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12V Solar Charger + Battery Capacity + Meter

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doublereefed
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167 Posts

Initially Posted - 05/03/2016 : 22:09:52

I need to replace the 12V solar charger that came with the boat. It's old, I can't find specs for the output capacity. Shopping West Marine I see this 5W 12V and it says it will charge the battery. My thought/plan is to just plug this in and leave it on the cockpit floor when I leave the boat. Any advice on this?

This is an impossible question I know... but how long with the battery last when using the cabin lights at night, with the anchor light on, running lights, etc. Could I leave the running lights and anchor light on all night?

My 6HP outboard is electric start and has a generator. It will be interesting to see how well that charges it when in use.

Finally, is there a battery capacity meter that would be useful?

Thanks,

-Richard

'95 C250 WB #61
Midway, UT

Tomas Kruska
Admiral

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Czech Republic
522 Posts

Response Posted - 05/04/2016 : 01:19:14

We do need a small compressor fridge on board, however I've found out that 50W panel is not enough to be shore power independent so I just bought recently two 20W additional semi-flexible panels in addition to my existing 50W panel.

Regarding the solar charger, definitively buy MPPT kind like Victron Energy BlueSolar MPPT 75/10 or similar. It's not cheap but suitable for boat use.

The best battery monitor I know is also the Victron Energy BMV-700 series, see my blog about it or this wonderful site.

Dalpol Phobos 21, 2013, Sole Mio, hull #27, current adventures - We sail Phobos 21

PO of Catalina C25, 1978, High Anxiety, hull #701, SR, FK, L-dinette, inboard diesel Volvo Penta MD2010C w/saildrive - more info

Edited by - Tomas Kruska on 05/04/2016 01:25:38

TakeFive
Master Marine Consultant

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2269 Posts

Response Posted - 05/04/2016 : 02:09:15

5 watts is way too small to provide any charging of a drained battery. It's basically a float charger that will counteract the natural discharging of a battery that is in storage. It's a nice size because you don't need a controller, since there's no chance of overcharging. Whether it's right for you depends entirely on how much motoring you will do and what your electricity consumption patterns are.

For monitoring, you can go high end or lowball. Personally, most are just voltmeters, so the only question is how you want to hook it up. I use one of these:

Rick S., Swarthmore, PA
PO of Take Five, 1998 Catalina 250WK #348 (relocated to Baltimore's Inner Harbor)
New owner of 2001 Catalina 34MkII #1535 Breakin' Away (at Rock Hall Landing Marina)

OLarryR
Master Marine Consultant

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USA
3367 Posts

Response Posted - 05/04/2016 : 09:49:54

Agree that a 5 watt solar panel is only enough to trickle charge the battery with no significant loads on the battery. A 10 watt would be needed in addition to trickle charge the battery, running the depth finder/fishfinder and perhaps an evening or two utilizing the running lights. I have a 20 watt panel for charging two batteries, running the fishfinder and occasional use of the running lights during a couple of hrs of the evening, hardly ever use the anchor light, maybe once a week use of a running a mini-boombox and infrequent use of the cabin lights and deck light. My boat is in the slip all year-round and I never have to charge my batteries by bringing them home.

You have listed what could by significant loads indicating leaving an anchor light and running lights on all night and for how many nights ?
The best way to figure what size panel is to calculate your loads and then calculate conservatively what your solar panel will generate during the daylight hours considering perhaps 2 days a week of overcast/rain days of no charging. A 20 watt panel will produce, ideally, about 1.2 amps but that is with sun directly overhead and in reality, depending where you live and characteristics of your specific panel, you may only get a max of .8 amps/hr out of it. If you figure conservatively , 3 hrs@.8A, 2 hrs@.6A and 3 hrs @.4A, a 20 Watt panel will produce ~4.8A, let's say 5A/day for 5 days =25Amps.
Then calculate your loads: Figure for trickle charging 1 battery, a battery loses a bit more amps in the summer (.5A) vs winter (.25A). That's for a flooded battery. (A Gel or AGM loses a bit less amps per day.) So trickle charging for a week in the summer, figure you need to ~3.5A. A 20 watt recharges conservatively, based on the above (w/2 days no charging), about 25A, so that leaves about 21.5A per week for your anticipated loads. Next, I would calculate based on the bulbs you have for cabin lights, running lights and the anchor light and expected hrs to be used each week, what those loads in amps total. I forget exactly but believe the festoon (incandescent bulbs)use about .7Amps/hr. So, for one bulb on from 9pm to ~ 7am is 10 hrs for a load of 7A per night !!! That means you can run approximately 3 bulbs for 21A and that is for only one night per week and a 20 Watt panel should be ale to handle that. But that is not including cabin lights for a few hrs nor a fishfinder.

Now you may get a bit more juice out of a 20 watt panel than what I conservatively estimated above but it is best to be on the conservative side. Also, if you change your anchor light to an LED and same goes for cabin lights and running lights, that will cut your loads significantly. Cabin lights are the easiest to change out to LEDs. You can change out the anchor light and running lights to LEDs but then you have to decide if you go with a so called equivalent LED that does not "officially" meet the USCG regs but many have gone that route or do you pay the bucks and get USCG LED anchor and running light fixtures. I replaced my anchor light with a photo-diode (shuts off automatically at morning daylight)LED USCG Anchor light that uses...can't recall the amps but probably in the neighborhood of .15-.2A LED vs incandescent .7A/hr and so you can see it reduces the night-time load quite a bit. Changing all the lights to LED makes the use of a smaller solar panel and more nights running the loads possible. So, you have some figuring to do.

