To Solar or not to Solar

That makes more sense…

I have lots of favorite upgraded in the FJ Cruiser and one of the many bests is the ARB Fridge in the back that keeps the water, sodas, and beers cold. I have been tuning it for years and made it a full-time item over two years ago. I ran into problems with battery fatigue caused by too many discharges. It turned out that the battery was not being adequately charged with the solenoid circuit and the alternator. So instead of purchasing another battery, I added in a RedArc BCDC2525D charging system. It conditions the AGM battery properly and during the Alaska trip, as long as I didn’t keep the 300W inverter running overnight, the battery would never go below 12.3V. However, now that I live in Mesa, Arizona and it is F****NG hot here, the fridge has a hard time keeping things cold. In its valiant efforts in a 150 degree vehicle, it sucks current from the battery and in less than a day can decimate the battery.

Since the RedArc charger has a solar circuit, I bought a 100W solar panel on Amazon Prime days and hooked it up. It puts out 4-6A of current consistently during the day and since the fridge should not take more than 1-2 Amps, It should not suck the battery dry. The problem, however is that it seems to maintain 12.2V when charging, but when I am driving, it ignores the alternator input and just uses solar. This would be OK if the system would boost charge at 14V, but it will not. I decided to send a note to RedArc and ask for some advice.

To RedArc: I have a yellow-top battery as a secondary in my FJ Cruiser. It is isolated from the main and I use a BCDC2525D system to charge it. The battery is only 55AH, but its primary job is to power USB and an ARB 60L fridge. It has worked great so far on a 7 week overlanding trip. However, I have noticed that if the temperature outside is in the 80’sF (26C), the battery will last up to 2 days with the fridge and the truck off. It has so far charged the battery perfectly with daily driving.

However, I recently moved to Phoenix Arizona, which has temperatures outside above 100 deg F (38C). This makes the truck interior hot and the fridge has to work extremely hard to keep the temperatures down. I generally keep the windows cracked, but basically the fridge will drain the battery in less than 12 hours in this heat. So I purchased a 100W solar panel and in full sun it puts out 4-6 Amps of current throughout the day, so I thought this would keep the battery charged. It seemed to work the first two days with the truck sitting. But the battery was down to 12.0 V about mid day today so I drove it around for an hour on errands and I noticed an issue: the solar keeps the charging voltage to 12.2 to 12.4 V rather than the normal 13.5-14.3V that it was charging from the alternator input alone (through the BCDC2525D). Is this how it is supposed to work? Tonight the battery was at 11.7V and I shut the fridge off to keep it from draining the battery to cutoff.

I understand the temperatures are hot here this time of year, but I would expect the RedArc charger to kick charging up to max 14V when the truck is operating, especially if the solar is only putting out 4-6A.

Should I rig up an isolator that disconnects the solar circuit when the truck is running so the BCDC2525D will use only the vehicle alternator charging circuit?

I will see what they say.

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