4 batteries - create 1 or 2 battery packs?

[sv_isara]

Hey all - recreating my lost post--

I have a question about the proper way to setup my battery bank. Typically, the wiring is done with all batteries connected together, and the positive and negative to load are taken on opposite sides of the battery pack (see attachment). My specific question which I have not seen answered anywhere online explicitly is - what about if you have about 6 feet of distance in between the cells?

->I have 4 batteries each at 12v and 210Ah
-> 2 are to port and 2 are to starboard, separated by about 6 feet worth of cabling

Should I still treat them as a single battery pack like in the diagram attached? Or should I create 2 battery packs and then wire those together?

[motion30]

The absolute best way to do that is bring equal length cables from each battery to a positive and negative bus bar and then connect the load to the bus bar as well

[sv_isara]

Originally Posted by motion30

The absolute best way to do that is bring equal length cables from each battery to a positive and negative bus bar and then connect the load to the bus bar as well

Makes sense but am not going to do that since it would be extremely difficult to access and add a large amount of complication. Instead I will add the two slightly newer batteries to each end of the pack since those end cells generally have faster wear.

[Statistical]

I would do it as two packs tied into a primary bus bar and then distributed to rest of systems from there. You could even put isolation switches on each pack and gain a limtied amount of redundancy. If the length from each location to the busbars are not the same ensure the same length wiring is used. Havings two packs with different wiring length means the one with shorter one will have less resistance and thus the load through it will be higher.

[hlev00]

You are violating two best practices - 1) adding new batteries to an old bank and 2) separating the bank in an uneven way. What you are doing right, based on your diagram, you are pulling the pos and neg from opposite ends of the two banks. So, short of two separate banks with a common point to tie them together you can do as you've drawn just be aware of the trade-offs. Here is a video that covers the issues briefly.

https://www.pysystems.ca/resources/v...g-batter-bank/

WRT old/new, your other alternative is to make them into two separate banks using a 1/2/both switch. That seems overly complicated and short-sited has having one bank is better and simpler. If it were me, I would bite the bullet and replace the two old batteries at the same time for a complete matched set of four.

[SailingHarmonie]

Originally Posted by sv_sharky

Makes sense but am not going to do that since it would be extremely difficult to access and add a large amount of complication. Instead I will add the two slightly newer batteries to each end of the pack since those end cells generally have faster wear.

I am so confused...

You have decided what to do. You ask if it is a good idea, everybody says. "No." You say you are going ahead anyway.

Why ask in the first place? Was it just to get somebody to say it was a good idea so you feel better?

Batteries are expensive. if you are on a budget, it would serve you well to take good care of them.

If the batteries "at the end of the pack" wear noticeably faster, then your bank is NOT assembled correctly and you are throwing money away with band-aides.

[hlev00]

Originally Posted by hlev00

...
If it were me, I would bite the bullet and replace the two old batteries at the same time for a complete matched set of four.

PS. Each year swap the two banks batteries so they will age more evenly.

[SailingHarmonie]

Originally Posted by hlev00

PS. Each year swap the two banks batteries so they will age more evenly.

Or... wire them correctly so the age evenly from the get-go.

[sv_isara]

Originally Posted by hlev00

PS. Each year swap the two banks batteries so they will age more evenly.

Yep

Originally Posted by SailingHarmonie

Or... wire them correctly so the age evenly from the get-go.

That's what I'm trying to accomplish here

Originally Posted by SailingHarmonie

I am so confused...

You have decided what to do. You ask if it is a good idea, everybody says. "No." You say you are going ahead anyway.

Why ask in the first place? Was it just to get somebody to say it was a good idea so you feel better?

Batteries are expensive. if you are on a budget, it would serve you well to take good care of them.

If the batteries "at the end of the pack" wear noticeably faster, then your bank is NOT assembled correctly and you are throwing money away with band-aides.

I get what you're saying, but while it's not in the budget or sensible for my situation to throw out 4 newish and hardly used batteries, I am 100% fine to re-wire them in the best way. I didn't think anyone else was going to reply to this thread after a few days.

However I disagree with your understanding on battery packs; in my experience, having testing hundreds (maybe thousands) of batteries (albeit they were LiFePO4), it was normal for the end cells to wear faster, however that was in a engine starting context, and given the proportionally low discharge rate it probably won't be a considerable issue in this situation.

