Why You Should Use Buss Bars in your Multi Battery Installation

[SolarPoweredRV]

There are several reasons to connect multiple batteries using Buss Bars instead of "Daisy Chaining" them together.

In the PDF attached (below) is a research paper that explains the electrical draw from each battery using various "Daisy Chaining" methods versus using Buss Bars to connect the batteries to the load and how Buss Bars even out the load on each battery.


Here is a Video explaining the advantages of using Buss Bars by analyzing an installation using "Daisy Chaining" and a new configuration using Buss Bars.

Note: pay special attention to the temperature differentials...

https://www.youtube.com/watch?v=eWqJjlHoW9A

PS: in order to make this post more useful in planning your installation, I have also attached a Wire sizing chart for your reference...

 

[Second Chance]

David,

As you know from my recent thread, I'm adding two more BBs for a total of four. I asked BB about a bus bar vs. jumpers and their response was, with just four batteries, to tie the load(s) to one of the middle two batteries and it will be fine for that few batteries. Was this poor advice in your opinion? If so, I need to order some more parts before I start the installation...

Rob

 

[ajg617]

Installing the Victron 712, I called BB to confirm the connection recommendation for two batteries. The picture BB sent is below and was their recommended parallel install with Victron connection. My positive and negative ends do go to bus bars but the implication was that for the Victron to correctly monitor, it needed to be the only connection on last in line battery. I didn't ask about 4 batteries though I am thinking about adding another 200ah.

View attachment 12v 200ah.pdf

 

[MoonShadow_1911]

David,

As you know from my recent thread, I'm adding two more BBs for a total of four. I asked BB about a bus bar vs. jumpers and their response was, with just four batteries, to tie the load(s) to one of the middle two batteries and it will be fine for that few batteries. Was this poor advice in your opinion? If so, I need to order some more parts before I start the installation...

Rob

Rob,

I can provide a little theory behind wire gauge size vs. bus bar.

Wire that carries current has increasing resitive properties as the current increase; this is due to several different electrical properties of the wire (which I won't get in to). Resistance manifests itself as heat and as the name implies, resists current flow; resistance of current flow also has a byproduct of reducing the voltage flow. For example, lets say we are putting 12VDC at 100 amps down a copper wire with a standard resistivity of 1.72e-8 megohms. It is travelling 12 inches. The voltage drop for an 18 AWG wire is 1.27394 volts; for a 4 AWG wire, the voltage drop is 0.0495735 volts; and for a 4/0 wire, the voltage drop is 0.00977913 volts, almost non-existent.

A bus bar is similar and calculated as to a solid piece of 4/0 wire, however, you can have multiple connection points along the bus bar and still have the circuit see it as a single point connection.

What Battleborn is saying is with a sufficiently large wire gauge, connecting it to the middle of the battery bank, is electrically similar to a bus bar, with a "small" number of batteries (I would assume 4 or less). This is true that it is similar to a bus bar, but the limiting factors are cost, future expansion, ease of replacement, loss of Ah because one cable or battery failed.

A picture is worth a thousand words.

 

[huntindog]

Installing the Victron 712, I called BB to confirm the connection recommendation for two batteries. The picture BB sent is below and was their recommended parallel install with Victron connection. My positive and negative ends do go to bus bars but the implication was that for the Victron to correctly monitor, it needed to be the only connection on last in line battery. I didn't ask about 4 batteries though I am thinking about adding another 200ah.

View attachment 42490

With only two batteries, there is no need for a buss bar.. It can be a "nice to have" for hooking up other items. They don't cost much, so I would do it just for that reason. None of this matters for the battery monitor. It jus measures total amps in and out.

 

[Soundsailor]

There are several reasons to connect multiple batteries using Buss Bars instead of "Daisy Chaining" them together.

In the PDF attached (below) is a research paper that explains the electrical draw from each battery using various "Daisy Chaining" methods versus using Buss Bars to connect the batteries to the load and how Buss Bars even out the load on each battery.


Here is a Video explaining the advantages of using Buss Bars by analyzing an installation using "Daisy Chaining" and a new configuration using Buss Bars.

Note: pay special attention to the temperature differentials...

https://www.youtube.com/watch?v=eWqJjlHoW9A

PS: in order to make this post more useful in planning your installation, I have also attached a Wire sizing chart for your reference...

