Move to Lithium

[Richpatty]

So as I get ready for my Lithium project, I began to think about the best way to wire them. I will have 8 100ah GC2 sized battleborns.

I know many of you use the wiring method on the left (see below). I have seen articles that say the diagram on the right pulls power from the batteries more evenly. A third method (not pictured) would be to run a positive and negative line from each battery to a busbar and then connect those busbars to the negative and positive lines on the RV. This third method would be a bit more challenging…..so based on the experience on this forum, am I good just going with the option on the right? And would this be implemented in two groups of 4?

Opinions welcome.

 

[Neal]

Paging Dr. @Chuggs

 

[redbaron]

Without a busbar, the option on the right is the best way to wire a battery bank of any type.

 

[Richpatty]

Thanks. Is it worth the effort to even pursue the busbar design? Would it make much of a difference vs the design on the right?

As a follow up question, what gauge of wire would be used in each scenario (2 or 3).

Thanks
Rich

 

[Jim]

I've not seen the option on the right before. What makes it better than the one on the left?

 

[redbaron]

the one on the left is supposed to use all cells, as it forces the electrons to enter and exit at far points. Think of how a home water heater works. Cold water enters bottom, and hot water exits the top (or vice versa--not sure really)

Some one much smarter than I am has suggested that it doesn't work like water flow, and somehow the battery at the end outputs much more energy. So the cells that are in parallel need to be drawn from equally. The ones in series will flow like water, as they are increasing the voltage.

 

[scottramer]

Interesting as I was just looking at my chassis batteries and kicking around adding a third battery. This attached drawing is on my London Aire with a Freightliner chassis where the 2 batteries are connected with a built in buss bar in the middle of the cables. I would have thought they would have been connected like pic 1 above but both my batteries are feeding the buss bar so the output, (in my mind anyway) is equal and power not passing from one through the other.

 

[Jim]

So the cells that are in parallel need to be drawn from equally.

If that is the case, and I have no reason to dispute your findings, wouldn't a setup like this allow for perfectly even draw? Assuming that all the cables were also exactly the same length?

Edit: Scottramer must have posted about the same time I was drawing this. His picture appears to be pretty much the same as my diagram.

​

 

[Richpatty]

Yes! This is what I was describing as my third scenario…. Having the Neg and Pos connected to bus bars.

I agree this is optimal, but is it worth the extra effort to do this with eight batteries?

 

[redbaron]

I plan on doing the bus bar with my lithium conversion.

 

[Richpatty]

Ok. So what gauge wires from the batteries to the bus bar? I think 4/0 is probably overkill. Maybe 3/0?

 

[redbaron]

Ok. So what gauge wires from the batteries to the bus bar? I think 4/0 is probably overkill. Maybe 3/0?

What power draw do you plan on? 3/0 is probably the right answer, but it may be 2/0

 

[Jim]

Ok. So what gauge wires from the batteries to the bus bar? I think 4/0 is probably overkill. Maybe 3/0?

Although I have never done a lithium conversion, I did upgrade my previous coach setup to 6 large 430 amp batteries. My thought process was the less resistance, the better, so I used 2 gauge wiring. Might have been overkill, but it made me feel better.

 

[scottramer]

Not to hi-jack Richpatty's original question but there seem to be some brain power here. I have room to add a 3rd chassis battery and I got the idea watching a video on a Prevost that had 3. My thought process is, with the hydraulic full wall slide the pulls tones of amps when operated this might be a good addition. So my question is, would the drawing attached be the proper way to do that. The red lines would be the added battery and the black the existing batteries. The Freightliner design of the cables looks to be a pseudo buss bar design so is adding the 3rd battery in the middle the proper way to to that? Thanks for any help.

 

[Richpatty]

Not sure….have not heard of folks doing that, it I dont see why it wouldn't work…. And I don’t see how it could hurt anything either. As long as all three batteries were approximately the same age and the same rating.

My 2 cents…

 

[redbaron]

Not to hi-jack Richpatty's original question but there seem to be some brain power here. I have room to add a 3rd chassis battery and I got the idea watching a video on a Prevost that had 3. My thought process is, with the hydraulic full wall slide the pulls tones of amps when operated this might be a good addition. So my question is, would the drawing attached be the proper way to do that. The red lines would be the added battery and the black the existing batteries. The Freightliner design of the cables looks to be a pseudo buss bar design so is adding the 3rd battery in the middle the proper way to to that? Thanks for any help.

Yes--and to tie it back into the original question and topic, you too are using a BUS BAR in the diagram. This would evenly spread the load.

Now -- for higher brains than mine-- @Chuggs or others--here is my question:


I think you should be sure the cable from the battery to the busbar is the same size and length as the others, so that it is evenly spread. Is that true?

Does the attachment of the load on the bus bar need to be placed in a certain position for optimal load spread?

 

[Neal]

Isn't there some engineering technical way to size this properly? Distance, voltage, etc??

 

[redbaron]

Isn't there some engineering technical way to size this properly? Distance, voltage, etc??

for the load side, I am aware of math. What I don't know is busbar rules, and the division rules when splitting between cells.

In my situation, I am going to have 2 Xantrex 3k inverters coming from the busbar. Each of those runs will be sized to their max load with comfortable allowance for overage.

The bus bar itself must be capable of the 6kw of power delivery.

I am thinking that each individual battery connection must also be capable of the 6kw power...otherwise if a cell where to die, then the power would cause a fire due to an overload situation.

If that is true, then all battery cables must be sized for the max load.

That means that I would need to have 4/0 cable between batteries and bus bar, and then each inverter would be 3/0 cable.

Going direct copper between batteries sure is intriguing, but I am worried about the movement of the batteries as I barrel down the US highways hitting potholes, slamming on my brakes, and doing emergency lane changes just to prove I can...would I harm the studs on the batteries?

Lots of stuff to research.

 

[Richpatty]

Interesting…and It would depend on the size of the individual battery…whether it be a 100ah or the 270ah that BB also makes. If using a regular 100ah battery, based on the chart below, and if you only run from the battery to the busbar, you should be able to use 2/0 since it will be less than 200 amp for each individual battery….

The cable from the busbar to the inverter and shunt/ground would need to be larger….up to 4/0…

I spoke to BB about cable gauges and connectivity and they felt that doing the normal parallel design that many use (option 1 at the beginning of this thread) would be fine due to the way lithiums charge and discharge…. Not sure I completely believe that, so I may go with option 2 to ensure I am “more” balanced, but short of running 16 cables (2 for each of the eight batteries) to busbars. And saving the cost of 2 busbars….

Still thinking.

Oh, and other thing they said….that using cables is better than copper bars…due to the threading of the cables vs the solid copper bar, you would have better connectivity. I need to google that some more.

 

[Richpatty]

Ok. Found a place that lists the amperage rating of copper bar. But when I look up the prices for what I would need, I am better off with heavy gauge wire….

Electrical: Busbar - DC Copper Busbar Ampacities

The following tables have been provided by the Alliance for Telecommunications Industry Solutions (ATIS), T1 Committee, and represent ampacities for busbar sizes and arrangements typically found in the telecommunications industry.

www.copper.org