Solar charging maintaining help

[champdog]

Hi all, Ive got some questions. Ive been reading ALOT of posts and trying to gather knowledge of what other rvers are doing and using. I have calculated my useage while boondocking and have decided to purchase the GOPOWER 120w portable kit. Other than the propane fridge, the occasional water pump and the led bulbs, we have a 600w inverter to run a tv and dvd player. I have 2 group 31 lifeline agm's. My question is in maintaining while rv is in storage. Rv is parked outside but has a cover over it and is pretty far from shore power. I would like to charge/maintain using a small solar setup with either a single or dual station float charger. Dont want to have to set up the go power kit and leave it out for weeks or months at a time. So will one small solar panel and float charger be ok or am I better off taking cables loose seperating the parallel connection and using two different chargers, one on each battery. Looking to maintain the batteries the best way to get as much life as possible. Thanks

[Jpbeck1]

Well I know my 320 watt system on my RV is small, and my voltage meter was "cheap" at 20$, but it reads the same as my expensive hand held voltage meter, so I'm going to keep recommending it. I don't feel the need to know what the voltage is to the 5 th decimal, my small battery bank of (4) 6 volt batteries are going on 6 years old... so I feel confident in my system.



Side note: we are completely off tether from the electricity company on our home, I personally installed 22 panels and a bank of 16 batteries, I use the same "cheap" voltage meter to correspond with what my home controller is displaying.

[Almot]

Jpbeck1 wrote:
One note, don't trust your solar controller to give accurate readings on the battery charge. Buy a separate voltage meter with a shunt ($20 on amazon). Even quality controllers without a shunt plate on them are not accurate.

On the battery state of charge - correct, you can't trust controller.

On the battery voltage - yes you can, if this is a better make that has a dedicated voltage sense wire OR if the current is low, ex. in storage/maintenance mode.

The best voltmeter with 3.5 decimal points will be a very rough measure of charge. Could work in storage though. For eventual camping use you need a "monitor", something that counts AH hours in/out and gives you the net result.

Cheap voltmeters with 2 decimal points are a joke, inaccurate readings. Could read 12.60 when it's really 12.45, and readings change with time as the meter warms up and for other unknown reasons.

[Jpbeck1]

One note, don't trust your solar controller to give accurate readings on the battery charge. Buy a separate voltage meter with a shunt ($20 on amazon). Even quality controllers without a shunt plate on them are not accurate.

[Harvey51]

Artum Snowbird wrote:
I bought a two decimal point voltmeter from China and connected it to my positive/negative distribution points inside the camper. In the fall, I charge my batteries, park the rig, and disconnect one side of the batteries.

About once a month I go check on things, connect up the batteries, check the voltage, check storage cabinets outside. Been sitting for months now, batteries are at 12.60 still. If I have to, I will take my Honda 2K generator over to it, and run it for an hour.

Me, too. I only need to top up once in the long northern Alberta winter. Mine is parked ten feet from a plugin in our driveway so easy to plug in but it just isn't needed. The solar panel controller leaves the batteries Fully charged so they stay over 12.6 for a long time. When I do top up, I use a variable power supply set to maintain 14.7 volts to get a full charge again.

[Searching_Ut]

Almot wrote:

Searching_Ut wrote:

For actual charging of the batteries, the best solar charger I've seen to date is the Bogart SC2030 coupled with a Trimetric 2030 to control it.

For 12V panels in parallel and if you need a battery monitor. 12V in parallel in itself isn't always the best layout though.

Unfortunately, the bogart charge controller only works with 12 volt panels. Capability wise however it is more like a high end charger you use while bench checking batteries for high end systems using voltage, current and temp to determine state of charge when hydrometer reading isn't an option. Most Solar chargers have to make assumptions on a batteries current acceptance rate based on voltage and time since readings of current at the battery aren't available to the charger.

As for series or Parallel, on an RV where it is highly likely you'll have some of your panels shaded to some extent during part of the day, parallel is my preference. If you have panels with bypass diodes, and can keep your voltage reasonable it's also a good option, and depending on the distances of your wire runs, and how much current your moving it might be preferable. When it comes to voltage, under 60vdc I don't really have any concerns but as you start getting above that in something like an RV that doesn't have a good earth ground, your risks start going up rather quickly as the voltage climbs. Should your rig become hot with AC power you'll probably feel it but find it just an annoyance. Same 120 volts or so in DC voltage is much more likely to have negative consequences.

[Almot]

Searching_Ut wrote:

For actual charging of the batteries, the best solar charger I've seen to date is the Bogart SC2030 coupled with a Trimetric 2030 to control it.

For 12V panels in parallel and if you need a battery monitor. 12V in parallel in itself isn't always the best layout though.

[Almot]

champdog wrote:
will one small solar panel and float charger be ok or am I better off taking cables loose seperating the parallel connection and using two different chargers, one on each battery. Looking to maintain the batteries the best way to get as much life as possible.

