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Catalina/Capri 25/250 Sailor's Forums

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Solar Panel w/ and w/o a Controller

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jerlim
Master Marine Consultant

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USA
1484 Posts

Initially Posted - 02/20/2015 : 15:35:59

So....we have a single 12 volt battery, that has been charged by a 6w panel for about 6 years, and all was good, except this past season, the charger wasn't really keeping up. The load is just the VHF and plotter, running for two 8 hr days per weekend.

I can either replace the 6w unit with another 6w panel, OR step up to a 15w panel, and add in a controller. Let's ignore budget for now.

The question is: Does a 6w panel w/o a controller charge the battery as well as a 15w panel w/ a controller, or will the 15w set-up work better/faster?

I just can't seem to find enough information - or the right person to speak with - to make an informed choice.

Please advise your thoughts.

Many thanks,

Jerlim

Jerry

Edited by - jerlim on 02/20/2015 15:38:59

OJ
Master Marine Consultant

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USA
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Response Posted - 02/20/2015 : 17:55:12

You might be forced to get into the math. Over what period of time are you wanting to get fully recharged? For example, our boat sits unused M-F, so we have 5 days to recharge.

Not sure I would give much thought to the charging rate with or without a controller. As you most likely know, the primary purpose of the controller is to prevent overcharging the batteries.

I didn't have the patience/time to crunch the numbers when I purchased my panel and controller last year. As panel prices had dropped so dramatically, I purchased a 30 watt panel and a 5 amp (max) controller. I know 30 watts far exceeds my current needs, but I plan to add more instruments in the near future.

Here's a nice article that will surely broaden your knowledge of panels and controllers:

Go to this link and scroll down to "Installing a Small Marine Solar System"

http://www.marinehowto.com/

Another helpful source:

http://landing.solar-electric.com/?id=102&st-t=google_&gclid=CMKh_8_t8cMCFVFp7AodX1AAGg

1989 C25 TR/WK, #5822
1973 McVay Minuet 19
1975 Jester 12
1981 C25 SR/SK, #2428
1981 C22 SR/SK,
Tanzer 16
Sunfish

"There is nothing, absolutely nothing half so much worth doing as simply messing about in boats." Kenneth Grahame

Edited by - OJ on 02/20/2015 18:12:37

Voyager
Master Marine Consultant

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USA
5434 Posts

Response Posted - 02/20/2015 : 20:32:38

Gotta agree with OJ on this, unless you're going to get into major electronics and coolers, a 30W or larger needs a regulator or else your battery will boil out over time. 30 W will deliver about 1.5A max, so a 7A regulator can handle about 90 W with some margin to spare. There's a very good article in this season's Mainsheet magazine on installing solar.

Bruce Ross
Passage ~ SR-FK ~ C25 #5032

Port Captain � Milford, CT

Dave5041
Former Mainsheet Editor

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3758 Posts

Response Posted - 02/20/2015 : 20:40:09

Keep in mind that 2 smaller panels in parallel offer the benefit of of only one panel losing 80-90% of its output if a single cell is covered by shade.

Dave B. aboard Pearl
1982 TR/SK/Trad. #3399
Lake Erie/Florida Panhandle

OLarryR
Master Marine Consultant

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USA
3480 Posts

Response Posted - 02/20/2015 : 22:12:01

a 6 watt panel only produces a max of about .4amps/hr and generally you cannot expect to get the max on a regular basis due to the sun not always directly overhead, not always sunny and there are limited hours per day when you get any charge at all. Just to do a rough order calc on this, you need to figure out what the 6 watt produces being on the conservative side and without even running the calcs, a 5 watt panel is generally what is considered only enough to keep a battery trickle charged just to recover what the battery would lose each day just sitting sround and with very little to handle any loads. A 6 watt will not produce much more than a 5 watt panel and so the fact that you have been getting your 6 watt to recover not only the battery loss each day but also some weekly loads has worked out well for you in the past.

