I am getting ready to add a small solar system to the top of my 5er to keep the batteries topped off when we leave the camper at the lake for extended periods. My wife and I generally pull the camper out on a weekend and then leave it there for weeks at a time. We pull it to a nearby dump station when we need to dump or add water. We cycle LP tanks to keep the fridge cold.Last weekend, we returned to our camper after two weeks of leaving it unattended. The batteries were COMPLETELY dead. This seemed odd to me. I mean, assuming we turn everything off before we leave, the only draws are the LP/CO detectors and the little current draw to run the fridge in LP mode, right? So how much juice do these items consume? After doing some internet research, I found one site where some dude claimed these items add up to approximately 37Ah in a 24 hour period. I've seen other sites say the fridge pulls 17-20Ah per day by itself in LP mode. The fridge is a Dometic fridge/freezer, I don't have the model number handy but it's from 2004.Do these numbers sound right? I have 210Ah of AGM batteries installed. If these numbers are close, then that would certainly explain the dead batteries. This brings me to the solar panel install. I guess a secondary question would be, do you guys think a single 100W panel would be sufficient for the sole purpose of keeping the batteries topped off when the camper is unattended?I don't mind occasionally running the generator(s) when we are actually out there using the camper. Thanks in advance!

This dude measured 51AH down in three days leaving everything off except the fridge on gas.The fridge draws 0.5amps when the burner is lit, and the whole trailer pulls 0.3a all the time besides, so with the burner , that makes 0.8amps the fridge cycles on and off all day--in my case it was on about 2/3 the time.So in 24 hours, 2/3 of that is 16 hours at 0.8 = 12.8 AH, and8 hours of 0.3 a is another 2.4 AH total =15.2AH so that cones out about right. I guess the fridge was on a little more than 2/3 the time to make it come out to 17AH per day.So, how much solar will pull in 17AH per day? That depends on so many things. a 100w panel flat on the roof could do it easily on any nice day. What happens on not so nice days? Now you get in to the requirement to have enough battery bank to get you by until the sun comes out again.

Your parasitic drain is not less than 15AH per day. 210AHs/14days = 15+AH/day.A 100W solar system would be plenty for storage. No use getting anything smaller as the 100W panels are priced right.HTH:John

We don't know if your batteries died on the 5th day or the 14th day. Given the 37ah/day, no, 100w would be short. The maximum output of that panel is 7 amps, only for a short time, and that doesn't include cloudy days. I'd go 200.

leaving the fridge on is NOT storage modethere is no solar at nightin the 5 hrs of mid-day peak solar you have to replace every ampHr removed from the batteries during the 19hrs of low solar & no solaralso what happens if you have (2) cloudy or rainy daysyour down 30ampHrs or morehow much overhead will you have to recharge the battery banki would prefer 200 watts of Solari assume the fridge has food in iteasy to have a $100 worth of spoiled stinky food in the fridgewhen the batteries are deadyou've already experienced this once, don't go short on the solar

Feeding a battery is like having water to fight a fireEither you have enough or you don't. No gray area. I would go with a 100 watt panel.

Parasitic Draw on RV? | Good Sam Community

LipschitzWrath
Explorer
Aug 21, 2018
Okay guys, back from my first weekend with the solar. It performed every bit as well as I'd hoped. Solar harvest did go up while inhabited, but the solar system certainly seems to be capable of more. Our lifestyle is pretty obviously not heavy on 12V usage, haha.

We didn't get the generator out of the compartment at all. That is a first for us. I couldn't be more pleased.
Harvey51
Explorer
Aug 19, 2018
This is like our boondocking. We have 100 watts of solar, no generator, never plug in. The batteries never go below 80%. The refrigerator is a Norcold model N510 with no extra features like defrosting. In your situation, I would be thinking it should work with a 100 watt solar panel, and measure the total load current and where it is going. A clampmeter would be very handy.
pianotuna
Nomad III
Aug 17, 2018
Hi,

The only time the panels will send power is if a heavy load is placed on the battery bank. Then they will help support the load.
red31
Explorer
Aug 17, 2018
yes, if the batt is full with no loads then at first light the voltage will climb to abs voltage and it will take very little power to keep it there (lots of off time). During use you may draw the battery down enough so it goes back to bulk charging (no off time) and once it gets back to set pt voltage of 14.?v the off time increases.

