features for dc to DC chargers

I read that part, but it does not say how it works; only says it does that. It comes from Oz, so it must be wizardry. What's behind the curtain?

This is how Green Power Priority works:

“ if a solar power input is available the maximum available solar power will be used before topping up the output charge current from another power source.”

Some Redarc products will have an AC input, an alternator input, and a solar input. In that case, if your solar panels are outputting any power at all, it will use it all then top it off with either the AC input or alternator input.

WHAT IS GREEN POWER PRIORITY?

:):)

https://www.redarc.com.au/dual-input-25a-in-vehicle-dc-battery-charger#:~:text=The%20REDARC%20BCDC1225D%20is%20a,Solar%20and%20DC%20inputs%20simultaneously.

It doesn't say how it does the Green Power Priority. I imagine they do it by keeping the solar voltage as the highest input.

The solar controller is MPPT, which usually means it has a buck converter in it, and if it has adjustable settings you can pick an output voltage, but that has to be under the input voltage IIRC. So that part would not be a buck/boost AFAIK.

The alternator input part is supposed to be via a boost converter and is also a buck converter with some models like that Stirling mentioned elsewhere. I got lost what this Redarc has.

I am happy I don't need a DC-DC charger! Too complicated :)

Yes it is in the manual, I just noticed they make a 25amp dual input model as well.

S Davis wrote:
The Redarc 40 and 50 amp dc to dc chargers have a built in solar controller that use solar charging first and then supplements with alternator charging, might be a useful feature for some.

Does the manual explain how it does that? If so I will read it, no need to write it up here, thanks.

With no DC-DC in the Class C, I get solar and alternator to add their amps, but with the solar set at 14.8v and the alternator at say 14.0v, I don't get all the alternator amps there are.

Example rough figures-- Turn off solar and get 20 amps alternator charging as seen on the Trimetric. Get 20 amps solar, engine off. Turn on engine and get 40? Nope. Get about 30 total. The voltage spread from battery to 14.8 is more than from battery to 14.0 so the alternator amps are already tapering from shrinking spread as they both raise the battery voltage. Once the battery reaches 14.0 all the amps are from solar.

(The battery bank has to be low enough to accept the total possible amps at the time or you can't tell if the 30 is just from that being the max acceptance)

So that Redarc is doing something like that too, but where it is the one with two inputs at different voltages, not the battery itself --or what? It must have just the one voltage for output, but two different input voltages?

If you already have solar, do you swap over to the Redarc controller or are you better off staying with the one you have? Depends I suppose.

theoldwizard1 wrote:

time2roll wrote:
Primary feature is amp rating. JMHO. Bigger is not always better and watch the input amps. The rating is output.

For any kind of trailer, you need to remember that the input limiting factor is the fuse on the battery wire in the 7 way connector.

Watch the video I linked before ! The first thing that happened when he started his test was that he blew the fuse !!

Which is a pretty good indication that trying to run a 40 amp DC charger through the trailer charging circuit isn’t going to work. When I was in my pre-purchase learning phase, I remember reading on one of the DC-DC charger manufacturer sites that the majority of the “This @#$& thing doesn’t work!” complaints they get are due to the installer not following the wire size recommendations in the instructions.

There were several things I didn’t like about the video, and the way he was demonstrating the charger. He initially suggested that the unit could be connected directly to the alternator (nope!) or the starting battery, he then reinforced that misinformation by referring to the starting battery in the RV (that you could clearly see he was connecting to) as the alternator, and finally hooking it up in such a half-a$$ed manner that the input fuse blew just left me shaking my head.

The smallest gauge wire recommended for the Renogy 40 amp charger he was demoing is 6 AWG, regardless of how short the circuit length is. What he was using wasn’t 6.

Just for grins, I read through the instructions for a Renogy 40 amp unit just to see what they said for an installation like mine. The circuit length between the starting battery and the Redarc charger is about 27-28 ft long, and Redarc recommended 4 AWG wire and a 60 amp fuse. Renogy also recommends 4 or 2 gauge wire and a 60 amp fuse on the input side.

:):)

The Redarc 40 and 50 amp dc to dc chargers have a built in solar controller that use solar charging first and then supplements with alternator charging, might be a useful feature for some.

time2roll wrote:
Primary feature is amp rating. JMHO. Bigger is not always better and watch the input amps. The rating is output.

For any kind of trailer, you need to remember that the input limiting factor is the fuse on the battery wire in the 7 way connector.

Watch the video I linked before ! The first thing that happened when he started his test was that he blew the fuse !!

time2roll wrote:
Primary feature is amp rating. JMHO. Bigger is not always better and watch the input amps. The rating is output.

As "Generic" info goes that is best response.

NOT ENOUGH INFO however for a more precise answer
What do you want to use it for?

There are several different DC>DC devices
Some are very simple.. Your 12 volt phone charger for example is likely nothign more than a 3 terminal regulator (if that) that drops the voltage.

A buck boost is much more complex starting with an inverter then some way of boosting the voltage (Transformer) then rectifier and filter and a regulator for the output.

NOTE that high frequency transformers and filters are not nearly as big as low (50/60Hz) units are.

Multiple battery chemistries and highly adjustable in terms of voltage. Nice to be able to save multiple programs. If you can control voltage and amps then it sorta future proofs you to newer lithium batteries that will have slight differences in volts per cell.

I have not done a firmware update to my charger in 5 years. It does not allow me to adjust charge voltage of Pb battery to 2.7v per cell. Sometimes you can unlock these chargers. Other times a firmware upgrade will allow for whatever new things comes out.

For example i have a smaller cheaper DC to DC charger. In order to get into the settings they made you do something very simple. Some type of code. Then you could adjust to a higher voltage when the newer high voltage lithiums came out a handful of years back.