Best Battery Bank?

[Sage Oldmann]

Hello Everyone
It appears I have set up my battery bank incorrectly based on input I've received here. I'm told using a buss bar or terminal point like in this image is the best way to connect my 6, 12 volt batteries.
6 Battery Bank W-Terminal.jpg
My question is this. Does the system see the difference in the length of the cable for Battery 1 verse Battery 3 going to terminal A? Is the resistance higher for Battery 1 verse Battery 3 going to Terminal A? With Terminal A being the take off point does it matter if the cables connecting the batteries to it are not the same length? I trying to understand why this method is better than other configurations. Thanks.

[SunEagle]

Hello Everyone
It appears I have set up my battery bank incorrectly based on input I've received here. I'm told using a buss bar or terminal point like in this image is the best way to connect my 6, 12 volt batteries.
[ATTACH]7842[/ATTACH]
My question is this. Does the system see the difference in the length of the cable for Battery 1 verse Battery 3 going to terminal A? Is the resistance higher for Battery 1 verse Battery 3 going to Terminal A? With Terminal A being the take off point does it matter if the cables connecting the batteries to it are not the same length? I trying to understand why this method is better than other configurations. Thanks.

Any difference in cable length will also be a difference in resistance. The longer the length of wire the higher the resistance.

If a low resistance metal bus bar was connected to the A terminal of all six batteries and a second low resistance metal bus bar exactly like the first is connected to the B terminal of all six batteries you can improve the chances of the resistances being very close to equal for each battery but there is no guarantee it will stay that way.

[Sunking]

Copper and aluminum both have fixed passive resistance. All electrical wire has a Resistance Spec expressed in Ohms/Kft. It is liner so if you have 100 feet of 6 AWG copper wire is .0395 Ohms. Thus any all battery cables should be the same length, type and gauge. Failure to comply completely defeats the purpose as you loose the gain you were trying to achieve.

[Sage Oldmann]

Any difference in cable length will also be a difference in resistance. The longer the length of wire the higher the resistance.

If a low resistance metal bus bar was connected to the A terminal of all six batteries and a second low resistance metal bus bar exactly like the first is connected to the B terminal of all six batteries you can improve the chances of the resistances being very close to equal for each battery but there is no guarantee it will stay that way.

So if I wanted to double the size of my battery bank like this image and all the cables are the same length would this work?
12 Battery Bank .jpg

[paulcheung]

The best bank of battery is a single string batteries in series. if you want to double the capacity. buy the single battery come with the AH you need. I have two bank of batteries now in parallel, I got nothing but trouble.

[Mike90250]

parallel batteries are bad. parallel banks are even worse.
in the sketches you show, the center batteries 3 & 4, have the shortest leads, and will be forced to do the most work, and then degrade quickly.

If you need that many watt hours of storage, you should be using a higher voltage bank, with batteries in series, 8, six volt golf cart batteries will give you 48V @ 200ah ( 9,600 watt hours) up to half of which, are usable on a daily basis.

With your massively parallel sketch, you have left out the individual 100A fuses & holders (or DC circuit breakers) at each battery. These would not be cheap automotive fuses, but high tech fuses that can quench a 24V 100,000 amp arc. If one cell fails as a short (which is a common failure mode, when residue builds up in the internal sump and shorts the cell) the rest of the bank will try to charge it. Ka-Boom !

[SunEagle]

So if I wanted to double the size of my battery bank like this image and all the cables are the same length would this work?
[ATTACH]7845[/ATTACH]

What you are doing is increasing the chances of a battery failure. Even with equal cable lengths you have way too many parallel wired batteries and will end up killing the ones in the middle or at each end.

Also without really knowing the battery Ah rating or CC amps I would say that you will exceed the amount of amps that any of those battery terminals were designed for and end up causing a failure which will include smoke and fire.

As the others on this thread have mentioned, wiring batteries in parallel is the wrong way to increase the system size.

[Sage Oldmann]

What you are doing is increasing the chances of a battery failure. Even with equal cable lengths you have way too many parallel wired batteries and will end up killing the ones in the middle or at each end.

Also without really knowing the battery Ah rating or CC amps I would say that you will exceed the amount of amps that any of those battery terminals were designed for and end up causing a failure which will include smoke and fire.

As the others on this thread have mentioned, wiring batteries in parallel is the wrong way to increase the system size.