Figure on the average getting about .25 amps/hr for about 6 hrs/day and for 5 days a week would equal ~ 7.5 amps/week charging. Meanwhile, a flooded battery (AGMs lose less) loses approximately .5 amps per day in the summer and .25 amps/day in the winter. Using .5 amps/day summer, that is a loss just sitting around of about 3.5 amps/ week. So, your 6 watt has about 7.5 - 3.5 = 4 amps per week for charging against loads for the week. If you figure out what the VHF and plotter are using up for the two days a week you use them, you can see that your 6 watt panel has been dojg very well for charging your battery against the loads you have each week.

I do not know exactly how much juice a controller absorbs if you go to a 15 watt panel but it is minimal and going with a 15 watt panel with a controller should still recharge at a higher rate than a 6 watt without a controller. Also, the benefit of a controller is not only that it prevents overcharging the battery, it also prevents some small drain that can actually go back out via the panel during night time hours.

I have a rigid 20 watt panel with a digital readout controller for charging two batteries. I also use light loads each week (VHF, fishfinder and sometimes the nav lights). My panel puts out a max of 1.2 amps/hr and has worked well for the past 10 years. My oriignal set of batteries were about 7-8 years old when I replaced them and still had life in them. What happened was that I had bought an AGM battery has a backup for my sump pump at home. I had rigged a bilge pump on a platform suspended in the sump in case of a loss of home electricity - I was concerned due to the path of a past hurricane. Turned out not to be an issue and then I had this new AGM battery lying around. I decided to buy another and replaced both my boat batteries.

Now my calcs could be off a bit - It was just a rough number without checking actually battery loss a day which could be .4 amps/day vs .5 amps/day but the numbers are pretty good. The big issue for you to decide if going with a larger panel is what kind to buy. The cheapest larger panel will generally be a larger footprimnt vs a higher quality rigid panel that could have a footprint as small as 20" x 14" for a 20 watt. So, a decision has to be made not only as to if going with a larger panel and a controller but at what cost versus footprint size and flexibility in placement. My rigid panel can be disassembled but i leave it permanently attached. See my website for details and photos.

Larry
'89 Robin's Nest#5820, Potomac River/Quantico, Va
http://catalina25.homestead.com/olarryr.html

Edited by - OLarryR on 02/20/2015 22:21:21

Davy J
Master Marine Consultant

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USA
1511 Posts

Response Posted - 02/21/2015 : 05:49:10

Could it be that the solar panel is not the problem?

Deep cycle battery life 4-8 years. Maybe the battery?

Here is a link that has lots of info on batteries and solar panels:

http://www.solar-electric.com/deep-cycle-battery-faq.html/

http://www.solar-electric.com/

Davy J

2005 Gemini 105Mc
PO 1987 C25 #5509 SR/SK
Tampa Bay

islander
Master Marine Consultant

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USA
4032 Posts

Response Posted - 02/21/2015 : 07:09:36

I agree with Davy, The culprit here might be the 6 yr old battery loosing its capacity to hold a charge. Jerry does your engine have a charge circuit?

quote:
The question is: Does a 6w panel w/o a controller charge the battery as well as a 15w panel w/ a controller, or will the 15w set-up work better/faster?

The answer is that a larger panel will charge the battery faster regardless if a controller is used. A controller is used to keep the larger panel from overcharging the battery. The smaller panels don't need a controller because they are essentially a trickle charger replacing the power that is normally lost on a daily basis and just doesn't have the amps to overcharge the battery.

Scott-"IMPULSE"87'C25/SR/WK/Din.#5688
Sailing out of Glen Cove,L.I Sound

Edited by - islander on 02/21/2015 07:42:21

jerlim
Master Marine Consultant

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USA
1484 Posts

Response Posted - 02/21/2015 : 08:25:18

As always - you guys are TOTALLY AWESOME! - thank you for your helpful insights, it is greatly appreciated.

Jerry

Voyager
Master Marine Consultant

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USA
5434 Posts

Response Posted - 02/21/2015 : 08:47:46

I'd suggest one more thing - pull your battery and take it to your local auto parts store where they can test it. If you have two or three auto parts stores nearby you can compare results, as some techs are better than others testing batteries.

I brought my battery for test yesterday and although it was completely charged to 12.6 VDC, the tech said that the battery was not holding the charge, and provided fewer amp-hours reserve than a new battery. Heuristically, I've noticed that after only a few hours of use with lights and music, the battery indicator shows a lower-than-expected voltage, showing its discharging more quickly than a new battery.

