Maintaining batteries with solar charger

[davidh82]

Hello all!

I'm looking for some advice on how to maintain my Sundancer 240's batteries while the boat is trailered.

Charging hasn't been a concern because in the past the boat was kept in my backyard. If I didn't use the boat for more than a week or two I would plug in the charger for a couple days to maintain the charge.

Recently I've had to start keeping the boat and trailer at a storage facility. Since I don't have access to power where the boat is stored, I'm unable to periodically charge the batteries as before.

As a solution, I've been thinking about using a solar charger to maintain the batteries and have come across this device from Battery Tender:

http://www.batterytender.com/Solar/15-Watt-Solar-Tender-Charger-With-Built-in-Controller.html

Does anybody have experience with either this device or something similar? I'm wondering whether or not this will meet the needs of keeping both of the batteries charged. I'm also wondering how this would be wired so that it maintains both batteries. I would also want to add some sort of quick disconnect so that I'm able to connect the charger when the boat is stored and quickly remove it when I'm taking the boat out.

As far as where I would put the panel physically, I'm thinking of rigging it to the top of the trailer guides and running the wiring through the aft hatch.

Any thoughts or ideas?

Thanks!

 

[blaster]

15 watts isn't going to cut it for maintaining two batteries. I have a 15 watt solar maintainer for the battery on my electric fence. All it does is buy time before I have to recharge the battery. If you want to actually charge the batteries, you need a bigger more expensive solar charging system that generates more power. Even then it's dependent on location, temperature, the duration of photoperiod, and the suns intensity.

 

[Skybolt]

That one is only 830ma or .83 Amps. Most battery tenders are 2A. I am not sure that one would do you much good. JMO.

 

[Skybolt]

This might do though: https://www.amazon.com/gp/product/B...rd_wg=D4j1C&psc=1&refRID=VZ28HS9JQWBDC70HGHK9

Although I don't have any experience with this brand, so I can't recommend it. But this is along the lines of what your looking for.

 

[sbw1]

Maybe Florida heat is harder on batteries than our up north temps, but I don't know anyone who would bother charging batteries on stored boat sitting on a trailer. We used to keep a Whaler tied up to our dock for our kids and did nothing. The batteries seemed to last about 3-4 years. We would store them in the garage during the winter, charge them in the spring prior to launch and that was it. No charging at all except before launch.

 

[MickT]

yes, heat is harder on batteries...

the higher the temperature, the higher the self discharge. however, charging at higher temperatures is also less efficient, and causes more water loss....

 

[davidh82]

15 watts isn't going to cut it for maintaining two batteries. I have a 15 watt solar maintainer for the battery on my electric fence. All it does is buy time before I have to recharge the battery. If you want to actually charge the batteries, you need a bigger more expensive solar charging system that generates more power. Even then it's dependent on location, temperature, the duration of photoperiod, and the suns intensity.

Hey Blaster, thanks for your input. I was worried about the wattage, but wasn't really sure what my requirements would be. Looks like I'll have to do my homework to figure out the minimum wattage I'll need to maintain my batteries.

This might do though: https://www.amazon.com/gp/product/B...rd_wg=D4j1C&psc=1&refRID=VZ28HS9JQWBDC70HGHK9

Although I don't have any experience with this brand, so I can't recommend it. But this is along the lines of what your looking for.

Thanks Skybolt, I'll take a look at that charger.

I found this link that talks about how to choose a charger:

http://www.westmarine.com/WestAdvisor/DIY-Charging-With-Solar-Panels

The formula this article claims works is to take half of the milliamp output from the charger, and that is the battery size (in amp hours) it can maintain. So, if this charger has an 830ma output, it can maintain a battery with a capacity of 415 Ah. Of course, that is mostly likely only under optimal conditions.

I'll swing by the boat today to figure out what the capacities of my batteries are.

yes, heat is harder on batteries...

the higher the temperature, the higher the self discharge. however, charging at higher temperatures is also less efficient, and causes more water loss....

Thanks Mick. I realized that heat was much harder on batteries (2 years on an auto battery is really good). I didn't realize, however, that charging batteries was less efficient and they have a higher rate of discharge. That will definitely affect the power output I'd require.

 

[MickT]

choosing a "plug-in-and-forget" type battery maintainer is very much a balancing act, charge too little, the batteries sulphate and die. charge too much, you overcharge the batteries and they die, or you drive the water from the electrolyte and they die.... and so on and so forth... the higher your ambient temperature, and the higher the humidity, the worse this balancing act gets, where if you lived where you got snowed in over winter, you could charge them once and forget them till spring...

if you get one of the solar powered jobs, make *DAMN SURE* that it has a charge controller. MPPT charge controllers are better than PWM, but PWM are fine.... (MPPT is more $, PWM is what I have, but mine limit both voltage and current.)

make sure you check and top up the electrolyte levels with distilled or demineralised water regularly - at least once a month, more often is better if you find you are going through lots of water.... if the level drops below the cell seperators and exposes the plates to air - buy new batteries.

 

[MickT]

the battery tender you first linked to will do an OK job..... but for the money the one skybolt linked to will do a much better job - to the point it just might be enough to run your beer fridge whilst you're out fishing!

the west marine link has a little misinformation in it.... did I mention charge controllers, NEVER leave a battery unattended with an uncontrolled solar panel attached - something needs to control voltage, if the solar cell is putting out 20volts, the battery will be trying to keep the voltage to about 12.8, the voltage difference (if the battery is not flat where it would charge) ends up splitting the water and driving it from the battery, in really sunny and hot weather this can kill a battery in under a week - even if the solar cell is much less than 1% of the AH rating of the battery.