solar

I don't know how much power a 15WATT Solar panel produces but a 120WATT Solar Panel only produces up to 14.4VDC @ 5 AMPS from its solar controller when in high sun during the day.

Not a whole lot of battery charging power.

My RV Trailer consumes around 1-2AMPS 24/7 with its so called parasitic drain running the sensor panels here and there including the propane detector. We always have a night lite going as well...

If the furnace blower ever kicks ON the blower fan consumes between 6-8AMPS DC current.

Not surprising that a 15WATT solar panel only charging during the high sun portion of the day would keep up with battery usage at night.

Roy Ken

I only wanted something like a batt tender. Not using solar to completely charge the batt or run thing on just keep the batt from losing charge while sitting in the back yard for long periods of time. There is no usage anytime it is stored. cutoff swith is off. And it is in the + side so there is no drain. Like I said just a maintainer. While camping I don't need it. In full sun it puts out about 18v @ 7amps. Thanks for the response.

64thunderbolt wrote:
...In full sun it puts out about 18v @ 7amps. Thanks for the response.

A 15W panel would only put out about 0.8333 amps when the panel voltage is 18 VDC.

64thunderbolt wrote:
I have a small 15w panel & 7 amp controller just for maintaining between trips. Is it possible for it to drain @ night? I have noticed that my batt voltage is less @ night than during the daytime in full sun. Thanks for any opinions. I don't remember the mfg of the unit. I just wanted a trickle charge when not in use.

At night the batteries are not being charged (where they will be over 13v) but are going back to regular 12v levels so naturally they have lower voltage at night.

Roy, a 120v solar panel should do more like 7.6 amps aimed a high sun using a PWM controller. With MPPT it might be more or less than that depending on panel temperature

OK that is what I was looking for. It is working as designed. I am just trying to save my batt. Before leaving on a trip I always plug it in to shore power to cool the fridge & top off the batt. It is a toyhauler with a 4K Onan & 2 GC2's so power while camping is a non issue. Thanks everyone

Yes the voltage will always drop at night as you have no power. You might see 13.5 during the day but will always drop to ~12.7 overnight. With 15w for storage you really need to have all loads disconnected. Typically I would recommend 40 to 100 watts for storage. Even if you had 1000 watts the voltage would still drop off at night.

smkettner wrote:
Yes the voltage will always drop at night as you have no power. You might see 13.5 during the day but will always drop to ~12.7 overnight. With 15w for storage you really need to have all loads disconnected. Typically I would recommend 40 to 100 watts for storage. Even if you had 1000 watts the voltage would still drop off at night.

As I said the cut off switch is in the + side so there is NO load & I am in Az so sunlight is not an issue. My batt are always ready just wondered about the voltage @ night. It is always about 12.7/12.9.

Thanks everyone. I have my answer.

V should drop to about 12.73 while still dark, right before the sun comes up and the panel starts making juice again. You might see 13.4V by 1,2 or 3 pm in the afternoon, when the panel is making and charging the battery.

Surface charge is what cause the V to be a little higher as the day comes to an end or the panel stops charging from sunlight. That tends to dissipate every night, back to 12.73V in the early morning.

In my motorhome, I installed a "E-Meter" and it shows the amp draw all the time. Basically the CO meter, propane detector and refrigerator draw about 1.2 amps 24/7. This adds up to about 35 amp hours per day, and that is about what one of my 120 watt solar panels will put out in a normal day.

I would suggest a larger solar panel.

SunElec.com

Of course your battery is being charged in the daylight, thus a slightly higher voltage than at night.

My guess is you will be really happy with a 100 - 150 watt solar panel. If you get a 12 volt panel, then the controller you have will work with it. It can handle a 100 watt panel.

The 15 watt panel can not overcharge a decent size battery bank, so you can leave it connected all the time. The main charge controller will probably turn on each morning, and shut off by around 9 am when the battery voltage goes over 13.4 volts. Then the 15 watt will keep charging all day long, and the main controller might only come on once in a while for say 10 minutes to bring it back up to 13.4 volts again.

While camping then the controller will keep the 100 watt panel on all day long, and the CO meter, refrigerator and propane leak detector will be consuming the power just about as fast as it is made.

You will be able to dry camp in silence, and save $10 or more per night over full hookup campgrounds, many times in a area that has much better views too! I figure that I paid for my $3,000 solar system many times over by saving $10 a night for 300 nights. Back in the 90's a 45 watt panel was over $350, while in 1997 a 75W was on sale for $375. Then in 1999, I bought the pair of 120W for $429 each. Now you can buy a 120 watt for less than $150!

Fred.

Golden, my little solar maintainer is wired directly to the battery's. Battery cut off is in the pos cable & is off so NOTHING is drawing. I only need it to keep them fresh while it is stored. I do not need the power for anything else. So far everytime I get ready to leave they are @ 12.8 or so. I simple asked a question about the nighttime. I have heard that some controllers will draw from the battery's @ night. I wasn't sure about that but it seems that I am only losing surface charge. Thanks for the reply.