Battery parallel question

[REO]

Just curious about 12 volt battery parallel connections.

I recently saw a photo on a manufacturer website that showed batteries being paralleled with equal length positive cables and equal length negative cables. But, the length of the positive versus negative cables was very different. Is this an acceptable way to parallel batteries?

 

[tiltrider1]

Yes. The key is that all batteries are seeing the same amount of cable.

 

[Bacchus]

Yes. The key is that all batteries are seeing the same amount of cable.

Agree and would add that its the total of Pos & Neg cables that's important and the +/- can be different sd long as the total is equal.
Fr Ex: ( This is for pairs of 6V but the same arrangement is used for 4 12V batty bank)
The # of short + long cables for each pair of 6V or individual 12V battys will be the same.

 

[Portage_Bay]

This should give the best parallel setup. Nigel Calder the Best way to Parallel Batteries

 

[SteveK]

post 4 has certainly become the suggested way for FLA batteries, I question whether LFP batteries which have BMS in each battery need to do this at all.
My 8 LFP batteries, each with BMS also talk to each other thru ethernet cable and self balance among themselves. But I don't know if all LFP can do this as these are the only ones I found with this feature

 

[Iggy]

This should give the best parallel setup. Nigel Calder the Best way to Parallel Batteries

Yep!

And in the case of 6v batteries. Than just use a jumper to make sets of 12V batteries and than use the buss bar method.

 

[tiltrider1]

post 4 has certainly become the suggested way for FLA batteries, I question whether LFP batteries which have BMS in each battery need to do this at all.
My 8 LFP batteries, each with BMS also talk to each other thru ethernet cable and self balance among themselves. But I don't know if all LFP can do this as these are the only ones I found with this feature

My research says that cable length is much less of an issue because of the BMS. However, it’s still good practice to balance the cables.

 

[Iggy]

My research says that cable length is much less of an issue because of the BMS. However, it’s still good practice to balance the cables.

I understand and your right. The larger the cables, less the effect. But how good is your BMS. What I am driving at is. Some cheaper batteries have poor BMS boards. Which Makes me wonder about them.

Oh well.. Getting off track

 

[DDW]

The self contained BMS that I have seen only balance cells internal to that battery. More elaborate Canbus connected ones could balance a whole battery banks. The problem with (particularly AGM) LA batteries not being well balanced, is that the low ones never get a full charge which limits their life expectancy. That is not true of LFP, so the fact that one in parallel with another is running slightly lower is of small consequence.

 

[Iggy]

By wire the batteries Nigel's way. If you have more than two batteries and add more. It is a simple task to do. Unlike in the #3 post.

 

[twistedtree]

The self contained BMS that I have seen only balance cells internal to that battery. More elaborate Canbus connected ones could balance a whole battery banks. The problem with (particularly AGM) LA batteries not being well balanced, is that the low ones never get a full charge which limits their life expectancy. That is not true of LFP, so the fact that one in parallel with another is running slightly lower is of small consequence.

I'm not aware of any BMSes that balance between batteries, whether via canbus or other communications. I think they only balance cells within a battery. Are you aware of specific BMSes that do otherwise?

 

[SteveK]

I'm not aware of any BMSes that balance between batteries, whether via canbus or other communications. I think they only balance cells within a battery. Are you aware of specific BMSes that do otherwise?

Twisted I said mine do thru ethernet cable connection between each. post 5

 

[Iggy]

Twisted I said mine do thru ethernet cable connection between each. post 5

Who manufactures your batteries?

Mine have a RJ45 port but its just used for firmware updates.

 

[twistedtree]

Twisted I said mine do thru ethernet cable connection between each. post 5

Yes, that post is part of what prompted my question. Like Iggy, I'd be interested to know the make/model battery. A number of manufacturers have inter-battery communications, but I have yet to hear of any balancing process where one battery does balancing in response to the SOC of another battery. It's not impossible by any means. I've just never heard of anyone doing it. It would only make sense or be necessary where you have batteries in series, and this is actually one reason why manufacturers typically limit how many batteries you can have in series.

 

[cafesport]

So a little bit of thread drift here.

I have a set of LiFePO4 with internal Bluetooth bms’s but they are wired in series. The bms’s don’t communicate with each other and as a result I had to add an external balancer for when the batteries became unbalanced.

At first I just top balanced both batteries individually. After a month i found that I needed to do this again. What seemed to happen is that one battery was discharging below the bms cutoff voltage for some short period of time. This dropped the combined voltage of the the series below a programmed system cutoff voltage. As a result the bank was Disabled by the dc to dc charger.

In the morning when the solar panels started to charge this bank the batteries started charging already out of balance. The internal bms’s top balanced the cells but the two batteries were not top balanced as a system. Over time the performance of the whole bank suffered as a result. The answer was to add an external balancer. This bank has now done over 380 cycles so I’m pretty convinced this is now working as it should.

