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Go Back   SailNet Community > On Board > Gear & Maintenance
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Old 11-04-2006
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Solar Charger Control

How do you charge the separated House and Starter Batterie with a solar panel?
Do you need two charger or a set of diodes to avoid that the two batteries charge/discharge each other at different consumptions?
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Old 11-04-2006
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If you are planning to use one solar panel to charge two separated batteries, you will need something like isolation diodes. They will also drop the voltage about 0.7v across each diode, so your solar panel will be a little less effective. But as long as the solar panel puts out well less than 1/10th of the battery capacity, that's all the charge controller it needs. Batteries can pretty much take that much current "forever" without getting into more expense.
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Old 11-04-2006
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1. Get a battery combiner switch so you can parallel all the batteries for a charge.
2. Get a smart regulator for the solar panel so that you can bleed off excess voltage if the panel can put out more than 14.3 volts or so.
The batteries will "self-level" when charged and during the night.
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Old 11-04-2006
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I have 2 batteries 12 volt that are sperated by a standard switch on every boat. You know the one it's red and reads battery one, battery two, both, and off.

I have a 30 watt solar panel and bought the cheapest charge controller on the market, I think it was $26. I ran the solar panel to the controller and the controller to my biggest battery of the two, which happens to be battery 2. during the day or when I think about it, I switch the battery switch to both and let the charger charge both batteries.

I only recommend this technique if you have one battery that is sort of old and the one you use as the sacrificial battery. Like when your sailing at night and running lights, you use it, when the lights go dead you go opps, and switch to the 2nd battery start the engine to charge things up.

However I will soon invest several hundred dollars in an expensive 48v system and then I will be using a much better charge controller and doing all the things that the nice sales man recommends.

But for now this has served me very well and both batteries hold a charge and work great... used them all summer, I was a live aboard. Never actually turned the engine on till this fall. 30 watt panel sitting in the sun all day gave me plenty for lights at night, and chargeing the gadgets. Great investment! would have spent more in gasoline.

Matthew
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Old 11-05-2006
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I'd agree with cam about getting the battery combiner and a charge controller. The charge controller is especially necessary if the maximum output of the panels exceeds 10% of the capacity of the battery banks... if the bank has a 200AH capacity, and the panels are capable of 20A/hr then a charge controller isn't an option, but a requirement, unless you like frying batteries. Most solar controllers have blocking diodes built into them, so a separate blocking diode on the panel is generally not necessary. The best charge controllers are the MPPT (maximum power point tracking IIRC) type controllers, which can increase the effective use of the solar panels.
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sd-
Not to pick nit, but don't you have that just a bit off?
Since a 200AH battery bank can withstand a 10% charge (i.e. 20A rate) indefinitely without being harmed, and a 20A rated solar panel will only put out 20A for about 5 hours per day (i.e. 20% of the time)...

Then a 20A rated solar panel should be able to be used with a 200AH battery bank indefinitely with no controller or regulator. All things being equal, since it won't be putting out 10%C for many hour at all...I'd even say 22A, 23A, would be perfectly fine without any regulator or controller, as long as there was some other load or use being made on the battery. I'd be more inclined to say 25A was a point where I'd definitely want to see a controller/regulator and even then, for short term and less than tropical sunlight? I don't think I'd worry a whole lot. More devices just means more stuff to fail and more worries.
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Old 11-05-2006
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Quote:
Originally Posted by hellosailor
sd-
Not to pick nit, but don't you have that just a bit off?
Since a 200AH battery bank can withstand a 10% charge (i.e. 20A rate) indefinitely without being harmed, and a 20A rated solar panel will only put out 20A for about 5 hours per day (i.e. 20% of the time)...

Then a 20A rated solar panel should be able to be used with a 200AH battery bank indefinitely with no controller or regulator. All things being equal, since it won't be putting out 10%C for many hour at all...I'd even say 22A, 23A, would be perfectly fine without any regulator or controller, as long as there was some other load or use being made on the battery. I'd be more inclined to say 25A was a point where I'd definitely want to see a controller/regulator and even then, for short term and less than tropical sunlight? I don't think I'd worry a whole lot. More devices just means more stuff to fail and more worries.
You'd be right if solar panels output 14.7 volts or so, which is what is normally required by 12V batteries...however, my experience has shown that the solar panels (two ICP Sunsei SE8000 130W 8 Amp panels) I use on my boat output almost 20 volts... Most panels have more cells than needed to produce the 14.7 volts that 12VDC systems require to help compensate for shadow losses and in low-light conditions.

Even though the panels are rated for 8 amps, under the noon sun, up here in New England, I had to install a 20 Amp fuse, since the panels kept blowing the 15 Amp fuse I had originally installed.

Once the connection from the solar panels enters the charge controller the effective amperage goes up a bit, as it drops the voltage and increases the amperage, since I use a MPPT-type charge controller.

A good charge controller increases the efficiency of the solar charging system and helps prevent the panels from boiling the batteries on a really sunny day.
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Last edited by sailingdog; 11-05-2006 at 06:57 PM.
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