Solar, Controllers, and trying to stay warm on a budget

[BStrummin]

I bought an 08 aerolite last year from a reputable rv rental operation. It is in fantastic shape, and when we bought it we noticed it had a solar panel installed already. We didn't do any boondocking with it at all last year, and I really only have one planned annual trip to the backcountry which will be next weekend. It's had several trips to resorts with connections.

I finally figured out the specs to the panel and sadly it is only an 18watt panel. Also they wired it right into the 12v system right behind the fridge with taps. I normally only haul one 12v battery with us for miscellaneous power needs on the road. This one boondocking trip will be at altitude (6,000ft) and it will be in the 20s. I'm not concerned with keeping the trailer warm all night, but it'd be nice to fire up the furnace in the am for a bit to cut the chill. The trip is roughing it trip - no kids or excess power usage either, just lights which I've already converted to led. I'll probably bring another battery with us so I'll have two at least. I've been reading A LOT about amp hours, various device loads, and solar panels and controllers.

So my questions:
1. Sounds like I can't expect much out of this panel, one calculation I found basically says 5.4ah/per day optimum. I guess this is basically a maintenance panel? For keeping up battery when not in use?
2. Is there a problem with it wired into the system? Would a cheap controller help?
3. Maybe they wired it that way just to run the fridge while on propane? Is it capable of doing that?
4. Do you think I can get away with running the furnace for 30mins/hour in the am? Only other use would be minimal LEDs and occasional water pump.
5. Would running my two vehicle (2014 f150) charge the batteries enough/or provide enough juice to run the furnace?

[BStrummin]

It's 4 days. I think it's going to be all right now - I just pulled the trigger on a 100W panel and controller. 🙂

[Majja13]

How long is the trip going to be? If only for a weekend you will be fine. Granted I run 2 6 volts, but i can run on my battery's for several days and that is setting the furnace to about 65 at night with the little ones.

[BStrummin]

Thanks for all the input. Sounds like my assumptions were mostly correct. I think I'll end up going the external/non mounted route for a new panel eventually. Good reminder about watching the voltage - I'll do that for sure. I've got a couple of extra deep cycles floating around (from the boat) and one of those jumpstarter battery packs that I'll take too.

[pianotuna]

Hi Chuck,

No one in their right mind would add an MPPT controller to an 18 watt panel. For 18 watts into twin batteries no controller is needed. Only a blocking diode is required.

Solar controllers do not run "for free". They consume some energy 24/7. Mppt style consume more than pwm. Therefore adding one to an 18 watt panel is foolish.

If the OP is serious about solar 300 watts is a good starting point.

[Chuck_and_Di]

pianotuna wrote:
Adding a controller to an 18 watt panel would only make things worse.

Not necessarily. A proper MPT controller will get the most out of the panel under all conditions, not just when it's perfectly aligned. But you do need to get a real controller, not the cheapest thing at Walmart.
I do agree that 18W won't help much no matter how efficient, but an MPT controller will get every last drop out of it.
Also, you might consider disabling some of those parasitic loads when you are trying to stretch your batteries. That will buy you far more capacity that the tiny solar panel. Disconnecting gas and CO detectors will certainly stretch the battery, but you then need to be extra vigilant. If you are really concerned, get 9V versions to use when off the grid.

[pianotuna]

Hi,

Welcome to the forums.

Adding a controller to an 18 watt panel would only make things worse.

[time2roll]

You need 100 to 300 watts to really get some charge in the battery.
Yes 18w is a good maintainer.

Some solarblvd kits to compare

Could use one of these kits as portable and direct on the battery for this trip.
Later you probably would mount on the roof.

[rexlion]

The charge line from the tow vehicle is small wire and it might recharge the battery (might) after a full day of driving. So don't depend on that method if you want to idle the engine for a half hour or so; instead, like others said, use jumper cables between the batteries.

I have a 75W solar panel and a controller, about $120. I wired it up to a 7 pin receptacle just like on the back of the vehicle. That way I can set the panel out in the sun and plug in the trailer's pigtail to it. This keeps my battery charged pretty well.

Batteries don't like to be discharged below 50%, which is 12.2V. Take a multimeter with you on your camping trip and check the battery voltage periodically (Harbor Freight has some for under $10). That way you can make sure you don't damage your battery.

[2oldman]

BStrummin wrote:

1. Sounds like I can't expect much out of this panel, one calculation I found basically says 5.4ah/per day optimum. I guess this is basically a maintenance panel? For keeping up battery when not in use? YES
2. Is there a problem with it wired into the system? Would a cheap controller help? NO. NO.
3. Maybe they wired it that way just to run the fridge while on propane? Is it capable of doing that? NO, BARELY.
4. Do you think I can get away with running the furnace for 30mins/hour in the am? Only other use would be minimal LEDs and occasional water pump. MAYBE.
5. Would running my two vehicle (2014 f150) charge the batteries enough/or provide enough juice to run the furnace?YES

[Shadow_Catcher]

The 18W panel is for maintaining the battery in storage and will not contribute significantly to recharging. A very simple temporary solution is to run a jumper cable from the TV to the trailer battery, this will contribute more to charging than the pigtail. You do not want to discharge the battery below 50%.
Our trailer is entirely powered using solar but our needs are modest.

[westend]

I'd bring some battery jumper cables and a freshly charged battery. That 18W panel will help offset any parasitic draws from circuit boards and alarms and that's about all.

[BStrummin]

Also: I'd like to put in a bigger panel and convert to the golf cart batteries but it's not in the budget and I probably can't pull that off before next weekend anyway.