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Old 05-01-2016, 11:19   #1
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Solar Newbie

Just researching the issue of installing solar panel(s) to top off my house battery bank.
I have a simple 1-2-Both-Off batter switch and
My question is:
if i start the engine on BOTH so that my Alternator is charging BOTH batteries, is it necessary to install anything between the solar controller and the batteries. Does energy from the alternator "backflow" through the batteries then controller to the solar panel???
Does that even make sense???
Thanks
Bill
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Old 05-01-2016, 12:42   #2
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Re: Solar Newbie

Your question does make sense, and the answer is "No". You do not need to install any kind of back-flow prevention device. You will want to look into an "echo-charge" or "battery combiner relay" or "Automatic Charging Relay" to let your solar panel (or your alternator) charge both batteries when the battery switch is not in the "both" position, but what you describe will work.
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Old 05-01-2016, 13:44   #3
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Re: Solar Newbie

Quote:
Originally Posted by Paul Elliott View Post
Your question does make sense, and the answer is "No". You do not need to install any kind of back-flow prevention device. You will want to look into an "echo-charge" or "battery combiner relay" or "Automatic Charging Relay" to let your solar panel (or your alternator) charge both batteries when the battery switch is not in the "both" position, but what you describe will work.
Hi Paul,
My thinking, again, please tell me if i'm on the right track
1. I was going to attach a solar battery controller directly to the panel...(two wires from here to there).
2. Controller will charge two separate banks. (two separate wires to each bank)
I can specify what bank to charge first (say house ) till it say 75% charged then it will go to next bank...then both

Just want to make sure nothing is going to smoke

Am i still good
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Old 05-01-2016, 14:21   #4
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Re: Solar Newbie

Is your alternator wired to the A/B switch? If so, I think there might be a problem if you operate the switch while the engine is running. There will be a moment where the alternator is unloaded, and the alternator output will spike up to a pretty high voltage. This could damage the solar controller.

However, if your two battery banks are a house bank (A) and a starter battery (B), with the alternator wired directly to the starter battery, then there should be no problem.

My boat is wired in a pretty common configuration, where there is an A/B/Both switch, with (A) the big house bank, and (B) the starter battery. My alternator is wired directly to (A), with an echo-charger going from (A) to (B). My solar controller is connected to the main buss (the common side of the A/B switch), although I could have wired it to the (A) house bank (*).

Anyway, as long as your alternator *always* sees a battery load, you should have no problems with smoke.

We've got some actual experts here, so let's stick around and see what they have to say...

(*) -- I have a vulnerability with this connection, where if the A/B switch momentarily disconnects the batteries, then the solar charger might briefly apply full solar panel voltage to my electronics. This would be very bad. Fortunately for me, I never use the A/B switch, except to occasionally test that it works.
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Old 05-01-2016, 14:32   #5
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Re: Solar Newbie

thanks
I have no idea how the switch is wired to the batteries ..(new -old boat) but i will find out this spring..doing a wiring diagram.
But in the normal course of doing things I DO NOT move the switch while the engine is running..
How i manage my energy now is to start the engine with the switch set to BOTH, that way i am charging both banks while underway. When i get to my destination i change the switch to my "house" bank. Leaves the other battery topped off for starting.
so just a little more info for the "experts" out there
Thanks
Bill
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