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Old 30-05-2012, 08:26   #1
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Solar Charging Battery Banks

Hello,

I'm a new boat owner. My club doesn't have shore power. I need to add a solar panel to keep my two 12 volt batteries charged.

I believe a need to wire the solar panel via a solar panel charger then to the two batteries. I.e. I don't go through the panel or the existing charger, alternator connections, etc...

Is that correct?

For a solar charger I'm looking at something like this:

Priority Solar Control 10 Amp - For Dual Battery Systems
Solar 10 Amp Dual Battery

Regards,
Brent
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Old 30-05-2012, 08:44   #2
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Re: solar charging battery banks

Hi Brent
It looks like a very inefficient on/off solar regulator, there are probably some better choices.

What size solar panels are you considering?
How much power do you use?
How are the two batteries used ( alternating, or one dedicated house one start)?
What type of batteries are they?
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Old 30-05-2012, 09:02   #3
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Re: solar charging battery banks

The boat came with two 12V Kirkland (Costco) flooded cell batteries, one in each bank. They have 90A hours each. I think they're poor quality batteries. I use one for house and one for start.

The boat is primarily used for weekend cruising on inland waters. Lots of time during the week for solar charging.

I installed a Xantrex LinkPro this year to keep an eye on them.

I have no panel purchased yet. I'm considering PowerFilm Solar or a rigid panel on a new bimini frame.


-Brent
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Old 30-05-2012, 09:26   #4
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Re: solar charging battery banks

Brent,

be careful with any kind of flexible panels and check their efficiency numbers first. Your boat is not very large so you probably do not have much space to waste..

I tried to find efficiency data on PowerFilm web site, but could not, and when they give dimensions, they are careful to not specify units, which makes calculations difficult..

As a rule of thumb, expect a minimum of 150W of output from every square meter of a solar panel (specified at full 'standard' insolation). That is for average-to-good panels, very good ones will approach 200W from the same area.

Marius
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Old 30-05-2012, 09:37   #5
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Re: solar charging battery banks

Unless he's running a fridge all weekend completely draining his batteries I don't think he needs to over think and over buy expensive controllers and panels. How many amp-hours do you think you consume over a weekend?
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Old 30-05-2012, 09:41   #6
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Re: solar charging battery banks

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Originally Posted by mrm View Post
Brent,

be careful with any kind of flexible panels and check their efficiency numbers first. Your boat is not very large so you probably do not have much space to waste..

I tried to find efficiency data on PowerFilm web site, but could not, and when they give dimensions, they are careful to not specify units, which makes calculations difficult..

As a rule of thumb, expect a minimum of 150W of output from every square meter of a solar panel (specified at full 'standard' insolation). That is for average-to-good panels, very good ones will approach 200W from the same area.

Marius
Good to know. The PowerFilm product I've been considering is 28W with a footprint of 44.8"x26.3" (0.76 square meter) which is about 37W/square meter so well below your 200W benchmark.
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Old 30-05-2012, 09:53   #7
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Re: solar charging battery banks

Have a look at the Gensun range of controlers

Genasun MPPT Solar Charge Controllers

Most people with your requirements just charge the house bank with their solar. Very few AHr are drawn from the start battery.

You can wire it direct to battery with a suitable fuse, or to your house battery switch if you leave this on when you leave the boat.
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Old 11-06-2012, 09:12   #8
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Re: solar charging battery banks

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Originally Posted by noelex 77 View Post
Have a look at the Gensun range of controlers

Genasun MPPT Solar Charge Controllers

Most people with your requirements just charge the house bank with their solar. Very few AHr are drawn from the start battery.

You can wire it direct to battery with a suitable fuse, or to your house battery switch if you leave this on when you leave the boat.
The direct route to the bank via a dedicated charge controller is straight forward.

If I wanted to wire it via the battery bank switch, would it be wired to the existing charge controller that the shore power uses? Are there charge controllers that are capable that way with two possible power sources, one AC one DC? Or do you always use separate charge controllers for shore and solar power sources?
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Old 11-06-2012, 09:42   #9
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Re: Solar Charging Battery Banks

bluenoser613,

Just get a VW solar panel. It comes with a controller. Would be perfect for your requirement. Can get them on ebay for around $30.

Haul Out, On The Hard, Antifoul & Winter Storage
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Old 11-06-2012, 09:50   #10
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Re: Solar Charging Battery Banks

AFAIK a shore power charger, and a solar charge controller, are always two separate devices. If you are using small panels and a small controller, just use a DPDT toggle switch to shunt the controller's output to either battery bank, separate from the main battery switch. And of course fused.
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Old 11-06-2012, 09:52   #11
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Re: Solar Charging Battery Banks

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Originally Posted by hellosailor View Post
AFAIK a shore power charger, and a solar charge controller, are always two separate devices. If you are using small panels and a small controller, just use a DPDT toggle switch to shunt the controller's output to either battery bank, separate from the main battery switch. And of course fused.
Thanks for the reply. For equipment drawing power I always fuse everything as close the battery as possible.

In this situation where I am supplying power to the batteries, is the best practice to have the fuse closer to the battery or panel end?

Regards,
Brent
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Old 11-06-2012, 10:09   #12
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Re: Solar Charging Battery Banks

A good question. In between the panels and controller, usually no fuse required or used. Between the controller and battery...They are both "batteries" i.e. power supplies and controllers can fail, but I think I'd place the fuse closer to the battery since that's the one capable of slagging down wires. Can't see that it would, unless there was an internal short in the controller, allowing the batteries to "backfeed" it.
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Old 11-06-2012, 11:02   #13
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Re: Solar Charging Battery Banks

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Originally Posted by hellosailor View Post
A good question. In between the panels and controller, usually no fuse required or used. Between the controller and battery...They are both "batteries" i.e. power supplies and controllers can fail, but I think I'd place the fuse closer to the battery since that's the one capable of slagging down wires. Can't see that it would, unless there was an internal short in the controller, allowing the batteries to "backfeed" it.
I was thinking the panel would be considered a power supply, and perhaps the fuse should be near that. If the charge controller has a diode it would prevent the "backfeed" you mentioned. However a short between the battery and the controller could start a fire given the available amps in the battery. Perhaps two fuses are needed.
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Old 11-06-2012, 11:18   #14
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Re: Solar Charging Battery Banks

"If the charge controller has a diode it would prevent the "backfeed" you mentioned." Yes, but diodes can fail. If it fails open, no problem it has become the fuse. If it fails and shorts--that's the fire potential. Hopefully it still becomes the fuse, but that would depend on what type of diode was used and how it was installed, too.

Two fuses? More points of possible failure. Nice theory but I've never heard of it being done that way. Bear in mind that if the controller can put out, say, 10 amps, and your wiring can safely carry 20, you simply don't need to fuse the controller side at all. Only the battery would be able to ignite the cables, so only that end would need fusing.
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Old 11-06-2012, 11:34   #15
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Re: Solar Charging Battery Banks

Awesome. Thanks for that info on the fuses. I'm tapping the brain trust for just this type of response.

Thanks!
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