 

[mvweebles]

So a little bit of thread drift here.

I have a set of LiFePO4 with internal Bluetooth bms’s but they are wired in series. The bms’s don’t communicate with each other and as a result I had to add an external balancer for when the batteries became unbalanced.

At first I just top balanced both batteries individually. After a month i found that I needed to do this again. What seemed to happen is that one battery was discharging below the bms cutoff voltage for some short period of time. This dropped the combined voltage of the the series below a programmed system cutoff voltage. As a result the bank was Disabled by the dc to dc charger.

In the morning when the solar panels started to charge this bank the batteries started charging already out of balance. The internal bms’s top balanced the cells but the two batteries were not top balanced as a system. Over time the performance of the whole bank suffered as a result. The answer was to add an external balancer. This bank has now done over 380 cycles so I’m pretty convinced this is now working as it should.

What is an "External Balancer?" Link?

Peter

 

[SteveK]

Who manufactures your batteries?

Mine have a RJ45 port but its just used for firmware updates.

Yes, that post is part of what prompted my question. Like Iggy, I'd be interested to know the make/model battery. A number of manufacturers have inter-battery communications, but I have yet to hear of any balancing process where one battery does balancing in response to the SOC of another battery. It's not impossible by any means. I've just never heard of anyone doing it. It would only make sense or be necessary where you have batteries in series, and this is actually one reason why manufacturers typically limit how many batteries you can have in series.

Renogy smart 100Ah

The Renogy Smart Lithium Iron Phosphate Battery enables the auto-balancing among parallel connections and provides more flexibility for the battery bank configuration. The integrated battery management system (BMS) not only protects the battery from various abnormal conditions but monitors and manages the charging and discharging process. The state-of-the-art battery cells ensures an extended cycle life and exceptional discharge performance.
Key Features Auto-Balance
Connects multiple batteries in parallel safely with the auto-balancing function to meet the power and energy requirements of different system setups.

Battery Cell Balancing
The battery employs bypass circuit to maintain the balance between each battery cell group. Each battery cell group is connected with a bypass resistor and a switch in parallel. During the charging process, if the highest-voltage battery cell group reaches the set balancing starting voltage and the voltage difference between the highest-voltage and the lowest-voltage battery cell group exceeds the set voltage difference, the switch connected to the highest-voltage battery cell group will be closed to shunt the charge current around the highest-voltage battery cell group through the bypass resistor until the voltage difference drops below the set value. To avoid excessive energy loss, the battery cell balancing is only performed during the charging process.

To enable the communication between paralleled batteries for the proper operation of the Renogy Monitoring Screen or the Renogy Bluetooth Module, connect the RS485 LINK Communication Ports of the former batteries to the RS485 UP Communication Ports of the latter ones using CAT5 (or above) Ethernet straight through cables (not included). The Renogy Monitoring Screen or the Renogy Bluetooth Module should be connected to the RS485 UP Communication Port of the first battery

 

[twistedtree]

Renogy smart 100Ah

OK, I read/interpret that as cell balancing within each battery. Paralleled batteries are inherently balanced battery to battery.


Series batteries is where you can end up with all cells in one battery balanced, but at a higher or lower SOC than all the cells that are balanced within a second battery. Both BMSes think they have done a splendid job, but one battery is ahead of the other. Conceptually there is no reason why those two BMSes couldn't compare notes and conclude that one BMS needs to lower all of it's cells equally to match the other battery. I'm just not aware of any vendors who actually does that. In a lot of cases, I don't think a BMS can even tell which batteries are in series together.

 

[SteveK]

I thought the third quote I gave showed they talk to each other thru the ethernet cable.
The claim you are not aware of is being made by Renogy.
BTW these batteries cannot be connected in series, only parrallel. Probably because in series they would not be able to reject charge if another needs more to be equal as the chain would be interupted.

 

[DDW]

I'm not aware of any BMSes that balance between batteries, whether via canbus or other communications. I think they only balance cells within a battery. Are you aware of specific BMSes that do otherwise?

Mainly balancing series connected batteries. Parallel connected can't get very badly out of balance unless they are very badly connected. But there are series balancers, and I've seen some batteries with internal BMS that communicate for series connection balancing (don't remember offhand the brand, and brands don't seem to last very long anyway).

 

[twistedtree]

I thought the third quote I gave showed they talk to each other thru the ethernet cable.
The claim you are not aware of is being made by Renogy.
BTW these batteries cannot be connected in series, only parrallel. Probably because in series they would not be able to reject charge if another needs more to be equal as the chain would be interupted.

Yes, but for monitoring, according to the quote.

 

[twistedtree]

Mainly balancing series connected batteries. Parallel connected can't get very badly out of balance unless they are very badly connected. But there are series balancers, and I've seen some batteries with internal BMS that communicate for series connection balancing (don't remember offhand the brand, and brands don't seem to last very long anyway).