[Uncle Bob]

Originally Posted by SailingHarmonie

I am so confused...

You have decided what to do. You ask if it is a good idea, everybody says. "No." You say you are going ahead anyway.

Why ask in the first place? Was it just to get somebody to say it was a good idea so you feel better?

Batteries are expensive. if you are on a budget, it would serve you well to take good care of them.

If the batteries "at the end of the pack" wear noticeably faster, then your bank is NOT assembled correctly and you are throwing money away with band-aides.

Originally Posted by sv_sharky

Yep

That's what I'm trying to accomplish here

I get what you're saying, but while it's not in the budget or sensible for my situation to throw out 4 newish and hardly used batteries, I am 100% fine to re-wire them in the best way. I didn't think anyone else was going to reply to this thread after a few days.

However I disagree with your understanding on battery packs; in my experience, having testing hundreds (maybe thousands) of batteries (albeit they were LiFePO4), it was normal for the end cells to wear faster, however that was in a engine starting context, and given the proportionally low discharge rate it probably won't be a considerable issue in this situation.

Now I too am confused, if as you say you have tested hundreds or mabee thousands of batteries (surely one would know), then would it not be reasonable to assume that you would have sufficient knowledge to install your batteries using the best available practice, without raising the question on a sailing forum?

[Eagle ITA]

Originally Posted by sv_sharky

Hey all - recreating my lost post--

I have a question about the proper way to setup my battery bank. Typically, the wiring is done with all batteries connected together, and the positive and negative to load are taken on opposite sides of the battery pack (see attachment). My specific question which I have not seen answered anywhere online explicitly is - what about if you have about 6 feet of distance in between the cells?

->I have 4 batteries each at 12v and 210Ah
-> 2 are to port and 2 are to starboard, separated by about 6 feet worth of cabling

Should I still treat them as a single battery pack like in the diagram attached? Or should I create 2 battery packs and then wire those together?

You could try to connect all the battery (including the ones of the same pack) with 6 feet cables, so you have the same cables lenght for each battery.
But remember, the longer the cable, the wider it must be...


Anyway I'm sure you can find a better place to keep all the batteries closed each others, that is absolutely the best option, even if you have to do some extra works

[sv_isara]

Originally Posted by Uncle Bob

Now I too am confused, if as you say you have tested hundreds or mabee thousands of batteries (surely one would know), then would it not be reasonable to assume that you would have sufficient knowledge to install your batteries using the best available practice, without raising the question on a sailing forum?

I'm querying the community because I know there are people out there who know more than I do. I have a lot of experience working with batteries but I don't pretend to be an electrical guru...because I'm not. I know the basics like many and happen to have tested and recovered many lithium batteries and battery banks (for motorsports).

It's really what I said - that I want to know the best way in this specific circumstance - or if there's an abyc code etc that I should be aware of for batteries in this specific situation where they are separated in 2 pairs. I don't like the separation distance, but there's really not another good solution space-wise here. The other solution would be to raise them up and move them to the side of the boat, taking up shelf space up high, or even higher up and in the very stern of the boat. Both would be moving 500lb from the low center of the boat to the high ends of the boat, which for me doesn't win out over an extra 4' of battery cabling.

I'm taking the suggestion of wiring them as one battery bank with equidistant cable lengths to load. I have both sides fused. I'll keep an eye out on the overall performance of each battery but despite the not-ideal battery ages, I don't think the decision of throwing away almost unused 1 & 3 year old batteries to start new is worth >$2500; I'll replace them all as a unit when the performance dips.

[sv_isara]

Originally Posted by sv_sharky

Makes sense but am not going to do that since it would be extremely difficult to access and add a large amount of complication. Instead I will add the two slightly newer batteries to each end of the pack since those end cells generally have faster wear.

Originally Posted by motion30

The absolute best way to do that is bring equal length cables from each battery to a positive and negative bus bar and then connect the load to the bus bar as well

Maybe this is what got some people (and myself) confused- this to me is choosing the option of treating them as 2 separate battery packs - parallelled together by a bus bar, all equidistant from the load.

The load happens to be next to one of the pair of batteries - so if the bus bar is by battery pack #1, should I actually have lots of extra cabling in the battery pack #1 location to create the similar resistance? That solution seems funny to me somehow.

