Battery Bank Design

AlleyCat67 · 10-07-2016, 09:44 AM

So, I've been thinking about my battery bank design....

What I have in mind is to run 6 pairs of 6V 215ah batteries to get 12V and 1290ah. (Used the 20ah rate to calculate it, did I figure that right?)

An alternative battery I am also considering

To keep the draw from each pair as even as possible, I plan to use equal length 4 or 6AWG cables* from each pair to connect to a bus bar type setup which will have an inverter and charger or inverter/charger connected to it using 1/0 cable or larger with a 250A breaker, as well as a small load center for the direct 12VDC loads (sizing to be determined after I see how much draw there will be).

The batteries will be held in place using a fabricated wooden framework with an insulated and vented cover to keep them warm during the cooler weather coming. Since they are lead acid batteries they will live in the underbay storage.... though I will have to figure a way to access the caps for required maintenance since 800 lbs of batteries aren't gonna move as a unit very easily.

Until I get my solar setup worked out, power to charge the bank will come from a generator. Figure charging the batteries will be less of a draw on the generator and require less running time than running all the AC loads.

Is there anything I should change or rethink?

* I ran a 2500 watt inverter on my big rig and it used two runs of cable each for positive and negative, can't remember whether it was 4 or 6 AWG but whatever it was is what I will use.

Iceni John · 10-07-2016, 10:09 AM

Quote:

Originally Posted by AlleyCat67

So, I've been thinking about my battery bank design....

What I have in mind is to run 6 pairs of 6V 215ah batteries to get 12V and 1290ah. (Used the 20ah rate to calculate it, did I figure that right?)

An alternative battery I am also considering

To keep the draw from each pair as even as possible, I plan to use equal length 4 or 6AWG cables* from each pair to connect to a bus bar type setup which will have an inverter and charger or inverter/charger connected to it using 1/0 cable or larger with a 250A breaker, as well as a small load center for the direct 12VDC loads (sizing to be determined after I see how much draw there will be).

The batteries will be held in place using a fabricated wooden framework with an insulated and vented cover to keep them warm during the cooler weather coming. Since they are lead acid batteries they will live in the underbay storage.... though I will have to figure a way to access the caps for required maintenance since 800 lbs of batteries aren't gonna move as a unit very easily.

Until I get my solar setup worked out, power to charge the bank will come from a generator. Figure charging the batteries will be less of a draw on the generator and require less running time than running all the AC loads.

Is there anything I should change or rethink?

* I ran a 2500 watt inverter on my big rig and it used two runs of cable each for positive and negative, can't remember whether it was 4 or 6 AWG but whatever it was is what I will use.

Your cables seem thin to me. I would use larger than 4 or 6AWG for each pair's feeds to the busbar. My house batteries are also available to augment the starting batteries, or even start the engine by themselves if needed, so I use 4/0 everywhere for all their interconnects and 2/0 for the main feed to the DC load center and inverter.

For six pairs of golfcart batteries you'll ideally need about 2500 to 3000 watts of solar panels to charge them at the suggested 5 to 13% charge rate. Do you have enough roof space for up to 12 grid-tie panels? I have eight golfcart batteries in series and parallel, charged by eight tiltable GT panels totaling 2040 watts, but because it's a 12V system I have to use two 60A charge controllers. My eight panels occupy about 22 feet of roof space.

John

AlleyCat67 · 10-07-2016, 10:23 AM

Quote:

Originally Posted by Iceni John

Your cables seem thin to me. I would use larger than 4 or 6AWG for each pair's feeds to the busbar. My house batteries are also available to augment the starting batteries, or even start the engine by themselves if needed, so I use 4/0 everywhere for all their interconnects and 2/0 for the main feed to the DC load center and inverter.

For six pairs of golfcart batteries you'll ideally need about 2500 to 3000 watts of solar panels to charge them at the suggested 5 to 13% charge rate. Do you have enough roof space for up to 12 grid-tie panels? I have eight golfcart batteries in series and parallel, charged by eight tiltable GT panels totaling 2040 watts, but because it's a 12V system I have to use two 60A charge controllers. My eight panels occupy about 22 feet of roof space.

John

Noted. On further reflection I guess dual 4AWG would be about equal to 3/0 or 4/0 so that makes sense. The cable runs will be as short as I can make them while still making them accessible for maintenance.

The inverter/charger I am looking into has an option to include 1/0 cables with it, but makes sense to go with the 2/0 for safety.

I'll have to measure to be sure but I think I can fit 12 panels on top if need be, though I might have to get creative with a couple of them if I need a little extra rooftop real estate (fabricate an extension with support brackets if I need an extra foot or so).

Thanks for the input!

Jolly Roger · 10-07-2016, 04:34 PM

Some of the best big wire I have found to use is old/new welder's leed. It is around 0/0 and is more flexible and it might be cheaper than smaller guage stranded wire?
I work around/in the welding trade so everytime we have to buy new Leeds I get what I can of the old ones. I have jumper cable 20' long that work great when I'm in a mud hole on a job? Most used Leeds are burnt up to a point inside but the wires not broke its just stressed.
If you do go took look at some old leed you can tell its life by looking at the end of it but it needs to be a fresh cut.
Strip an inch and look at it. If more than half of the wires are blackish then it would probably still work fine but I would negotiate the price.
My salvaged leed is about 3/4 black and I know what use and abuse it went through but have never had a problem moving current when needed?
The last time I bought brand new leed it was 300$ for two 100' runs so that's about 3$ a foot so it might be cheaper than a heavy guage and very stiff stranded elec. Wire?
Food for thought and good luck

retiredChemist · 10-07-2016, 07:13 PM

I'd suggest a stronger method to hold the batteries in place. E g site toolbox with a vent or two and reinforced with angle. Most manufacturers engineer for battery boxes to withstand 10g+ in the horizontal directions.

