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Mon, May 23 2022, 03:53Login ] [ Contact Forum Admin ] [ Main index ] [ Post a new message ] [ Search | Check update time | Archives: 123456[7]8910 ]

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Date Posted: - Monday - 04/16/07 - 4:46pm
Author: Randall, Murre, M31
Subject: Solar charger hook up when batts in parallel

I can't seem to find a direct answer in Casey or Calder, so here goes

Murre came with a small, old (but as I've learned, very functional) Unisolar 11 watt/.7 amp solar mat. I unhooked it a few years ago without checking to see if it worked OR how it was then installed (go ahead, shoot me.) I re-installed it a few weeks ago so as to avoid shore power charging during the week.

I've hooked it to my battery bank, but found that it's only charging one battery (I think). So, I'm must be doing something wrong.

The bank is two 12 volt, deep cycle, 105 amp hour batteries in PARALLEL. I put the red lead from the solar panel to the positive post of battery #1 and the negative to the negative post of battery #2. Seemed obvious at the time.

At the end of a week, battery #1 is charged to 14.4 volts (i.e. overcharging, no?) and battery #2 is more or less unchanged (12.6 voltsfully charged, yes, but where I left it on Sunday night).

A drawing in Casey suggests splitting the read lead from the panel into two red leads, one positive post per battery, and grounding the negative lead. But presumably the panel has been installed on the boat for years and does not have two red leads.

So Im stumped.

And another question. When I do get this going, and when deciding if the panel needs regulation diods, can I figure the amp hours per TWO batteries? i.e. 210 amp hours?

If so, an 11 watt charger is still about 4 watts too much (3.5 x 2 = 7) and needs regulation, right?

Thanks in advance,


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[> Solar panel hookup -- Doug Wilson ,Cactus Tree, - Tuesday - 04/17/07 - 5:38pm

I'm having an electrician do a few things on Cactus Tree next week, including hookup of a 65 watt panel. I can print your post and ask his input on your questions. I want to charge all three of my TM27's, and it will also run thru an isolater.
We'll see what he says.

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[> [> Much appreciated... -- Randall, - Tuesday - 04/17/07 - 7:52pm

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[> You might look at the West battery combiner -- John Bye, - Wednesday - 04/18/07 - 2:29pm

I used one on "Promise" and it worked great. It combines the start and house batteries only for charging. If the start battery is the 'primary' (determined by wiring) it will charge only that until it gets up to a certain voltage level and then it charges both batteries. You can wire it so it works either with the alternator or the solar panels.
Makes battery management simple. You only need to worry about which battery you are using. (Start for starting and house for everything else).
You don't need an isolator with on of these.

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[> A few thoughts, -- Bill Kranidis, - Friday - 04/20/07 - 3:52pm


First, I would install a blocking diode in that panel, regardless of it's size and connection configuration. Look at West Marine's catalog. They'll tell you how to do that.

Second, I would hook that panel on to the house battery, only.

Why ???

First, you do have a 1-2-BOTH-OFF switch, right ???

1. When you leave the boat for a certain amount of time, leave the switch to "BOTH". The panel will be charging BOTH batteries while you're gone.

2. When you come to the boat, use the "BOTH" setting to start your engine. Engine will be charging BOTH your batteries when it's running.

3. When you shut the engine off and while you're still on the boat, turn the switch to "House Battery" (whatever that might be, 1 or 2). This setting will keep the "Starting Battery" always charged, your panel is charging only your house battery.

Hope this helps.


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[> [> solar panels -- marcus, - Friday - 04/20/07 - 8:43pm

Hi Randall: Does sound like a bit of over charg at 14.4V. How many amp hrs are your bats and what typ of bat are they. I use gel cells and have been told by the people at blue sky charge controllers to charge to 13.8 no higher. I really doubt you panal of 11 watts is too big, but that it is not being charge controlled well. The blue sky controller also optimises the out put to charge more quickly, but it takes 10 ga wires to get enough amps to activate that feature with my two 40 watt panels. a simple charge controll er should make your expensive bats live longer. thanks again for the heater connection pics!

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[> How were your voltage readings taken? -- Capt'n Mike - Gypsy Mariner TM36K, - Sunday - 04/22/07 - 1:36pm

I may have misunderstood what you wrote - but with both 12v wet cell batteries wired in parallel into one battery bank (I think this is what you have described), I would begin trouble shooting by checking the specific gravity of each cell of the battery showing 12.6 volts with a hydrometer. You may have a bad cell on that battery. You have quite a bit of voltage difference between two batteries that are normally part of one battery bank, and until you figure where the difference is coming from I wouldn't keep the two batteries wired in parallel.

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[> [> The solution, for now -- Randall, - Monday - 04/23/07 - 1:08pm

Thanks for all the input, gents.

It is with some embarrassment that I admit my first question turned out to be a red herring. With the switch in the OFF position (which it was in my example) there is no way the single solar panel could have charged both batteries given the way Id installed it. With the red lead to battery #1 and its ground to battery #2, I didnt make a connection in the physical sense (or, in this case, metaphorical either).

In the short term, at least, Ive rigged a small regulator to the panel and connected the panel to battery #2, the house battery (kind of following Bills advice, but without using the BOTH strategy for the moment).

Why? The starter battery is 4 years old and seems as fresh now as when I bought it even with a charging regime that ONLY includes running the engine. Its twin, the house battery, which I just replaced, was dead as a door knob after 4 years of the same. So it seems the house battery needs the more care.

Thanks again.


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