We recently received this question from Joe in Vermont about the alternator charging circuit in his Cirrus 800 truck camper:
Hi Mike! We have a 2014 Ram 3500 and a 2016 Cirrus 800. While doing some electrical wiring, I rediscovered that the only way to cut power in the camper was to unplug the camper from the truck. This essentially means the camper is running on it’s two AGM’s with solar AND the truck battery! I have confirmed this with NuCamp. With all the chatter about types of batteries and charging I have missed any mention of including the truck battery as part of the system. Why is there not more talk of this? Is this unique to the Cirrus? We are really running on three batteries. You have had good coverage of upgrading truck charging capacity, but with a heavy-duty alternator I have not gone that route yet where a battery isolator could be installed. I am hesitant to mess with the truck. Maybe we will just continue to monitor the camper closely and unplug if we are in a situation when there is the danger of potentially impacting the truck battery. Keep up the good truck camper coverage and stay well.
Thanks, Joe, for letting us know about this problem. We use the word problem because it is, a BIG one. Every alternator charge circuit should have a battery isolator or solenoid to prevent draining the truck’s starting battery when connected to the camper. When we asked Joe if he was sure he said that he had confirmed this with NuCamp who emailed him, “the only way to completely cut power to the truck camper is to unplug the 7-pin tow connector. If you do not disconnect the tow vehicle when stopped for long periods of time, the RV battery will drain your starter battery.” Since the Cirrus 800 is an early model—NuCamp’s first truck camper—we emailed the company to see if this problem has been corrected and we are waiting on a response. We will post the answer here. For those who have this problem, we recommend installing a battery isolator in the alternator charging circuit. This is a relatively simple modification that can be accomplished by anyone with a basic understanding of DC battery circuits.
Of course, a dedicated, heavy-duty alternator charging circuit would be a much better option. The OEM charge circuit found in most trucks uses only 10 AWG wire that provides a trickle charge of maybe 4 amps. A dedicated alternator charge system using 2 AWG cable can provide up to a whopping 100 amps for battery charging. The amount of charge, of course, depends on the alternator in your truck and the solenoid’s quality, but results this high are pretty common. The benefit with this approach, of course, is that your truck camper batteries will receive a full charge each and every time time you drive your rig. We’ve published two articles outlining how this modification can be done in your truck and camper and something that we will soon be doing with the Truck Camper Adventure Rig. For additional information on truck camper batteries and battery charging, check out our introductory Truck Camper Battery 101 article.
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