Solar panels to keep coach batteries charged over winter

[casefarmri]

I am trying to get info on what size(watts, amps, volts)solar panel I would need to keep coach batts charged. I am only able to store coach at end of street at private lot an there is no outlets. Went to use slides and could not open due to batteries at 6v vs 12v. Started motor and gen to charge and they came up to 12v.
I would like to put a small solar panel on roof with suction cups to charge coach batts. The factory panel on 07 Fleetwood Revolution roof seems to be crapped out cause sure doesn't charge.
What specs are needed for basic charge and do I need a battery minder to prevent over/under charge or can I elim that? I have 4 coach batteries.
As always the experts are out there. Thank you.

[Denver_Transpla]

I had a portable 100W "suitcase" system I got when we had a travel trailer and now use it to keep the batteries charged when our motorhome is in storage.

https://www.amazon.com/gp/product/B00MGLIIQO/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

I bought a couple of mid-price jumper cables are from Walmart and spliced them together - battery clamps at one end and a 12V plug connector at the other. I cut the battery clamps off of the solar panel controller output wiring and put in another connector. I might get some ring connectors an put in a semi-permanent plug in at the battery end too.I also use this cable to power my portable macerator pump that I use to dump tanks at home.

https://www.amazon.com/gp/product/B00JZR3IEO/ref=oh_aui_detailpage_o03_s00?ie=UTF8&psc=1

I lay the solar unit flat on the ground behind the motorhome (I'm parked basically E-W in the storage site I rent and this gives me sun most of the day) The jumper cables are run along the side of the motohome to the battery compartment (We have an ACE 30.1, so its behind the front driver's side wheel). The panels are laid flat so they won't get picked up by heavy wind. I'm backed up to a spot on the boundary, so the panels are pretty well hidden. I doubt they will get legs, but you never know. Our lot is limited access and video monitored and the owner is there every day.

This keeps the batteries charged (I have 2 6V batteries, but will be going to 4). The controller that came with the system is holding 13.1 volts on the batteries

I plan to install at least 200W of solar on the motorhome roof sometime this year, and probably will add another 200W next year. I'll use a MPPT controller so I can series all of the panels and keep the wire size down to the controller.

[crasster]

Lwiddis wrote:
I'm using a 15 watt panel and built-in controler to keep my TT charged up when the cover is on. I start with a full batteries however and I don't live in Illinois. We get sunshine almost every day here in SoCal.

This is about right, especially a good quality one that comes with a float charger function.

[CA_Traveler]

Wrenching is good. I prefer full battery disconnect switches directly on the posts.
Chassis: Blue Seas 3000 1325A @ 1 Min $62
House: Blue Seas m series 300A $27

Battery monitor shunt installed first then the switch later, otherwise the switch would be connected to the battery post first. Copper straps are 3/4" flattened copper pipe. Smaller cable on the battery post is for parallel connected battery.

[Jim]

Winter weather, short daylight hours, snow or rainfall on the panels, and nightfall all conspire to reduce charging from solar panels.

Best solution, IMO, is to just carry a wrench with you, park the rig with the batteries charged, then disconnect the two grounds from the chassis and house battery sets. Done. And the batteries will be fine after weeks of just sitting...assuming they were good with appropriate specific gravity when parked.

Takes all of 5 minutes and the cost of a used wrench from a thrift shop. Three winters in Fairbanks Alaska showed this works well.

[OLYLEN]

100 watt panel at 80percent, about the best you can do, will be at best 7 amps. & amps for 4 batteries is 1.5 amps per(these are ruff figures but so is the sun time) so you are at a maintain level. And on looong sunny days you get a bit above maintain level.

LEN

[Hank_MI]

CA Traveler wrote:

Hank MI wrote:
Most small battery maintainers are 1.5 to 2 amps and do the job quite well.

Yes but they are also charging 24 hours a day while solar not so much.

I plan on about 2/3 of the panel wattage for 4-6 hours a day for my flat mounted panels. Tilted panels are an improvement. Tracking panels are another step up but very few have that capability.

A 15W panel might not keep up with the self discharge of a battery.

You may be right, I just know the small panel on our MH keeps the batteries charged as long as there is no load. I say no load, the ECM is a load but the panel seems to handle that okay.

[time2roll]

casefarmri wrote:
Another question I would like input on is this one. Is there a preferred way to connect to house batteries. I have a gang of 4. Do I connect red lead of chg controller to positive terminal on one battery and the black lead of of charge controller on the neg term of same battery? Is this the same as the pos lead on pos term of 1 batt and neg lead on neg term of an entirely different battery of the 4. Will they all get charged up with either connection I do?
Thanks all again.

As long as all are in parallel they will charge just fine. Best to connect the positive and negative from the controller to opposite ends of the stack of batteries. Your main RV connection should be same.

Also depending on your RV configuration it is best to check that the chassis start battery will also be charged. Some do automatic and some don't. Easy fix if needed. Once solar is connected a few days check in the early afternoon on a sunny day that all batteries are 13.2+ volts.

100w panel $80

morningstar-sunsaver-10-10a-12v-pwm-charge-controller $50

[CA_Traveler]

Hank MI wrote:
Most small battery maintainers are 1.5 to 2 amps and do the job quite well.

Yes but they are also charging 24 hours a day while solar not so much.

I plan on about 2/3 of the panel wattage for 4-6 hours a day for my flat mounted panels. Tilted panels are an improvement. Tracking panels are another step up but very few have that capability.

A 15W panel might not keep up with the self discharge of a battery.

[CA_Traveler]

casefarmri,

Either connection will charge the batteries. However, balanced wiring provides longer battery life and should be used for both chargers and loads. Look up the many posts and pictures on balanced wiring and see if that is what your describing in the second method.

[casefarmri]

Another question I would like input on is this one. Is there a preferred way to connect to house batteries. I have a gang of 4. Do I connect red lead of chg controller to positive terminal on one battery and the black lead of of charge controller on the neg term of same battery? Is this the same as the pos lead on pos term of 1 batt and neg lead on neg term of an entirely different battery of the 4. Will they all get charged up with either connection I do?
Thanks all again.

[Hank_MI]

femailyetti wrote:
given volts times amps is watts, then 15 be a trickle at around 1.4 amps, I vote for the 100 watts my self, with a controller. Most solar cells are not 12 volts exactly, so my math may be a little off. but you get the idea I hope.

If you're trying to charge up dead batteries a 15 watt panel won't be much good. If you just want to maintain a charge 15 watts may be all you need. Most small battery maintainers are 1.5 to 2 amps and do the job quite well. We have a small factory installed panel on the roof, not sure of wattage but due to size it can't be much. I use disconnect on house batteries, solar panel still charges batteries when they are disconnected. I then jumper the positive post of house to chassis battery. Solar panel keeps them charged up just fine as long as there is no load on them. We live in Michigan so it's not like the panel is bathed in sun all the time.

[casefarmri]

Thank you all for your info. From my reading I think the 100W panel and controller is the way to go. Thanks all.

I love this site!

[femailyetti]

given volts times amps is watts, then 15 be a trickle at around 1.4 amps, I vote for the 100 watts my self, with a controller. Most solar cells are not 12 volts exactly, so my math may be a little off. but you get the idea I hope.

[corvettekent]

OLYLEN wrote:
I'll second the 100 watts. much below the 100 and you might as well put nothing on.

LEN

X3