Alternator on the outboard....

[Shawn]

Bob,

Yup, propane storage for the BBQ grill. 3 of the 1 pound tanks fit in that and it is vented in the bottom (outside of the boat) in case one ever lets go or leaks.

Shawn

[Shawn]

Skip,

""Amps are what? In minutes or hours?" So amps are always in hours I take it. Thanks. "

Amps are simply amps.

When you include time along with the amps that becomes amp/hours. If you use 1 amp for 1 hour then that is 1 amp/hour.  If you use 50 amps for 1 hour that is 50 amp/hours, if you use 1 amp for 50 hours that is also 50 amp/hours, 2 amps for 25 hours is 50 amp/hours... etc..etc.

Shawn

[curtisv]

"I get 18 to 23 volts dc but ONLY 300 miliamps......... Watts don't mean a lot to me."

Watts are the measure of power, the amount of work that can be done. Power = current X volts, so in your setup if you have 18v and .300 amps you are getting a touch over 5w of power.

If you like to think about this in current take the wattage of a panel and divide by the voltage, that will give you the amperage. For example I have a 40w panel on my sliding hatch, it outputs at 18v. So 40/18 = 2.2 amps.

Shawn

Shawn,

If you are getting 18V, your battery is already fully charged and you are cooking it.  Every solar panel has an open circuit voltage, a short circuit current, and a voltage and amperage at peak power.  The panels used to change a 12V battery all have an open circuit voltage in the 18V range.  That means that if you can't force any current through, the voltage will rise to 18V.  You battery being fully charged is close to an open circuit, but you are able to get 300 mA through, which is probably just boiling the battery.  If you were to put a big load on the panel with no battery, the voltage would drop to near zero and the current would go way up.  At a near short the current can be measured giving another of the solar panel specs.  The most important is the peak power voltage and current, which is typically 13-14V and some current that yields the rated power.  If your battery was low, say 12.7 V, for a while the solar panel would be operating at a high current but just below its peak power.  As the charge increased, the charge current would drop a little and the panel voltage would increase until the peak power point was reached.  Beyond that the current would drop and the voltage would go up more slowly, producing less charging power as the batter was nearing full charge.

So if your battery was low and the sun was shining brightly, you'd be getting full power.

Wet cells shouldn't be charged much over 14V.  AGM shouldn't be charged over 13.8 and gels shouldn't be charged over 13.6.  When either reaches this point, they should be considered fully charged and the voltage reduced to a float charge, usually 13.1.  In all cases, a fully charged battery at rest is about 12.9V.  18V is way overcharging.and you may be damaging your battery.  Consider getting a charge controller and you won't have to worry about it.

Curtis

[Shawn]

Curtis,

I'm getting about 18v from the panel, that is to my charge controller, not what the battery is seeing.

The MorningStar SunSaver Charge controller I am using charges flooded cells at 14.4v (14.1 for sealed) and it floats at about 13.2.

Shawn

[curtisv]

Curtis,

I'm getting about 18v from the panel, that is to my charge controller, not what the battery is seeing.

The MorningStar SunSaver Charge controller I am using charges flooded cells at 14.4v (14.1 for sealed) and it floats at about 13.2.

Shawn

The battery is fully charged then.  The 14.4V and 14.1V are on the high side but 13.2V seems like a very reasonable float voltage.  The only reason that over 14V is probably OK is that the solar panel can't produce enough amps at that voltage to do damage and as the current drops the charger will kick into float mode.

So you are probably seeing 300 mA at 13.2V on the battery side, which is just fine.  I have a Flexcharge with a tiny panel on a huge battery, a 6W panel on an 255AH battery.  This type of controller shuts off the current completely when the battery side goes over 13.8 and then turns it back on when the battery settles below 13.1V.  This works well.  When the battery is well charged it very quickly goes up to 13.8 and then very gradually drops to 13.1.  The panel can only provide about 350 mA since its peak power comes above 13.8V, but it still is capable of completely topping off the very large battery.

