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Old 08-23-2011, 11:36 PM   #1
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2 batteries outside and two batteries inside

Assuming I have a solar setup with a MPPT controller..

Would it do harm to the batteries to have two of them outside on the tongue and 2 inside the trailer?

Also is this a too good to be true deal?
MorningStar TriStar TS-45 Solar Panel Charge Controller | eBay
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Old 08-23-2011, 11:53 PM   #2
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I don't see why. How would it hurt them. Unless you leave them out in the cold like I do. But mine still made it. they get cold inside too.
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Old 08-24-2011, 09:39 AM   #3
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I would think you would be ok as long as you sorted out any venting issues (if you don't already have a trailer setup for "interior" batteries. You would also want to make sure you used heavy enough cable (6?8? gauge) to interconnect them. The only other problem I could see is the controller not being able to optimize the charge due to the temperature variations between the interior and exterior batteries. I am sure some other folks with direct experience will chime in with their thoughts.
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Old 08-24-2011, 12:15 PM   #4
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The question is what you expect to get by adding a couple kWh of total energy capacity.

The rule of thumb is at least a watt of solar per pound of battery. With 4 batteries, that'd mean a 250 watt solar system or better. Even that much solar isn't going to be very vigorous in battery charging and that tends to impact age expectancy adversely.

Soyboy has a good point on the impact of environmental conditions. This would be especially important when batteries are not being used and under maintenance charging - and battery maintenance techniques are a weak area of many solar charge controllers (I see some of the newer ones are beginning to address this).

When it comes to electrical energy storage in an RV, the options are limited, the amount you can carry is limited, and there are no magic bullets. Take care when seeking one as it can be a fun hobby, rather expensive, but not likely very fruitful.
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Old 08-24-2011, 12:30 PM   #5
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We are planning on fulltiming in the Airstream for a year or two, so more than a hobby for now. 250-400w is what I am aiming for panel wise. That should fit no problem. The issue seems to be where to put 4 batteries on my 25'. Looks like the simplest and easiest way would be to modify the tongue to hold 2 and build a battery box under the middle of the front couch for the other 2. I will got the AGM route since they will be inside.

Thanks
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Old 08-24-2011, 12:32 PM   #6
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Originally Posted by timmaah View Post
Assuming I have a solar setup with a MPPT controller..

Would it do harm to the batteries to have two of them outside on the tongue and 2 inside the trailer?
I'll leave aside the general problems with safety and venting for batteries inside, and the possible weight distribution problems with batteries on the tongue.

The problem with having some batteries inside and some batteries outside is that the battery temperatures may differ and that will cause either overcharging of the warmer battery or undercharging of the cooler one. You will want to place the temperature sensor for the MPPT controller on whichever battery you think will run the hottest.

The temperature difference only becomes a big deal if the difference is large as might happen if you use the furnace during sub-freezing weather. AGMs with their greater potential for damage due to overcharging would be somewhat more of a problem.
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Old 08-24-2011, 12:49 PM   #7
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If separating the batteries may cause issues, having them inside is supposedly frowned upon, and then issues with tongue weight; where does one put the batteries?

Obviously there has to be some tradeoffs. Ranking the tradeoffs is what is I'm trying to figure out.
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Old 08-24-2011, 01:39 PM   #8
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If separating the batteries may cause issues, having them inside is supposedly frowned upon, and then issues with tongue weight; where does one put the batteries?

Obviously there has to be some tradeoffs. Ranking the tradeoffs is what is I'm trying to figure out.
Mine has a battery in each of the stock locations accessible from the front of the trailer, plus a third one in a battery box behind the propane tanks. I have no idea where I'd slap a fourth one.
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Old 08-24-2011, 02:38 PM   #9
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I was going to do the same thing with my batteries upon solar install ... and also considered putting two or three in the bed of my truck with 4/0 welding cables and a quick-disconnect plug to connect / disconnect them from the system.

But Lewster talked me out of it, for the reasons that Soyboy and Jammer allude to ... a good charging system these days takes into account the battery temperature, and you likely will have one temp. sensor ... so do you put it inside or out? Either way, one set of batteries is gonna' see overcharge conditions while one set sees undercharge. May or not be significant, depending upon the temp difference between inside and outside. I panned to (and do) boondock a lot, so there is often a big difference ...

So the solution Lewster came up with was to put three AGM batteries under the shelf under the sofa. So far (2 years), this has worked well for me, in all sorts of climates. I've got 2 panels on the roof ... either 130 watt or 150 watt (can't reember and too lazy to go look it up) and they always manage to keep the batteries up to snuff. In sunny weather, no matter what I've been doing overnight, the batteries never get below about 85% charge, and are always fully charged by 9 or 10 a.m. If it's winterish and somewhat overcast and/or I'm parked in partial shade, and I've been running furnace and lights a lot overnight, sometimes the batteries get down to 80% or so, and seem to be fully charged by noon or a little after.

So for two years, I've never used my generator. I run: Fantastic Vent, Fantastic Endless Breeze fan, refrigerator and water heater circuit boards, lights (all LED), bath and kitchen vent fans, stereo, small 15" (?) tv with built-in DVD player, computers, printer, phone chargers, air compressor the few times it's been needed, antenna booster (that thing's a power hog!), small inverter that runs chargers for the DW's odd cell phone and for 14.4V power tools ... can't remember anything else. I do NOT use a big inverter to run coffee maker, hair dryer, vacuum, etc. Sure works for me.
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Old 08-24-2011, 04:11 PM   #10
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First, when connecting the batteries in parallel, you want the wiring to be equal length (actually equal resistance) between the two parallel sets so that the current is balanced:

SmartGauge Battery Wiring Examples
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Old 08-24-2011, 04:15 PM   #11
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AirsDream..

Your usage sounds about the same as what ours would be. What size batteries are you using? And how do you have them mounted?
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Old 08-24-2011, 09:19 PM   #12
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Tim:

FYI, my setup on my '99 28' Safari consists of 2 Trojan 6v T105 Golf Cart Batteries mounted on the tongue where they stock battery was located. I found a plastic battery box that would fit in that space and hold the two batteries, had a small metal frame built to hold the bottom of the plastic box in place. It fits fine between the propane tank cover and the body of the trailer. I run a 100 Watt and a 50 Watt AM Solar panel with a Morningstar Controller.
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Old 08-25-2011, 08:02 AM   #13
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The ts 45 is an PWM controller I would put in an Mppt controller. If you buy an Mppt controller by a good one. Get a Morningstar Mppt or a Rogue. These are somewhat inexpensive for the effieciency. I would not recommend a BZ controller, I've heard on the AZ wind and solar forums that they are less effecient that a PWM controller.
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Old 08-25-2011, 08:18 AM   #14
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Ah... that is why it was cheaper. I was trying to compare it to the MPPT model.

It is odd they would name it so similar with mostly the same design.
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