I appreciate all the input from everyone who obviously knows a lot about this. If I had the option I'd change what I have, but I don't. I'm stuck with 6, 35 amp batteries and a very small but well ventilated space. I muddied the waters with my 12 battery alternative. I went to extremes in an effort to understand all of this. Thanks to you and others I am not beginning to see the problems I face.

If all of the cables are the same length then there isn't a "middle" or "end" battery. It's like they are in a circle. So why would any one battery get killed when all are exactly equal?

If I can't make what I have work in some less than ideal, but safe, fashion I will have to scrap the whole thing and lose a lot of money. What I take away from all of this is that if I use equal length cables from each battery to a buss bar, with each battery individually fused, I can safely make this work. If all the cables are the same length than there should be no problem with added resistance right? Would each battery provide more or less equal current? Can I use ANL type fuses for the batteries? What size?

[SunEagle]

I appreciate all the input from everyone who obviously knows a lot about this. If I had the option I'd change what I have, but I don't. I'm stuck with 6, 35 amp batteries and a very small but well ventilated space. I muddied the waters with my 12 battery alternative. I went to extremes in an effort to understand all of this. Thanks to you and others I am not beginning to see the problems I face.
If I can't make what I have work in some less than ideal, but safe, fashion I will have to scrap the whole thing and lose a lot of money. What I take away from all of this is that if I use equal length cables from each battery to a buss bar, with each battery individually fused, I can safely make this work. If all the cables are the same length than there should be no problem with added resistance right? Would each battery provide more or less equal current? Can I use ANL type fuses for the batteries? What size?

How you wire your batteries is dependent on how you plan on charging them. So before I answer your questions I have a couple of mine I would like you to answer first.

What is the make and model of the battery charge controller you plan on using?

What is the solar panel specs and how do you have them wired to the CC?

[Sage Oldmann]

How you wire your batteries is dependent on how you plan on charging them. So before I answer your questions I have a couple of mine I would like you to answer first.

What is the make and model of the battery charge controller you plan on using?

What is the solar panel specs and how do you have them wired to the CC?

I have 4, Renogy, 100 Watt panels, 5.29 IMP, 18.9 VMP wired in parallel going to a 30 Amp LCD Renogy PMW positive ground charge controller (Model#PMW30CC-LCD) using #8 wire. My normal load is 150 watts per hour with a maximum load on the system of 300 watts per hour for about 3-4 hours. (no motors, just lights, TV and PC at different times.) I have a Sunforce 1000 watt pure sine inverter but am probably going to trade it down to my friend for his 600 watt inverter. I really don't need the 1,000 watt capacity and it uses more power at standby. I use #2 wire between batteries and also to the inverter. 6 Batteries are 35 amp AGM.

[SunEagle]

I have 4, Renogy, 100 Watt panels, 5.29 IMP, 18.9 VMP wired in parallel going to a 30 Amp LCD Renogy PMW positive ground charge controller (Model#PMW30CC-LCD) using #8 wire. My normal load is 150 watts per hour with a maximum load on the system of 300 watts per hour for about 3-4 hours. (no motors, just lights, TV and PC at different times.) I have a Sunforce 1000 watt pure sine inverter but am probably going to trade it down to my friend for his 600 watt inverter. I really don't need the 1,000 watt capacity and it uses more power at standby. I use #2 wire between batteries and also to the inverter. 6 Batteries are 35 amp AGM.

Thanks. I do remember you mentioning the 100 watt panels but I could not find what your CC was.

Even though you do not have enough wattage to get there, with that 30amp CC you need to use wire to handle up to 30 amps so that #8 wire is ok. To be safe please make sure you use a 40 amp fuse to protect that wire.

The #2 wire should be more than adequate to run between the batteries and to the inverter. Just make sure you have a fuse to protect the wire to the inverter.

Try to look at current flowing in a circuit like water in a pipeline. If the water has to flow from one battery to the next then the last battery may not get enough to properly charge it. A bus bar is like a manifold that will improve the chances of an equal flow to each battery. The same goes for discharging. For each battery to stay equal it must be able to discharge the same amount of amps as all the other batteries in the system. Lower resistance for each "flow" helps that happen.

So to answer your question, if you keep all of the wiring between the battery terminals and bus bars as short as possible and solidly connected at each termination you should be able to get somewhat of equal charging (and discharging) across all 6 batteries. It is not the ideal way to wire a battery system but you should get a couple of years out of them.

