Dual Battery in a Trailer Question

[R_Lefebvre]

Ok, so I'm stating to do the wiring and have to figure out my battery situation. I have an old Group 31 battery of quesitonable performance I was thinking of using, and I was going to place it between two frame rails, but it's too long to place width wise in the cavity, so I would have to turn it sideways, in which case it would take up more space.

Alternatively, I could buy a smaller battery with a length that will fit nicely width-wise in my frame, and take up less space. But then I won't have much capacity. I could go with two batteries to give me more capacity than the 31 while taking up the same space.

Question is, how could two batteries be wired up? If they're simply in parallel, will they do that "seesaw discharge" thing? I don't want to get into the cost and complexity of a battery switching system at this point.

I'm wondering if two of those massive 6V batteries would work? I'm interesting in getting massive amounts of capacity if possible, because I'd like to be able to run a fridge for a long time with no recharge.

Also, I think I'll need a battery box in any case?

 

[Tucson T4R]

I run two grp 31 Deka Intimidators (AGM) in parallel in my trailer. As long as you use two identical batteries that are healthy, directly wired in parallel works fine. I have a Xantrex 20 amp charger that charges them together as one bank. I've been running this set up now for over a year and it works great.

They are on their side, strapped down inside an angle aluminum frame.

 

[cnynrat]

As far as how to wire two batteries, you have three choices.

1. You can use two 12V batteries wired in parallel but switched with a relay (either mechanical or electronic) so that you are only using one battery at a time. This is essentially the way dual batteries are typically installed in a 4x4.

2. You could wire two 12 V batteries in parallel (negative to negative and positive to positive). There is at least a theoretical problem with this approach that you alluded to in your post. Batteries have a very low resistance. If there is a small difference in resistance between the two batteries it will cause more charging current to pass through the battery with the lower resistance. Given the small resistance we're talking about, a small difference can result in a large difference in charging current, and you may not actually get the increased capacity you expect. The general advice in the RV world for people who want to go ahead and use this configuration anyway is to use two batteries of the same make/model, and with the same date code. The thought is you minimize the chance that there is a significant difference in the resistance.

3. The third choice is to wire 2 6V batteries in series (connecting the negative of one battery and the positive of the other to your load, with the other two terminals being connected together).

I used option 2 in my camper for a while. I never found that it gave me the capacity I expected, so I eventually switched to a single very large 12V AGM battery from Lifeline. So a fourth option to consider would be to think outside the standard automobile battery form factors and stuff the largest 12v battery you can in the space you have available. Odyssey also makes batteries in some other form factors you might consider.

I would have gone to dual 6V in series, but 6V batteries are typically quite tall and that would not fit in the available space. The Lifeline batteries are quite pricey, and I have not had it long enough to tell you whether I think it's worth the cost.

Hope this helps.

 

[R_Lefebvre]

How tall are the 6V? I have about 12" available. Probably 16" I think. I know I've seen them at the TSC store. I just don't know much about those for capacity, etc. Also weight, I don't want to get too crazy. Most importantly, never seen a plastic battery box for those batteries, so I wonder how you handle that.

 

[R_Lefebvre]

Basically, I have 10 7/8" between the chassis rails. Looks like this battery would fit real nice:

http://www.trojanbattery.com/Products/T-145Plus6V.aspx

I think 2 of these would give more power than 2 Group 31 deep cycles. Are these type typically cheaper than 12V batteries? Now we're talking 150lbs in batteries in any case. Yow.

I almost wonder if there's any point. At 530 minutes @25 amps, I figure is 3312 minutes @4 amps (I know it's not linear, not sure which way it goes though?) which is 55 hours, just over 2 days. I would like to be able to run a fridge for a whole week without charging, but I don't know if it's practical to get there with just batteries.

 

[Hilldweller]

A pair of 6V AGM golfcart batteries wired in series will give you a good 220 amps.

From the Lifeline site:
Lifeline GPL-4CTDeep Cycle RV Battery Specifications:

Voltage 6v
Length - 10.28"
Width - 7.06"
Height - 9.63"
Weight 66.00 lbs / 30.00 kgs

 

[Titanpat57]

Basically, I have 10 7/8" between the chassis rails. Looks like this battery would fit real nice:

http://www.trojanbattery.com/Products/T-145Plus6V.aspx

I think 2 of these would give more power than 2 Group 31 deep cycles. Are these type typically cheaper than 12V batteries? Now we're talking 150lbs in batteries in any case. Yow.

I almost wonder if there's any point. At 530 minutes @25 amps, I figure is 3312 minutes @4 amps (I know it's not linear, not sure which way it goes though?) which is 55 hours, just over 2 days. I would like to be able to run a fridge for a whole week without charging, but I don't know if it's practical to get there with just batteries.

But remember you're not supposed to run them them (the batteries) lower than 50% in a perfect world. The fridge won't run continous so wouldn't the run time go out much further? Maybe you could manually run it 4-5 times a day. The 6v Trojans are da ********....that's what they put in alot of golf carts.


See this helpful link:
http://www.ccis.com/home/mnemeth/12volt/12volt.htm


:smiley_drive:

 

[ntsqd]

I have experienced the see-saw discharge between two dissimilar batteries and two batteries purchased at the same place & time.

