Multiple battery banks?

[XERTYX]

I seem to remember jimindenver saying something about if you have more than 3 batteries you need to have multiple banks "shoestringed" together. 

I have so far always had 4 batteries in a bank. Usually SLA (sealed lead acid) alarm system type batteries. I havent had any problems. 

The first system I built was when I lived on a boat. The system I currently use implements the same 4 5 watt panels my first system did. The first system I built I didnt include a solar charge controller. It was a shoestring budget at the time. If I had to advise someone now I would say the charge controller is absolutely necessary. 

Back then I used it beyond capacity every day and prayed for sunny days to refill it.

Now I am on shore power and use my meager solar bank to charge my phone and USB battery bank. Still I daily have excess power I could use for other uses.

My next system I want to design will have more than 4 batteries. Also they will be flooded lead acid batteries.

So how would I wire 8, 12, or 16 walmart group 29DC batteries? Parallel pairs of 4 that are interconnected? Parallel  pairs of 3 that are interconnected for a total of 6, 9, or 15 batteries? 

I have researched it a teeny bit. The best answer so far has been parallel pairs of 2 interconnected. 

To be clear my goal would be to have 16 29DC batteries and 2kw of polycrystaline solar panels comprised of 8 250 watt panels arranged as 4 pairs of 2 series panels ran thru a 40A MPPT controller. 

16 batteries, 8 panels, 4 controllers. All matched.

Imagine you were wiring a self contained island in the pacific. How would you do it? If it had to be 12 volts. 

The reason I'm planning on doing it this way is that 29DC batteries are cheap. So are 250w panels from santan. Also I have found 40a MPPT controllers that support the input voltage for a price I find to be reasonable.

 

[B and C]

Here is the proper way to wire 4 batteries:



Take the second one and extrapolate it out.

 

[highdesertranger]

you would be better served using 6v golf cart batteries. they are true deep cycle.

16 group 29 batteries? my lord, I hope this isn't mobile.

highdesertranger

 

[RvDreams]

When I said extrapolate, I meant making 4 sets just like the diagram and then treating each set as a single battery and wire like the diagram. There will be some serious copper cables connecting all of these.

 

[highdesertranger]

OMG we were just talking about youtube experts on another thread. highdesertranger

 

[Trebor English]

I used to work for a 2 way radio company.  One of our clients was a gold mine in Suriname.  They had 8 sheds each containing 7 VHF radio repeaters and 7 8D batteries.  They had the batteries wired in parallel with the shortest fattest wire possible, the traditional way.  About once per year there was a failure where one battery spewed acid with vigor.  All the sheds had plastic shower curtains hung to keep the acid off the radios. 

What happens is that one battery develops a short in one cell.  Then there are 6 high power 12 volt batteries trying to charge one 10 volt battery and it gets hot.  The simple solution is to use a bus bar and connect each battery to the bus bar through an in line fuse all using equal length stout wire.  AWG #6 or #8 wire and 40 or 50 amp fuses for each battery are sufficient to supply 250 to 300 amps from a bank of 7 or 8 batteries.  If one battery gets a shorted cell it will only get hit with 40 amps, blowing its fuse rather than spewing acid.  The remaining batteries continue to function normally. 

You still want to have the plastic shower curtain.  Each cell still contains a mix of hydrogen gas and oxygen gas in just the perfect proportion to rapidly make a little bit of water and some heat.

When one 12 volt battery develops a high self discharge rate or an open cell you can easily test it.  The voltage drop from the bus bar to each battery plus terminal should be about the same when they are being charged or loaded.  One odd battery can easily be discovered, disconnected by pulling its fuse, and then tested all by itself.  Using the traditional fattest shortest wiring you will never know if one battery develops an open or high resistance cell unless the hydrometer tells you it's bad.

The key to equally charging and discharging multiple batteries is to have the same amount of resistance in series with each battery.  When a bunch of batteries have a plus connection at one battery and the minus connection at the farthest battery then they all get the same total length of wire.  Using separate equal length wires with fuses does the same.  The separate wires scheme must also be applied to the minus wires so that they also have the same resistance.

You do want deep cycle batteries with plates made of a lead / antimony alloy.  Trolling motor batteries and golf cart batteries are more likely to do what you want than marine starting batteries.

 

[highdesertranger]

"He knows what he's talking about."

this is exactly what I am talking about. go back and watch his first videos when he first started out. if they are still up and come back and tell me the same thing. you know the ones where he is using speaker wire, no connectors, wires just twisted together, bare wires laying everywhere.

highdesertranger

 

[Weight]

-No one posting on a forum is qualified to advise anyone how to build a system with more than 700 amp hours of battery.
-Will just started to wear safety glasses a few months ago! He does take a lot of short cuts to make things seem easy for his fans.

 

[XERTYX]

Sorry folks I forgot to check back before now.

No this wouldnt be mobile. My next goal after building out a vehicle is to build a cabin with more juice than I could ever use under normal circumstances. But also as much juice as I would want in the summer months to build a homestead.

Ex. Cement mixer, air compressor, possibly an arc welder, etc. Construction equipment with light duty usage. Then also once various new buildings are constructed (greenhouse, irrigation water tower for the garden, summer kitchen/ gazebo) tying them into the massive power source I built in the beginning.


That is some great advise about the bus bar. I hadnt thought of that eventuality. Boiling acid flying around my power shed is not something I want. Lol

Thanks for the replies folks.

P.S. the image on the left of how to wire 4 batteries is how I have always done it. That's what I have now. My current setup only ever has a load of around 12-13 watts at a time. USB & 12v LED light rated at 5 watts but measured at 7. The USB ports I use are on the controller and are 1.1a I havent installed my 12v QC 3.0 amp USB ports yet. It's just a backup more or less at the moment.

 

[B and C]

A generator might be a better choice for big hitters like a cement mixer.

All you really need batteries for is everyday living at night and a few rainy days. A solar farm would give you quite a bit of power with sunshine and probably some with rain.

 

[highdesertranger]

x2 on the generator.. I have found that for the occasional high load coupled with a short run time that a generator makes a lot more sense.

highdesertranger

 

[XERTYX]

Yeah I would probably also have a generator.

The smaller cement mixers I looked at used umm... off the top of my head around 180 watts for the small one and 370 watts for the slightly larger one. An arc welder would most likely have to be ran off of a generator. But the ultimate long long long term plan would ideally also include a root cellar.

That lead me to also explore meat lockers. And DIY walk in coolers. That lead me to the coolbot i believe it's called. It's a device you attach to an air conditioner. They of course have preferred models but if it was viable with the smaller energy star aircons that run around a few hundred watts maybe I could insulate the hell out of a root cellar and have a walk in cooler section as well.

So I wanna build a solar farm basically. With as much flexibility as possible. Some things may simply not be viable. Like the walk in cooler. And I'm ok with that. But I'd like to research it as much as possible and thru a process of elimination incorporate as much as possible into a homestead.

As the vehicle build would be the first part I could also go places. Semi nomadic lifestyle with a home base that has everything I could possibly need. That's the dream anyway.

If anyone is interested in the cool bot they are a few hundred bucks I think. It has 3 probes. 1 to measure the temp of the cooling fins to make sure they dont freeze. 1 to measure the room temperature. And the third is a heater probe that connects to the air conditioners temp probe. It fools it into thinking its warm in the room and it cycles on. If it is working too hard and the fins are about to freeze up it cycles off. Pretty neat invention.