In April of this year, during a Mojave Road trip I began noticing that under certain conditions, my National Luna dual battery controller would not charge my secondary battery. Very disturbing when you are relying on the perishable food in your fridge to feed your family in the back country, not to mention the risk of warm beer at the end of the day.
The controller works by isolating the secondary battery for the first 5 minutes after you start your vehicle to give the primary battery a chance to recharge after spending it's energy on starting. After 5 minutes, the controller checks the voltage of the primary and if it's above the threshold, it let's the alternator charge both batteries.
At the same time that I noticed the problem, my friend who has the same system (and vehicle but more on that later) noticed that his secondary wasn't charging.
Over the next few days, we managed to have enough juice from intermittent periods when the secondary would get charged to keep our fridges going. A pattern appeared to emerge.
-Start the vehicle after a long rest, five minutes later the secondary is charging as it should.
-Drive for a period, secondary stops charging...******?
It seemed to me that heat was somehow responsible. Both of us drive Land Rover D2s and were well aware of how hot it gets in the engine compartment after long runs. We postulated that maybe the little controller unit was overheating and shutting down....the best we could do was guess.
Possibly it was an alternator issue and our alternators were not performing to full spec and so the Luna controller was just doing it's job and isolating the secondary and charging the primary because the alternator couldn't keep up with charging both batteries.....but my friend's alternator was new and I hadn't had any voltage issues on the primary while running A/C, High-beams...etc.
We saw that National Luna would have representation at Overland Expo and we sought them out during our 4 days camped at Mormon Lake.
Peter, from National Luna was kind enough to hike over to our campsite and take a look at my setup. Armed with his voltmeter, Peter dived in with his probes measuring voltages across the batteries while I ran the engine in all possible permutations of Lights on, Aux Lights on, A/C on, etc.
He determined that my alternator was very healthy and that his unit was performing as it should. We obviously couldn't reproduce the high heat conditions sitting there in the meadow but Peter who was aware of the issue and seemed to think it was connected to the D2s alternator possibly reducing it's output in high heat conditions to protect the battery from damage.
My buddy and I were armed with Goal Zero Nomad 27 Panels (2 each) which we daisy chain and plug into the Goal Zero Guardian charging unit and finally to our secondary batteries. We were very easily able to keep our aux batteries topped off during our 4 days of no driving in the meadow at Mormon Lake. Even a few hours of good sun can bring the secondary battery back to health after a day of driving with only intermittent National Luna charging. Not only that, we put all four panels together and rescued a fellow camper whose fridge had drained his single battery. The sun isn't always out, the charge control system needs to work, even when it's hot.
My question to the hive mind is: Does anyone know if the stock D2 alternator does indeed have this temperature sensing/voltage reducing feature?
I'll be diving into this thread to see what other isolator/charge control solutions folks are using in the event National Luna doesn't come up with a solution before my next trip.
The controller works by isolating the secondary battery for the first 5 minutes after you start your vehicle to give the primary battery a chance to recharge after spending it's energy on starting. After 5 minutes, the controller checks the voltage of the primary and if it's above the threshold, it let's the alternator charge both batteries.
At the same time that I noticed the problem, my friend who has the same system (and vehicle but more on that later) noticed that his secondary wasn't charging.
Over the next few days, we managed to have enough juice from intermittent periods when the secondary would get charged to keep our fridges going. A pattern appeared to emerge.
-Start the vehicle after a long rest, five minutes later the secondary is charging as it should.
-Drive for a period, secondary stops charging...******?
It seemed to me that heat was somehow responsible. Both of us drive Land Rover D2s and were well aware of how hot it gets in the engine compartment after long runs. We postulated that maybe the little controller unit was overheating and shutting down....the best we could do was guess.
Possibly it was an alternator issue and our alternators were not performing to full spec and so the Luna controller was just doing it's job and isolating the secondary and charging the primary because the alternator couldn't keep up with charging both batteries.....but my friend's alternator was new and I hadn't had any voltage issues on the primary while running A/C, High-beams...etc.
We saw that National Luna would have representation at Overland Expo and we sought them out during our 4 days camped at Mormon Lake.
Peter, from National Luna was kind enough to hike over to our campsite and take a look at my setup. Armed with his voltmeter, Peter dived in with his probes measuring voltages across the batteries while I ran the engine in all possible permutations of Lights on, Aux Lights on, A/C on, etc.
He determined that my alternator was very healthy and that his unit was performing as it should. We obviously couldn't reproduce the high heat conditions sitting there in the meadow but Peter who was aware of the issue and seemed to think it was connected to the D2s alternator possibly reducing it's output in high heat conditions to protect the battery from damage.
My buddy and I were armed with Goal Zero Nomad 27 Panels (2 each) which we daisy chain and plug into the Goal Zero Guardian charging unit and finally to our secondary batteries. We were very easily able to keep our aux batteries topped off during our 4 days of no driving in the meadow at Mormon Lake. Even a few hours of good sun can bring the secondary battery back to health after a day of driving with only intermittent National Luna charging. Not only that, we put all four panels together and rescued a fellow camper whose fridge had drained his single battery. The sun isn't always out, the charge control system needs to work, even when it's hot.
My question to the hive mind is: Does anyone know if the stock D2 alternator does indeed have this temperature sensing/voltage reducing feature?
I'll be diving into this thread to see what other isolator/charge control solutions folks are using in the event National Luna doesn't come up with a solution before my next trip.
