DC to DC Charger

[TSL]

boogielander,

I respectfully disagree. I have had 2 separate stock travel trailers (maybe pop ups are wired differently) and both of them use the +12V 7 pin to charge the house battery. Easy enough to verify, disconnect your house battery, plug in the 7 pin and see if you have 12v in camper.

Also, my 7 pin +12v has a 30A stock fuse. The OEM would not use that on smaller gage wire. I recently made my own 7 pin pigtail to OEM and it used 10 gage for +/- 12V, 12 gage for brakes and 14-16 gage for blinkers and brake lights.

TSL,

To keep it simple, you could add 12/12 20A charger to your popup and just remember to unplug so you don't drain vehicle battery. I switched to lithium house battery and the vehicle battery actually starts draining the house battery when not running because the lithium is at a higher voltage.

Thanks for the input. The pop up is wired as you describe, near as I can tell. I'm still working on the conversion project, so far I've installed the Lithium battery and installed a new power convertor that will charge Li properly ( A Progressive Dynamics 4100 model ). I've wired everything up but haven't buttoned it all up yet. I did hook up to the truck's 7 pin, with the motor running and what I observed was that voltage across the trailer battery terminals stepped up from ~ 13.6 to ~ 14.4 or something like that with the 7 pin connected. So I know the truck was sending power to the battery. The battery has a bluetooth app which shows me current flow ( + into the battery or - if it's draining ). I'll have to experiment with it over a few weeks and see what happens.
Adding a DC charger in the camper running off the +12V from the 7pin would certainly be simpler than running separate cable from the truck battery and putting an Anderson connector on the back of the truck, albeit that might well be the "best" way to do it.
I did also figure out that the Absorption Fridge on the camper pulls 10A when running on 12V, which I would be doing while on the road, switching over to Propane when at the campsite.
I think the "corner case" I was concerned about was let's imagine the case where the camper battery is depleted at the end of camping trip - it's a Li battery with low internal resistance, so it might put a strong current pull on the +12v pin from the truck. Meanwhile the fridge is also pulling 10A. I suppose that's where that 30A fuse in the truck comes into play right? Worst case that blows. Then I know I need a DC-DC charger. Or maybe it doesn't, and I get home and find the camper battery barely charged on the way home. In which I don't care because I'm going to plug in to shore power at home and charge it up.
Now if I was going to drive from CA to the top of Alaska like @boogielander is planning on, well then I'd need my battery to charge up during the day's drive, so that's a different story.

 

[boogielander]

Thanks for the input. The pop up is wired as you describe, near as I can tell. I'm still working on the conversion project, so far I've installed the Lithium battery and installed a new power convertor that will charge Li properly ( A Progressive Dynamics 4100 model ). I've wired everything up but haven't buttoned it all up yet. I did hook up to the truck's 7 pin, with the motor running and what I observed was that voltage across the trailer battery terminals stepped up from ~ 13.6 to ~ 14.4 or something like that with the 7 pin connected. So I know the truck was sending power to the battery. The battery has a bluetooth app which shows me current flow ( + into the battery or - if it's draining ). I'll have to experiment with it over a few weeks and see what happens.
Adding a DC charger in the camper running off the +12V from the 7pin would certainly be simpler than running separate cable from the truck battery and putting an Anderson connector on the back of the truck, albeit that might well be the "best" way to do it.
I did also figure out that the Absorption Fridge on the camper pulls 10A when running on 12V, which I would be doing while on the road, switching over to Propane when at the campsite.
I think the "corner case" I was concerned about was let's imagine the case where the camper battery is depleted at the end of camping trip - it's a Li battery with low internal resistance, so it might put a strong current pull on the +12v pin from the truck. Meanwhile the fridge is also pulling 10A. I suppose that's where that 30A fuse in the truck comes into play right? Worst case that blows. Then I know I need a DC-DC charger. Or maybe it doesn't, and I get home and find the camper battery barely charged on the way home. In which I don't care because I'm going to plug in to shore power at home and charge it up.
Now if I was going to drive from CA to the top of Alaska like @boogielander is planning on, well then I'd need my battery to charge up during the day's drive, so that's a different story.

