Adding 3rd 24v battery question

[UGT]

I have two LiTime 24 volt 200ah batteries that have only been in service 2 weeks and are connected parallel. Am thinking on adding a 3rd battery the same as the other two.
First is there any reason that I am not aware of concerning connecting this third battery parallel to the others that would be advisable not to. The first two batteries are practically new so I'm thinking there would be no problem with equalization and compatability. I would just unhook them from the system and connect all three together and let them rest for 24 hours or so to make them happy together. Yes? thank you, George in Austin

BTW I just got my system installed on my roof and it is working great. It is just a back up system for my house. I purchased the 1200 watt 24v system from Rich Solar with the 60a solar controller. I installed the six 26 lb panels on the roof myself and did everything except that I had a electrician install a transfer switch next to my in house sub panel. I've been on the planet 74 years. Very pleased with the system. Just thinkin' on adding another battery.

 

[sunshine_eggo]

Sensible paralleling of bateries in accordance with best practices (link #5 in my signature) is rarely an issue. Manufacturers and installers are likely to shout that you can only use same size, same age, same brand, same everything or your system will explode.

The reality is that if you parallel a bunch of stuff together... different ages, sizes, brands, capacities, etc., AND you verify that all batteries are working within specifications with a DC clamp ammeter during heavy load/charge, you're good.

 

[BenQ]

Yeah buddy, adding a 3rd battery is as easy as that!

 

[HRTKD]

Two batteries is pretty easy to wire up. Yes, you can still screw it up, but a little common sense will get it wired right. Three or more batteries requires a bit more work. The goal is for every battery to have equal access to the rest of the system. They all need to have the same resistance. The most straightforward way to do that is to connect all batteries to a common bus bar using cables that are the exact same length. All positives the same length, all negatives the same length. No direct connections between the batteries. You don't want the batteries daisy chained.

 

[UGT]

Thank you. Will the batteries be damaged daisy chaining them. My cables are all the same length on the batteries I already have. It looks like when I install the third battery the positive and negative cables will still all be the same length from one battery to the next.

 

[HRTKD]

Thank you. Will the batteries be damaged daisy chaining them. My cables are all the same length on the batteries I already have. It looks like when I install the third battery the positive and negative cables will still all be the same length from one battery to the next.

If you do it wrong, one of the batteries could have a lower charge/load than the other two. For AGM that can be the kiss of death (lower life). If you want a more technical discussion of the various ways to connect a battery, check out this excellent thread:

Calculation of parallel string battery currents

Hi, everybody! I'm a retired EE. I didn't want my EE skills to fade away after retirment, so I exercise them when I can. Whenever I see a non-trivial circuit analysis problem on one of various forums I frequent, I challenge myself to solve it. Recently I watched Will's video about current...

diysolarforum.com

 

[UGT]

okay, thanks again.

 

[UGT]

I like the bus bar setup. Can someone give me a link to where I can get the appropriate bus bars for my system. My LiFePo4 batteries are just off the floor side by side length wise with the neg. and pos. terminals all at the same end and up against a wall. Bus bars would be mouned on the adjacent wall and would probably need to be 32 inches long. Thanks for your help. George in Austin

 

[HRTKD]

On the high end are the Blue Sea bus bars. These are the mid-amp versions. They have 1,000 amps versions, which are overkill for your setup. When shopping for bus bars, be sure the base metal is copper. A lot of the less expensive bus bars are brass which has a higher resistance than copper.

https://www.bluesea.com/products/category/18/4/BusBars/Common_BusBar

 

[Black Pearl]

I used 4 of these on my last build. Like them pretty well, but a bit expensive. Ended up enlarging the holes on the covers with a drill, because they were a bit to tight. All of my gear is indoors, so I choose to use the cheaper zinc hardware version.

Pike Industries

Pike Industries

www.amazon.com

 

[UGT]

I was thinking on getting bus bars the length of my batteries like those that Will suggests in his video like in my drawing.

 

[HRTKD]

I was thinking on getting bus bars the length of my batteries like those that Will suggests in his video like in my drawing.

That arrangement will leave the middle battery in a suboptimal situation. The link I provided in post #6 explains why, using math behind the scenes. You have to move the charger attachment points away from the ends of the bus bars.

 

[UGT]

Phew I read that. My head still hurts. I am electrically challenged of sorts. So do you mean like this.

 

[UGT]

Does the cable lengths from the charger to the bus bar need to be the same length? Thanks

 

[HRTKD]

Phew I read that. My head still hurts. I am electrically challenged of sorts. So do you mean like this.

Still not right. The positive needs to be between batteries 1 and 2 and the negative between batteries 2 and 3.

Or, you could use a small bus bar like Black Pearl linked to in post #10 and connect all three batteries to it with equal length cables.

I don't like the bus bar setup in your picture. That's too much exposed copper that you have to mount somehow.

 

[HRTKD]

Does the cable lengths from the charger to the bus bar need to be the same length? Thanks

It's less of a concern than the interconnections between the batteries. But I tried to keep all my cables the same length, even from the charger.

 

[UGT]

Okay do you mean like this with the smaller bus bars with 4 lugs? I am using 2/0 wires so might be challenging. Thanks for your input. Is most appreciated.

 

[HRTKD]

Okay do you mean like this with the smaller bus bars with 4 lugs? I am using 2/0 wires so might be challenging. Thanks for your input. Is most appreciated.

Yes, like that.

 

[UGT]

One last question. Do the neg. wires from the batteries to the bus that are all the same length, have to be the same length as the positive wires that are all the same length from the batteries to the bus bar? Thanks

 

[HRTKD]

One last question. Do the neg. wires from the batteries to the bus that are all the same length, have to be the same length as the positive wires that are all the same length from the batteries to the bus bar? Thanks

Ideally, yes. Practically, no. As long as the total length of positive and negative cables on each battery are the same it should be OK. I haven't seen anyone prove that with math, but I can't come up with anything to disagree with it.