The dissimilar batteries was how the truck came to me. They worked great for several years, but as age started to influence them the system went downhill pretty fast.

I replaced them with the simultaneous purchase batteries, Exide spiral cells from NAPA. They lasted about 14 months before the first one wouldn't hold a charge. Pro-rated that one out and the other failed about a year later.

I replaced them with a pair of regular old DuraLast's. Those have been in the truck for going on 3 years, but about 2 months into their service I changed the wiring. In analyzing why the previous batteries might have failed I realized that the grounds were at different places on the engine. The resistance through the various mounts and the engine block was apparently enough to cause a problem. I changed that to both battery grounds coming to a marine combiner switch and running a single ground from the switch to the engine block. Since those batteries also start the truck I can use the switch to hold one in reserve. I have not had any trouble in starting the truck and it now frequently sits for a month or more between starts.

 

[R_Lefebvre]

Yeah, there's the 50% thing...

I went to TSC, and they have US Battery 2200 XC for $170

http://www.usbattery.com/usb_us2200xc_sol.html

And Deka 8L16 for $270. Now that's quite the battery. :Wow1:

http://www.apexbattery.com/deka-8l1...0ah--miscellaneous-6-volt-batteries-deka.html

But I don't think I'm going to achieve what I want with this route. Probably 2 8L16's would do it, but at 115lbs each, 230 lbs and almost $600 in batteries... that's crazy. I think I'd be better off keeping a simple small deep cycle, and then figure out how to charge it. Solar, wind, or generator.

 

[R_Lefebvre]

Pat, that's a good link. The venting part concerns me. I made no provisions for that. I could easily put smaller batteries into a marine box and run a vent tube, no problem there, that's what I had planned on doing. But reading that link, I like the idea of using to T105 batteries. They will have more capacity, and last longer, and can be drawn down to 80%. But you can't get battery boxes for them. So then I have to put them on a box on the tongue, which maybe isn't a terrible way to go... I think I could use some more static tongue weight. As it is now, there's very little, and I still haven't even hung the tire on the back yet.

I intended to keep the tongue weight low, because the bike on the front will really load it up, but it's a real design challenge because sometimes the bike won't be there.

 

[JIMBO]

:sombrero: I wasn't going to interfere, but this system has worked for me for 2 years of camping in the Sierras

I have my cooler and trailer lights hooked thru the towing ckts and always use the vehicle battery while under way

When I'm camped, I also use a single battery in my trailer and don't ever jeopardise the vehicle battery


This 60 watt solar can be moved for sun exposure and has always kept my battery topped, running the Cooler, lights and I've even used the inverter to run my little electric chain saw (not often)

If you have a lot more demands, then you will need a dual battery set up to protect your vehicle battery, but I've kept mine pretty simple

My solar is wired to the battery, thru 7-amp controller and I have a 25 ft 3-cond, insulated cable using a 12vdc/10awg, power plug for the panel hookup

I don't know the exact current output at varies times, cause it works very well and it's effeciency doesn't really matter

:victory::wings::safari-rig::safari-rig: JIMBO

 

[Hilldweller]

How big and what make fridge, Jimbo?

 

[Titanpat57]

Nice setup Jimbo..

Rob

I only have a grp 28 interstate...and I'm running all LED's at night, hopefully a fridge is on the Christmas list.

If you check out the electrical panel part of my build you'll see my panel, and I put a tongue box on too with the battery in it. I found a nice metal box on CL and drilled vent holes high and low on the sides, and it works perfect.

My next will have 2 6v batteries and a Honda 2000i though..with a solar charger. They seem to really become more affordable by the day. As a backup I made a set of booster cables out of 10 awg wire with clamps on all ends to give the battery a needed charge if it really falls. Right now I only run a fan in the tent if it's hot..my iphone to watch movies, and some led sidelights for addtional area lighting at night.

A little addtional planning will give a great power range and will fun to set up. I threw in a couple redundent dissconnects to assure I don't leave something on to drain the battery, coupled with fuses on all circuts too.

Once you get going it'll be fine..I hope...lol

 

[JIMBO]

:sombrero: Yo HD, I've used the 60 watt pnl with the Koolatron (4 amp draw)

And the ENGEL MT35

The MT35 is too small for you guys with larger families-camping, but it's just right for my wife and I and it has such a low current draw, my battery never complains bike_rider

:costumed-smiley-007:smiley_drive::safari-rig::safari-rig: JIMBO

 

[R_Lefebvre]

Jimbo, that's a small panel for 60W? I have a lot to learn about the different panel types. Since I'm using Maggiolina, I've thought I could just mount it on top, no problem. I just wonder about the angle it will be pointed, as well the fact that I can't necessarily place it in the best place for sun exposure. But, it would be less likely to be damaged...

I don't plan to have a lot of electrical loads. Just the fridge, a small water pump, and some lighting. Probably some large area lights that would have infrequent use. I'll attempt to use the propane lantern as much as possible. I'll also have a light source inside the kid's area, for reading and such, and also need a night light. Haven't sorted that out yet. And then some reading lights and stuff for us. Maybe occaisional DVD player or something like that.

I know somewhere somebody posted a REAL measured power draw on these fridges, but can't find it.