Question on planning for Solar - Page 2 - Fiberglass RV


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Old 06-15-2015, 05:30 PM   #15
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Name: JD
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There are two things involved and these are amps (current) and voltage. The current rating might be 30 amps but it will not flow until the voltage is high enough in relation to the impedance of the load. For example if you have a battery charged to 12 volta amd place a power supply with an output of 10 volts no current would flow into the battery.
If that voltage applied was 15 volts then current would flow. The amount would be determined by the load state of the battery and it's state of charge.
I think that the Bogart charge controller (and battery monitor) would take any source of charging current at a high enough voltage and pulse width modulate it to properly charge the battery. A MPPT controller would be slightly more efficient since it would find the optimum voltage and current for the panel as well. I don't think this would do any good for us , but it might since I think it can increase the output voltage if it has to to charge the battery.
Given enough voltage you could use diodes to automaticallytransfer to the on board charger if the solar was not producing power or more likely if the system were plugged in and available. The typical voltage drop across a diode is 0.6 volts so there would be this loss in any circuit using them. The 12 volt converter could engage a relay or contactor as well. The losses in the coil would be negligible when under shore power.
After the basic battery monitor and controller are done then the solar panels can be added at any time.
I will see if I can draw up some doodles for the electrical systems when I get a chance,
Right now I am hoping someone who had doen it or knows more than I do about solar and eggs chimes in. As above I would like to be second or third.
Also if you are waiting on me I am th the stage in my rebuild that I am finishing up cabinets, tops beds and A/C and the batteryes and charging are n the future.
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Old 06-15-2015, 10:41 PM   #16
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Question on planning for Solar

If you are plugged in why would you care if the solar system was charging?

Just leave solar controller and battery charger both connected to the battery. Do not connect the chargers output to the input of the solar controller. The battery will always be fully charged when you are plugged in, the solar controller won't do anything. When you are not plugged in the battery charger will be 'off' even if connected to the battery and the only charging will be from the panel.

My system has been wired like this for two years, works fine.


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Old 06-15-2015, 10:57 PM   #17
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Originally Posted by MCDenny View Post
If you are plugged in why would you care if the solar system was charging?

Just leave solar controller and battery charger both connected to the battery. Do not connect the chargers output to the input of the solar controller. The battery will always be fully charged when you are plugged in, the solar controller won't do anything. When you are not plugged in the battery charger will be 'off' even if connected to the battery and the only charging will be from the panel.

My system has been wired like this for two years, works fine.


Denny Wolfe
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Denny I think the issue is that in some situations the Solar can do a faster/better job of charging. In those situation one could simple unplug from power and let the solar do its thing but I think what some want not to have to do that as they might forget to plug back in at night.
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Old 06-16-2015, 07:18 AM   #18
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I posed the question on another rv technical forum, results came down pretty solidly on the "do not do it" side. The long and the short of it was that you can damage the solar controller and maybe the converter. Best plan may be to get a decent multi stage converter/charger and hook it and the solar controller up in parallel to the battery/s.

FWIW, the most I've gotten out of a single 160W 8.6A panel on a sunny summer day if 50A total here in Western MA during some testing I did last July. If I start a sunny day with more then a 50A deficit I can't recover in a day whereas I can if I were to use hookups. In this instance our WFCO 55 amp converter is faster as the charge day is longer and I can get more then 8 amps an hour out of it. Adding another panel would obviously speed up charge time via solar.
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Old 06-16-2015, 07:48 AM   #19
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Denny I think the issue is that in some situations the Solar can do a faster/better job of charging. In those situation one could simple unplug from power and let the solar do its thing but I think what some want not to have to do that as they might forget to plug back in at night.

You can leave them both hooked up all the time.


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Old 06-16-2015, 01:04 PM   #20
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You can leave them both hooked up all the time.


Denny Wolfe
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Yes Denny I am well aware of that and that is how mine has been set up for a number of years now BUT as you can see from comments above some people want to the solar to actually do the charging when they are plugged into power rather the on board charge system taking over as it does and they don't want to have to hit a switch to do it!
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Old 06-16-2015, 01:12 PM   #21
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I posed the question on another rv technical forum, results came down pretty solidly on the "do not do it" side. The long and the short of it was that you can damage the solar controller and maybe the converter.
The above would be my fear at doing what was suggested in regards to just running the onboard charger system through the solar controller.

If rerouting the onboard 110 power charging system through the solar controller was viable & beneficial I suspect we have a lot of people here who are known to be the masters of all things solar for a LONG time that would have done that. Then again perhaps one or two of them have and will speak up on the topic, assuming they are all not out enjoying camping season.
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Old 06-16-2015, 03:03 PM   #22
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call me confused

"the most I've gotten out of a single 160W 8.6A panel on a sunny summer day if 50A" (???) so is that 8.6A times 6 hours or so ???

anyway, the way this discussion is going....I'm glad I got rid of my converter in favor of a stand alone charger (on it's own breaker) ALL 12V power now comes from my batteries ALL the time....