[inetdog]

If all of the cables are the same length then there isn't a "middle" or "end" battery. It's like they are in a circle. So why would any one battery get killed when all are exactly equal?

Even though the batteries are electrically in a star rather than a line, the voltage and internal resistance differences that will produce a large current difference are small enough that the physical arrangement of the batteries, particularly as it effects heating and cooling, becomes important too.

[Sage Oldmann]

Thanks. I do remember you mentioning the 100 watt panels but I could not find what your CC was.

Even though you do not have enough wattage to get there, with that 30amp CC you need to use wire to handle up to 30 amps so that #8 wire is ok. To be safe please make sure you use a 40 amp fuse to protect that wire.

The #2 wire should be more than adequate to run between the batteries and to the inverter. Just make sure you have a fuse to protect the wire to the inverter.

Try to look at current flowing in a circuit like water in a pipeline. If the water has to flow from one battery to the next then the last battery may not get enough to properly charge it. A bus bar is like a manifold that will improve the chances of an equal flow to each battery. The same goes for discharging. For each battery to stay equal it must be able to discharge the same amount of amps as all the other batteries in the system. Lower resistance for each "flow" helps that happen.

So to answer your question, if you keep all of the wiring between the battery terminals and bus bars as short as possible and solidly connected at each termination you should be able to get somewhat of equal charging (and discharging) across all 6 batteries. It is not the ideal way to wire a battery system but you should get a couple of years out of them.

Thank you SunEagle. This is practical information I can actually use given my limitations.

What did you mean when you said

you do not have enough wattage to get there

Could you be more specific? What is my deficiency? Not enough panels? Not enough batteries?

Also can I use ANL fuses? I came by dozens of them for almost nothing awhile back but not sure I can use them on this system. Smallest is 100 amp. Can I use that from the panels to the controller? I also have a lot of 150 and 250 amp fuses. I'm guessing I should use the 250 for the line from the batteries to the inverter? How about from the batteries to the buss bar?

I'm curious. would physically rotating the batteries every 6 months so they would all at some point be both the best and the worst in the bank help longevity?

Thanks

[SunEagle]

Thank you SunEagle. This is practical information I can actually use given my limitations.

What did you mean when you said Could you be more specific? What is my deficiency? Not enough panels? Not enough batteries?

Also can I use ANL fuses? I came by dozens of them for almost nothing awhile back but not sure I can use them on this system. Smallest is 100 amp. Can I use that from the panels to the controller? I also have a lot of 150 and 250 amp fuses. I'm guessing I should use the 250 for the line from the batteries to the inverter? How about from the batteries to the buss bar?

I'm curious. would physically rotating the batteries every 6 months so they would all at some point be both the best and the worst in the bank help longevity?

Thanks

To answer your first question. With 4 panels each with an Imp = 5.29 amps the most you will get out of them is 4 x 5.29 = 21.16amps. So with that 30amp PWM CC you could go to 5 of those panels and increase the charge amps to ~26.5 but will never get to 30amps which is ok.

I use ANL fuses but a fuse is sized to protect the wire so if you use a 100amp fuse the wire needs to be able to handle more than 100 amps which a #2 wire is more than enough to do so but I would not go over 150amp fuse for a #2 wire.
To determine both the wire size and fusing between the battery and inverter you should used the quick rule of thumb by dividing the Max wattage rating of the inverter by the battery voltage. So if yours can go to 2000 watts then it might draw up to 167Amps ( 2000w / 12v = 167A) which is just about what a #2 copper wire in free air is rated.

You could try to rotate the batteries but you have a higher chance the disconnecting and re-connecting the wires could damage a battery terminal or not get properly tightened which would lead to high resistance and heat generation at the terminal.

[Sage Oldmann]

To determine both the wire size and fusing between the battery and inverter you should used the quick rule of thumb by dividing the Max wattage rating of the inverter by the battery voltage. So if yours can go to 2000 watts then it might draw up to 167Amps ( 2000w / 12v = 167A) which is just about what a #2 copper wire in free air is rated.

Thanks! Great information. Even if I get a few years out of this system I'll get something for my investment, and by then I'll be able to afford to rebuild it the right way.

If I trade my 1,000 inverter for that 600 watt inverter (1200 peak) then how would that affect the size of fuse I use to the inverter? Would I need to use 100 amp, or could I still use the 150 amp?

What size individual fuses should I use from the batteries to the buss bar?