DC to DC charger

Bedlam wrote:
What I have not seen posted is the fact that even if you use like chemistry batteries in the camper and truck, the capacity and age of the different batteries also affects charging (in addition to the small gauge trailer plug wiring). When you look at the diesels with dual start batteries, they have to be changed out in matched sets to keep optimal charging and power delivery (discharging). Putting in a DC to DC charger helps overcome these differences.

My two lifePO4 (560ah) will charge at 50 amps until they are almost completely charged with the low internal resistance unlike lead acid or agm.

What I have not seen posted is the fact that even if you use like chemistry batteries in the camper and truck, the capacity and age of the different batteries also affects charging (in addition to the small gauge trailer plug wiring). When you look at the diesels with dual start batteries, they have to be changed out in matched sets to keep optimal charging and power delivery (discharging). Putting in a DC to DC charger helps overcome these differences.

ticki2 wrote:

Hemi Joel wrote:
I just use a pair of 8 gauge wires from the truck battery to the camper batteries. That eliminates the voltage drop of the 7 pin and puts a nice charge into the camper batteries whenever I drive. I use a 200 amp blade switch that is mounted on the truck battery to isolate the truck battery when the situation calls for it, but that is rare.

The reason it’s working for you , and also for me , is the age of the truck . Newer trucks , last decade , have smart charging , meaning as soon as the starting batteries are satisfied charging goes way down , so the house batteries would get very little , especially with the voltage drop.

That is not true on newer GM HD trucks, my 2019 Chevy 2500HD sits above 14 volts, when changing my batteries it will ramp up to just above 15 volts @ 50amps.

According to the above statement I should have a smart alternator, but I have yet to see this mysterious lowering of voltage a few people on here keep stating. So maybe Ford and Ram do but my 2013 and 2019 Chevys don’t or if they do the alternator is smart enough to ramp up under heavy load.

Hemi Joel wrote:
I just use a pair of 8 gauge wires from the truck battery to the camper batteries. That eliminates the voltage drop of the 7 pin and puts a nice charge into the camper batteries whenever I drive. I use a 200 amp blade switch that is mounted on the truck battery to isolate the truck battery when the situation calls for it, but that is rare.

The reason it’s working for you , and also for me , is the age of the truck . Newer trucks , last decade , have smart charging , meaning as soon as the starting batteries are satisfied charging goes way down , so the house batteries would get very little , especially with the voltage drop.

Here's my experience with adding a DC to DC converter. 2016 Ford and Lance camper with all the wiring per their recommendations. While I got some charging out of the truck it was less than optimal and trying to run the refrigerator on DC meant I got to my destination with low batteries. The longer I drove the lower the batteries got. It just didn't work. I also got tired of messing with running the refrigerator on propane. Sometimes it worked fine and other times I arrived with it out...added baffle....new thermocouple... etc. Based on recommendations from a lot of people I decided to add a DC to DC converter.

Bottom line. The DC to DC converter just works and works well so I arrive at my destination with fully charged batteries and a cold refrigerator every time. I went with the combo Renogy MPPT and DC to DC all in one (DCC50S) to replace my PWM solar controller while I was at it. It gives 25 amps from solar and 25 amps from the truck with priority from solar. It will also charge the truck battery from solar if it gets low when you are parked for a long time. For me it was the right option and I should have added one a long time ago. It is also LiFePO4 compatible so when I upgrade batteries I only need to change the setting. If your rig charges while driving, or you don't need it to, then a DC to DC charger is not for you. For the rest of us.... they are awesome.

Hemi Joel wrote:

theoldwizard1 wrote:

Hemi Joel wrote:
I just use a pair of 8 gauge wires from the truck battery to the camper batteries. That eliminates the voltage drop of the 7 pin and puts a nice charge into the camper batteries whenever I drive.

It has been proven 100s of times, that with modern vehicles, large gauge wires will NOT give you a 100% charge on your auxillary battery bank.

Some charge, yes. Just not 100%.

That makes no sense at all. The alternator doesn't know how many batteries are connected to it. It senses voltage. Batteries that are connected equalize over time.

Regardless, it has been working for me for over 10 years. If you want to buy a device to charge your 12 volt batteries better than a 12 alternator that was designed to charge 12 volt batteries, that's your call.

what you seem to be forgetting is that a altanator output is for charging starting batteries, and as long as you use thoes in your camper/trailer/motorhome for house batteries you'll be fine, might not have that much capacity but you'll charge them up good. the problem comes into when you go to different types of batteries like deep cycle, gell, lithium etc. they require different charge profiles for efficient and proper charging in order to get charged fully and with out doing dammage to the battery its self. a dc to dc charger alows you to charge using proper profiles for your battery type alowing longer life and proper charging.

Hi HMS Beagle,

With lead acid house bank and lead acid starter I had charging. Enough that a 60 amp fuse fell on its sword.

My upgrade was to dual #8 (oem was #8) with twin 50 amp automatic circuit breakers. My ammeter maxes out at 70 amps--and I did have occasions where it would not display.

The lead acid were replaced with telcom jars, and whoops there was no charging from the alternator to the house unless I was running the microwave or other heavy draw. In fact it regularly sent power to the alternator. I replaced the starter battery with an AGM. No improvement.

My 20 amp renogy 20 amp dc to DC charger is sending up to 19.6 amps to the house bank. It is NOT a short run and is #8 wire. There is no voltage sensor.

I'm happy as a clam to have charging going on.

With a modern vehicle the charge voltage will be at least 13.5 volts, probably more. That will charge the house batteries 100%, though it may take a long time, and only if the charge wire to the camper is large enough to service the house loads. If you have your refer on DC for example, it is drawing around 30 amps. The #10 typical of a 7 pin harness will be dropping about 1.8V in the 60' round trip on the wire. Now your 13.5V is only 11.7 and, yeah, no charge, in fact it will drain the house. May burn up the 7 pin too. Change that wire out to #6 with a proper connector, and even at the same length and amperage, you will have a 0.7V drop, your 13.5 volts is now 12.8, almost no charge but at least not draining the house battery

A DC to DC charger placed near the alternator, without remote sense, does not solve this wiring problem, voltage will still be low. Placed near the load, or with remote sense near the load, it band-aids the problem: It will boost the voltage back to where is it supposed to be, at the cost of drawing even more current through the inadequate wires.

You need to address the wiring problem first, then consider a DC to DC charger. Or don't run large house loads (like the refer) on DC.

theoldwizard1 wrote:

Hemi Joel wrote:
I just use a pair of 8 gauge wires from the truck battery to the camper batteries. That eliminates the voltage drop of the 7 pin and puts a nice charge into the camper batteries whenever I drive.

It has been proven 100s of times, that with modern vehicles, large gauge wires will NOT give you a 100% charge on your auxillary battery bank.

Some charge, yes. Just not 100%.

That makes no sense at all. The alternator doesn't know how many batteries are connected to it. It senses voltage. Batteries that are connected equalize over time.

Regardless, it has been working for me for over 10 years. If you want to buy a device to charge your 12 volt batteries better than a 12 alternator that was designed to charge 12 volt batteries, that's your call.

theoldwizard1 wrote:
Of course, you now know that wiring upgrade is not required when you get a new truck !

No, I don't know that.
I can't envision how the excessively long wire run of smaller gauge wiring of the stock truck wiring (on a new truck) will provide the amperage I see with my upgraded system