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post #11 of 15 Old 06-13-2014
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Re: Battery voltage rises after use?!

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Why would a 12v panel put out 18v?



Not to me. Once you connected them in series, it should be 24v. We need an expert here, I get a headache.

But there is clearly something more to it, if you test the panel and it shows 12v (or more likely something in the 13s). But I don't see how, from that diagram.
Easiest to demonstrate with a couple of AA batteries. You get 1.5V from each. The only way to get 3V is to touch the narrow end of one to the wide end of the other AND measure across BOTH of them. If you only measure one battery, you will get 1.5V, regardless of whether it is touching another battery or not.
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post #12 of 15 Old 06-13-2014
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Re: Battery voltage rises after use?!

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Originally Posted by Minnewaska View Post
Why would a 12v panel put out 18v?

Not to me. Once you connected them in series, it should be 24v. We need an expert here, I get a headache.

But there is clearly something more to it, if you test the panel and it shows 12v (or more likely something in the 13s). But I don't see how, from that diagram.
Don't need to be an expert. The diagram clearly shows the panel drawing from one battery. How can it be 24v if it is only drawing from one battery?

And the job of the regulator is to set the output voltage to the batteries at an acceptable level. The OP said that the solar array was unregulated.


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post #13 of 15 Old 06-13-2014
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Re: Battery voltage rises after use?!

Got it now. Serial connections just don't sink in for some reason. Probably because I've never needed to rig one.


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post #14 of 15 Old 06-13-2014
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Re: Battery voltage rises after use?!

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Originally Posted by Minnesail View Post
I have no idea if it's accurate, but it is consistent. I've taken multiple readings and it stays +- 0.01 vdc.




This seems odd to me too, but it works. Here's the setup:

You need to define "works"... Electrically it can create problems for the batteries even though it appears to work..

That type of wiring can lead to short battery life. You create out of balance cells/batteries for the 24V bank. Any series batteries really need to be parallel balanced before being placed into service then regularly equalized and charged at proper gassing voltages to ensure they both get "full". Otherwise or they can become out of balance...

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post #15 of 15 Old 06-13-2014 Thread Starter
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Re: Battery voltage rises after use?!

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Originally Posted by Maine Sail View Post
You need to define "works"... Electrically it can create problems for the batteries even though it appears to work..

That type of wiring can lead to short battery life. You create out of balance cells/batteries for the 24V bank. Any series batteries really need to be parallel balanced before being placed into service then regularly equalized and charged at proper gassing voltages to ensure they both get "full". Otherwise or they can become out of balance...
It's far from ideal, that's for sure! I have printed out your article Installing A Small Marine Solar System. Having two batteries in series complicates things.

Frankly I'm surprised at how well the batteries hold a charge. They're different brands and different ages, one four years old and the other older. But they both charge up to about 12.8 and seem to be working well. I've been checking them every time I get to the boat.

I think the way I would like to set it up is with the primary system being 24v, since the primary load is the 24v trolling motor. So I'd get a 24v solar panel and a good solar charge controller, a DC to DC converter to supply 12v for the relatively modest demands of the lights and iThing charging (and possible tiller pilot), and maybe an inverter so I could run power tools and my wife's CPAP on our rare overnights.

I realize that's three different voltage systems on a 22' boat.... I might be overdoing this...

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