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Old 06-30-2019, 02:16 PM   #1
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Solar powered battery charger

For reasons that are immaterial I would like to not use the shore power at my marina when I am gone. But I would like to keep a floating charge on the batteries. I was thinking about a solar powered battery charger and wondered if anyone might have some experience/recommendations.

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Old 06-30-2019, 02:40 PM   #2
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Do you want just a trickle charger or solar power to run stuff.
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Old 06-30-2019, 02:42 PM   #3
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Do you want just a trickle charger or solar power to run stuff.
Probably a good trickle charger would do it.
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Old 06-30-2019, 03:13 PM   #4
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I used a 100 watt panel to keep my batteries up when I was docked on a mooring for a season. A 100 watt panel is only a few bucks more than a small 10 trickle charger and lets you completely recharge the battery over the week if you come in with partially discharged batteries on a weekend.


I wrote several articles on solar power that are in the Library section. One change to consider is that Victron is now selling very competitively priced MPPT chargers at not much more than a Morningstar PWM charger. The MPPT controllers produce about 15% more power.


You should be able to put together a 100 watt panel and the Victron controller for about $200 including cable.


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Old 06-30-2019, 03:25 PM   #5
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how many batteries


do you have room to mount a solid panel someplace?


Or a flex soft panel


If you size it right you can run a small exhaust fan to move air thru the cabin to keep it fresh.


the post above recommended a 100w panel which may do fine but they are so cheap a 150W will give you better charge if it's overcast several days in row and will power a fan.
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Old 07-01-2019, 06:25 AM   #6
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Depending on the location for the panel the largest that fits would be my choice.

You will need a charge controller that is easy to adjust.
Dockside the float voltage would be lower say 13.2 to conserve water .
Cruising a higher voltage would assure a full 100% charge to give better battery life.

I would install a bilge pump or a sinking alarm to notify others of a problem.

A shore power cord and a battery charger might keep your boat afloat , but a battery only system will probably run out of power the first night.
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Old 07-01-2019, 08:37 AM   #7
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A shore power cord and a battery charger might keep your boat afloat , but a battery only system will probably run out of power the first night.
Depends a lot on how much your boat leaks. My wooden boat does take on some water and my pumps run periodically. My 100 watt panel with a Victron MPPT controller keeps up with the pumps just fine and maintains my batteries at full charge. I do not have shore power.


As far as the bilge pumps go, if you have an actual hole in the boat, they won't keep up no matter where the power is coming from.


My wooden boat leaks quite a bit when it is first launched each season causing my pumps to run every 10 minutes or so for 8 seconds right after launch. I have two pumps that draw about 9 amps together when they run. That works out to under 3 amp-hr per day. My 330 amp-hr battery bank can handle that for about a two months before the batteries are depleted much below 50%. Even if my pumps ran once a minute, my batteries could handle the load for about 5 days before going below 50%. Note that my leak rate starts slowing down within minutes of launch and stabilizes at 1-2 bilge pump runs per day after about a week.


A 100 watt panel will maintain batteries just fine. On sunny days in the summer a 100 watt panel has the capacity to produce around 40-50 amp-hr and even on cloudy days will produce 5-10 amp-hr.


An MPPT controller will only provide the current needed to maintain the batteries at float voltage no matter how big the panels connected to it are. In my experience, floating a several hundred amp-battery bank at 13.8 volts but only enough current to maintain float voltage will not cause significant water loss from flooded batteries over the course of a season.
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Old 07-01-2019, 08:56 AM   #8
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For David -
Would you just connect the panel directly to the battery (thru the controller of course)? How about for maintaining a battery bank? (you can tell I'm new at this)
Thanks -
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Old 07-01-2019, 10:05 AM   #9
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batteries on solar tend to need more fluid checks


I run 8 6volt RE (made for solar) they get topped up every two months or so
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Old 07-01-2019, 10:17 AM   #10
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Thanks for all the replies, and the useful info. I ordered a DuraVolt 20-watt 1.0 amp solar charger from Amazon. Although I have two battery banks, I just ordered one charger, figuring that I can put the battery switch on BOTH and that will parallel the two banks.

Since I am in a slip at the marina, and can always hook up the shore power when I am down there, I can run the regular battery charger every now and then if needed.

The suggestion about a small 12-volt fan to keep the air moving is a good one, and I will do that.
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Old 07-01-2019, 10:25 AM   #11
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For David -
Would you just connect the panel directly to the battery (thru the controller of course)? How about for maintaining a battery bank? (you can tell I'm new at this)
Thanks -
Joe C.