I don't have to wonder about unplugging the trailer (or not) to charge with solar....I just flip the breaker and stay pugged in

that's the way my trailer "lives" in my backyard...plugged in to keep the firdge going....charger off...solar panels out

quite the "puzzle" this solar stuff.....lots of fun...cheers, F
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Old 06-16-2015, 05:01 PM   #23
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"the most I've gotten out of a single 160W 8.6A panel on a sunny summer day if 50A" (???) so is that 8.6A times 6 hours or so ???
That is correct Franswa, 50 amps is what I gained in a full day of full sun in mid summer.

The panel is rated for 8.6 amps, I've not seen it that high but it will hit 8 occationally. Keep in mind this is flat mounted in New England, not pointing at the sun in Phoenix.

Using the fridge as a load, I ran the batteries down 100 amps overnight then turned off the fridge.

By the end of the day solar has replenished 50 amps according to the battery monitor.
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Old 06-16-2015, 06:37 PM   #24
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I assume you mean 50 amp hours.
My Norcold draws about 40 watts on 12 volts or 40 watts / 12 volts = 3.3 amp hours and runs lets say 50% of the time or a total of 3.3 X 12 Hours (50% of the time) = 40 amp hours.
That 50 amp hours would seem to be marginal for my needs.
I hope to install 200+ watt panels and do a little better than I need to keep the Refrigerator running on Solar alone. Perhaps I need to plan on a little more rating.
The reason that the current delivered into the battery is not as high as the panel rating (for one reason) is that the voltage at the current rating is higher than the battery charging voltage pulling the panel down the curve. An MPPT controller has a DC to DC converter to translate the higher voltage at the peak of the panel and converts that to the voltage to properly charge the battery.
Bogart says the trade offs are not as serious if the battery charge is maintained closer to 13 volts and the panels are nearer normal temps and not cold.
It seems to get pretty complicated.
I think I will start with the Bogart system powered from the converter to maintain the battery in good condition when plugged in. Later I think I will add two of the flexible Renology panels to make sure I have enough keep the 12 volt system in good shape plugged in or not.
I want to be able to park the rig anywhere leave it for a day or so and not worry too much about the electrical systems. Also I want the electrical system to not rely too much on the power from the tow car to keep the thing charged.
I am also working on LED lights and I haven't decided if I want an inverter or not for the microwave etc. For cooking other than the Convection microwave I am looking at the Propane grills that hang on the side of the camper next to the door.

Redoing this Scamp os a work in progress!
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Old 06-16-2015, 06:45 PM   #25
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get it now....

sounds like you are very well equipped in the measuring tools department.....at the other end of the scale all I got is a permanent display volt meter (don't tell you much, no detail)...so I'm going by feel sorta

my fridge (large) is a 2 way...so it's either on propane or AC...besides the usual trailer stuff all I need DC for is to run the ghetto blaster, the computer and recharge gadgets....being that my needs are minimal I seem to be way "ahead of the game"... so far... with a permanent 40W on the roof (flat) and a 40W deployable.....so it's hard for me to justify, at the moment, investing more trailer bucks in more sophisticated measuring equipment....the old hydrometer checks will have to continue cheers, F
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Old 06-16-2015, 06:50 PM   #26
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For cooking other than the Convection microwave I am looking at the Propane grills that hang on the side of the camper next to the door.

Redoing this Scamp os a work in progress!
Why do you want to hang it on the trailer? You can't control where the smoke goes and your work surface is 'over there'.
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Old 06-16-2015, 07:04 PM   #27
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Why do you want to hang it on the trailer? You can't control where the smoke goes and your work surface is 'over there'.
I was unwilling to build in a cook top for the inside cabinets since I think we will be using the trailer like a mobile motel room with a refrigerator and microwave. The small barbecue is for the occasional ceremonial burning of various dead animals etc. Not for everyday use.
We thought the campground tables might not be close to the trailer where the (yet to be bought and installed) awning would give some protection from possible rain.
We plan to try to keep meals simple.
The Scamp (it seems) not too much. one change begets several more.
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Old 06-16-2015, 07:40 PM   #28
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Also confused

Now we are on to barbecues but no problem! This thread seems to me to be an exercise in futility. I agree that sometimes the solar will recharge the battery faster than the converter. But sometimes there is no sun or its night time. I agree with MCDenny. Just leave it be! Maybe take a walk, read a book, volunteer or plant some beans. It just would not be the end of the world if you forgot to plug you camper back in at night after letting the solar quick charge the battery.
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