24v Bank Balancing

[BradKW]

A while back I bookmarked a nice site that Jim had, that details the importance of balancing multi-battery banks to maintain health of all the batteries in the chain. Battery Connections

Problem is, all the examples and diagrams deal with parallel 12v banks. I need to connect four 6v batteries in series for a 24v bank.  Googling "balancing 24 volt bank" yields many interesting results that don't seem to apply to what I want to do...and no diagrams. And a brain cramp at 6am. Anyone have experience with 24v banks, or can link a good resource?

Also, the battery has both threaded terminal and lug available for connections. Lugs certainly would look like they'd provide better connection through larger contact area, but early googling results favor terminal connections with SS nuts. Opinions welcome.

 

[Optimistic Paranoid]

You're overthinking this.

With four 6 volt batteries, there is one and only one way to wire them together to get 24 volts.  No options, no "A" is better than "B".

 

[BradKW]

Ah, good...I hate too many options. In fact, that's why I don't eat at Subway...far too many questions just to get a sandwich.

Also meant to ask about cable size for battery to battery connections...I was thinking 2/0

 

[ccbreder]

I use 2/0 on my six 6 volt, parallel-series 12 volt system. I have no measurable voltage loss on the 12 inch lengths. I do recommend; http://www.genuinedealz.com/custom-cables/custom-battery-cable-assembly?size=48

 

[ccbreder]

And I used these as catastrophic failure fuse. Which means stud connections. I didn't use any lugs only so the cables were exchangeable if something failed. http://www.genuinedealz.com/blue-sea-systems-5191-fuse-block-for-battery-terminal-fuse

 

[BradKW]

That looks like a nice solution for a fuse...but I'm not sure how it works. does it thread onto the stud through that hole in the bottom plate, and then it has it's own stud that you connect to?

From my 24v bank I think I will have direct wiring to the inverter and then wiring to a 24v subpanel...should I size the fuse for the inverter (probably 300A), and then a smaller fuse for wire going to subpanel?

 

[LeeRevell]

What are you intending to power with 24VDC?

 

[BradKW]

Primarily the 3k inverter and 'fridge.

 

[BradKW]

Here's a handy fuse guide I came across. It's shows max amps for different size wire, thus telling you what fuse to use:

 

[Mobilesport]

@ ccbreder
Do you have any pictures of your fuse block mounted to your battery post ?
I'm trying to get a idea how it attaches , it looks like a nice solution for a fuse setup.
Thanks

 

[Mobilesport]

That looks like a nice solution for a fuse...but I'm not sure how it works. does it thread onto the stud through that hole in the bottom plate, and then it has it's own stud that you connect to?

From my 24v bank I think I will have direct wiring to the inverter and then wiring to a 24v subpanel...should I size the fuse for the inverter (probably 300A), and then a smaller fuse for wire going to subpanel?

I was wondering the same , found these pictures , the second picture is the fuse

 

[SternWake]

Only real .issue is the height added, and the price of the fuses. Also with tall gassing wet batteries, terminal corrosion.

While lithium batteries in Series should all be individually at the same voltage when hooked together.... Not sure lead acid is as finicky.

Ideal would be a 6 v charger to top charge them individually. Then put them in series over as fat of cabling as you can afford. Not sure a 6 v charger is worth that. Trojan now calls for 16.2v for eq charges on 12v systems.

Max out sg on all cells. If some lag. Then it would be 'better' to not subject other cells to eq voltages.

Establish baseline fully charged specific gravity when new for comparison later, if inclined to pay that much attention.

 

[BradKW]

Good picture MS...having never used terminals, that pic actually makes me wonder if stacking multiple terminals is really something to plan on, given how that lock nut is flush with top of stud.

SW: I did read about individually charging batteries before adding them together in a bank, but did kinda hope it wasn't TOO important as I don't have the means to do that without buying something I'd only use once. Actually, I still haven't found or decided on what I'm going to do for a 110 -> 24v charger. I mentally checked out of the last Meanwell discussion when I saw that MS was having problems with a larger unit and I figured I'd need one both larger and unknown for 24v bank (bulk 29.6, eq 32.4 ).

Sure seems like there should be a way for a good Moringstar solar controller to accept 110 and make my life simpler

edit: that got me thinking...couldn't I use my Morningstar 60a to charge the 6v batteries individually before hooking together? https://www.amazon.com/gp/product/B0052UIPIC/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

 

[ccbreder]

With lead acid chemistry you will not have to charge each battery before connecting. They should all be close to the same as they must be matched from the same purchased batch. The pictured fuse is used on battery banks throughout the marine world. If there was a problem with corrosion it would be noted someplace in the many articles I have followed. Yes they require room above the battery. But they eliminate extra cables and terminals to connect a linear fuse block. Sorry, I can't post photos. I will try to answer any questions. The fuse fastens as shown in MS photo. The cable fastens with a nut on a stud. With any such connection it is best not to have more than two cables. I run mine to a terminal block, keeping battery cables the same length. With batteries in series, you will not have that problem, keeping the inter connections the same length and as short as possible. MaineSail.com has very good articles about fusing, cabling, charging, monitoring, and other battery stuff.

 

[Mobilesport]

I searched google images for keywords such as ,,,,,,,
Blue seas fuse block
Blue seas buss barr
Blue sea connector
Blue sea wiring
Blue sea pass thru
Blue sea outlet
And many nice wiring pictures popped up that can give you some ideas how to wire some stuff up really nice .
I'll post a sample picture.

 

[Mobilesport]

Blue seas has a Bussbar with bigger lugs that you could probably run a thick gage positive wire to and then bolt down multiple of those fuse blocks that ccbreder posted , if needed.