cheap solar trickle charger

[FourPoints]

Considering one of the two chargers linked to below. I am just looking to keep the batteries topped off as I don't always run the engine enough to make up for my battery usage (although it made a HUGE difference last year after switching to LED Nav and Cabin lights), and sometimes when we go out a couple weekends in a row and I end up having to run the engine just to put a little charge into the batteries, which I HATE having to do!

Almost exclusively use the boat on the weekends, and the occasional week night, so this is nothing like a live aboard configuration, as long as come Friday the batteries are 100% charged from anything I've done the previous weekend I'm happy.

very simple battery config, I have 2 deep cycle auto/rv batteries in parallel.

Looking at the following two chargers

iMob 12 Volts DC / 5.5 Watts, 400 mA / Waterproof / Shock Resistant
http://www.defender.com/product.jsp?path=-1|328|49497|1471364&id=1476138

Sunforce 12 Volts DC / 5 Watts / Weatherproof / Maintenance Free
http://www.defender.com/product.jsp?path=-1|328|49497|1471364&id=1469736

They almost look like they are the same product, different packaging. Has anyone had experience, direct or indirect with either of these solar trickle chargers?

I have a mount picked out that will easily hold either of these above the bimini from the rear frame.

 

[chp]

I also have a 5.5 watt trickle charger. The term trickle is an understatement. When you do the math you only get about a 1/4 to 1/2 amp. It can take a couple of weeks to charge your batteries at this rate. It is good to keep an already charged battery fully charged, which is what I do with mine. I'm in the process of building a 60 watt solar panel for my boat. This will give me about 3.5 amps of charging. Depending on how much juice you use you may want to consider a 30 watt panel.

 

[Johnb]

What CHP says above is quite true. The self discharge (loss) in a battery in good condition can be up to 1% per day so 2 X 100 ampere hour batteries could need 14 ampere hours per week just to stay even. If you get 5 hours per day charging at 0.4 amps times 7 days a week to get 5 X 0.4 X 7 = 14 ampere hours that will all go just to balancing the self discharge.

If you really want to have much impact start looking at about a 30 watt panel. I have a 60 watt panel that will actually push about 3.2 amps (it is 60 watts in ideal sunlight at mid day on the equator into a mythical 17 volt battery) and it takes all week to charge one deeply discharged 100 ampere hour battery. An inexpensive battery charger will do the same job in 12 hours at dockside for about 20 cents in electricity cost.

Careful - rant alert........

 

[FourPoints]

hmm, I can't find a mount that will work to attach a 15 amp to my bimini frame (it would also add roughly twice the weight / wind load of the 5amp, but given it's an all SS frame, and a fairly small bimini I think I'm fine)

I only had to plug into shore power for charging one time last season, although I did run into a time or two last season where I got low voltage warnings (from my chartplotter's configurable alarm) and decided to motor sail even though I had good wind, just to charge the batteries. It was after that trip I plugged into shore power for a couple days with a battery charger hooked up.

My engine is an 8hp Tohatsu outboard, and from what I have heard it only outputs ~5 amps of charging power.

Given the little need for additional charging I have had, does the 15 watt really seem necessary?

Does anyone have a suggestion for mounting one of the 15 watt panels above the bimini?

 

[Warren Milberg]

I have been using a 5-watt ICP solar panel for years to maintain my 2 Group 24 wet cell batteries. This small panel is not a "charger" in any sense of the word, but it does seem to be able to compensate for the normal loss of power fully charged batteries experience. I normally switch this panel between the two batteries after each sail. FYI, I found that keeping my batteries connected to my on-board 10-2 amp Guest shore power charger (hardly ever used), resulted in a faster loss of power in my batteries, which were not under load. I now keep the hot wire to the charger disconnected and only connect it on the few occasions I plug up to shore power.

 

[Stu Jackson]

If you want to extend the life of your expensive batteries, leaving them partially charged will rapidly kill them. A solar panel is the way to go. The panel will charge the batteries up to 100% during the week you're away. The alternator will simply make up for your use on the weekends. Sure you could "depend" on the alternator, but your batteries will NOT be fully charged when you return, and you will shorten their life. See the discussion of charging in the Gotcha topic, here: http://c34.org/bbs/index.php/topic,4922.0.html, reply #3.

The very best thing you can do is to buy a solar panel and a battery monitor. For your use a solar panel anywhere from 11 watts to 25 watts should do, and wouldn't need a regulator, depending on the size of your house bank, which you didn't mention. Less than 10% of the house bank in ah.

 

[estopa]

I used a 5watt solar panel last year on a group 24 battery and it kept it topped off all summer. Where as before I would have to remove the battery and charge it every so often (2-3 weeks). Get it if all you want to do is top off your battery. I got mine for like $20 on ebay. Had to wait for the slow boat from china but was worth it. I also did LED with all my lighting. Again ebay is your friend if you don't mind the slow boat from china.

 

[Technodad]

I've used a 5.5 watt panel for a few years and it works great, it keeps my group 24 deep cycle battery fully charged during the week easily. I even use an auto-tiller as well.
Led lights are king too.
The panel comes with wires with clips that lead through the vent direct onto the battery.
I have never had to charge my battery in a sailing season.

I made alum clamps to hold a length of 7/8 SS tube to the pushpit and 1 1/2 x 3/16" alum flat bar under the panel.

 

[ifmdalvey]

Last season i used a flexible/fold up panel. No worry about mounting it, just used bungee cords across the coach roof to keep it in place when not on board and put it away while sailing, it seemed to keep my 4 year old batteries charged up well.

 

[tcoursey]

smaller charger

I have one similar to this that came with the boat I acquired in 2006. I havn't had to replace the battery since I bought the boat. Of course I only go out about once a month. I use the battery only for the dept meter and speed.

http://www.solar-green-wind.com/archives/solar-battery-trickle-charger-12-volt