solar trickle charge for 36v setup...

I have a 101 minn kota trolling motor with no electric at my slip. I'm thinking about a solar trickle charger. Is there a way to charge the 36volt setup as a whole or would I have to charge each battery 1 at a time? I found a 6 watt charger by colman online for $50 with over charge protection, or I have a local one on craigslist off a sailboat with 40 watt but not sure if there is overcharge protection. Any recommendations?

Re: solar trickle charge for 36v setup...

First, you need three of whatever you pick. They will be connected directly to each of the batteries. Or you need a single 36 volt output panel, but that just means you take the physical size of the panels you are looking at, and triple them. (or take the capacity by 1/3, some result)

Now as far as capacity, might want to rethink that... Lets say you get three of the 6 watt chargers. If you have perfect conditions for charging 8 hours a day, you will put in 3.4 amp/hours per day per battery. An average group 27 deep cycle can have a capacity well over 100 amp/hours, so its going to take 29 days of perfect sunlight to charge that. The problem is that batteries also have self discharge, so its going to take more like double that. Toss in some cloudy weather, and it becomes impossible for the charger to even outrun the self discharge, let alone get ahead.

If you go to 3 of the 40 watt panels, its going to take about 5 days of perfect 8 hours of sunshine.

So those numbers are all under perfect conditions with a tracking mount system. A fixed panel is going to average less than half of its rated output for an average day. Also keep in mind that New Jersey averages 4.21 sun hours a day...


In other words, overcharging the batteries is the absolute LEAST of your problems! Solar panels are fine for minimal use systems and keeping already charged batteries topped off. If you plan on using them to recharge a dead 36v trolling system, you are going to be covering the entire top surface of your boat in panels and still having to wait a week or more for a full charge.


(have to wonder, why a bike helmet?)

Re: solar trickle charge for 36v setup...

smokingcrater said:

First, you need three of whatever you pick. They will be connected directly to each of the batteries. Or you need a single 36 volt output panel, but that just means you take the physical size of the panels you are looking at, and triple them. (or take the capacity by 1/3, some result)

Now as far as capacity, might want to rethink that... Lets say you get three of the 6 watt chargers. If you have perfect conditions for charging 8 hours a day, you will put in 3.4 amp/hours per day per battery. An average group 27 deep cycle can have a capacity well over 100 amp/hours, so its going to take 29 days of perfect sunlight to charge that. The problem is that batteries also have self discharge, so its going to take more like double that. Toss in some cloudy weather, and it becomes impossible for the charger to even outrun the self discharge, let alone get ahead.

If you go to 3 of the 40 watt panels, its going to take about 5 days of perfect 8 hours of sunshine.

So those numbers are all under perfect conditions with a tracking mount system. A fixed panel is going to average less than half of its rated output for an average day. Also keep in mind that New Jersey averages 4.21 sun hours a day...


In other words, overcharging the batteries is the absolute LEAST of your problems! Solar panels are fine for minimal use systems and keeping already charged batteries topped off. If you plan on using them to recharge a dead 36v trolling system, you are going to be covering the entire top surface of your boat in panels and still having to wait a week or more for a full charge.


(have to wonder, why a bike helmet?)

Click to expand...

Thanks for the great advise.. I can't imagine using the trolling motor more then 2-3 straight hours a week. So I'm thinking a 40 watt panel might do the job, otherwise I'll have to keep lugging these batteries from marina to boat and back to charge them.

Re: solar trickle charge for 36v setup...

ericp501 said:

Thanks for the great advise.. I can't imagine using the trolling motor more then 2-3 straight hours a week. So I'm thinking a 40 watt panel might do the job, otherwise I'll have to keep lugging these batteries from marina to boat and back to charge them.

Click to expand...

You will have to either go with three of them, or have to deal with swapping the panel daily.

Re: solar trickle charge for 36v setup...

I hope that you can lock them down somehow, too...

Re: solar trickle charge for 36v setup...

I am glad that you got the strait up information about the sun charging your large battery system! Some people have a gym membership you will be in good shape just moving batteries around. If you charge those batteries off of a solar panel you will destroy them by the end of the summer. You need alot of current to recharge a deep cycle!!!! You don't want to pull them down below 12.3 volts durring the discharge cycle. Put a heavy duty plug connection in your car and charge them individualy on your daily drive to work. Now if we could just inform the rest of America of the real short cummings of Solar Energy.

Re: solar trickle charge for 36v setup...

Star said:

I am glad that you got the strait up information about the sun charging your large battery system! Some people have a gym membership you will be in good shape just moving batteries around. If you charge those batteries off of a solar panel you will destroy them by the end of the summer. You need alot of current to recharge a deep cycle!!!! You don't want to pull them down below 12.3 volts durring the discharge cycle. Put a heavy duty plug connection in your car and charge them individualy on your daily drive to work. Now if we could just inform the rest of America of the real short cummings of Solar Energy.

Click to expand...

real short cummings of Solar Energy..... lol and i wonder y Solyndra went backrupt, hey im glad i didnt invest any money in solar energy companys..... wait, darn it