Thanks [MENTION=22656]SolarPoweredRV[/MENTION], the article you posted is where I learned what I needed to decide on a busbar installation. The video confirmed what I've observed in practice, no observable increase in temperature on the cables and nodes while the inverter is in operation (and thus higher efficiency).

The busbar also helped with another issue. The BMS on my batteries limited them to 100 Amps. So in a daisy chain setup, my understanding (I didn't try it) is that the BMS on the last battery in the chain would limit the entire battery bank to just 100 Amps at a time, not good for me since I have an inverter that can easily pull more than 100 Amps.

Yes, the busbar takes more room and was a little less tidy than a daisy chain, but the results speak for themselves (I'm very happy with the way my setup works).

 

[Soundsailor]

David,

As you know from my recent thread, I'm adding two more BBs for a total of four. I asked BB about a bus bar vs. jumpers and their response was, with just four batteries, to tie the load(s) to one of the middle two batteries and it will be fine for that few batteries. Was this poor advice in your opinion? If so, I need to order some more parts before I start the installation...

Rob

Rob:

With 4 batteries I think you'll be better off with a busbar installation.

Stephen

 

[Soundsailor]

[MENTION=30847]MoonShadow_1911[/MENTION], could you comment about cable size when using a busbar setup? I (probably incorrectly) assumed that all cables in the system should be capable of carrying the max expected load (300 Amps) and so I used 4/0 cables from the batteries to the busbar and from the busbar to the fuse and shunt on the load size. I've seen elsewhere the suggestion that smaller cables would be sufficient for the connections between the batteries and the busbar. Is that correct in your estimation? I'm personally not sorry to use heavier cables, but they do cost more and probably were not necessary.

 

[SolarPoweredRV]

David,

As you know from my recent thread, I'm adding two more BBs for a total of four. I asked BB about a bus bar vs. jumpers and their response was, with just four batteries, to tie the load(s) to one of the middle two batteries and it will be fine for that few batteries. Was this poor advice in your opinion? If so, I need to order some more parts before I start the installation...

Rob

Taking the load off of the two middle batteries would be fine, however, by adding two extra cables to your battery bank, you can achieve the same results as you would get by using the Buss Bars. I am referring to method 4 in the research paper linked above.

Bottom line, unless you are running your Air Conditioner, taking the load from the two middle batteries (Method 4 in the research paper above, without the long wires added) is definitely better than the typical "Daisy Chain" installation that is very common in RV battery bank installations.

If you are planning to run your A/C from your Inverter, I would definitely recommend using the Buss Bar installation method.

 

[ajg617]

[MENTION=30847]MoonShadow_1911[/MENTION], could you comment about cable size when using a busbar setup? I (probably incorrectly) assumed that all cables in the system should be capable of carrying the max expected load (300 Amps) and so I used 4/0 cables from the batteries to the busbar and from the busbar to the fuse and shunt on the load size...

[MENTION=30847]MoonShadow_1911[/MENTION] Same question as I also ran 4/0 but only because the factory had 4/0 to the inverter. In your diagram it appears that if you lose the load side battery, you lose the capacity of anything behind it without bus bars?

 

[Second Chance]

Taking the load off of the two middle batteries would be fine, however, by adding two extra cables to your battery bank, you can achieve the same results as you would get by using the Buss Bars. I am referring to method 4 in the research paper linked above.

Bottom line, unless you are running your Air Conditioner, taking the load from the two middle batteries (Method 4 in the research paper above, without the long wires added) is definitely better than the typical "Daisy Chain" installation that is very common in RV battery bank installations.

If you are planning to run your A/C from your Inverter, I would definitely recommend using the Buss Bar installation method.

No AC - just the residential fridge (2,000 watt inverter), house lighting, etc.

Rob

 

[JCR GD]

I'll start my comments by saying my cables may be under-sized (#4 welding type cable) but I don't have an inverter so it shouldn't matter much since they are all bigger than the OEM cables that connect the converter and batteries to the camper.

When I switched over to Lithium I went with 4 LifeBlue batteries (they have built in BlueTooth so each battery can be monitored individually) and put 2 on each side of the generator in the front compartment. I wired them using the bus bar method. 2 Batteries had 6Ft. cables and the other 2 had about 2-1/2Ft. cables.

After a couple of trips boondocking for 3-5 days each I kept finding the batteries at different SOC levels (80, 79, 65, 64 as an example.) I thought that was odd because I would have thought they would equalize as they discharged. (I should also note I had solar suitcase providing charge to bus bars.)

