Couple of questions about DC-Dc charging
I've been thinking about adding a DC-DC charger now that I've added 400 amp hours of AGM batteries. There are lots of useful posts but I haven't run into a couple of things I'm curious about. One ...
Forum Discussion
Yes otr, I misunderstood where you were saying the parasitic draw was coming from. This topic is about DC chargers though, and I didn’t want to leave the impression with those who might be considering installing one that there was a parasitic draw on the camper battery from the charger they needed to worry about. At least we agree there’s not.
Now if the + input wire to the charger isn’t ignition switched, then your going to have to do something to keep the charger from running down the starting battery when the engine isn’t running. There’s several ways to handle that. You handled it by installing a battery separator, I handled it by installing a constant-duty solenoid close to the starting battery and putting the trigger wire on an upfitter switch that isn’t energized unless the engine is running. I’m not saying one is better than the other because maybe there’s a reason I just can’t think of that makes a separator the better choice, but I know there’s no parasitic draw associated with the solenoid. I can also turn it off easily.
As you may know, I also have a 40 amp DC charger installed in my camper. Redarc also recommends 4 awg wire for circuit lengths of 16-30 ft. The input circuit length on mine is very close to 30 ft from the truck starting battery, through a CB and isolation solenoid mounted at the front of the truck, and then to the DC charger through the campers umbilical cord. It’s 4 awg from end to end, and the wires don’t even get warm. I’m also actively using the camper battery while we’re driving to run the fridge in AC mode with an inverter, which is about a 28 amp intermittent load on it. The DC charger spends a lot of time outputting it’s full rated charging amps, essentially acting as a power supply and either charging the battery or keeping it fully charged.
I know this to be true because I can monitor the charger’s output amps, and the battery SOC. I don’t monitor the input amps to the charger though because like I said, the wires don’t even get warm. The charger input is fused at 60 amps, and as long as it doesn’t blow the fuse, I don’t care what the amps are. I have plenty of alternator to supply it with. The charger is working to its full rated specifications, nothing is overheating, nothing is overloaded, and I’m not short on alternator capacity. I installed a DC charger specifically to get away from having to obsess over tenths of a volt on the charging circuit.
If your friend’s wires are heating to the point where they’re burning off ~15 amps of current, he should probably be looking for materials and/or workmanship problems with his install. I don’t believe the wire gauge difference from 4 to 2 or your shorter circuit length can account for all of that.
:):)
Now if the + input wire to the charger isn’t ignition switched, then your going to have to do something to keep the charger from running down the starting battery when the engine isn’t running. There’s several ways to handle that. You handled it by installing a battery separator, I handled it by installing a constant-duty solenoid close to the starting battery and putting the trigger wire on an upfitter switch that isn’t energized unless the engine is running. I’m not saying one is better than the other because maybe there’s a reason I just can’t think of that makes a separator the better choice, but I know there’s no parasitic draw associated with the solenoid. I can also turn it off easily.
As you may know, I also have a 40 amp DC charger installed in my camper. Redarc also recommends 4 awg wire for circuit lengths of 16-30 ft. The input circuit length on mine is very close to 30 ft from the truck starting battery, through a CB and isolation solenoid mounted at the front of the truck, and then to the DC charger through the campers umbilical cord. It’s 4 awg from end to end, and the wires don’t even get warm. I’m also actively using the camper battery while we’re driving to run the fridge in AC mode with an inverter, which is about a 28 amp intermittent load on it. The DC charger spends a lot of time outputting it’s full rated charging amps, essentially acting as a power supply and either charging the battery or keeping it fully charged.
I know this to be true because I can monitor the charger’s output amps, and the battery SOC. I don’t monitor the input amps to the charger though because like I said, the wires don’t even get warm. The charger input is fused at 60 amps, and as long as it doesn’t blow the fuse, I don’t care what the amps are. I have plenty of alternator to supply it with. The charger is working to its full rated specifications, nothing is overheating, nothing is overloaded, and I’m not short on alternator capacity. I installed a DC charger specifically to get away from having to obsess over tenths of a volt on the charging circuit.
If your friend’s wires are heating to the point where they’re burning off ~15 amps of current, he should probably be looking for materials and/or workmanship problems with his install. I don’t believe the wire gauge difference from 4 to 2 or your shorter circuit length can account for all of that.
:):)