What this means is that for all practical purposes, I have the equivalent of a 40 AH battery now instead of the original 75-80 AH battery. This is due to my battery's age (June 2008) and sulfation of the plates and loss of electrolyte that occurs naturally over time.

I could try a few tricks like:
(1) replacing the acid electrolyte with new acid - this has a downside of disposal, what do you do with a quart of waste H2SO4?

(2) charging the battery at 16.4 V for 12 hours. This can reduce sulfation and can partially restore the battery

Or I could buy a new battery. West has a deal on a better Group 24 battery at $129. I have a $15 off coupon code "WMAPP" that should cover my sales tax. W*M offers an exact replacement of my current battery that has lasted 7 years for about $79.00
Hmmm....

Bruce Ross
Passage ~ SR-FK ~ C25 #5032

Port Captain � Milford, CT

islander
Master Marine Consultant

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4032 Posts

Response Posted - 02/21/2015 : 08:58:04

Jerry if you can take the battery to a local repair shop, See if they can do a load test on the battery. I think you will find that it will fail and is shot. Most 12 volt Deep cycle batteries are only good for around 300 charge/discharge cycles before they are shot. Over 6yrs I think you have reached that point. Also may I recommend if you do need a new battery that you get the largest you can. Even Deep Cycle batteries don't like to be fully discharged and are made with thicker plates to resist the damage better than a starting battery. A group 24 battery will discharge faster and deeper than a group 27 or better yet group 31. I use a group 31 myself for this reason. A battery is like your bank account but instead of money you have Amp hours. Smaller batteries equal a smaller amount of money in your account and the account will run out of money faster.

Scott-"IMPULSE"87'C25/SR/WK/Din.#5688
Sailing out of Glen Cove,L.I Sound

Edited by - islander on 02/21/2015 09:09:40

Voyager
Master Marine Consultant

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USA
5434 Posts

Response Posted - 02/22/2015 : 15:19:50

Scott -
I took your advice - swapped out my Group 24 for a Group 27 (I'm just too cheap to go Group 31!)

The 27 was about $10 more than the 24, so it made sense for 15 more AH.
I brought the battery home today - measured the voltage at 12.1 VDC. It's in my unheated garage.
I put it on the charger since they warn you NOT to let a discharged battery freeze. It's bulk charging now at 3A and I'd assume it will continue charging for at least 18-24 hours.

Doing the math: 90 AH/2 = 45 AH if the battery were at 11.8 VDC. Since its 5/8 discharged, then 5/8 x 45 = 28 AH. As the battery charges, the amperage will decline, so the average amps can be safely estimated at 1.5A. To charge 28 AH at 1.5 A it will take about 19 hours.
I assume charging the battery will also heat it up somewhat, so it should not freeze, but I will check it tonight.

Bruce Ross
Passage ~ SR-FK ~ C25 #5032

Port Captain � Milford, CT

Edited by - Voyager on 02/22/2015 15:20:20

islander
Master Marine Consultant

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USA
4032 Posts

Response Posted - 02/22/2015 : 16:51:50

Good for you Bruce, Having 90 amps available is better than having 75. Lets say you go out sailing for 8hrs and in that 8hrs you use up 15 amps. 15 amps removed from the 90 amp battery is less of a % then the 15 amps removed from the 75 amp battery meaning you didn't discharge the 90 amp battery as deeply as you would the 75 amp battery and IMO this does less harm even to a Deep Cycle battery. An added plus is that in an emergency situation your radio and electronics will stay on and working much longer than with the smaller battery or you can stay out some nice night running your Nav. and interior lights longer. Well worth the extra $10.

Scott-"IMPULSE"87'C25/SR/WK/Din.#5688
Sailing out of Glen Cove,L.I Sound

Voyager
Master Marine Consultant

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5434 Posts

Response Posted - 02/22/2015 : 19:12:41

Your logic is impeccable!
BTW, the battery is still charging.

Bruce Ross
Passage ~ SR-FK ~ C25 #5032

Port Captain � Milford, CT

Edited by - Voyager on 02/22/2015 19:20:11

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