The simplest way is to connect the controller directly to the house battery bank but through a 15A fuse at the battery. You could also connect it through an unused 15 amp breaker on your DC panel and it would back feed the battery. The breaker or fuse would protect the wire from the controller to the breaker or battery if it is at least 14 gauge which it should be for a 100 watt panel.


Yes, this should maintain the battery bank.



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Old 07-04-2019, 08:44 AM   #12
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batteries on solar tend to need more fluid checks


I run 8 6volt RE (made for solar) they get topped up every two months or so

I also have 8 6V golf carts (East Penns) that almost never need water. I water them at the end of each season. What I did after installing my panels and Victron controller was to set the float to that recommended by the battery company. Might be worth checking your float voltage setting.
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Old 07-04-2019, 11:11 AM   #13
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Would an ACR, automatic combiner, keep 2 banks charged ??
I'd guess if the voltage from the solar control was high enough it should connect them.

Really if the only thing on the starting batteries is the starter not too much need to charge both banks. Should hold a charge a long time. Months ??
House bank would be the only one drawn from and needing recharged.
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Old 07-04-2019, 12:38 PM   #14
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I also have 8 6V golf carts (East Penns) that almost never need water. I water them at the end of each season. What I did after installing my panels and Victron controller was to set the float to that recommended by the battery company. Might be worth checking your float voltage setting.

This raises a question I was thinking about a while ago....

Lifeline gives a float charge range of 13.2-13.4v. Over years of being left on a charger at float, would 13.4 be harder on the battery than 13.2v? Also, what would be the long term affect of a float charge of 13.0?

I know that many are rolling your eyes at my questions but... Sometimes it really is interesting and useful to know how many angels can dance on the head of a pin.
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Old 07-04-2019, 01:13 PM   #15
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Every battery maker has published specs, you need to go by them
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Old 07-04-2019, 01:17 PM   #16
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Would an ACR, automatic combiner, keep 2 banks charged ??
I'd guess if the voltage from the solar control was high enough it should connect them.

Really if the only thing on the starting batteries is the starter not too much need to charge both banks. Should hold a charge a long time. Months ??
House bank would be the only one drawn from and needing recharged.

A combiner or ACR connects two battery systems when the voltage on one of them is about 13.2 or higher. These are simple set and forget solutions to keeping the starting bank charged from a single shore power charger or charging the house battery from the engine's alternator.


Victron has a new 120A one for less than $50 on Amazon.



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Old 07-04-2019, 01:20 PM   #17
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I researhed solar installs a lot on boats & for my RV, mixing two banks with different configs was always not recommended


So maybe there's some new be cautious
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Old 07-04-2019, 04:06 PM   #18
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I use a 250 watt solar panel to keep my house and start batteries topped up. During the summer, it puts out enough to keep the beer cold in a small Waeco fridge as well.

All charging is direct to the house bank and then to the start battery via and ACR. All batteries are the same type/size deep cycle AGM's. I have no issues starting my little 42 hp engine with a deep cycle battery.
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Old 07-04-2019, 04:52 PM   #19
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In an ideal world you wouldn't mix FLAs and AGMs much less Gels and you wouldn't mix old and new batteries of the same type. In practice I have found it doesn't really matter except for Gels which have quite different charging parameters.

You should set your shore power charger whether it has 1, 2 or 3 outputs to the parameters that the manufacturer recommends for the largest bank, presumably the house bank. Why? Well it is cheaper to replace just one starting battery than multiple house batteries if the slight difference in charging parameters harmed it any.

But it won't happen. Also for most shore power chargers the 2 and 3 outputs get exactly the same charging parameters that the 1 gets. You can't set them differently. So you compromise.


The same is true of the engine alternator which is often hooked up to the starting battery. 95% of the time it is a fixed voltage internal regulator set at about 14 volts that isn't optimum for any battery type. So you just live with it. If it does have an external regulator and you spend lots of your time cruising to your next destination, then I would probably set it for the house bank rather than the starting battery which it almost always is hooked to. Same reason as above. When the combiner/ACR/1,2,all switch kicks in, start and house are all tied together.

Batteries on boats are a compromise and so are charging voltages, but it rarely matters much.

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Old 07-04-2019, 05:53 PM   #20
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Every battery maker has published specs, you need to go by them
Yes, you are correct. Obviously I was a bit vague in my questions.

Lifeline gives a range of 13.2-13.4 for float voltage. What I'm wondering is what difference there is at either end of that range.
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