When I got back home, and on shore power, the batteries would charge but they would individually shut down as they reached full charge while the others continued to charge. This was probably fine but had to be confusing to the converter/charger (for Lithium batteries) which would eventually go into float mode when all were charged. (Although a few times I noticed it switching to float before 1 or 2 were fully charged.) This is probably a symptom of undersized wires and different distances to the bus bars.

I realized if I had gone the "system monitoring" route instead of the "individually monitored" route I would probably not even know this was happening.

Since I didn't like this happening, I switch all wiring back to series as I had had on my 4 lead acid batteries. Now, as you may have guessed, they all have the same SOC levels and charge at the same rate.

All this to say, in my real world use, the bus bar method was not the best way to go. If you can not individually monitor each battery, you will probably never know the difference.

 

[triplethreat]

Something that has not been mentioned yet, as far as using buss bars to connect batteries...or in my case, individual cells tied together to make a battery, is the possible movement between the batteries or cells. Probably most of us strap down, tie down, or use some method to secure the battery or batteries in a given location, and that is all well and good. But once you start using buss bars to tie batteries or cells together, you really need to make sure that ANY movement whatsoever causes ALL the batteries or ALL the cells to move equally. Doing this relieves any/all the stress off of the battery terminals. In my case, I built a jig that contains the battery cells together. In the case of using complete batteries, the principal would be exactly the same. You simply do NOT want one battery (or cell), moving a different direction that the rest of them. Here is a pic of the jig that I made for my four LiFePO cells, tied together with buss bar and clamped together to stop individual movement of the cells....

Notice that the buss bars have not been installed yet, but the point is that the cells are all "locked" together and will not depend on the buss bars to help hold them in place....

 

[Soundsailor]

I'll start my comments by saying my cables may be under-sized (#4 welding type cable) but I don't have an inverter so it shouldn't matter much since they are all bigger than the OEM cables that connect the converter and batteries to the camper.

When I switched over to Lithium I went with 4 LifeBlue batteries (they have built in BlueTooth so each battery can be monitored individually) and put 2 on each side of the generator in the front compartment. I wired them using the bus bar method. 2 Batteries had 6Ft. cables and the other 2 had about 2-1/2Ft. cables.

After a couple of trips boondocking for 3-5 days each I kept finding the batteries at different SOC levels (80, 79, 65, 64 as an example.) I thought that was odd because I would have thought they would equalize as they discharged. (I should also note I had solar suitcase providing charge to bus bars.)

When I got back home, and on shore power, the batteries would charge but they would individually shut down as they reached full charge while the others continued to charge. This was probably fine but had to be confusing to the converter/charger (for Lithium batteries) which would eventually go into float mode when all were charged. (Although a few times I noticed it switching to float before 1 or 2 were fully charged.) This is probably a symptom of undersized wires and different distances to the bus bars.

I realized if I had gone the "system monitoring" route instead of the "individually monitored" route I would probably not even know this was happening.

Since I didn't like this happening, I switch all wiring back to series as I had had on my 4 lead acid batteries. Now, as you may have guessed, they all have the same SOC levels and charge at the same rate.

All this to say, in my real world use, the bus bar method was not the best way to go. If you can not individually monitor each battery, you will probably never know the difference.

Could your experience be due to the different cable lengths you report? The article cited by SolarPoweredRV suggests that the cables in a busbar installation should all be the same length and resistance. Also, I believe that to get the system "balanced", they should all be fully charged before being connected together. As the video cited showed, with the busbar system the draws are similar on each battery in the group, not the case in the other types of setup. So if the battery bank is started as recommended, then each battery should always have a similar SOC.

 

[MoonShadow_1911]

@MoonShadow_1911, could you comment about cable size when using a busbar setup? I (probably incorrectly) assumed that all cables in the system should be capable of carrying the max expected load (300 Amps) and so I used 4/0 cables from the batteries to the busbar and from the busbar to the fuse and shunt on the load size. I've seen elsewhere the suggestion that smaller cables would be sufficient for the connections between the batteries and the busbar. Is that correct in your estimation? I'm personally not sorry to use heavier cables, but they do cost more and probably were not necessary.

It is best practice to use 4/0 when connecting to the bus bar. In this way it maximizes the efficiency between the batteries and the load.