Also, once you get above a solar panel's rating that only trickle charges a battery, then you have to add a solar controller to the circuit to ensure you do not overcharge the batteries when you do not use the anticipated daily loads. My website has details of my 20Watt panel install. As mentioned above, if you really are using significant loads for frequent nights each week, then a larger panel will be necessary. Going with LEDs and figuring out accurately just what your weekly load usage is likely to be will assist in making the right decision on panel size.

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

OLarryR
Master Marine Consultant

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USA
3367 Posts

Response Posted - 05/04/2016 : 15:53:46

I read your posting again and have following addl to add:
If you run the anchor light, running liights on all night, for one night, that's 1 anchor light, 2 bow running lights and 1 stern light and if all are the festoon incandescent bulbs, that is 4x ~ .7A = 2.8A and if really all of them overnight, figure 9pm - 7am (10hrs, that's about 28 Amps. Your battery can handle that drop in capacity but then if you add a cabin lights, depending on how many bulbs on, that is a significant drop in battery capacity. You should never drop too much in capacity before recharging. I forget what the rule of thumb is...maybe not more than 40% but I could be off a bit. Also, you have to figuRe that you probably were using your depth or fish finder during the sailing hrs. But there are many factors. Many would only keep an anchor light on at night and then have cabin lights on at night for perhaps 4 hrs and not al of them. Also, many have
E switched to LEDs for cabin lights and they draw much less amps. If you ran loads overnight of aboUt 20-30 amps, you then have to consiider what is the capacity of your battery - what percentage will one night run down the battery. If it is sunny the next few days and you have a 20 watt panel and you do not use loads during the next few days, then your battery can mostly or fully recharge. Definitely, if you are using LEDs. But if you have incandescence, use loads for more than one day/night and really are going to keep those running lights on all night besides the other loads, you rare going to need a large solar panel.

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

doublereefed
Navigator

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167 Posts

Response Posted - 05/07/2016 : 20:25:13

Thanks for the help guys. And apologies for the delay. I should have mentioned my use of the boat. Basically sailing after work, and maybe we few overnights camping on the hook on the lake. Fish finder draw for the most part, other than at night for use of the lights. I think I'm going to cheap out and see it if works. I'll get a 10W solar trickle charger and see if it keeps up after the daysailing. For the overnight we'll see how it goes, see how much motoring I do. Worst case I can take the battery home at the end of the trip and charge it.

Thanks!

-Richard

'95 C250 WB #61
Midway, UT

Voyager
Master Marine Consultant

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USA
5231 Posts

Response Posted - 05/08/2016 : 19:28:58

I find that with a 30W solar panel, it takes all week to recharge my Group 27 battery from 40% discharge to fully recharged. It generates about 1.5A in direct sun.
Since I motor in and out of the harbor, my 12A alternator can replenish the battery much more quickly than the solar panel.
Adding to this... It's best never to allow your battery to remain discharged for any length of time, as it will shorten its life dramatically. A process called sulfation occurs when the battery remains discharged. This causes a hard crust of Lead Sulfate to overspread the lead plates, thus reducing the surface area of the plates. Over time this reduces the reserve Amp Hours (AH) or capacity of the battery.
It's best to replace the charge as soon as possible to reduce or eliminate sulfation.

Bruce Ross
Passage ~ SR-FK ~ C25 #5032

Port Captain � Milford, CT

Edited by - Voyager on 05/08/2016 19:34:02

doublereefed
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167 Posts

Response Posted - 05/08/2016 : 20:04:38

Bruce, thanks for that advice. So is a 30W charger OK to leave plugged in all the time? I've read a bit... I can't really tell which size panels are safe to leave on a trickle charge without a smart charging device. Or, do I need to bite the bullet and get a smart charger that the solar panel plugs in to?

Thanks,

-Richard

'95 C250 WB #61
Midway, UT

doublereefed
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167 Posts

Response Posted - 05/09/2016 : 08:34:52

I found this online, a few other sources gave similar advice. So, I think I'll go with a larger panel (30-40W as you suggest Bruce) with the charging circuit:

"Anytime you use a panel that is over 5 watts rated output, we recommend using a solar controller. Actually, a charge controller is a good idea in a majority of applications. A charge controller can provide several benefits such as preventing overcharge, improve charge quality, and prevent battery discharge in low or no light conditions. Some solar panels are made with blocking diodes pre-installed that prevent battery discharge during low or no light conditions. In most case where a 6-watt or larger solar panel is installed use of a charger controller is highly recommended. In a nutshell, solar charge controllersact like an on and off switch, allowing power to pass when the battery needs it and cutting it off when the battery is fully charged. Something to be aware of when selecting a controller is that they are typically rated in amps, while photovoltaic panels are typically rated in watts. So the morningstar SS-6, 6 amp controller will work with nearly every panel we sell right up to about 70 watts. - See more at: https://www.batterystuff.com/kb/articles/solar-articles/solar-info.html#sthash.4cXqZKSV.dpuf"

'95 C250 WB #61
Midway, UT

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