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mattd
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# Posted: 25 Dec 2018 10:23pm - Edited by: mattd
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Is there such thing as an electrical check valve? For my solar setup I’d like to go from controller to a small battery that would run a few minor 12v devices, and from that battery go to a set of deep cycles that will have an invertor and run the rest of the cabin.
The check valve would be between the 12v battery and invertor batteries. That way, when lights and fans are on all nite running off the invertor, in the morning when the deep cycles are run down, the 12v appliances would still run because that battery hasnt bled its power back towards the deep cycles.
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darz5150
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# Posted: 25 Dec 2018 11:07pm
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Might be easier to use an rv battery selector/combiner switch.
Run your inverter on one side and 12 volt on the other side. During the day when charging, use the switch to connect the batteries together. Then before you go to bed, flip the switch to separate the batteries. Then you can hook your charge controller to either side. But........your charge controller works best when your positive side connects to one end of your battery chain. And the negative is connected on the other end of the chain with ALL the batteries in between.
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darz5150
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# Posted: 25 Dec 2018 11:12pm - Edited by: darz5150
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Why not just get a set of batteries that with run your total load?
That would be the best/easier option.
Quoting: mattd to a small battery that would run a few minor 12v devices, and from that battery go to a set of deep cycles that will have an invertor and run the rest of the cabin.
Mixing different battery types isn't the best option.
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darz5150
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# Posted: 25 Dec 2018 11:29pm
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Here's a switch from amazon. Less than $20 bucks. You can select battery A. Battery B. Both A and B. Or no batteries.
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justinbowser
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# Posted: 26 Dec 2018 12:29am
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Well, a check-valve allows fluids to only go in one direction so the electrical/electronic version would be a diode.
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kittysmitty
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# Posted: 26 Dec 2018 06:12am - Edited by: kittysmitty
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Your looking for a battery isolator, which is just a big diode. Depending on how much charge current you have, amps, you could get away with something with a lower amp rating.
https://www.princessauto.com/en/detail/90a-battery-isolator/A-p8235673e
Here's one
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Old and Slow
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# Posted: 26 Dec 2018 10:21am
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A diode has a voltage drop of 0.7 volts across it. This is significant on a 12 volt system. A fully charged lead acid should read 12.7 several hours after charging while a 12 volt is discharged.
Bob
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MtnDon
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# Posted: 26 Dec 2018 10:46am
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There are battery isolators that use FET's instead of diodes and have a very low voltage drop, but not quite zero. The isolated battery still may never reach 100% full as measured with a hydrometer but comes much closer than what happens with a diode system.
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kittysmitty
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# Posted: 26 Dec 2018 12:17pm
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As MtnDon has stated, there are solid state units, some times referred to as ACR's. Automatic Charge Relays.
https://www.bluesea.com/support/articles/1366/Automatic_Charging_Relay_%5BACR%5D_Expl ained
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MtnDon
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# Posted: 26 Dec 2018 09:31pm
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The ACR sounds to be even better than the FET equipped isolators I was thinking of. Maybe the ACR are newer; I have not needed an isolator for many years and just went by what I had found best to use way back. 
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creeky
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# Posted: 27 Dec 2018 12:34pm
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If your inverter is programmable you could put the inverter cut off at a higher level and thus leave some power for the 12v appliances in the a.m.
Also, the 12v loads could be run out of the solar controller load center with a lower cutoff. Still protecting the battery bank.
Those acr s look good.
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