Conversely if I treated the batteries as 1 pack, I could have the positive lead shorter than the negative lead to load, which would seemingly give a more equal resistance load to each battery (kind of nuanced here) - but I'm not sure.

[Statistical]

Originally Posted by sv_sharky

Maybe this is what got some people (and myself) confused- this to me is choosing the option of treating them as 2 separate battery packs - parallelled together by a bus bar, all equidistant from the load.

The load happens to be next to one of the pair of batteries - so if the bus bar is by battery pack #1, should I actually have lots of extra cabling in the battery pack #1 location to create the similar resistance? That solution seems funny to me somehow.

Conversely if I treated the batteries as 1 pack, I could have the positive lead shorter than the negative lead to load, which would seemingly give a more equal resistance load to each battery (kind of nuanced here) - but I'm not sure.

All that matters is the distance (and thus resistance) through each battery. I think people were confused by your explanation but there is no issue with having two banks one of the port side and one of the starboard side for example.

1) All batteries should tie in at the same primary bus bar.
2) All should have equal gauge and length wires to create the same resistance across each circuit.
3) All load and charging circuits should go to the primary bus bar not individual batteries.
4) Any connectors, fuses, and switches should be identical to create the same resistance across each circuit.
5) Ideally all batteries will be identical in capacity, brand, and age because the resistance can vary across models and will increase with age.

Note having different length for positive side and negative side is irrelevant. The total circuit length is all that matters.


If you do all that the resistance across each path through the four batteries will be nearly identical which means the current flow will be nearly identical. 100A drawn on the primary busbar will produce roughly 25A across each battery and they will age similarly.

The easiest way to do that is with all four batteries all together wired as you have them in your diagram but it isn't the only way. The same thing can be done logically with the batteries separated into two banks one port and one starboard.

The problem is when the resistance isn't the same and since wires produce resistance that is usually caused by unequal length wires. If the resistance differs for each battery so will the current load. In the 100A draw example if the resistance varies significantly the least loaded battery might only be 18A and the highest 32A. That highest loaded battery is going to die first. Yes that means if the primary positive and negative bus bars aren't at the boat centerline that the battery for one or the other banks will be longer than needed. You should not use a shorter cable because it will reach because now that bank will have lower resistance and when current flows it will flow unequally more to the bank with lower resistance.

[sv_isara]

Originally Posted by Statistical

All that matters is the distance (and thus resistance) through each battery. I think people were confused by your explanation but there is no issue with having two banks one of the port side and one of the starboard side for example.

1) All batteries should tie in at the same primary bus bar.
2) All should have equal gauge and length wires to create the same resistance across each circuit.
3) All load and charging circuits should go to the primary bus bar not individual batteries.
4) Any connectors, fuses, and switches should be identical to create the same resistance across each circuit.
5) Ideally all batteries will be identical in capacity, brand, and age because the resistance can vary across models and will increase with age.

Note having different length for positive side and negative side is irrelevant. The total circuit length is all that matters.


If you do all that the resistance across each path through the four batteries will be nearly identical which means the current flow will be nearly identical. 100A drawn on the primary busbar will produce roughly 25A across each battery and they will age similarly.

The easiest way to do that is with all four batteries all together wired as you have them in your diagram but it isn't the only way. The same thing can be done logically with the batteries separated into two banks one port and one starboard.

The problem is when the resistance isn't the same and since wires produce resistance that is usually caused by unequal length wires. If the resistance differs for each battery so will the current load. In the 100A draw example if the resistance varies significantly the least loaded battery might only be 18A and the highest 32A. That highest loaded battery is going to die first. Yes that means if the primary positive and negative bus bars aren't at the boat centerline that the battery for one or the other banks will be longer than needed. You should not use a shorter cable because it will reach because now that bank will have lower resistance and when current flows it will flow unequally more to the bank with lower resistance.

This is perfect thank you, and thanks to the others who I may have confused who helped me to clear up the situation at hand.

Based on a few of the posts here, I'm going to wire it up as one bank to a bus bar, I believe that will be the most efficient as well as proper way.

As to the differently aged batteries, it's a concession and we'll see how long they'll last. On my list of projects is to get individual voltage metering for all of them so I can see how they're faring.