yeah i like to build things for extreme use case so i know it can handle whatever i throw at it that is not the extreme.
i mean, with my build i can just run an extension cable to the truck and charge the EcoFlows every 4-5 days with the truck not running and the fridge on all the time without using DC-DC, but i like to have that peace of mind knowing i can lol

the alaska trip will probably have multiple nights at RV sites with hookups instead of wild camping, since it's my first time in bear country and i figured at RV sites with people it'd be less chances of bear coming to me. so... i probably overkilled it LOL

 

[rdugedug1]

Thanks for the input. The pop up is wired as you describe, near as I can tell. I'm still working on the conversion project, so far I've installed the Lithium battery and installed a new power convertor that will charge Li properly ( A Progressive Dynamics 4100 model ). I've wired everything up but haven't buttoned it all up yet. I did hook up to the truck's 7 pin, with the motor running and what I observed was that voltage across the trailer battery terminals stepped up from ~ 13.6 to ~ 14.4 or something like that with the 7 pin connected. So I know the truck was sending power to the battery. The battery has a bluetooth app which shows me current flow ( + into the battery or - if it's draining ). I'll have to experiment with it over a few weeks and see what happens.
Adding a DC charger in the camper running off the +12V from the 7pin would certainly be simpler than running separate cable from the truck battery and putting an Anderson connector on the back of the truck, albeit that might well be the "best" way to do it.
I did also figure out that the Absorption Fridge on the camper pulls 10A when running on 12V, which I would be doing while on the road, switching over to Propane when at the campsite.
I think the "corner case" I was concerned about was let's imagine the case where the camper battery is depleted at the end of camping trip - it's a Li battery with low internal resistance, so it might put a strong current pull on the +12v pin from the truck. Meanwhile the fridge is also pulling 10A. I suppose that's where that 30A fuse in the truck comes into play right? Worst case that blows. Then I know I need a DC-DC charger. Or maybe it doesn't, and I get home and find the camper battery barely charged on the way home. In which I don't care because I'm going to plug in to shore power at home and charge it up.
Now if I was going to drive from CA to the top of Alaska like @boogielander is planning on, well then I'd need my battery to charge up during the day's drive, so that's a different story.

Now thats an interesting one. Does a lithium battery "pull" amps like a motor or just accept was is available on the wire?

If you find that out please let us know, that could certainly change things only having 30amps available. Also, the newer 12v only fridges draw about 4.5-5 amps while running. My 200W solar panel easily keeps the fridge running 50-70 degree weather. There is a point when cabin temperature is too high and the fridge out runs the panel, found out the hard way.

In my case of discharging the lithium, I was also trying to charge 3 lead acid batteries in the bed of my truck, maybe that resistance interfered with the lithium. Sounds like another experiment.

 

[TSL]

Now thats an interesting one. Does a lithium battery "pull" amps like a motor or just accept was is available on the wire?

If you find that out please let us know, that could certainly change things only having 30amps available. Also, the newer 12v only fridges draw about 4.5-5 amps while running. My 200W solar panel easily keeps the fridge running 50-70 degree weather. There is a point when cabin temperature is too high and the fridge out runs the panel, found out the hard way.

In my case of discharging the lithium, I was also trying to charge 3 lead acid batteries in the bed of my truck, maybe that resistance interfered with the lithium. Sounds like another experiment.

Our popup camper, in addition to the 3-way absorption fridge, also has a "shoilet", which I consider of no value and would happily remove that and put an ARB or Dometic chest fridge in it's place. ( for eg this one, which claims 3.1Ah power draw ) Better yet, I'd put it on a slide with an exterior door in the wall of the camper so it could be accessed from outside and when the pop-up is closed up. Then I could look forward to pulling much less DC power for my refrigeration needs. However, the other members of the family, in particular those of the female variety, are stridently against removing the "shoilet" because "you never know, it could be useful" ! The one thing those 3-way fridges do have in their favor is when running on propane they will run "forever" on a 20lb tank, it is amazing how little propane they use.
As for the Lithium battery "pulling" amps.... I don't know either. I'll have to see what happens. Being a "data-aholic", I wish I could wire some sort of a DC current data logger in line with the battery. While there are such things of course, I can't find any at a price I'm willing to pay ( I don't need to know that badly ! )