Double diagonal parallel connection???

[TommyinMiami]

Hi guys I have 4 batteries, due to space constraints 3 batteries are on the bottom level and 1 is on top of the 3.

Instead of hooking up all 4 in standard parallel fashion couldn't I benefit from hooking the bottom 3 in standard fashion, then hook the 3rd battery diagonally to those 3 and then opposite diagonally going to my system/inverter.

If diagonal connection is best to hook up 3 batteries then would logic say it's best to hook up that 4th battery that way. And than still use diagonal again on the opposite end posts to the system/charger/inverter???
All cables are 4/0 ga.
Any thoughts.

Here is a pic before hooking up the 4th.

 

[mopat]

Diagonally =What?

Batteries connect in series or parallel; no diagonal.

 

[Bluedog225]

Electrical matters. Spatial not so much.

Get it wrong and boom.

 

[timselectric]

Hi guys I have 4 batteries, due to space constraints 3 batteries are on the bottom level and 1 is on top of the 3.

Instead of hooking up all 4 in standard parallel fashion couldn't I benefit from hooking the bottom 3 in standard fashion, then hook the 3rd battery diagonally to those 3 and then opposite diagonally going to my system/inverter.

If diagonal connection is best to hook up 3 batteries then would logic say it's best to hook up that 4th battery that way. And than still use diagonal again on the opposite end posts to the system/charger/inverter???
All cables are 4/0 ga.
Any thoughts.

Here is a pic before hooking up the 4th. View attachment 93501

I see what you mean.
Sure, why not.
Go for it.

 

[joanna_lannie]

If you have to do this, have you considered using a cable? After all, your space is too limited. I'm curious, did you not consider the size when you purchased the battery? Also, what is the diagonal connection? Please select parallel or series. Of course, the recommendation is not to use four batteries anymore, it's not a good thing to have batteries crammed irregularly in a confined space.

 

[TommyinMiami]

I have not heard that using 4 batteries is no longer the recommendation. I don't see why not.
My set up is 4 100ah batteries, I'm working with what I got and that's what actually fits the best also. 200ah batteries did not fit in the space and all my consumption calculations are based on 400ah.

Ok so I plan to connect it all this weekend. Here's some photos to better illiterate what I mean by "Double Diagonal" (DD) connection.
1 diagonal connection goes to Bus
1 opposite diagnal connection goes to 4th battery.
My thoughts are that doing the 4th battery Diagonal instead of off the 3rd battery would be better since it would matter less the length and resistance of those 2 longer cables. That this DD connection would be better than connecting off the 3rd battery with longer cables, thus not matching the resistance, and I don't really want the cables from each battery to be that long as that would look pretty aweful.

The 6ga wires are there as an illustration so don't flame me for that. All cables will be 4/0ga

Any suggestions or if anyone has connected like this before feel free to chime in. If the consensus is that this is stupid then maybe I'll change to doing the "posts" connection style.
Or try this and somehow measure resistance while under load and then measure each batteries voltage after load testing it..... this way and posts connection way, then see which is better. But I don't have a bench loader and really not wanting to spend any more $ on this. Everything is Ancor brand tinned copper and super crazy expensive right now.

 

[timselectric]

I have not heard that using 4 batteries is no longer the recommendation. I don't see why not.
My set up is 4 100ah batteries, I'm working with what I got and that's what actually fits the best also. 200ah batteries did not fit in the space and all my consumption calculations are based on 400ah.

Ok so I plan to connect it all this weekend. Here's some photos to better illiterate what I mean by "Double Diagonal" (DD) connection.
1 diagonal connection goes to Bus
1 opposite diagnal connection goes to 4th battery.
My thoughts are that doing the 4th battery Diagonal instead of off the 3rd battery would be better since it would matter less the length and resistance of those 2 longer cables. That this DD connection would be better than connecting off the 3rd battery with longer cables, thus not matching the resistance, and I don't really want the cables from each battery to be that long as that would look pretty aweful.

The 6ga wires are there as an illustration so don't flame me for that. All cables will be 4/0ga

Any suggestions or if anyone has connected like this before feel free to chime in. If the consensus is that this is stupid then maybe I'll change to doing the "posts" connection style.
Or try this and somehow measure resistance while under load and then measure each batteries voltage after load testing it..... this way and posts connection way, then see which is better. But I don't have a bench loader and really not wanting to spend any more $ on this. Everything is Ancor brand tinned copper and super crazy expensive right now.

View attachment 94511View attachment 94512

I think that it's a good plan. Your reasoning is sound. And appears to be a good option for the available space. You can parallel as many batteries as you like. It's not recommended (at least by me, and several others) to series connect batteries with BMS's.

 

[TommyinMiami]

Diagonally =What?

Batteries connect in series or parallel; no diagonal.

I cant tell if you're being sarcastic orrr I'm an idiot. You have 540 posts and I have like 4 so I assume sarcasm or something went over my head. My electrical knowledge is like a 5 out of 10. So at the threat of sounding stupid... and since other people in this post also are asking what the heck diagnal donnection is, and I can't tell if these are trolling posts or serious, I'm just going to upload this. The batteries in my setup are connected in the "diagnal" connection. And my question is on adding a battery in "oposite diagnal".

 

[Solarod]

What is the manufacturer's specification for the internal resistance of the batteries?

The link cables between the batteries look like 4/0 cable, but the cables running off to your load don't look that big; are they also 4/0?

 

[Solarod]

OK. I have analyzed the 3 battery parallel string in another thread: https://diysolarforum.com/threads/calculation-of-parallel-string-battery-currents.37937/post-481671

To analyze your proposed connection of 4 batteries, I'll start with the 3 battery parallel string configuration. I assume the three batteries have an internal resistance of .2 milliohms, and the link cables also have a resistance of .2 milliohms, the batteries all have an open circuit voltage (OCV) of exactly 12.000 volts. I set up the circuit equations and solved for the voltages at all the nodes in the circuit. Note that I'm solving for voltages, not the current in the batteries as I usually do. The results are shown in this image:

Your proposed double diagonal connection would connect your fourth battery from node E to node C.
The voltage between those two nodes is 11.992 - (-.02) = 12.012 volts with only the 3 batteries wired as a parallel string; the fourth battery is not connected yet. The fact that this voltage difference is greater than 12.000 volts is a major problem. It means that the fourth battery will not supply current to the load. In fact, it will absorb current from the other three batteries; it will be charging!!

Edit: Here are the caculated currents: With the fourth battery connected, the theoretical currents in amps would be:

50
25
50
-25

This would not be good!!

Interestingly enough, if I change the initial parameters to: all battery internal resistances are .5 milliohms, and the link cable resistances are .1 milliohms and go ahead and connect the fourth battery in your proposed double diagonal connection, the fourth battery now supplies current to the load, but the currents are very unbalanced. The calculated theoretical battery currents in amps with a 100 amp load in that case would be:

31.82
26.52
31.82
9.85

The last value is for the fourth battery.

If the batteries are good batteries with very low internal resistance, you run the danger that the fourth battery will absorb charging current rather than supplying load current. If the batteries are not so good with higher internal resistance, then the fourth battery will supply current rather than charging, but not very much; the whole hookup will be unbalanced.

The double diagonal connection is not a good option. You could use the post method, or the "halfway" connection shown in the Victron document.

 

[Solarod]

So, TommyinMiami, have you decided what hookup you're going to use?

 

[Bobert]

Can you lay your 4th battery on its side and wire it as if it was on the floor next to the other batteries?

 

[time2roll]

I recommend equal length cables to a common bus. Not sure 4/0 is needed for these connections.