At a minimum, and I stress minimum, you could get away with 6 AWG, but again, you are increasing your potential for failure and introducing a voltage drop between the batteries and the bus bar. The difference in cost between a 12" 6 AWG wire and a 12" 4/0 AWG wire is noticeable, but in my opinion, not worth the voltage loss.

Now, from the bus bar to the load, I would strongly recommend 4/0 AWG wire. This is the largest wire available to carry the maximum amount of amperage, with the caveat of distance. If you are running a distance from the battery bank to the load, you might have to double up the 4/0 AWG wires (this would have to be calculated). Most installations that I have seen, the batteries are within 2'-3' of the converter and inverter. 4/0 AWG should be plenty for this.

@MoonShadow_1911 Same question as I also ran 4/0 but only because the factory had 4/0 to the inverter. In your diagram it appears that if you lose the load side battery, you lose the capacity of anything behind it without bus bars?

It really depends on which cable or battery you lose. It it's the first in line, you lose everything, if it's the third in line, you just lose the 3rd and 4th battery capacity. If you are middle connecting, anything before the failure is lost; so ostensibly, you could lose a cable or battery on each side and the entire system might go down.


Hope this helps!

 

[MoonShadow_1911]

Could your experience be due to the different cable lengths you report? The article cited by SolarPoweredRV suggests that the cables in a busbar installation should all be the same length and resistance. Also, I believe that to get the system "balanced", they should all be fully charged before being connected together. As the video cited showed, with the busbar system the draws are similar on each battery in the group, not the case in the other types of setup. So if the battery bank is started as recommended, then each battery should always have a similar SOC.

You are correct, the cables should be the same length and type. It would be best to fully charge the batteries before connecting them so that it takes less time for the charger to balance them.

 

[JCR GD]

Could your experience be due to the different cable lengths you report? The article cited by SolarPoweredRV suggests that the cables in a busbar installation should all be the same length and resistance. Also, I believe that to get the system "balanced", they should all be fully charged before being connected together. As the video cited showed, with the busbar system the draws are similar on each battery in the group, not the case in the other types of setup. So if the battery bank is started as recommended, then each battery should always have a similar SOC.

Yes (as mentioned at the end of the 4th paragraph) but since the cables are very expensive, I didn't want to have to make them all 6ft. long. And yes, I had "balanced" them all before installing.

 

[SolarPoweredRV]

Something that has not been mentioned yet, as far as using buss bars to connect batteries...or in my case, individual cells tied together to make a battery, is the possible movement between the batteries or cells. Probably most of us strap down, tie down, or use some method to secure the battery or batteries in a given location, and that is all well and good. But once you start using buss bars to tie batteries or cells together, you really need to make sure that ANY movement whatsoever causes ALL the batteries or ALL the cells to move equally. Doing this relieves any/all the stress off of the battery terminals. In my case, I built a jig that contains the battery cells together. In the case of using complete batteries, the principal would be exactly the same. You simply do NOT want one battery (or cell), moving a different direction that the rest of them. Here is a pic of the jig that I made for my four LiFePO cells, tied together with buss bar and clamped together to stop individual movement of the cells....

Notice that the buss bars have not been installed yet, but the point is that the cells are all "locked" together and will not depend on the buss bars to help hold them in place....

The original post was referring more to installing individual batteries into your RV versus using Buss Bars to build a battery from individual cells like you pictured. When building a battery from cells there are definitely different considerations (expansion for example) for using Buss Bars.

 

[SolarPoweredRV]

No AC - just the residential fridge (2,000 watt inverter), house lighting, etc.

Rob

You'll be fine taking the load from the middle two batteries.

 

[SolarPoweredRV]

[MENTION=30847]MoonShadow_1911[/MENTION], could you comment about cable size when using a busbar setup? I (probably incorrectly) assumed that all cables in the system should be capable of carrying the max expected load (300 Amps) and so I used 4/0 cables from the batteries to the busbar and from the busbar to the fuse and shunt on the load size. I've seen elsewhere the suggestion that smaller cables would be sufficient for the connections between the batteries and the busbar. Is that correct in your estimation? I'm personally not sorry to use heavier cables, but they do cost more and probably were not necessary.

SoundSailor, you are correct, the cables from the batteries to the Buss Bars do not need to be as large as the cable from the Buss Bar to your Inverter. The cables from the batteries only need to be large enough to carry the max expected amperage from each battery (i.e: 100 amps,or whatever the max discharge amperage the battery is rated at). Being able to use smaller cables is one added advantage of using the Buss Bar system.