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Old 01-09-2020, 12:08 AM   #1
Mini-Skoolie
 
Join Date: Jul 2019
Posts: 57
Charging 2 battery banks with different voltages with one solar array.

Our bus has 3 battery banks. 12v starting, 24v main storage, and 12v secondary storage for backup power. The two different storage banks are the result of an upgrade to a 24v system that left us with 6 Wal mart RV batteries that still had Lisa life, as well as a 12v 2500w inverter.
For some time we maintained the secondary system with an a.c. powered multi bank charger that got its power from the inverter connected to the solar array. We put it on a timer so that it wouldn't be charging when the sun was down. Not very efficient.
Recently I had an epiphany. I could place a second solar controller in the system on the output side of the main solar controller. The second controller would drop the 24 volts to 12 and charge the secondary bank. It is set to go into evening mode from 6pm to 8 am to prevent drawing on the main storage bank.
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Old 01-22-2020, 08:36 PM   #2
Mini-Skoolie
 
Join Date: Mar 2018
Posts: 42
They do make 24V to 12V converters designed to do just that. I saw a bunch on Amazon. That would be a much better choice that trying to use a solar charge controller for the same purpose. Good Luck!
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Old 01-23-2020, 12:39 PM   #3
Mini-Skoolie
 
Join Date: Jul 2019
Posts: 57
Quote:
Originally Posted by glenncooper View Post
They do make 24V to 12V converters designed to do just that. I saw a bunch on Amazon. That would be a much better choice that trying to use a solar charge controller for the same purpose. Good Luck!
Dc to DC convertors do just that. They do not provide charge voltage nor do they provide overcharge protection. The second charge controller gets its power from the excess that the system is not using to charge the main battery bank and run appliances. It provides all the protection for the batteries that it would if it were supplied by a solar array. Not reinventing the wheel here, just using it on a trailer.
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Old 01-23-2020, 12:42 PM   #4
Mini-Skoolie
 
Join Date: Mar 2018
Posts: 42
You didn't mention what type of charge controller your using. With something like an MPPT it is trying to dynamically increase the current to pull down the solar panel voltage to a maximum power point where the panel is very efficient. That would be a disaster to have that system on the secondary of another solar charge controller. Not sure if that same issue would exist with a PWM controller, but I would be skeptical. There are unseen ways that this idea could bite you, and then again - it might just work.
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Old 01-23-2020, 12:56 PM   #5
Mini-Skoolie
 
Join Date: Jul 2019
Posts: 57
Quote:
Originally Posted by glenncooper View Post
You didn't mention what type of charge controller your using. With something like an MPPT it is trying to dynamically increase the current to pull down the solar panel voltage to a maximum power point where the panel is very efficient. That would be a disaster to have that system on the secondary of another solar charge controller. Not sure if that same issue would exist with a PWM controller, but I would be skeptical. There are unseen ways that this idea could bite you, and then again - it might just work.
You don't spear to understand how the second charge controller is hooked up. This is not a theory or south g I am thinking about doing. Kit is something I am doing and it works fine. The second charge controller is not hooked to the array. It gets its power from the load circuit. This circuit exists to draw off excess that is not being used to charge the main bank or run appliances. In wind systems they call it a dump load and usually use it to power a heat core or light bulbs.
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Old 01-24-2020, 12:14 AM   #6
Bus Nut
 
Join Date: Dec 2018
Location: Mt Vernon, WA
Posts: 265
Year: 1996
Coachwork: Bluebird, Collins
Chassis: G30 Bluebird Microbird, E350 Shuttle Bus
Engine: 1995 Chevrolet 350, 1992 Ford 460
I’ve heard mention of a second charge controller connected to the Load output of a primary charge controller. What model and types are you using.? I have 3 battery banks also and am looking for options. Thanks
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