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Old 09-02-2018, 11:11 AM   #1
2 Rivet Member
2017 Interstate Grand Tour Ext
Ventura , California
Join Date: Jun 2017
Posts: 85
Blog Entries: 1
Solar upgrade, what to expect

With the help of several of you on this forum, I made an upgrade to an mppt controller, 300 watts of solar panels, and added two more house batteries. Who hoo! Charges like crazy!
I have a couple of questions as to what to expect with my new system.

Both house and chassis batteries always read very close to the same. When will the isolator isolate the chassis battery from using any more electricity so that the engine will always start? Are things working right?

With the power off to the house, my system charges the batteries to 14.something in a hurry. Even with the frig off, the system charges to 13. something. So, is the Magnum the main drain culprit? If so, has anyone added a cut off switch?

Running the frig only, what kind of a draw will this make?

Please, for the sake of this newby who's electrical prowess is limited to switching out a light fixture and plugging in a toaster, speak in terms of battery readings 12.4 from 13.7, etc.

Thanks for any use info you can share. With your help, I've come from wanting to cry and push the thing off a cliff to actually enjoying a trip!
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Old 09-02-2018, 01:38 PM   #2
Rivet Master
2013 Interstate Coach
Raymond , Iowa
Join Date: Jun 2014
Posts: 1,189
Unfortunately you cannot speak just in terms of volts unless it has been several hours since there has been any load on the battery. This is not the case with the fridge (and other stuff) running. It takes a long while until the battery voltage can accurately reflect state of charge. I have a battery monitor that records state of charge, and this is what I use to monitor things.

I have 200W solar with the standard two batteries, and no GT fridge/freezer. My batteries are generally OK with 200W of solar with some sun and (usually) some driving each day. We just had ours sitting on a ferry for 1 1/2 days - no solar, no engine charging, fridge running - and we were down to 75% when we drove off the ferry. We then parked overnight soon after leaving the ferry and were down to 65% the next morning. Then we drove all day and got back to 100%.
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Old 09-02-2018, 08:22 PM   #3
4 Rivet Member
2016 Interstate Grand Tour Ext
Houston , Texas
Join Date: Oct 2015
Posts: 333
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