So, I just bought a new 5th wheel toyhauler. It currently has a single 12v battery. I want to seriously upgrade the battery capacity. I had 2 Costco 6v golf cart batteries in my last rig. I think I want to go to 4 batteries in the new RV. I'm interested in the Trojan T-1275 (12v 150AH at 20hr). I can get them for $158 each plus core locally.I have space for 2 batteries on each side of the RV. This means I would have to run cable between the sides, which looks like it will be fairly easy. Some more variables. I currently have 150 watts of solar with a Zamp charger. Looking to upgrade to ~450 watts. I also have a 2k watt pure sine wave inverter.Here is how I *think* it should be wired.This would require 3 wires (1 power and 2 ground) to the other side of the RV. I'm thinking some like 1/0 or 2/0 for these runs.So, my questions are these. Is it ok to have the battery banks spread apart like this? Is 1/0 big enough?

It is possible to have TOO MUCH battery capacity and exceed your ability to keep them charged.....or overload the charging equipment in the rig or the tow vehicle.I think you need a somewhat sophisticated controller to handle 4 batteries but there are some "experts" on here who can be more specific.

Yes you can do that all sorts of ways. -If you run parallel links to join each "pair" you only need to ground one to the frame.-You can have one side only do the inverter and give it its own solar set for recharging plus a portable charger when no solar. the other side can do the usual rig stuff, and have its own solar set and charger. Now you don't need the long parallel links-You can put the inverter in the middle and have two wire sets for it.Two wires from pos terminal and two from its neg terminal. One pos and one neg to each "pair". Now the inverter-battery wires are also the parallel links and they don't have to be so fat since each is carrying about half the amps.-If you have a Trimetric with its shunt, it means if you split the bank you can only monitor the pair the shunt is on, but you don't really need a momnitor anyway :)I have played with these set-ups a different times and they all work.You need to recharge those T-1275s seriously to 14.8v temp adjusted or they won't last, so don't expect to keep them going with a 14.4 volt converter. A solar controller with adjustable voltage will help with that, plus an adjustable voltage charger for when not using solar. This type would be a good choice for that--he can do one up as a 100 amper for you.http://www.bestconverter.com/Boondocker-BPCM-75-75-Amp-Adjustable-Power-ConverterCharger_p_587.html#.VkJ-FHmFNjoHere is one of my past set-ups with the two T-1275s on inverter only with the Solar30 controller and the four 6s (two are out of sight to the right) doing the rest of the work with an Eco-Worthy controller for them. The Trimetric would only do the four 6s in that set-up.

I'm not sure why you'd need the ground to go to the other side; just find a good ground on the ground side of the RV. Maybe I'm missing something (perhaps needing a lower impedance ground than the chassis provides for the inverter).What you post at the top is not quite balanced, as it turns out, but only pretty close. See http://www.smartgauge.co.uk/batt_con.html for a more thorough explanation, and (at the end) this nifty approach:

DrewE wrote:I'm not sure why you'd need the ground to go to the other side; just find a good ground on the ground side of the RV. Maybe I'm missing something (perhaps needing a lower impedance ground than the chassis provides for the inverter).What you post at the top is not quite balanced, as it turns out, but only pretty close. See http://www.smartgauge.co.uk/batt_con.html for a more thorough explanation, and (at the end) this nifty approach:If you draw a horizontal line separating the four batteries shown you will see the positive needs to be connected on one set and the ground on the other set. If he uses existing conditions both + & - will be on same side.

Battery Upgrade | Good Sam Community

BFL13
Explorer II
Nov 11, 2015
smkettner wrote:
Really need the shunt on the other side to keep the batteries balanced.

Yes but it is difficult to arrange when the pairs are 8 feet apart. You have to lengthen all the installed positive wires to reach or add a wire to the pos and bring it back over to where the installed pos lugs are (now you have two 8 ft positive wires between the pairs!

I gave up on all that. Too much wiring and awkward routing. Went for the split bank with each bank doing some of the loads. But now you need two sets of chargers, including two sets of solar, and two battery monitors if you want to keep track that way (not required, but good to have)
Supereri73
Explorer
Nov 11, 2015
I can run a second ground from the far side and use that for the Shunt/Load- . Running the cable will be easy.

Would 1/0 be big enough for say 100 amp load?
Salvo
Explorer
Nov 11, 2015
This should work with minor mods.

