2.5W solar maintainer

Apr 5, 2009
2,774
Catalina '88 C30 tr/bs Oak Harbor, WA
I am looking for a way to maintain my start and house batteries while in winter storage. I will not have shore power available and can't really afford to go to a full solar system at this time. I have seen 2.5W solar maintainers and was wondering if they would work without over-charging the batteries. I also need it for a car that is in long-term storage.
 
Feb 26, 2004
22,760
Catalina 34 224 Maple Bay, BC, Canada
Hayden,
Maine Sail has taught us to never use a solar panel without a controller. Ever, even a small one, 'cuz the voltage can rise and kill your batteries. If there is no load on them, disconnect them after a FULL charge and they'll be fine for months.
A 2.5W is useless; not even worth the wiring. I bought a pwm controller for $22 and put my very old but still working flexible 11W panel on it when we left the boat for a month before we sailed her up to Canada. It did just fine. It was summer time.
You don't need to "maintain them over the winter," just charge 'em and disconnect them.
Those are your options.
 
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Mar 26, 2011
3,401
Corsair F-24 MK I Deale, MD
I am looking for a way to maintain my start and house batteries while in winter storage. I will not have shore power available and can't really afford to go to a full solar system at this time. I have seen 2.5W solar maintainers and was wondering if they would work without over-charging the batteries. I also need it for a car that is in long-term storage.
Really, you can afford it. Find a cheap 50W-100W flexible panel from Ecoworthy or similar ($80-120) and attach it to the cabin top. A simple controller should be about $25. Another $10 in wire, connectors and so forth, and you are done, without risk of overcharging. So long as you don't walk on it, you should get at least 10 years, which is far better than "maintainers" generally do.
 
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Apr 5, 2009
2,774
Catalina '88 C30 tr/bs Oak Harbor, WA
Hayden,
Maine Sail has taught us to never use a solar panel without a controller. Ever, even a small one, 'cuz the voltage can rise and kill your batteries. If there is no load on them, disconnect them after a FULL charge and they'll be fine for months.
A 2.5W is useless; not even worth the wiring. I bought a pwm controller for $22 and put my very old but still working flexible 11W panel on it when we left the boat for a month before we sailed her up to Canada. It did just fine. It was summer time.
You don't need to "maintain them over the winter," just charge 'em and disconnect them.
Those are your options.
A small system would work for the boat but I also need to keep the battery charged in the car and it has small parasitic loads that will drain it in about a month. We are gone for the winter but leave the car available for our daughter to use for if/when her car quits and I would like to keep it drive ready.
 
Jan 11, 2014
11,323
Sabre 362 113 Fair Haven, NY
A fully charged battery with no loads on it should survive a winter season. The colder the battery is, the lower the discharge rate. The last set of batteries I replaced lasted 8 years or so. Charge them, make sure there is water and disconnect the battery.
 
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Feb 26, 2004
22,760
Catalina 34 224 Maple Bay, BC, Canada
We are gone for the winter but leave the car available for our daughter to use for if/when her car quits and I would like to keep it drive ready.
Can you not teach her how to simply reconnect one wire to the car's battery? :) I'm sure that with you as her father she'll have some of your "good" genes. :)
If the car is inside your garage, is it not heated? If heated, what's the issue? If it's outside, and super cold then I understand.
 
Aug 22, 2017
1,609
Hunter 26.5 West Palm Beach
The self discharge rate of your batteries comes into play here. Unfortunately, that rate changes over time as sulfates build up in the battery & I don't know a good simple way to measure it accurately without investing in some equipment. If your little solar maintainer does not put out enough amps to overcome the self discharge rate, then it is not going to help you. In a 12v system, each watt only puts out roughly 0.08 amps, when the solar panel sees full sun. You are not going to have even close to full sun in the winter, so you will get less than that. In my opinion, anything less than 15 watts isn't worth bothering with & even at that size, a battery with a bad self discharge rate will still run itself (& the rest of the bank) down. Around 50 watts is where things start to get more real. You might actually be able to get an amp out of a 50w system in the winter, assuming that the panel isn't covered with snow.

As was already said, having any solar panel wired up without a controller is a dangerous thing to do, especially long term & even more especially when not monitored.

How about taking the battery out of the boat & sticking it in a utility room somewhere with a maintainer that plugs into a wall socket? That's what I always did when I lived up north.
 
Last edited:
Apr 5, 2009
2,774
Catalina '88 C30 tr/bs Oak Harbor, WA
I am not worried about her, it is the battery that I am worried about. They do not survive long when discharged.
 
Jan 7, 2014
395
Beneteau 45F5 51551 Port Jefferson
For the car, try a cigarette lighter adapter for easy disconnect. Leave the solar panel on the dash or behind the back seats. Just make sure the cigarette lighter is powered when the ignition is off or it won't charge. If no power at the lighter, then hard wire a 12V SAE plug to a positive lead -they are easy to unplug. Use a controller so you don't overcharge.