Battery Upgrade

[Supereri73]

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?

[DrewE]

mchero wrote:
Something else to throw in the mix folks.

Should their be a 300Amp fuse between the inverter & positive post?


I have zero gauge between the positive inverter post and the batteries BUT that &^#$ fuse heats up! Not hot enough to burn but hot. Not sure what I'm loosing thru it. Ideas?

Absolutely there should be a fuse or circuit breaker there. If you think the fuse is getting hot, consider what a short circuit would do; several thousand watts being dissipated is no laughing matter.

You could measure the voltage drop across the fuse under load pretty easily with a decent voltmeter. It might also be good to check that the connections to the fuse are good and tight and clean; quite possibly some of the heat isn't due to the fuse itself, but due to a resistive connection there. (That would incidentally also tend to cause the fuse to blow earlier than it otherwise should, since it's basically vaporized by heat when it blows.)

[time2roll]

I would sooner build a custom battery box to vent outside vs pull wire between those two small compartments. Maybe go back to the 12v or even L16(6v) if you want to go big. Consider AGM and skip the venting in the large compartment.

[mchero]

Something else to throw in the mix folks.

Should their be a 300Amp fuse between the inverter & positive post?


I have zero gauge between the positive inverter post and the batteries BUT that &^#$ fuse heats up! Not hot enough to burn but hot. Not sure what I'm loosing thru it. Ideas?

[MEXICOWANDERER]

Heel and a toe and a heel and a toe, and slide-slide-slide.

One of the bigger mistakes I see with golf car batteries is a tendency to want to bolt a large lug down onto a relatively tiny post. Unless they've changed designs, a well positioned automotive type clamp is a hundred times better. Or to prove the point, load a thousand watt inverter heavily for a minute then run down to the batteries and feeeeeeeeel the energy with an almost burned finger tip. High amperage versus the stud contact area do not jibe. Not even close. This is why standard issue for an L-16 is an L-pad post.

For lesser amperage, no sweat. For big inverters, sweat...

[pianotuna]

Yup, that is balanced and the best way for 6 six volt jars.

Supereri73 wrote:


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!!!!!!!

[BFL13]

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.

[Supereri73]

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

[Supereri73]

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!!!!!!!

[time2roll]

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.

[Salvo]

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?

[DrewE]

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.

[BFL13]

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.

[Salvo]

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.

[Supereri73]

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?