Try putting a load on the battery just as a test and see what sort of ampherage the panel will provide.  Turn on all of your lights even if its broad daylight and see what the voltage and current reads on the panel side.  Depending on how much load you add the panel should try to provide all the current needed to to handle the load.  For a 45W panel that should be about 3.5A in bright sunlight if the load is more than that with the voltage dropping to 12.9 and the battery providing the rest.  If the load is under 3A, the panel should provide a bit more than the load at 13.2V.

I think the rule of thumb is W / 3 gives AH/day in Florida and W / 4 in higher lats like where I am.  So I can expect a tiny 1.5 AH/day.  You can expect 11-15 AH per day, depending on where you sail.  If you have the typical 100AH or so battery, then this is fine if you mostly just use lights.  If you only draw the battery down 20%, a sunny day should get you back to 90% and the next sunny day or two would top off your battery.

Curtis

[Shawn]

Curtis,

They run the flooded at 14.4 to try to avoid stratification to increase battery life. It is a full PWM controller so it isn't simply charging or not.

I haven't rigorously tested the output of the panel (might try it this year) but in bright sun I can run the autopilot and GPS and my voltage stays at 13.2 so the panel is handling the load. Later in the afternoon the voltage drops to about 12.9 as the output of the panel is dropping. I do have a 100 AH battery. My Tohatsu has an alternator which I'm wiring into a switch so I can hook it up to charge if I need it. Most times I expect it will be disconnected so I don't overcharge my battery.

The autopilot is my highest draw. I'm adding a water pump which can pull 4 amps but it will be able to drain the tank in about 6 minutes so its total draw would only be about 0.5 AH per tank.

I'm a little south of you in Narragansett Bay.

Shawn

[skip1930]

Also the constant 'COOKING' of the battery by a solar panel can slowly boil the water out of even the most sealed no maintenance battery.
Just a precaution to prise off the tops to the cell to make sure they remain covered with electrolyte.

skip.

[Salty19]

Skip, without a doubt, attaching a solar charger to any 12V battery indefinitely without a charge controlller is a recipe for cooking the battery every time. 

It's pretty dangerous to boil it, it could explode at worst case, but likely would just ruin it or leak electrolyte.  Even a tiny charger would do this.

The problem is you cannot put 18V of charge into a 12V battery for long without damage.  14.4--14.5 is about as much as you want to put on the battery when it needs charged.  that depends on the battery type though (glass matt, flooded cell, lead acid).  That's what a charge controller does..it senses the battery state and regulates the charge accordingly.  Some controllers can sense the battery type, others are designed for a certain type of battery.  The controller will take in 18V volts from the panel, but will only output what the battery needs to maintain charge.  Thus saving from being cooked.  When the battery has a low charge, it will increase voltage.  As the battery gets charged, it will reduce the voltage. 

Pretty good article here:
http://alphasolar.com/solar-charge-controller/

Among others.  really encourage you to look into one, they are a lot cheaper than new batteries or fixing acid damage.

Hope that helps...are you in the water yet?

[skip1930]

"are you in the water yet?"  Hummmmmmmm  36 deg F this morning. I'm not in the water yet.
Yes I know about the limiter for solar cells and have one picked out from our local Bay Marine Electronics store.
Getting the scratch together.  Boiling the water, I really meant a relentless evaporation of water from the electrolyte leaving behind crystallized gunk on the battery's cells. It's a slow process that needs watching.

Thanx. skip.

[Shawn]

Skip,

For an inexpensive (but good) charge controller check out:

http://www.emarineinc.com/products/SunGuard-SG4.5--4.5A%7B47%7D12V-charge-controller.html

which is a full pulse width modulated (PWM) charge controller.

For a less expensive option:

http://www.emarineinc.com/products/CLP03-3-Amp-Charge-Controller.html

This is a diverter controller. It basically connects the solar panel to your battery until the voltage reaches a specific point. Then it disconnects the panel from the battery until your battery voltage drops below a certain voltage.

Of the two you effectively get more solar power out of the PWM controller.

Shawn