[El Guapo]

I'm thinking about adding a second battery to my system. Currently have one Renogy 200ah. Below are pics of how it's wired. Would the correct method have the second battery connecting to the bus bar like the first one or should it connect directly to the first battery?

 

[SteveSS]

Check out this thoughtful discussion of connection options:
http://www.smartgauge.co.uk/batt_con.html
I think I also read (somewhere?) that your new one should match the old one as closely as possible. And that a battery bank is only as good as it's weakest member, your old one in this case.

 

[El Guapo]

Thanks for the link. If I read their recommendation correctly for two batteries - connect the pos of the two batteries together and the neg of the two batteries together, connect battery 1 to the pos bus bar, connect battery 2 to the neg bus bar (or vice versa). I'd use the same battery for the second one.

 

[RDinNHandAZ]

Yes if they are 12 volt that is correct, it is called wiring in parallel. I’d caution those buying 2- 6volt golf cart batteries that those must be wired in SERIES to increase the voltage to 12.
By two similar batteries they mean the same battery twice OF THE SAME AGE AND HISTORY. One old and one new are not electrically similar.

 

[keeponvaning]

Those buss bars are interesting - my only question is how do you prevent shorts when they are so exposed? I realize they are opposite sides but, still, shouldn’t you at least have some physical protection on the positive bar?

 

[El Guapo]

They're in a dedicated compartment. Nothing else is stored inside it but protection from accidentally shorting from a wrench or something would be good. The bars are made by Blue Sea. I'll look to see if they have any kind of a cover I can add.

 

[carnut]

...By two similar batteries they mean the same battery twice OF THE SAME AGE AND HISTORY. One old and one new are not electrically similar.

I concur on that. The calculations on that site assume all batteries have the same internal resistance and all connections resistances are identical. I'm not discounting it entirely. It would be very good advice for 4 or more batteries in parallel. With only 2 batteries, equal voltage drops across all the connections is easy to manage. The key takeaway from that is too make sure the total cable length on each bank is identical.

I don't like charging batteries in parallel for all the same reasons the author outlines in that article. On my electric powered boat I use one of these 3 pole transfer switches to manage parallel battery use.

With a switch like that you can manually select how that batteries are charged and used. I always charge each battery individually since I'm charging on-shore. With solar or other low rate charging, you could charge parallel. I usually use parallel mode mode to spread the draw load and reduce depth of discharge in each bank. Sometimes, to make sure I can get back if exploring, I keep one bank in reserve. The switch make it easy to manage the best approach. With a second switch, you could even charge one bank in isolation and maintain the integrity of the charge algorithm in a multi-stage charger while using the other battery.

 

[SteveSS]

My take-home from that connection article was the small differences between many of the alternatives. It's good to know what's perfect, but it's also good to know how close (or not so close) the various alternatives are. All those 12V alternatives are parallel, just different wiring paths with different efficiencies. Figure out what works best in your situation, including how much tinkering you'll enjoy doing to maintain it.

 

[proeddie]

Thanks for the link. If I read their recommendation correctly for two batteries - connect the pos of the two batteries together and the neg of the two batteries together, connect battery 1 to the pos bus bar, connect battery 2 to the neg bus bar (or vice versa). I'd use the same battery for the second one.

El G,

I would think that the buss bar has more current carrying capability than the wire you would put between the two battery positives and two battery negatives.

I suggest that you leave what you have in place... no changes... then, get two more wires, one long enough to go from the neg of the new battery to the neg buss bar, and one long enough to go from the pos of the new battery to the pos buss bar. That is the best way to get the two connected to the buss bars AND have the least amount of wire resistance. They would be wired in parallel which gets you 12V and twice the amps as your current setup.
I added a second battery about 9 months after my first... same make, same model, same battery.... no ill effects because of the slight mismatch created by the age difference!

Looking at your pics, I would suggest making a small wooden U cover ( 3/4" plywood ) with a few cutouts for wires to cover the positive buss bar. Just in case something (wrench, screwdriver, metal anything) gets in the wrong place... Both don't need to be covered.