Batteries get heavy quickly.

If you're running to an inverter exclusively, is there any reason why you can't run the solar at 24,36,48 volts. To keep the current down while still doing the same job?

cadillackid · 10-07-2016, 07:19 PM

I held my battery boxes in with an old 4 leg seat frame and the original bus Seatbelts attached to said seat-frame.. big seat frame, battery boxes bolted to floor and 4 seatbelts.. i got worse things to worry anout if that gets loose..

-Christopher

AlleyCat67 · 10-07-2016, 10:52 PM

I'm going 12v because that's the inverter I have on hand. When I get ready to deploy solar I'll look at other voltage options..... but I do have 12v loads that will be in place so I'll have to have some means to power them, plus I want the option to use the house batteries to start the engine if I need to.

The wood framing.... I was going to use that because wood is easier to work with than metal... and since most of my time is going to be spent parked anyway I didn't think it was that big of a deal... and if there is enough motion stress to cause them to break free of the wood framing I would have bigger things to worry about. Maybe I'll see if I can find something second hand that is big enough to hold them.

I will be keeping the cable runs as short as possible to minimize voltage loss by keeping the batteries, charger and inverter in the underbay storage, and just running a single 120v line up through the floor into a four outlet box that I can plug a power strip or two into.

superdave · 10-08-2016, 06:04 AM

12 batteries = 36 2 volt cells, thats alot of cells to maintain. you should consider bigger batteries so you have less cells. your bank is only as good as your weakest cell, it will bring all the others down to its level. i live off grid on 4 l-16s. deep cycle batteries require a charging cycle a alternator cant accomplish. you will ruin your battery bank this way. you can go with any system voltage you want and use a converter to drop it to 12 volt. never use a battery watering system, if one cell doesnt get water the whole bank will have to be replaced. never mix old batteries with new. good luck with your build.

rjnye79 · 12-11-2016, 08:18 AM

So, the cables that came with my battery bank were 2/0 cobra wire... I tried using some of it to link the disconnect>inverter and disconnect>battery charger. Unfortunately, the lugs don't fit into the terminal housing on either Cotek product. Is it ok to use the type of wire below for this application?

http://m.homedepot.com/p/Southwire-B...1399/204724931

AlleyCat67 · 12-11-2016, 01:33 PM

As long as you use multiple runs equalling or exceeding the current carrying capacity of the 2/0 it should be ok.... just make sure to check the connections regularly to make sure they're secure, you don't want one to come loose thereby overloading the remaining runs which could result in a fire.

My initial design used a 3000 watt inverter to a 12 volt 1380 ah bank which calls for 4/0 for connection.... was instead going to use 4 gauge from each pair of batteries, thru a fuse/breaker, directly to the inverter, which would be 6 runs. Failure of a conductor in that scenario would be safe because that pair of batteries would be out of the circuit.

I've since redesigned for a 24v battery bank and 4000 watt inverter/charger which will use 1/0 between battery bank and inverter, which again I believe (but have not checked) that I can get away with runs of 4 gauge between each 24v string and the inverter, with appropriately sized fuse/breaker at the battery string.

rjnye79 · 12-12-2016, 07:52 AM

Quote:

Originally Posted by AlleyCat67

As long as you use multiple runs equalling or exceeding the current carrying capacity of the 2/0 it should be ok.... just make sure to check the connections regularly to make sure they're secure, you don't want one to come loose thereby overloading the remaining runs which could result in a fire.

My initial design used a 3000 watt inverter to a 12 volt 1380 ah bank which calls for 4/0 for connection.... was instead going to use 4 gauge from each pair of batteries, thru a fuse/breaker, directly to the inverter, which would be 6 runs. Failure of a conductor in that scenario would be safe because that pair of batteries would be out of the circuit.

I've since redesigned for a 24v battery bank and 4000 watt inverter/charger which will use 1/0 between battery bank and inverter, which again I believe (but have not checked) that I can get away with runs of 4 gauge between each 24v string and the inverter, with appropriately sized fuse/breaker at the battery string.

Intersting... but how do you fit six runs of cable into one terminal? This seems to be counterproductive for my application.

The sizing of my cable was suggested (by my solar component provider) as 8awg, or better, for the charger and 3awg, or better for the inverter. However, my question is more about the type of wire. Can this "THHN wire" be used instead of "battery cable"? I can get one at Home Depot for a grand total of about $30 and the other would have to be from a marine supply store for closer to $60.

AlleyCat67 · 12-12-2016, 07:04 PM

Quote:

Originally Posted by rjnye79

Intersting... but how do you fit six runs of cable into one terminal? This seems to be counterproductive for my application.

I'll just stack the lugs with an appropriately sized nut between them for spacing. The terminals on my inverter are pretty long so I figure with the way the lugs are made, I can attach the first one, a spacer nut, then two together back to back with the wire connection on opposite sides of the lug, another spacer nut, two more, another nut, then the last one with two nuts to hold everything together. If that turns out to not be doable, the backup plan is to connect all the runs to a bus bar made of angle iron with a single short 4/0 cable to the inverter.

Quote:

The sizing of my cable was suggested (by my solar component provider) as 8awg, or better, for the charger and 3awg, or better for the inverter. However, my question is more about the type of wire. Can this "THHN wire" be used instead of "battery cable"? I can get one at Home Depot for a grand total of about $30 and the other would have to be from a marine supply store for closer to $60.

Wire gauge is only in even numbers so you'll have to go up to 2AWG. And I would not use THHN as it is not rated for moisture resistance. You'll need THWN for that. I'm not sure if it is stranded or not, you'll want that for flexibility in running it.

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