Others may suggest that the current tapers as the battery charges but what actually happens is the OFF time increases so that the average current over time tapers.

A recent thread about

Solar wasted watts/volts
LipschitzWrath
Explorer
Aug 17, 2018
red31 wrote:
LipschitzWrath wrote:
will it "count" amp-hours harvested even if it can't use them to serve loads or charge the battery?

No, absolutely not. During 'regulation' the controller is basically an on/off switch, when it is on it charges but during regulation it maintains batt voltage, during the OFF time no power is generated.

As the battery can not accept current (cuz it would exceed set pt voltage) the OFF time is increased, this on.off @ high frequency is how the constant voltage is maintained with increasing off time as the battery gets fuller. then it regulates float voltage the same way.

So it's entirely possible that I will get out there tomorrow and it will show little/no increase in harvest compared to at home, assuming the battery is full?
red31
Explorer
Aug 17, 2018
LipschitzWrath wrote:
will it "count" amp-hours harvested even if it can't use them to serve loads or charge the battery?

No, absolutely not. During 'regulation' the controller is basically an on/off switch, when it is on it charges but during regulation it maintains batt voltage, during the OFF time no power is generated.

As the battery can not accept current (cuz it would exceed set pt voltage) the OFF time is increased, this on.off @ high frequency is how the constant voltage is maintained with increasing off time as the battery gets fuller. then it regulates float voltage the same way.
LipschitzWrath
Explorer
Aug 16, 2018
Thanks for the information, a lot to digest.

When I got home last night, the panel array had harvested more than enough power to run the RV. And that was on the side of my house where the array was partially shaded for several good sun hours due to neighboring houses and trees.

We pulled it out to the lake last night and got it set up with the intent to return tomorrow night to camp over the weekend. There are no shade sources anywhere close so I am hoping to see even greater harvest.

I know this question is probably highly dependent upon the individual controller I have (Renogy Adventurer 30A), but will it "count" amp-hours harvested even if it can't use them to serve loads or charge the battery?

For example, if the load on my unattended camper is only 20Ah per day but the array is capable of harvesting 40Ah, would my controller say that I harvested 20Ah or 40Ah?

The controller has a logging feature on the bluetooth enabled app, so when I get there tomorrow night I should be able to see what it harvested today and tomorrow.
Almot
Explorer III
Aug 15, 2018
The difference in losses btw #10 and #8 cable from 200W array (with MPPT) would be less than 0.2 AH a day. Not enough to worry about.
I couldn't justify running #8 (as opposed to #10) even with 500W array. Big arrays are so much easier with MPPT.
BFL13
Explorer II
Aug 15, 2018
With MPPT, One percent drop on output watts of 200w and battery voltage of 13v, is 15.39 amps at 200 vs 15.23 amps at 198w

Five percent drop is 14.62 amps at 190w

That output watts is after panel heat loss of 10%, voltage drop on wire, and controller efficiency loss, so the actual panel rating was more than 200w of course. (In case you wanted to do it for equivalent PWM and chose 200w unfairly :) )
Almot
Explorer III
Aug 15, 2018
BFL13 wrote:

The voltage on the controller to array wires is battery voltage with PWM, so voltage drop importance is not so clear to me. You do want the amps though.

With MPPT on the controller to array wiring, voltage drop is important because it affects the "watts in" to the controller, which then has "watts out"

1. I understand that as long as the V-drop doesn't cut below your desired voltage on the battery, it's all good. Then at some point it suddenly becomes not good at all. Series PWM installs without roof junction box are typically limited to 300W, with higher wattage people use wire #6 or better and need a J-box. Some pain... 400W with #8 "might" still let him get away without J-box.

2. Voltage drop with MPPT with RV-sized array of 24V panels is more of an academic point, it does exist but of very low importance. I run the numbers when deciding on whether to use #10 or #8 with 500W in series, and the difference on 60-something ft was 0.5% at max output. Literally a couple amp-hours a day, since most of the time it is below the max current.

Higher MPPT losses with higher voltage - that Piano mentioned - are more important.

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