Solar charging a 24 Volt bank

[Bad Obsession]

Battery Bank: 2 deep cycle Group 29 flooded batteries in parallel to get 24Volts at approximately 120 amp hours.

Goal: To charge the battery bank without plugging in to the grid. The bank will have periods of inactivity so it will have time to charge up and then trickle charge.

So here is the questions for you solar experts: Is it better to charge the batteries separate by doing two 50 watt panels and two charge controllers OR use one big 100 watt panel at 24 volts and 1 charge controller?

Any suggestions on the components to use?

These can and probably will be rigid panels and not flexible panels. Keeping the expense down is probably a good idea too.

How would you do it?

 

[dlochner]

When batteries are wired in parallel, the available amphours increase and the voltage remains the same. When they are wired in series, the amphours remain the same but the voltage is added.

To get 24 volts the batteries would need to be wired in series, positive to negative. To get 240 amphours, wire the batteries in parallel, positive to positive, negative to negative.

Solar cells are sensitive to shade, even partial shade. Better to have 2 separate solar panels wired in parallel. If one panel gets partial shade then it won't affect the other panel. Wired in series it will.

 

[Bad Obsession]

The bank has to be 24 volts and I wired it as such, I just get parallel and series confused. The bank is 24 V and about 120 amp hours. I am not worried about shading at all with where the bank and panels will sit.

 

[Stu Jackson]

The bank has to be 24 volts and I wired it as such,

Matt, that just sounds wrong for your boat. Are you sure?

 

[Bad Obsession]

Yes.....This is a trolling motor battery bank.

 

[Ned Ludd]

1 panel and 1 charge controller. You can get either a 24 volt panel or a CC which will take a 12 volt input and step it up to 24 volts.

 

[Chief RA]

BO: Pay attention to Stu as I suspect 24v is not what you want! Most home systems use 24v but boats are usually 12v systems. Chief

 

[kappykaplan]

BO said it was a trolling motor battery bank in post #5.

 

[Sumner]

I use the controller above on my 24 volt trolling motor bank. It is connected to two sets of two 60 watt panels wired in series and two 12 volt batteries in series. At night I can switch the batteries to parallel and add them to the house bank,
Sumner

=============================================
1300 miles to The Bahamas and Back in the Mac...
Endeavour 37 Mods...
MacGregor 26-S Mods...http://purplesagetradingpost.com/sumner/endeavour-main/endeavour-index.html
Mac Trips to Utah, Idaho, Wyoming, Canada, Florida, Bahamas

 

[Chief RA]

My concern isn't can he do it, its, should he do it! If all this is going into a 23' boat it seems just too much weight! Chief

 

[dlochner]

My concern isn't can he do it, its, should he do it! If all this is going into a 23' boat it seems just too much weight!

Depends on where the battery bank is located. A group 29 weighs ~ 65 lbs. so that 130 lbs of battery, the same as one lightweight crew member. Even throwing in a 3rd battery, it is still only ~200 lbs. Compacs are fairly heavy boats for their size and he won't have 75lbs of out board hanging off the stern.

 

[Sumner]

I wouldn't be concerned about the weight either as like Dave said he might be getting rid of an outboard.

I also think weight for some of us is not that much of a deterrent for how we sail. Our Mac is about 3000 lbs. with the ballast in. For the trip to the Bahamas I was probably 1200-1400 lbs. over that and the boat sailed just fine and I sailed for 400-500 miles of the trip in very light winds to heavy winds with the outboard up. I feel that in heavier seas the boat is actually more stable and the waves don't effect it as much. I also was towing an inflatable the whole trip.

Here is a video the second day out when Scott and Gracie ,the dog, came aboard for the day. The boat was fully loaded for the trip along with their weight.

With the boat heeled over and the water ballast in effect the boat is quite stable in gusts and even when Scott goes below for a moment,
Sumner
===========================================================
1300 miles to The Bahamas and Back in the Mac...
Endeavour 37 Mods...
MacGregor 26-S Mods...
Mac Trips to Utah, Idaho, Wyoming, Canada, Florida, Bahamas

 

[Bad Obsession]

Guys...I sold the Compac and I am between sailboats. I am working on the bank on my bay boat.

As far as sailing, I am probably a few years away from the next sailboat (if I don't go crazy first). In the mean time I have friends that I sail with. This whole saga is a topic for another post. I am going to save back to get back into a bigger boat. I have a HUGE laundry list of preferences for the next boat.

This is the battery bank for the trolling motor on my Bay Boat. This boat is part of the larger plan to get my wife into boating because she likes going out on the bay boat. I plan to get her into that and then transition her back to sailing.

 

[jepomer]

Battery Bank: 2 deep cycle Group 29 flooded batteries in parallel to get 24Volts at approximately 120 amp hours.

Goal: To charge the battery bank without plugging in to the grid. The bank will have periods of inactivity so it will have time to charge up and then trickle charge.

So here is the questions for you solar experts: Is it better to charge the batteries separate by doing two 50 watt panels and two charge controllers OR use one big 100 watt panel at 24 volts and 1 charge controller?

Any suggestions on the components to use?

These can and probably will be rigid panels and not flexible panels. Keeping the expense down is probably a good idea too.

How would you do it?

My Capri 22 has spent the past four years on a mooring. 100 watt nominal 12 volt solar panel, charge controller booting the voltage to a nominal 24 volt charging levels for 4 series connected GC2 6 volt batteries (215 amp-hour). Motor is a Torqeedo Cruise 2.0 made in 2011.

Flexible solar panels are even lighter weight if you have a place to mount them.

The advantage of using a voltage boosting charge controller is that the solar panel array can use different physical sized panels as long as the panel voltages are rated the same.