Charging battery question

[waterlogged59]

OK. I have a 1961 Evinrude motor that does not have a way of charging back to the battery. no generator or alternator. my question is this. I have been told i could get a solar panel charger and have it hooked up so it will recharge the battery. Is this a good idea or other ideas? What I am trying to do is while the boat is running have the panel hooked up so it will keep the battery charged up. I have the following hooked up

Starter
Lights
Stereo 4 speakers
Car amp pushing single sub
.

I know that the stereo and Amp pull the most but i just want to make sure that i am keeping the battery up when we may pull over and anchor the boat and turn the motor off and just listen to music for alittle bit. while we are sitting listening to music i would like to have something to recharge while its being on. so let me know. Northern Freight has solar panel ranging from 5 watts to 15 watts. not sure what i would need. i mean wouldnt think i would need much. also they have 2 types. regular charger or trickle charger. I have a deep cycle marine battery.. so which one would be better..

 

[Silvertip]

Re: Charging battery question

Neither one will charge a battery. You have a car amp and a subwoofer that is drawing a bunch of current. Without a number I will just grab one out of the sky and say 10 amps. P(watts) = E (volts) x I (amps). Lets say you have a 100 watt amp. It operates on 12 volts. So 100 divided by 12 = 8+ amps. The larger of the two solar panels you saw was 15 watts. 15 watts divided by 12 volts = 1.2 amps. So in this example with just the amp running you are using roughly 8 times more power than the solar panel is putting back into the battery. Even if the engine had an alternator, on most mid size two strokes they produced only 16 amps or so running wide open. Even at that rate, you would need to run wide open for hours to keep the battery charged. A solar panel big enough to actually do you any good would need to be half the size of your boat and it would cost a grand or more and you then need a charge controller. Forget solar. -- It is effective only over a very long period where it does not have to try and keep up with demand.