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Old 04-19-2014, 06:14 PM   #61
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Originally Posted by ko777 View Post
Because of my TV tongue weight 350# limit, I may have to store a spare battery at the rear storage. Just connect it temporary when needed. The extra weight will help decrease my TW which I need badly. I currently have over 50# of TW limit when I travel.

What happens if you connect the spare to the weak battery in parallel, will it charge the weak one?

sort of but not a good idea as it will pull the system voltage way down.

What setup could you recommend for temporary connection of the spare battery to the TT? I assume a cut off switch is necessary for this set up.

you would disconnect the main one and hook a harness to the spare.
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Old 04-19-2014, 06:21 PM   #62
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Battery cut off switch

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you would disconnect the main one and hook a harness to the spare.

That is simulated in my diagram from previous post, it makes it easy to connect and disconnect the spare battery.
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Old 04-20-2014, 12:17 AM   #63
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Battery cut off switch

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Observation: Solar panel

Yesterday it was raining and no Sun, the TT battery was draining naturally...

Today the Sun is bright and the Solar Panel is pumping out 14.2V charging power but the TT battery is reading 12.2V.

I'll check tonight if the battery gets fully charged by the Sun.

I now know when the battery is fully charged by the solar panel, the volt meter reading spikes to 13.5V. It started from 12.2V to fully charged but took almost the whole day.

I purposely drained the battery by running the fridge using battery for 2.5 hours, it dropped to 12V. Turn on the amber light for 3 hours, it dropped to 11.8V.

At one point I had the furnace on for 10 minutes at the same time the fridge was on, it dropped to 11.2V but after I turned off both devices the battery recovered back to 12V.

Tomorrow will be another sunny day, let's see if the 40W solar panel will charge the battery to 100% from 11.8V. This time the cut off switch will be enabled, so the battery is not being drained by the TT internal devices while it is being charged.
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Old 04-20-2014, 10:18 PM   #64
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The results are in, the battery got charged to 12.4V on a full day of sun light:
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Using this chart, the battery from 35% and was charged to 75% by solar.

Luckily I have a gas generator which I'll bring in my trips but I like the idea of using solar panel to recharge the battery for free.

My challenge on my next dry camping trip is conserve energy, use the solar panel and avoid using the gas generator.
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Old 04-21-2014, 03:34 PM   #65
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Cmon, you lose valuable capacity and service life if you keep them separated. and if you buy them and use them together, they will equalize capacity very quickly. ALL of the good reference books recommend a single large house battery bank. I have had sailboats for 40 years in all kinds of situations, and been crew on long time full timers and none of them every kept separate banks, except for having a starting battery dedicated to starting the engine. If you want an emergency spare get a small separate 12 volt and keep it unconnected from anything unless you need it.

IMO, of course.
Yes, I am normally operating on the "spare" battery concept, except that the spare is the same as the regular. Whether it's a good idea or not depends upon loads relative to battery capacity. If the load is small enough that the single size 24 is adequate 90% of the time of better, then the spare concept works out well. Yes, one battery will likely out-live the other - not necessarily a bad outcome to me.

Using 2 size 27s wired through a selector switch on my outboard-powered (9 amp alternator) 25ft sailboat also worked well. Of course, a single battery could go a week or two (and did) when the only draws were cabin lights, and during an occasional night sailing, compass and running lights (6 amps draw there). Anchor light used separate 6 volt lantern battery. Quite successfully cruised the northern Bahamas for 4 weeks with only 3 nights with dock power and 3 nights sailing all night.

As has been pointed out, you cannot know a battery's charge level from a voltage measurement unless the battery has been idle for a while. In my scenario, I can measure the state of the backup, but I cannot accurately measure the battery in use.

But what would be a lot more helpful is to know the current draw of the furnace when running, the anticipated duty cycle, and the normal (furnace not running) parasitic load of the camper. Then I can make a good assessment of whether or not I need to combine the batteries for a weekend boondock. Hope to get some of these measurements on an outing in 2 weeks - our first trip was lost to a leaking propane fitting where the lines connect to the trailer plumbing.

If I truly normally need 2 size 24 batteries paralleled to handle the load for a 3 day weekend, then I should be looking at wiring upgrades to more efficiently charge the larger battery bank. Or, switch to a catalytic heater to drive the load way down.

Fred W (keeping things simple so we use the camper more)
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Old 04-21-2014, 08:42 PM   #66
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Battery cut off switch

Does the solar panel drain the battery when cloudy and at night?
The rate my 40W solar panel is going, it will never fully charge the battery.

My guess the 12.4V I got yesterday was just the surface charge. Today was mostly cloudy and the charging results is disappointing, it started at 12.1V am and now it still 12.1V pm.

The only good news is the cut off switch prevented the battery to drain.

Is it safe to store a spare battery in the back storage of the TT? During travel, can the floor handle the focus weight of the battery?
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Old 04-21-2014, 09:33 PM   #67
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There should be some diodes in the solar panels or the charge controller to prevent current back flow.
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Old 04-22-2014, 08:52 AM   #68
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For these types of solar panels, in order for them to run/charge at full potential you have to have all the cells collecting sunshine, the output will drop even if you have shade from a tree on part of the panel.
Im using an 80 watt panel ... and during cloudy days and at night i leave the entire system hooked up. There is a blocking diode in the panel itself . Some charge controllers are pretty piddly ... like the one for a 40 watt solar ... so basically its just a charge controller that cuts off and prevents overcharging of the battery.
I also have a 40 watt that i use to charge up a Xantex power box .. similar to the one in the pic provided ... but this power box is used exclusively for a CPAc machine ... when camping off line.
The nice thing about the power box is that you can plug the panel directly into the unit without a controller .. which helps deliver more raw power and speeds up the charging of the unit.

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Old 04-24-2014, 07:58 PM   #69
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Battery cut off switch

What wire size for the connector do you recommend for the spare battery?
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My revised plan, the spare battery will be my power pack. I plan to use this for emergency only when the TT battery run out in a cold night, the power pack has enough power for several hours taking care of the furnace fan, I think.
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Old 04-25-2014, 08:05 AM   #70
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you may want to rethink that again ... i have the same battery box as you do.. and it only powers my CPAC machine. In the morning the battery box is sitting at 60% charge, and requires recharging .. or attachment to the solar panel. no heat is used in my CPAC when camping .. so while these boxes are a great idea .. i wouldnt use it as a backup.
Just trying to save you some issues in the future..

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