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Old 10-07-2012, 10:14 PM   #1
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solar to batteries, direct connection?

the rv i bought came with two roof mounted solar panels, initially i thought it was not working as for past month i was puzzled by the fact that the batteries drained heavily - dropping from 100% to 96% overnight albeit both chassis and coach main switches were turned off. today i climbed up to roof and found this:

1) 2 BP solar panels 36 cells each, so total 72 cells
2) traced down the wires through a vent behind fridge all the way to battery bay
3) there is no controller; the red wire was connected to coach battery positive terminal; the black wire to negative.

i was surprised on this connection - no controller, no diodes. to my layman knowledge, during daytime the voltage could be very high feeding batteries (damaging batteries?) while at night the current could be backflow. can somebody comment if this is correct and what i need to do? much appreciated.
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Old 10-07-2012, 11:12 PM   #2
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Mine came with a charging controller so it was installed in the system as designed. The instructions claimed there was a possibility of damaging the system (batteries and all) by not hooking up the controller.
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Old 10-08-2012, 12:44 AM   #3
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Quote:
Originally Posted by Possum View Post
Mine came with a charging controller so it was installed in the system as designed. The instructions claimed there was a possibility of damaging the system (batteries and all) by not hooking up the controller.
Thanks Possum for confirming what I thought. Now I need to buy a controller at least. 72 cells (probably 60w) is too small, it could merely act as a battery maintainer I guess. Just read some very valuable posts here, most boondockers were talking about 400-500w panels... I might look into replacing the panels/wires/controller to make it a system self contained.
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Old 10-08-2012, 01:26 AM   #4
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Before investing in more solar, I'd suggest you read Handy Bob's Blog.

The RV Battery Charging Puzzle « HandyBob's Blog

He got mine straightened out.
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Old 10-08-2012, 02:09 AM   #5
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Some panels do have a blocking diode mounted in the terminal block on the back.

You say there were two panels. Connected in series or parallel. Still, regardless, it is highly irregular to connect standard 12V panels with the standard OC voltage rating of around 17V or higher directly to batteries.

You say the charge on the battery is dropping from 100% full to 96% full overnight. State of charge is a pretty rubbery figure anyway so such a small drop isn't necessarily all that significant.

(There are smaller panels with fewer cells in parallel that are designed to connect straight across the battery with no regulator)
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Old 10-08-2012, 09:34 AM   #6
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Quote:
Originally Posted by okmunky View Post
Before investing in more solar, I'd suggest you read Handy Bob's Blog.

The RV Battery Charging Puzzle « HandyBob's Blog

He got mine straightened out.
i read it last night and gained a lot knowledge i hadn't known. i might follow his suggestions. thanks for the link.
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Old 10-08-2012, 09:48 AM   #7
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Quote:
Originally Posted by Tony Lee View Post
Some panels do have a blocking diode mounted in the terminal block on the back.

You say there were two panels. Connected in series or parallel. Still, regardless, it is highly irregular to connect standard 12V panels with the standard OC voltage rating of around 17V or higher directly to batteries.

You say the charge on the battery is dropping from 100% full to 96% full overnight. State of charge is a pretty rubbery figure anyway so such a small drop isn't necessarily all that significant.

(There are smaller panels with fewer cells in parallel that are designed to connect straight across the battery with no regulator)
the connection between two panels is beneath of one panel i couldn't be sure without removing the screws affixing the panels to fiberglass; i am reluctant to do so in fear of leaking. i am guessing it is parallel. while the main switches were off yesterday at 2pm, sunlight was strong, i measured the voltage on 110v receptacles (inverter was supposedly off), it read 18vdc. did this tell something?

when i saw no controller yesterday, my first reaction was - hmmm, the installer should know what he was doing... the panel installation and wire routing appeared to be professionally done; was omitting controller on purpose?

i flipped the receipts the previous owner left to me, the battery pack was dead in interval of three years. the current set was put in dec 2010. could it be the case the solar setup damaged the batteries all along?
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Old 10-08-2012, 10:19 AM   #8
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Quote:
Originally Posted by sdlcrazier View Post
can somebody comment if this is correct and what i need to do? much appreciated.
Add a controller as close as possible to the batteries. There are 2 types of controllers, PWM or MPPT.
Examples:
PWM- Amazon.com: SunSaver Duo with Remote Meter: Home Improvement
MPPT- MPPT Solar Charge Controllers from Outback, Apollo, Morningstar, Solar Boost, BZ - Blue Sky Energy, Solar Boost 2512iX, MPPT Charge Controller, 25 Amp, 12 Volt, SB
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Old 10-08-2012, 10:31 AM   #9
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thanks lonestarace. yes i will install it right in the battery bay. looks like mppt type is the way to go (25 amp capacity gives me more room to grow).
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Old 10-08-2012, 03:12 PM   #10
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Quote:
while the main switches were off yesterday at 2pm, sunlight was strong, i measured the voltage on 110v receptacles (inverter was supposedly off), it read 18vdc. did this tell something?
With the inverter off, there shouldn't be any voltage at the AC receptacles. To measure the solar panel output, you have to measure at a DC house battery output or at the battery itself.
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Old 10-08-2012, 05:03 PM   #11
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From Bob's Blog:

"Many people with only one or two small panels would actually improve their system’s performance and not hurt their batteries if they removed their cheap, nonadjustable charge controller and connected the panels directly to the batteries. (2 or 3 amps will not hurt a 225 amp hour battery, no matter how many volts you push it with.)"

I have two portable 48 watt panels wired in parallel and directly to my house batteries without a controller. The panels put out ~6 amps and an open circuit voltage of 17 volts. When hooked to a 12 volt battery, the battery regulates the voltage down to 13 volts. Hardly enough to hurt a battery. When I used the panels on my 5er, on a good day, my TriMetric would show full charge if I was not using much more than my laptop and maybe a light.
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Old 10-08-2012, 06:08 PM   #12
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True that a small panel isn't going to do much harm, but Bob's blog specifies 1 or 2 amps and that isn't the same as 6 or 8 amps. A largish battery may require an input of 1 amp or so to maintain it in float mode so a 20 watt panel will likely be OK and merely replace the normal loads placed on batteries by clocks, radios and propane alarms.

Poke 6 or 8 amps into batteries day after day and it is very likely the voltage will rise above the optimum float level and this will cause some degradation of the battery over time. How fast that happens will depend on how much above optimal the float voltage is. At least it is only for a few hours a day rather than 24/7 so that helps.
Some people slowly murder their batteries anyway, so may consider three or four years life quite normal while others with better systems know that 5 years and up is normal.

To the OP - check in cupboard corners that there isn't a regulator installed somewhere - often near where the wires come through the roof or down the fridge vent. Very bad practice to install any electronics in the actual battery compartment (unless they are "sealed") so also check in adjacent compartments.
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Old 10-08-2012, 06:31 PM   #13
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It's not putting 6 amps in when my MH is powered up with all the sensors, radio/TV, laptop and etc is on, plus there is line loss from the panels to the battery. The 6 amps was measured right at the panels with them aimed directly at the sun, which almost never stays that way where I camp and when out and about.
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Old 10-09-2012, 12:07 AM   #14
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What size wires are you using? Any splices or other connections in the run to the batteries?
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