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solar panels questions Answered

In the quest to turn my garage 'green' I started with a purchase of a Sunforce 60 watt solar panel charging kit. I already own a 12v 15amp charge controller that I bought from Green Energies. The Green Energies controller is bigger than the kit supplied so I'm currently using this one. My questions; The Green Energies charge controller is supposed to have a blocking diode in it. When I put my volt meter on the leads going back to the panels (panels dis-connected, controller still hooked to battery) I'm getting approximately 10 volts. Should there be any reading at all? I went out this rainy morning to see if there was any power coming from my panels. To my surprise I read 8-10 volts (depending on cloud cover). This leads to my next question. It is worth adding a boost converter? I suspect the amperage would only be that of the incoming voltage, not what it is boosted up to.. Close? If my guess is correct, my 5amp (system at full power, rated at 24vdc), would only be about 1.6- 2 amps @ 8- 10 vdc. I also suspect the controller is stealing some amperage. 0.5 amps??? That should leave me with at least 1 amp coming in and giving me a 10 amp day. Not bad for a rainy day. Right, wrong or hopefully close? I'm not seeing my battery come up to full charge. I'm using a marine deep cell acid battery from my boat. Every 5 years I replace it to insure the boat will start as needed. Paddling that craft back to shore is not an option. One reason could be the fact of the battery being 5 years old and it will never get back to full. Second I believe would be the draw going back to the panels at night. Will the panels draw power?


Big Bwana

11 years ago

If your charge controller has a blocking diode, then no there shouldn't be any thing going back threw it to the panels, however most panels contain a there own blocking diodes, now with that said having two diodes is a waste of power, each will give you anywhere from a .3 to 1 volt drop, most are around 0.7 volt drop.. While this doesn't seem like lots when your talking small scale solar it all adds up.... About not getting a full charge, consider taking your battery into a good battery store and having an cell equalization charge done on it, with some care you can get a good number of years out of a battery... And is it a marine deep cycle or a marine starting battery ?? the starting batteries while they do work, they are not the most ideal candidate for solar usage... Yep, thats why they should have a blocking diode in them, measure it and see if they are drawing any current at night....

olddawgBig Bwana

Reply 11 years ago

First of all, thank you for your response. I agree, small scale, it adds up fast. Now that I've tracked for a few days, your numbers seem real close to what's happening. I'm dropping .5 volts overnight. I'm getting a better gain than I expected, so in the long run I'm feeling much better. I will bring the battery in and have it checked. It is a deep cell, my old trolling motor, transfered to my boat for starting. I bought a new this year that has twice the power for the same dollar I bought the old one. I'm having a hard time not going out and buying another just for the system.... I would like to see the old battery add to the system, but I wonder if it doesn't ever get up to power if it would be a deterrent to the system. A weak battery drawing from a good.... just don't know enough about this to be certain We're in the mist of 'in & out' thundershowers currently. Most of the day has good sun, but those big dark ones are rolling through all day. With all this I went from 10 volts to 11.5 in one day! Ya, I lost .5 volts overnight, but still I gained 1 volt! Very impressed! Today I noticed I only gained 1 volt, now with my potential .5 loss that will put me at a .5 gain overall. The question becomes; Is it typical to gain slower as you reach optimal voltage? I.E. quicker to go from 10.5 to 11.5, than 11.5 to 12 volts....? I'm not getting this voltage to amperage gain thing yet.... Once again, thank you for answering my questions. I have found this group to be very helpful and only hope that in some time I can return the favor.