DC-DC Charging ?

Good that you fixed that! Not allowed anywhere AFAIK.

BFL13 wrote:
Keeping the charger to house battery wires short will help preserve the charger's voltage settings for each type of battery as instructed in the manual for using the dip switches.

Voltage variations on the longer run from the unit to the starter batt should be taken care of by the unit's buck/boost as I understand it.

You could make the unit portable by using MC4s on its input and output wires?

EDIT--the breakaway on a trailer puts the trailer's brakes on right from the trailer's batt (not to be fused), nothing to do with the 7-pin.

While I agree that the break away switch should be an unfused run from the trailer battery, (and mine now is), my trailer came with the break away switch connected to pin 4 of the 7 pin connector. Maybe this is allowed in Canada?

Keeping the charger to house battery wires short will help preserve the charger's voltage settings for each type of battery as instructed in the manual for using the dip switches.

Voltage variations on the longer run from the unit to the starter batt should be taken care of by the unit's buck/boost as I understand it.

You could make the unit portable by using MC4s on its input and output wires?

EDIT--the breakaway on a trailer puts the trailer's brakes on right from the trailer's batt (not to be fused), nothing to do with the 7-pin.

Do remember that if you have a TT with a break away switch and add a DC to DC charger in the 7 pin charge line, since it is a one way device the trailer battery will no longer be connected to the switch. Same problem if your electric tongue jack is connected to the 7 pin charging wire. You will need to add a new wire from the trailer battery to the break away switch.

The cleanest connector I've figured so far is the trolling motor 3 pole - + and - from vehicle battery plus + wire to turn on the DCDC charger.

On my pickup there is no need to wire into the cab from the battery. I think I can get where I need to go by using long booster cables wire as it is joined and easy to protect inside loom.


I've seen a video where the owner jumped the DCDC turn on from the + battery cable coming in. He said this works but you have to remember to unplug the tow vehicle or the RV will continue to draw on the starting battery of the tow/haul vehicle.

DCDC chargers are also isolators so current on flows one way from the starting battery.

Again, any I've seen are supposed to be install close to the batteries they are charging.

Yes it would be super convenient to have it on the truck because I have 2 trailers with batteries and a truck camper.... I'm thinking of a weather proof enclosure where it can still cool somewhere near the rear of the truck.

When I'm done wasting time on that idea I'll throw hat on the ground and order more chargers :)

In Europe these are called "Battery to battery" or B2B chargers - which kind of explains what they are for.

The "tiny wire" in the 7-pin in the truck's wiring has enough ampacity for the 30a draw of the 20a charger. The issue is really the voltage on it tapering with whatever is going on with engine battery voltage, alternator heating, and all that.

I expect it will work ok using the 7-pin with the camper. I also am using the behind the cab 7-pin, not the bumper receptacle so that makes the wire a few feet shorter. (Truck has both 7-pins fitted OEM)

The camper's 7-pin wiring is maybe two feet in my case. With a trailer, you have to add whatever more it is in the truck for the bumper receptacle and then however long the trailer's 7-pin wiring is back to the trailer's battery. That could choke some of the amps besides the amps reduction from the voltage drop at the truck's battery soon after you start the engine.

Whatever works in each set-up! I tried running fat wires back from the truck's battery to the box for an inverter set-up and could not find a good route past the firewall. Going under and back up behind the cab got the wires too close to hot things and one got its vinyl covering melted some. :( People do that somehow, but I gave up. Didn't need it anyway.

BFL13 wrote:
Is everyone getting one of these things? :)

It says to put the unit as close to the house batteries as possible. Makes it tricky for using with a trailer or truck camper and have fat wiring to the truck.

Not clear to me, but they want to reduce voltage drop between unit and starter batt, but want the unit closer to the house batts. So longer wires will be from unit to starter batt, but they will need to carry the higher input amps. Maybe putting the unit closer to the starter batt makes more sense? Guess it depends on your set-up and what your voltmeter tells you once you try it out.

I have been looking at them for a while. I do not have any 12V power from the truck right now as I dont like the limited capacity of the tiny wire in the 7 way.

I am going to put the signal wire (12v hot switch wire) to one of my upfitter switches that is still run off the key. that way if I know it is close to 100% I will leave the switch off and no charging will take place from the DC-DC, just the solar pannels. but I can manualy turn it on and off via the switch but since the switch is key also if I forget to turn it off it wont be a big deal.

Steve

Hi BFL13,

I got the impression you were running a new charge wire from the chassis battery. Obviously, I got it wrong.

Easy as pie to check quiescent draw in the chassis battery but you need to follow directions :)

Connect a DIGITAL WIRE ammeter from the negative battery post. The post. To the engine block.

Lift the negative battery cable from the post leaving the ammeter connected.

The digital ammeter reading you see is the correct RAM PRAM DRAM reading draw.

If you disconnect the ground cable first, it wipes the ECU and BCU and renders a WRONG reading.

This mode should preserve processor units memories. Sometimes a 3rd hand to lift the cable makes it easier. Sometimes it's easier to do this where a single negative connects to the engine.

Multiply milliamps by time. to reveal fractions or whole amp hour depletion.

Depletions are CYCLES. Aggravated by depth of discharge AND length of discharge.

BFL13 wrote:

As is, the truck and camper batts are in parallel with the 7-pin connected whether or not the ignition is on. I left the 7-pin connected for the signal lights etc, but disconnected the charge line so now no "alternator charging".

My Dad many yrs ago when trucks came factory with no trailer hitch or wiring connected the charge line constant battery hot..

Worked OK, but discovered by accident that it was actually a bad idea when he was caught traveling in a severe snow storm and had to get off of a now closed Interstate at the nearest exit.. And found a closed gas station to pull into.

Had to run the furnace in his 5vr all night, the next morning he discovered that the furnace not only flattened his RV battery but his trucks battery.. Now he was stuck in a snow storm with no way to start his truck, no heat, no solar panels, no gen.. Had to wait for someone to open the gas station to get a jump..

Discovered the hard way that needed to test the trailer battery and replace it when weak periodically, and never leave the trailer plugged into the truck overnight..

Because I KNOW this can happen (even to the smartest folks) trying to remember everything that must be done manually can and will eventually bite you in the behind..

I try to automate things as best as possible so I have far less things to deal with or remember to do.

If trickling your vehicle battery is an issue when parked and you have shore power, I would suggest a cleaner way to do this is to buy a small ready made multistage chargers that is designed for that job and run it from 120V..

I bought one of these..



To use on my whole home generator, 12V three stage at 5A..

Bought it back in 2018 and so far, I have zero complaints, it seems to keep the starting battery in tip top shape.. Automatic charging, no buttons to remember to push, no need to disconnect it.. Just lights up and charges and does it's thing when 120V AC is present.

$36 HERE

I am sure you could easily setup a 120V connection back to your truck to make that happen..

Adding that would allow you to isolate charge line with a relay that is turned on via ignition key.

All fully automatic, no more voltage differences worries..

Generally though, you should be able to park your truck for several months without the need to charge the truck battery.. If you have to have a constant charger on it, you may have issues with something drawing power (IE something not turning off?).

Good FLA batteries can easily sit for two or three months or so without the "need" of being recharged provided there is no other major current drains than the battery self discharge and if connected to the vehicle only radio memory and body control computer drain..