DC-DC Charging ?

There’s more than one way to configure it, but for the most part it’s a parallel scenario, and often* necessary to protect the alternator when using LiFePo4 batteries - Why?? Because of (if one dare believe Victron, et al...) LFP’s high current receptivity...Also, for newer vehicles, the dc to dc converter needs to be ‘Smart Alternator’ or Euro 5&6 compatible...

*depending on components and load

Here’s an interesting primer on the subject:

https://www.youtube.com/watch?v=dzU_pQFa19s&feature=youtu.be

3 tons

Parallel would imply bi-directional flow and that is not really the case. The DC-DC just allows power in one direction. Then it is just a matter of how the DC-DC is connected to the truck and if that connection has any isolation.

Thanks, interesting.

My question was more about the Renogy 20 amper with input from starter and output to house. After some more reading of its manual, it says: (after saying the input and output negs are all on the same chassis for grounding) for the positives:

"the DC-DC output will connect to the 12V auxiliary or house battery that you are intending to
charge. These batteries may be a different chemistry from the starter battery. The DC-DC input
and output terminals are isolated, meaning that the output voltage can be kept stable without
interference from the input circuit. This ensures stable and correct charging of auxiliary batteries. It is best to place the DC-DC closer to the battery you will be charging primarily."

I don't want my SiO2s in parallel with the FLA starter although I am told that is not a problem when floating or charging them. So right now in the TC I have disconnected the 7-pin charging to the camper batts.

I would like to have "alternator charging" as a back up to the solar, since we can't carry a portable gen along in the TC set-up.

I was thinking of using the 7-pin pos and neg in the camper that normally go on the house batt terminals as the inputs to the Renogy and output to the battery. Not too worried about the amps that would supply and the truck has a 40 amp fuse for the pin 4 charging wire so that would cover the higher draw from input than max output of 20 amps. I think.

So would that work like it says and not put my SiO2s in nparallel with the starter batt?

https://www.amazon.com/Renogy-Battery-Batteries-Multi-stage-Charging/dp/B07Q5VYPCF/ref=sr_1_3?crid=24ISMNS5CEXIC&dchild=1&keywords=renogy+20a+dc+to+dc+charger&qid=1613847979&sprefix=Renogy+20a%2Caps%2C399&sr=8-3

EDIT--could I get the same thing by just using a solar controller with the 7-pin pos and neg into the array side?

Put the dc to DC charger in the existing "house" charging circuit on the "house" side of the isolation solenoid.

While in use--there is no back feed path.

Then when the truck is shut off, the dc to DC will be isolated from the chassis battery.

pianotuna wrote:
Put the dc to DC charger in the existing "house" charging circuit on the "house" side of the isolation solenoid.

While in use--there is no back feed path.

Then when the truck is shut off, the dc to DC will be isolated from the chassis battery.

This would be in the Chev truck using the 7-pin which is always live. No isolator as with a Ford. so when engine off, the input to the Renogy would be live and still charging the house? except no charging to the starter batt? OOPs ?

OK same as usual with the 7-pin , have to unplug it when parked and no shore power. Except with the Renogy there, shore power won't float the starter batt too. I put a trickle charger on the starter batt now if parked for a longer time. Could still do that- so the Renogy and the converter would be in parallel on the house. that's ok.

DC to DC converter should be a "one way" device but to ensure it is..

Insert a Schottky Diode in front of the DC to DC converter to ensure your vehicle battery and charging system are not going to damage your house batteries.



Read HERE

"Low Forward Voltage Drop

One of the chief characteristics Schottky diodes are known for are their low forward voltage drops.

Their low forward voltage drops means that they consume less voltage than a typical diode.

A typical silicon diode consumes about 0.7V across its junction.

A typical schottky diode may consume only 0.3-0.4V across its junctions. Thus, it saves about 300mV of power. "



5 pack of 40A Schottky diodes HERE for $9

Those actually are a "dual diode" package, contains two diodes that you can parallel if you like..

BFL13,

It is easy enough to add a solenoid. I'm not familiar enough with dc to DC charge devices--but I would hate to end up with a dead starter battery.

I added a switch to give me manual control of the solenoid(s).

Perhaps write Renogy and ask?

I ordered the Renogy gizmo since it seems to be what I am after. I will do a test with the Trimetric to compare ordinary 7-pin vs same 7-pin with the Renogy for amps to the battery (and report here of course).

I am used to the Chev's 7-pin being always live, so no worries.

Also test for if I need that diode (hope not)

Better to do a solenoid than a diode. Why? because a diode introduces voltage drop--about 0.7 iirc.

The device you ordered has a sense wire so it will only be active when the truck is running. If that is so, then there is no need for a diode or a solenoid.

BFL13 according to Renogys manual you wil have to instal 6-4 Wire from truck to FW as distance 20-30’
Frank.