How do I connect battery banks that are in 2 different locations (distances) to the one source & keep them evenly balanced

[400bird]

Your shunt is worthless. It can't measure the "24 v" accessories, or the alternator charger.

Slight change: the shunt position in the drawing is worthless less. But, if the OP put it in the squiggly negative wire, it would measure all current in/out of the battery. I assume you want the shunt for battery monitoring? If so, the squiggly line is where I'd put it. I think that's what the OP meant I post #14

Your easiest and most accurate solution is to rely on the readings from the Overkill BMS.

I guess I assumed the shunt was to have one SOC, not two from theo different BMSs.

You can go fancy and use Solar Assistant with the Uart converters in place of the bluetooth modules on the BMS, or go cheap and use the Liontron Multi app on your iPhone to simultaneously monitor the two BMS's.

Not bad propositions. Depends on the OP's technical ability and desires.

 

[Tomthumb62]

There must be a better way than just having a huge coil of wire sitting there.

There are, as HarryN and others point out, but they’re more complicated.

The equal lengths cable thing is more fool proof than other methods. It’s told to beginners so they get it mostly right without adding danger to their system. Once you start messing with breakers, unless you know what you’re doing, things can go south. Many breakers look alike. One is suggested and they buy the knock offs which then fails or worse.

 

[Brett V]

The Liontron Multi app for IOS monitors the bluetooth from up to 4 bms and gives a nice summed display. Clicking on a battery icon, shows the details of that battery.

 

[Brett V]

The discrepancy between the summed screen shot and the individual screens is the time between when I did the captures. In real time, they are all the same.

 

[HarryN]

Yes I have a 200amp fuse on the positive line from battery terminal & there is also a big 2 poll dc breaker switch before the lines attach to my “all in one unit” is a 24v 3kw version.

From a safety perspective that will work.

From a "re-setting the BMS" perspective, life is a lot easier if you can individually isolate the batteries from each other for maintenance and other stuff.

But - 200 amps is the upper limit of that breaker series and I have never used them beyond 150 amps.

 

[Tomthumb62]

The Liontron Multi app for IOS monitors the bluetooth from up to 4 bms and gives a nice summed display. Clicking on a battery icon, shows the details of that battery.View attachment 160643View attachment 160644View attachment 160646

Dang that’sa nice app! Wish these budget battery makers would produce a nicer looking app like this.

 

[YOTA]

Tha

If you put your shunt here, it will see current in and out of the batteries. It will not tell you where the current is coming from or going to in relation to the accessories, inverter, and alternator, but it will give you an accurate SOC

 

[YOTA]

Thanks ??

 

[ericfx1984]

I would not worry about the difference... What will happen is that while charging, the battery that is closer to the charge source will charge slightly faster... And the battery that is further away will charge slightly slower

And then once you are first battery is fully charged all the current from that battery will be shunted over to the one that is not quite reached full charge... And honestly with what you're describing they'll probably reach full charge within a few minutes of each other

Virtually the same thing will happen when discharging...

This is very similar to what happens when you have mismatched battery sizes in parallel with each other

With lithium iron phosphate it really just isn't a big deal

The big thing you need to watch out for is transient current between the batteries and just make sure that that transient current does not overwhelm the BMS or the wiring

What I mean to say is if one battery is significantly discharged relative to the other battery, the high charged battery will shift current to the low charge battery until the equalize

If you have 100 amp BMS then you can only allow for a hundred amps to transfer from battery to battery at any given time

But even with my massive difference in size 460 amp hours versus 1300 amp hours in my mismatched bank I've never seen more than 80 amps transfer between the different batteries and that was just when I initially brought the system online

In short don't worry too much about it

 

[JoeHam]

I agree with Eric.

I have 4 ea. 48V batteries in parallel and stressed over wire lengths for a while before finding more important things to worry about.

Some of my batteries work harder than others (one with shorter wires) and may have a slightly different lifespan but I doubt it will be significant in the end.

 

[YOTA]

I would not worry about the difference... What will happen is that while charging, the battery that is closer to the charge source will charge slightly faster... And the battery that is further away will charge slightly slower

And then once you are first battery is fully charged all the current from that battery will be shunted over to the one that is not quite reached full charge... And honestly with what you're describing they'll probably reach full charge within a few minutes of each other

Virtually the same thing will happen when discharging...

This is very similar to what happens when you have mismatched battery sizes in parallel with each other

With lithium iron phosphate it really just isn't a big deal

The big thing you need to watch out for is transient current between the batteries and just make sure that that transient current does not overwhelm the BMS or the wiring

What I mean to say is if one battery is significantly discharged relative to the other battery, the high charged battery will shift current to the low charge battery until the equalize

If you have 100 amp BMS then you can only allow for a hundred amps to transfer from battery to battery at any given time

But even with my massive difference in size 460 amp hours versus 1300 amp hours in my mismatched bank I've never seen more than 80 amps transfer between the different batteries and that was just when I initially brought the system online

In short don't worry too much about it

Thankyou for the reply! Makes sense thankyiu!