Solar Panel Wiring query

[hellosailor]

bony-
If your batteries are something like Group27, maybe 75AH capacity, and you run one of them down 1/2-way, that's ~37AH of power you need to recharge it. You'll get about 350 mA (which is 0.35A) out of your panel, for about the equivalent of five hours on a sunny summer day. Which is about 1.75AH.

So your panel could recharge one half-way discharged battery after three full weeks of sunny days.

But as a charge maintainer, to ensure they come up from, say, 90-95% to full charge, and they are maintained at full charge (which extends their life) it should work well enough. If that's your goal, you might want to add a second, run one to each battery, and leave out the switching.

[bony]

socaldmax,

Oops! Made a dumb mistake in the drawing.

Thanks for noticing it.

hellosailor,

Charge maintenance is my goal. I went for a 5 watt solar panel thinking it would be right because the boat had a similar unit when I first bought it.

If I add another panel am I going to need another controller as well?

bony.

[socaldmax]

Originally Posted by bony

socaldmax,

Oops! Made a dumb mistake in the drawing.

Thanks for noticing it.

hellosailor,

Charge maintenance is my goal. I went for a 5 watt solar panel thinking it would be right because the boat had a similar unit when I first bought it.

If I add another panel am I going to need another controller as well?

bony.

You don't need another controller for 10 watts. Some controllers won't even turn on for 5 watts, or they may consume a couple of watts themselves. Just wire the 2 panels in parallel if you add another.


I did a quick search for self discharge rates and found numbers all over the place, so your batteries have a specific discharge rate, what it is, I don't know. You should be able to find it on the mfr's website. If you can find it, please post it up and maybe we can figure out how beneficial this is, or if you need another panel.

[Ex-Calif]

Originally Posted by bony

I wonder if someone can take a look at the Solaring wiring circuit I've drawn up and tell me if it is correct.

I have incorporated a solar charge controller but also wanted to install an On/Off/On Toggle switch into the system to allow me to switch the solar charge to either of my dual batteries. I don't know if I have set it up correctly, I'd appreciate your opinions on this please.



bony.

I don't see any reason to switch the negative. Wire the negative directly and then just switch the positive current.

Single pole triple throw switch allows an off position.

BTW - If the plan is to leave the boat unattended for a while and maintain the batteries this circuit won't do it. You will only be maintaining one battery at a time.

if you are investing in a controller you really ought to think about enough solar power to minimally charge the batteries and at least maintain both at the same time.

20-40W of solar and a dual output controller would do it.

[hellosailor]

Yes, two separate panels feeding two separated batteries would mean two controllers. Unless you had the batteries combined all the time.

[bony]

Well, many thanks to everyone for the replies and good advice.

Looks like it's a waste of time messing around with the panel I have and I'll need to upgrade to one of a higher wattage. Sjpould have done my homework a bit more thoroughly in the first place. Bur thanks again to all for putting me on the right track.

Cheers,
bony

[Ex-Calif]

Hey bony - Sorry about the thread getting off track. Maybe if you tell us what you'd like this panel system to actually do we can give some advice.

The original parameter, "Maintain a trickle charge to the split batteries" is probably beyond the capabilities of a single 5w panel.

For example - I sailed weekend to weekend with 40W, no controller and 3 X 70ah batteries for a year.

The reason it worked was the batteries were usually depleted by the end of the weekend (about 100 amps out) and 5 days of 3 amps X 6 hours basically meant my system was in balance week in and week out.

Probably wasn't the best solution but is was very cheap. The panels were like $50 each on sale.

[socaldmax]

Originally Posted by bony

Well, many thanks to everyone for the replies and good advice.

Looks like it's a waste of time messing around with the panel I have and I'll need to upgrade to one of a higher wattage. Sjpould have done my homework a bit more thoroughly in the first place. Bur thanks again to all for putting me on the right track.

Cheers,
bony

The purpose of a solar charge controller is to convert the output V of the solar panels (lets say 19 V) down to the charge voltage for the batteries (let's say 14.5 V) AND to drop the charge down to a float charge once the batteries are full. You could put 20, 40, 100, 400 watts of panels on your system (as long as your controller can take it) and once your batteries are full - the solar controller will stop absorption charging and go into float mode.

Which controller did you buy? Maybe we can help you find another panel to do the job.

[hellosailor]

bony-
If you read the many solar threads, there are other issues to consider. Very few controllers can charge two separate batteries at once, so if you want to keep the batteries isolated, that's a key feature to look for.
You also want to match the controller's output voltages to what your batteries need. Most controllers match most wet lead batteries but if not, some can be adjusted.
The good news is that once you've puzzled through the bits, solar panels keep batteries very happy with very little effort.