DC-DC Charger Topic in Tech Issues

I'm asking... not making fun of, but how can you get a higher voltage charging from something that receives less voltage? Sounds as if they are saying there is such a thing as a free lunch after all.:h

covered wagon wrote:
I'm asking... not making fun of, but how can you get a higher voltage charging from something that receives less voltage? Sounds as if they are saying there is such a thing as a free lunch after all.:h

Step up transformer.

covered wagon wrote:
I'm asking... not making fun of, but how can you get a higher voltage charging from something that receives less voltage? Sounds as if they are saying there is such a thing as a free lunch after all.:h

Same way you can get 120V out of an inverter connected to 12V. The price for the higher voltage out than in is a less amps out than going in.

When electricity is not my major, I replaced enough batteries to know that they don't like above 14V charging.
In Fords no battery lasted me longer than 5 years, when in cars, who charged at 13.9V I had batteries lasting 13 years.
That said technology changes a lot in last years.
My 2017 Ford not only has 250 amps with dual alternators, but also 400W build in inverter.
So far when driving last year I used refrigerator on propane, but being against open flame on the road, I am thinking about running 120V wire from the truck to my TC refrigerator.
This way the standard charging wire will be all I need for TC battery charging.
Much cheaper and no need to find space for another big box.

Batteries are fine with above 14V charging, as long as it is cut back when they are charged. They don't like above about 13.4V after they are charged. Most automotive alternators are set up with a low voltage so they don't ruin the start battery. The price for that is slow charging if the battery is in a low state of charge. I see many automotive alternators seem now to start at a higher voltage then cut back when they get warm - sort of a cheap and dirty 2 stage charge profile.

In boat where you live on DC power, the chargers are all 3 or 4 stage profiles: maximum current until absorption voltage is reached (around 14.4V for flooded cells), then voltage controlled at 14.4V cutting back current until the charge current is below a small value (say 2% of battery capacity), then dropping back to a float voltage (13.4V or so for flooded). This is both the fastest, and kindest way to charger your batteries.

It looks like the Redarc Dc-Dc charger is a three stage charger. Dc - Dc converters can be built that raise or lower voltage, or just keep it the same and regulated. Since your camper house battery is very often in a very different state of charge than the engine start battery, a charger like this makes a lot of sense - though 20 amps is pretty slow.

I had expensive inverter/charger in my previous RV. Don't remember how many stages it had, but it had to be good since golf-cart batteries lived 11 years and I recall adding water to them only twice.
Other members report adding water monthly, what would indicate crappy charger.
From what I see my new Ford charges at lower voltage than previous models, so I hope that will extend batteries life.
No reason to add system who will kill batteries faster for some time gain IMHO.

I just put this update on my Redarc DC-DC Battery Charger topic on Tech Issues if you’re interested.


“I’m really liking this Redarc DC-DC charger.

I’m in California right now, Desert Center to be exact, where today’s high was 113. Driving from Phoenix today the fridge was running in DC mode, and for the first time in the 15 years I’ve owned this TC, the fridge was holding its own in extreme heat using the DC heater.

Temps in the fridge bounced back and forth between 35 and 38. It may have even been cycling off and on. When it’s in DC mode I can’t tell when it’s cooling as easily as when it’s in AC mode because the battery SOC meter on the front of the camper stays with it’s highest indicator lit all the time. When we stopped this evening, the Trimetric said the battery was at 97%.

I have to say that despite the Redarc’s painful price, and a slightly difficult installation process due to the limited amount of space available in my camper, I would highly recommend this to anyone needing to improve the charging performance to the camper battery from the truck alternator.

Remember, you must follow the manufacturer’s recommendation regarding wire sizing based on the length of the run from the truck batteries to get the full rated charge amps from the Redarc.

Remember also that this unit has a built in MPPT solar controller, and I could install a panel on the roof and connect it to the Redarc if I wanted. I may try that some day.

My only question now is “Is it reliable?” I’ll let you know.

For now, I give it a thumbs up!”

:):)