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Old 09-07-2015, 10:42   #1
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Connecting solar to battery banks

I have recently connected 325 watts of solar power to one of my battery banks. Its great for charging that bank but I would rather have it charge whichever bank is in use. I have a 1, 2 or both selector switch so I'm thinking thats where I need to connect my Positive wire coming off the charge controller, but where should the negative line run? The selector switch only seems to switch the positive run. I have a negative bus bar and am guessing that's the correct placement but I don't want to break anything.
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Old 09-07-2015, 11:22   #2
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Re: Connecting solar to battery banks

I connected mine to the main DC panel, it charges the banks in service the start battery via the isolator
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Old 09-07-2015, 11:44   #3
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Re: Connecting solar to battery banks

The negative wire of pretty-much everything, including the solar panels go to one common ground, usually an engine block or a common bus just before the engine block, so you are on the right track there.
The charging circuit runs through the positive wire. The best option if you have two battery banks and you need your panels to charge either/or, is to buy a Voltage Sensitive Relay, like this one...


They are around $80. You connect the positive output from your solar-panel charge controller to one of the battery banks, usually the house bank. You can do this at the permanently positive side of the battery switch if it suits. You then connect the VSR with one positive wire between the two separate banks. When the battery bank is charging, it senses the increased voltage and automatically opens the circuit so that both banks can charge. When the charging stops and the voltage decreases, it closes the circuit so that the battery banks cannot discharge into each other. If one of your banks is already charged, the depleted batteries will automatically accept the highest rate of charge.
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Old 09-07-2015, 13:33   #4
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Re: Connecting solar to battery banks

Thanks guys, I just wired it up to both of my bus bars, positive and negative.
So it looks like the solar charge will now go to whichever bank I have selected.

The VSR switch seems pretty cool and raises another question. Without it and I run the motor and solar at the same time do I have a risk of nuking the the batteries, or are solar chargers smart enough to shut off effectively when the alternator is putting out a load?
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Old 09-07-2015, 15:00   #5
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Re: Connecting solar to battery banks

As long as your alternator and solar controller are set up for 12v systems you'll be fine. Alternators and solar panels can put out a lot of voltage so they are regulated down to suit 12v systems. As long as the voltage doesn't go above 14.4v, the batteries will look after themselves and will only accept charge when they need it. To make sure, just put a cheap volt meter across the battery terminals when everything is charging. Be careful how you wire your alternator. Don't put it on the outgoing side of a battery switch. If it is running and you switch the switch over to a different battery bank, even if it is not connected to a battery bank for a brief second it can damage the alternator.
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Old 10-07-2015, 14:14   #6
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Re: Connecting solar to battery banks

It's amazing how chargers will play well with each other, as long as their settings are in line. If one were to get very picky, a case could be made that the absorption phase time span might be shortened in the case of multiple chargers, but that's not an issue at all with batteries that are getting a good charge. There are often multiple solar controllers hooked to one bank, or solar and wind.

Here's another combiner, not as pretty, but a little cheaper and can be triggered to connect if you need to start off the house bank.

Amazon.com : Victron Cyrix-ct 12/24V 120 Amp Battery Combiner : Sports & Outdoors
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Old 10-07-2015, 20:15   #7
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Re: Connecting solar to battery banks

Your engine batt should be isolated from the house by a batt switch that jumps to the house batt switch common terminal. with solar charging to the same on the house switch and alternator to the engine batt. turning on the engine switch and the house switch off when starting the engine will protect the alt. from too much initial load at startup. once the engine batt is brought back up switch on the house batt ( 1 or 2 ) and charge from the alt. this keeps it simple and doesn't have expensive components to brake/replace. a charge controller will shut off charging when the proper voltage is reached that's what there for Hence no over charging. same with the regulator on an alternator.

hooking to your buss bars is OK but when your running a few things in the house, that other bank that's only 80% charged won't be getting that much of that solar energy. you can spend the money for stuff that will switch it for you or you can try to remember to switch it your self. after replacing a not so old battery from sulphation. I don't forget to switch very often ;-)
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Old 13-07-2015, 11:32   #8
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Re: Connecting solar to battery banks

awsome, thanks for all the great advice everyone.
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