Plastic Classic Forum

I've calculated my future electrical requirements at 17.53 daily amp hours. This is conservative; it'll probably be more like 10 on average. I will be charging the battery solely with a solar panel. Is it correct that to keep the battery charged, you need to simply put in the number of amps each day you take out? In my case, would I need to send about 17 amps to the battery each day? If this is correct, then do you think a 50 watt solar panel would do the job? Fifty watts / 12 = 4.16 amps X 5 hours of sunlight = 20.8 daily amp hours.

Regarding capacity of the battery -- taking into consideration that ideally you don't want to discharge below 75%, then a 100 amp-hour capacity battery should be fine, right?

I'm counting on you electrical geniuses out there!

Thanks.

Keep in mind that a solar panel alone usually won't output at 12V, it is typically more like 15VDC-18VDC. The combo you are proposing really requires that you use a controller to charge the batteries from the panel. The controller will regulate the panel's output and keep the battery in good health.

Also remember when doing your calculations that you aren't likely to get a full 5 hours of sun everyday, so you may want to have enough capacity to use battery power on days when you can't solar charge.

What you take out requires slightly more to go back in. It is on order of about 110% - 125% of what you used that needs to be put back in in terms of energy. Also, the last 10% of charge takes the longest due to acceptance tapering.. A 50W panel should be decent but you'll also want a good charge controller such as the the Morningstar Pro-Star PS-15 or similar. This is a PWM controller that does three stage charging and is not a shunt or relay type controller and thus will charge slightly faster. I would not bother with an MPPT controller on a 50W panel unless it is one of the Genasun MPPT's which are specifically designed for small panels. The MPPT gains would be negligible if any with a Morningstar or Bluesky and may not out weigh the added cost. The Genasun units are great and very affordable.

Jay; My system is similar in demand. I use 2 Golf cart bateries in series, and chose 2 32 watt amorphous panels mounted on the Dodger with a charge controller. This system worked without grief for over 8 years now never letting the batteries get below 90%. I like the Amorphus panels for their shade tolerance. The one modification I made was to fill the junction boxes with dielectric silicon to preclude wire corrosion. Hope this helps Phil