If you come across any specifics, I'd be interested in hearing more about them. I see not reason why it's not possible, and valuable with series batteries. It's just not something I have seen so far.

 

[Iggy]

The 3rd quote is confusing and you must read it like a lawyer would.

They use the would battery and "battery cell groups" alone. So the cell groups make up the one big battery as a whole.

As to this point/quote:
"To enable the communication between paralleled batteries for the proper operation of the Renogy Monitoring Screen or the Renogy Bluetooth Module, connect the RS485 LINK Communication Ports of the former batteries to the RS485 UP Communication"

There not say the ports are used for balancing between batteries. Only for the screen and Bluetooth.

 

[SteveK]

Please avoid too high a voltage difference between paralleled batteries, despite the auto-balancing function, to avoid triggering the over-current protection.

It is not recommended to connect more than 4 batteries in parallel if taking advantages of the auto-balancing function

Written english language is very difficult to understand the meanings

 

[twistedtree]

Please avoid too high a voltage difference between paralleled batteries, despite the auto-balancing function, to avoid triggering the over-current protection.

I think the above is telling you to not connect together two batteries when they are at significantly different SOCs. ABYC cautions against this too. If there is too much SOC difference, and hence too much voltage difference, you can get a significant current between the two batteries after you connect them. If the current is high enough, it can trigger the over-current protection in one or both batteries.Wasn't that clear?

It is not recommended to connect more than 4 batteries in parallel if taking advantages of the auto-balancing function

This one I'm not sure about. It sounds like there is some limitation in their balancer that shows up with more batteries in parallel, but it's not obvious to me what that might be. Actually, maybe I do know. If a balancer is acting on one cell in one battery, it is trying to lower that cells voltage (assuming resistive/subtractive balancing), and that in turn tries to lower the battery voltage. But you have another paralleled battery that is trying to keep the battery voltage the same which will create a counter-acting current. It might have something to do with this.

 

[mvweebles]

Question of cross-battery balancing got me thinking. Server Rack batteries seem to have the most communications these days. So I pinged the folks at Signature Solar about the EG4 batteries. As long as they are installed with a bus bar (vs cabled parallel), they will balance across batteries.

https://signaturesolar.com/eg4-life...MDo5NWgwKahtcX_cpOQx-UUUxMgNr9_iexKd2dRfxk2F0

Frankly, when I looked at the manual and the couple screen shots of the BMS Software for PC, not sure it makes a difference as many of the parameters can be set with granularity. As long as they are accurate, not sure why they'd get out of balance.

BTW - these server rack batteries are $999/400AH (12V). That is dang cheap - While Will Prowse is not a fan of 12V, he is impressed with EG4 and Signature Solar.

Pete

 

[tiltrider1]

Question of

BTW - these server rack batteries are $999/400AH (12V). That is dang cheap - While Will Prowse is not a fan of 12V, he is impressed with EG4 and Signature Solar.

Pete

Wow, just 3 months ago they were $1,500. If they had been $999 then I would have picked up 3 of them.

 

[mvweebles]

Wow, just 3 months ago they were $1,500. If they had been $999 then I would have picked up 3 of them.

Right???? Battle Born 100ah are not much less.

While relatively energy dense, the accumulated capacity means these weigh in at close to 100 lbs. A handful if not planned for appropriately.

I will say that if I were buying a new-build boat, it would have something resembling a server rack vs battery boxes - hopefully with an inverter charger that can also be rack mounted. The off-grid solar guys are developing some interesting kit. At some point it will more greatly influence yachts and RVs that are still hobbled by old-school currency of batteries measured in group-size and CCA.

Peter

 

[SteveK]

The initial battery literature advised that each battery voltage must be close to the others or charged separately until it is and then the self balancing can work. I cannot find it right now but it did say that an entire battery will halt receiveing to allow a lower one to catch up as long as they are close and not trigger the high volt shut off. Technology advances are moving along. BTW I would not have needed to attach ethernet cables if balancing was not the reason. The shunt SOC works well outside the BMS monitor system.

 

[Rob R]

I'm getting ready to order 2 EG4 batteries from InvertersRus. $999. I get free shipping (to Seattle) if I order 3. Anyone else in the Seattle area ready to purchase one or more? I'd combine the order and get reimbursed when its picked up from me.
The batteries will get housed in a modified (cooling fans) molded server rack.
I'd like to get these ordered within 20 days so pm me if interested.

EG4 LifePower4 Lithium Battery 12V 400AH Server Rack Battery

EG4 Lithium battery 12.8V (12V) 400AH 5.12kWh with 200A internal BMS. Reliable and rigorously tested, with a 99% operating efficiency.

invertersrus.com

Rob