 4 battery setup is in the normal parallel arrangement. Like some, room to best connect the batteries individually to a busbar, with same length cables, etc, would be a little tough. The current arrangement of the Multi Plus II would also make this very tough. Can I wire the batteries in 3 banks of 2 each, or possibly 2 banks of 3, to my busbar, with same cable lengths, etc. and achieve a better setup then the normal parallel configuration with all the batteries?

Thanks for the input.

One of the things you may be missing is your BMS. The ones on my batteries will only manage 4 batteries. I went to 2 banks of 4 in my camper. Both banks hook to the same Lynx shunt.

 

[Butcher]

My point is don't get frozen by precision and close is often good enough.

This is what too many people do. What we are doing is not really all that high tech that it might matter.

 

[Lance Glogowsky]

Each of my Safari Batteries have a BMS system. Like many Bluetooth where I can look up the batteries status on my phone.

I agree, sometimes we get to caught up in it. But at the same time, it doesn’t hurt to make our power supply somewhat efficient.

The other day I changed the six AA batteries in my handheld Ham Radio and then the batteries in my LabelMaker. I tested the batteries in both devices. The center batteries are always depleted before the end ones.

 

[Butcher]

The other day I changed the six AA batteries in my handheld Ham Radio and then the batteries in my LabelMaker. I tested the batteries in both devices. The center batteries are always depleted before the end ones.

Again, we get caught up with thinking old school and apply it to the new stuff. It's hard not to do but it's like apples and oranges.

Nobody is saying it's not a bad idea to make it easy for the electrons to move along the wiring, but a good BMS will keep things in check. Not every battery will charge/discharge at the same speed. You will never ever make that happen.

 

[Lance Glogowsky]

Again, we get caught up with thinking old school and apply it to the new stuff. It's hard not to do but it's like apples and oranges.

Nobody is saying it's not a bad idea to make it easy for the electrons to move along the wiring, but a good BMS will keep things in check. Not every battery will charge/discharge at the same speed. You will never ever make that happen.

I agree. You just give it your best shot.