1. Connect + 12V loads to the top left battery.
2. Connect chassis ground to the bottom side of shunt.
BFL13
Explorer II
Nov 11, 2015
Supereri73 wrote:
I can run a second ground from the far side and use that for the Shunt/Load- . Running the cable will be easy.

Would 1/0 be big enough for say 100 amp load?

To be clear on terminology, you don't want a second ground. The "far side" pair of batts will not have a frame ground near to them. They will be grounded to the frame as part of the four-battery bank, and the ground for that will be via the shunt's load side (the end away from the battery) to the frame, over by the "near side" pair of batts.

I think 1/0 would do (probably overkill) for the 8 ft parallel links between the pairs, but others might have other opinions on that.

The "near side" pair of batts will be a busy area, having nearby your inverter, solar controller, maybe a deck mount converter, Trimetric shunt, and positive and negative buss bars for all the wires. Also a battery cut off switch if you want one.
DrewE
Explorer II
Nov 11, 2015
Basically, you need either the positive or the negative connection to the battery bank to be at the far side, and the other one to be at the near side, and only one of each. You can achieve that in a few ways: by using a long wire to connect the far side ground connection to the current near side ground (via the shunt), by using a long wire to connect the far side positive to the near side positive stuff, or by making the ground connection for the batteries at the far side (via the shunt). It seems to me the last option is the simplest, and requires only lengthening the sense wires to the shunt and finding or making a good ground connection on the far side.
Salvo
Explorer
Nov 11, 2015
No, not enough if you want to run 100A through an inverter.

A battery is full at 12.8V. The inverter alarm goes off at about 11.1V. You got 1.7V of headroom. You don't want a large percent of this headroom going to cable voltage drops.

For example, if you use 0 AWG, 10ft per side, that will drop 0.2V at 100A. That's already 12% of your headroom. You still need to account for the cables to the inverter, perhaps decreasing headroom by 18 to 20%.

I would go with 000 AWG. If the inverter cable length is 6 ft (one way), and battery connect is 10 ft (one way), then voltage drop is 0.19V, or 11%.

Supereri73 wrote:

Would 1/0 be big enough for say 100 amp load?
time2roll
Nomad
Nov 11, 2015
1/0 ampacity is at least 250 amps so yes it will work fine at 100 amps.
Keep it short and neat for best results.

http://www.genuinedealz.com/voltage-drop-calculator

The side to side run will cause some voltage drop and should be added to the inverter cable length calculation. Probably better overall to get all batteries in one compartment near where the inverter will be installed. Far better to lengthen the wire to the house loads and keep the inverter connection short.
Supereri73
Explorer
Nov 11, 2015
DrewE wrote:
Basically, you need either the positive or the negative connection to the battery bank to be at the far side, and the other one to be at the near side, and only one of each. You can achieve that in a few ways: by using a long wire to connect the far side ground connection to the current near side ground (via the shunt), by using a long wire to connect the far side positive to the near side positive stuff, or by making the ground connection for the batteries at the far side (via the shunt). It seems to me the last option is the simplest, and requires only lengthening the sense wires to the shunt and finding or making a good ground connection on the far side.

I think this shows your last suggestion. Please let me know if I still don't have this.

Thanks to everyone for all the GREAT feedback on this!!!!!!!
Supereri73
Explorer
Nov 11, 2015
smkettner wrote:
1/0 ampacity is at least 250 amps so yes it will work fine at 100 amps.
Keep it short and neat for best results.

http://www.genuinedealz.com/voltage-drop-calculator

The side to side run will cause some voltage drop and should be added to the inverter cable length calculation. Probably better overall to get all batteries in one compartment near where the inverter will be installed. Far better to lengthen the wire to the house loads and keep the inverter connection short.

Inverter is within 1-2 feet of the near batteries. See below pics
BFL13
Explorer II
Nov 11, 2015
You have to pick whether you are going for the upstream /downstream set-up or try to put the negs on one pair and the positives on the other pair 8 feet away. Then look at wire size.

If you do the upstream/downstream thing, the inverter with short fat wires goes with the upstream side, that also has the Trimetric shunt there. Now the two 8 foot wires to the downstream pair don't need to be so fat at all.

The upstream pair will get worked harder on big draws and high amp charging, but you can swap the battery pairs sides every six months to achieve a sort of even wear over the years as another way to get some balance.

You have to do some picking and choosing what's more important.

Forum Discussion

Battery Upgrade

About Technical Issues

Related Content

Suspension Upgrades

TC Battery Replacement - Upgrade Options

Suspension upgrade

Upgrade

Lifeline GPL-27T AGM Battery Upgrade