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Old 09-16-2020, 10:30 AM   #1
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Solar Trickle charging

Sorry not sure where to ask. Have 2020 3930FB.
I'm wondering if there is any documentation on how many watts of solar is needed to trickle charge batteries. I have 2 - 6V 225 amp hour interstate deep cycle batteries, controller is 100W. Partly the reason I ask is I ALSO have a CalAmp GPS (for theft) unit that I would like to leave powered during winter storage months. I live in CO so mostly sunny. I currently have a 240W solar panel but NEVER, even on hot days, have i seen over 180 watts generated. Usually around 80-120W which concerns me as well.
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Old 09-16-2020, 12:43 PM   #2
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First you have to do an energy audit. You need to know what is drawing power and how much. You mentioned a tracking device, you also have parasitic draws, radio, CO, smoke, propane detector. Some of these are hard wired in. No fuse. You said you have a 100W controller and 240W panel. Is that correct? If so you may want to upgrade that.
If you dont have a battery monitor, that would be a good investment too. You will be able to monitor that state of charge on your batteries. I have a Victron BMV-712 bluetooth monitor. I can keep an eye on the batteries from the house 100' away. Could be handy for you if your RV is in storage. Pull up out front and check the batteries without leaving your car. Victron also makes a Bluetooth MPPT controller that you can also monitor remotely. I have a Victron Smart Solar 100/30 MPPT controller. I should have got the 100/50 model.
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Old 09-16-2020, 12:56 PM   #3
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You need to let us know how you use your rig to help with your answer.

If you primarily use campgrounds with shore power and are only worried about keeping your batteries charged in storage your current set up should be plenty unless your GPS draws a lot. Normally you would want to totally disconnect your batteries in storage but if the GPS is a priority you will want to keep it connected.

If you are considering boondocking with solar as your primary power source you need to do more homework to determine your needs.
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Old 09-16-2020, 12:56 PM   #4
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Agree with the audit. if you are using 30 amps(as an example) per day, you have 3.75 days of battery power to draw on (225ah*50%usable/30amps=3.75 days.). if you figure that the solar is giving you 80-120 watts and we use the nominal 5 hours per day of usable sun... you are still looking at 40ish amps replaced by the solar every day. methinks you have plenty for the job if that is all you are running. Do the audit. Extra solar would not hurt, extra pair of 225AH batteries would provide more peace of mind too... but... you gotta run the numbers.

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batteries, gps, solar

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