Low Voltage Solar Panels

[SeaKing]

I have come across a couple of panels that according to their specs. do not require a charge controller. I have 8 group 24 AGM batteries in my house bank. Can I hook these to my system and still run the generator to charge or will the panels need to be disconnected when the xantrex inverter/charger is charging.

Siemens solar panel model SM46. rated at 46 watts, 3.15 amps, 14.6 volts
http://www.a1solar.co.uk/sm46.html

[roverhi]

The capacity of this panel may be low enough that it won't cause your batteries to overcharge, off gas hydrogen and explode, btdt. Then again it migh not with a fully charged set of batteries and a clear sunny day. Why take the chance. The panels typically put out over 18 volts with no load. Why are these panels only putting out 14.6 volts? That would seem to indicate poor charging capability into a discharged battery as the voltage will be considerably less than the 14.6 volt maximum.

[kb79]

as rover points out, flooded cells will outgas explosive hydrogen if overcharged. i also agree with the point that if 18V is possible, you've got a potentially dangerous situation.

i s'pose if your batteries aren't flooded, you'd only ruin the batteries and not blow yourself up...

i wouldn't go for that option personally.

[djmarchand]

You have a big house battery bank, something like 600-800 amp hours. A 3 amp solar panel should not overcharge your batteries unless you leave them connected for months at a time with no other use.

So if all you want to do is keep them topped up and compensate for self discharge, then the 3 amp, 46 watt solar panel will probably work fine.

You can leave them connected while you use your inverter.

David

[SeaKing]

Originally Posted by djmarchand

.

You can leave them connected while you use your inverter.

David

I guess my question should have been asking if using the charger only would be ok, would the double charging hurt the panels or the xantrex charger. Or could the voltage of the panels fool the xantex into thinking the batteries were fully charged.

The price of the panels is not as attractive as I thought at first, but I am still troubled with the issue of how to intergrate panels into my entire recharging system. Can panels and a generator work together without blowing each other up?

[kb79]

Originally Posted by djmarchand

You have a big house battery bank, something like 600-800 amp hours. A 3 amp solar panel should not overcharge your batteries unless you leave them connected for months at a time with no other use.

i'm not sure i agree with that math. if you figger 15Ah/day, then you're at 400Ah after just under 27 days (a month, not many months).

if you actually motored into port and your batteries are full or close to full, then you're potentially overcharged in no time at all.

i know it's not the question you're trying to answer, but just sayin'

[hummingway]

Originally Posted by SeaKing

I guess my question should have been asking if using the charger only would be ok, would the double charging hurt the panels or the xantrex charger. Or could the voltage of the panels fool the xantex into thinking the batteries were fully charged.

The price of the panels is not as attractive as I thought at first, but I am still troubled with the issue of how to intergrate panels into my entire recharging system. Can panels and a generator work together without blowing each other up?

The controller monitors the battery charge and doesn't feed current to the battery when the battery is charged so yes, everything can play nice. At least that's been my experience (and that's a good thing )

[djmarchand]

This is how it works:

If you stay on the hook for two days and use, say 300 amp hours, then your batteries will be about half discharged and the resting voltage will be 12-12.2 volts. Hook up the 3 amp solar panels and that voltage will rise to maybe 12.5 volts.

Then head back to the dock and plug in or start your genset. The AC battery charger will be seeing batteries at 12.5 volts and will start its three stage cycle. It will first put out 20, 30, or near whatever its rated capacity is. The voltage will rise to about 14 as the batteries charge and will finally drop to about 13.5 in the third, float stage. The extra 3 amps from the solar panel won't matter much to the charger and it will do its thing just fine.

The 46 watt panel will really only supply enough amps to keep your batteries topped off. As the previous poster noted, 3 amps is higher than self discharge rate and practically speaking (depending on where you are located and how much sunshine you get) may put out 450 amp hours in a 100% sunny month and half of that in an average month. But if you use your boat every week or so, it should probably be ok with that.

But 46 watts is niether fish nor fowl. Not enough to really do much good on the hook, maybe 15 amphours each day and too much to to top off with.

So, you have never said- what are you trying to do with these panels?

David

[SeaKing]

There are actually two panels available. but for the cost of them I could probably get a 175 to 200 watt single 18v panel and go longer without needing the generator but will need to get a controller. I can easily fit two large panels and possibly more if I get creative in placement. I would like to be able to have my fridge run continously and power for the autopilot, lights and electronics when sailing. I know whatever amount of solar I can get up there we can use the power and go longer without running the generator.

I need to get a controller that will handle 400+ watts, so at least now get one panel of 200ish watts then later add another panel.