If there is a theft risk (with portable kit) - yes, a "small panel and float charger" will do. Or not. Depends on how small and what float charger.

I don't see how and why separating two 12V batteries and using two separate chargers would help though.

[Searching_Ut]

champdog wrote:
Thanks for the replies. Im still green when it comes to solar but Im reading enough that its making me want to dive head first into being as solar efficient as possible. I have another question. In learning how mppt works it sounds like its way way better for actually recharging a battery bank. Do the mppt controllers work like a good 3 phase type float charger and if I have 12v panels on the roof in series with a mppt isnt that going to be way better than my roof panels wired parallel with a pwm controller? I have 2 group 31 agm batt's and would like to get as close as possible to never have to worry about charging with the genny or ruining my batt's. If a mppt would always be a better choice to try and achieve those goals Ill opt for the mppt. Are 24v panels a better choice than 12v if your using mppt? THANKS!!!!!!

For actual charging of the batteries, the best solar charger I've seen to date is the Bogart SC2030 coupled with a Trimetric 2030 to control it. By monitoring temp, and both voltage, and current flow right at the battery it can do some very controlled charging of your batteries, neither under or overcharging. The Bogart setup is PWM. Where MPPT controllers shine is in converting excess voltage into increased amperage. Unlike batteries and the like which are primarily fixed voltage variable current devices, solar panels are more fixed current variable voltage units. (Lost a lot in trying to simplify there) With high voltage panels, you'll be able to flow more current into your batts with a MPPT controller vs. PWM. Good solar controllers are adjustable 3 stage controllers, and at least in the case of the Bogart setup mentioned you have 4 stage charging options available.

As for parallel vs series. Myself for the most part I prefer parallel, unless you have bypass diodes in the panels and can keep the system to a single string. From what I've seen MPPT controllers don't do well with parallel wired panels if one panel drops out for shading etc so PWM tends to work better here. With parallel strings I think the best option is 1 mppt controller per string, with of course bypass diodes, or use a PWM controller for the parallel setup.

[MrWizard]

Series panels are great if your a snow bird always in the Sun
How ever if you like shade even partial shade
Then parallel panels can be the better choice
Camping in winter in the sun
Or camping in summer trying to keep the RV cool
??
Different ways, make use of different solar setups

[champdog]

Thanks for the replies. Im still green when it comes to solar but Im reading enough that its making me want to dive head first into being as solar efficient as possible. I have another question. In learning how mppt works it sounds like its way way better for actually recharging a battery bank. Do the mppt controllers work like a good 3 phase type float charger and if I have 12v panels on the roof in series with a mppt isnt that going to be way better than my roof panels wired parallel with a pwm controller? I have 2 group 31 agm batt's and would like to get as close as possible to never have to worry about charging with the genny or ruining my batt's. If a mppt would always be a better choice to try and achieve those goals Ill opt for the mppt. Are 24v panels a better choice than 12v if your using mppt? THANKS!!!!!!

[Lwiddis]

Champ, I'm trying out a 15 watt solar battery maintainer and so far it's keeping my two T125s fully charged while the 300 watt WindyNation system sleeps under a cover.

[Sam_Spade]

champdog wrote:
so I was thinking Id try to set that up via small solar panel that I could set up outside the storage cover while parked.

Keeping the batteries FULLY charged is the best way to "extend" their life. If they are indeed healthy (that is don't exhibit a large self-discharge) then simply disconnecting is good enough for 3-4 months. If they are AGM, you can extend that to 6 months and beyond.

Then.....I see absolutely NO reason to buy two solar chargers. A really good one will automatically drop to "maintain" and they are made to be outside 100 precent of the time. Don't make this more complicated than it needs to be.

Edit: Just re-read your original post. Since there are two batteries in parallel, and you don't know their condition, you should individually charge each one once, let them sit disconnected for about 24 hours and then check the voltage and specific gravity of each. This will tell you a lot about their general health. If they match and appear able to hold a full charge, then back to the two suggestions above.

Batteries in parallel need to be similar in size, capacity and health. Mis-matches can be problematic.

[champdog]

Thanks for that. I just purchased this class c. My 5th wheel had 80w on the roof. Never had to mess with or worry about it. This one has no solar at all and will be covered. Wanting to set it up in the best possible way. We boondock in heavy forest alot so thats the reason for the portable solar. My rv storage is at my inlaws property about 15 miles from me. No problem doing like you stated. I do know that a constant 3 stage charge maintainer is the best for the batteries so I was thinking Id try to set that up via small solar panel that I could set up outside the storage cover while parked.

[Artum_Snowbird]

I bought a two decimal point voltmeter from China and connected it to my positive/negative distribution points inside the camper. In the fall, I charge my batteries, park the rig, and disconnect one side of the batteries.

About once a month I go check on things, connect up the batteries, check the voltage, check storage cabinets outside. Been sitting for months now, batteries are at 12.60 still. If I have to, I will take my Honda 2K generator over to it, and run it for an hour.