DC-DC Charging ?

[BFL13]

When you add a DC-DC charger from the truck as in several threads about that, does that put the house batts in parallel with the engine batt? (as with normal "alternator charging" via 7-pin)

Or is it just charging the house batts, which are isolated from the engine batt being charged from the alternator?

[BFL13]

Good that you fixed that! Not allowed anywhere AFAIK.

[vermilye]

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?

[BFL13]

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.

[vermilye]

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.

[noteven]

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.

[BFL13]

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.

[StirCrazy]

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

[pianotuna]

Hi BFL13,

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

[MEXICOWANDERER]

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.

[Gdetrailer]

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..

[BFL13]

pianotuna wrote:
BFL13,

The 7th pin may back feed from the trailer when the engine is running. I don't think that is too productive for presenting 14.7 to the house batteries. A simple dc rated switch on the 7th pin feed wire would solve the issue.

Lost me there? The 7-pin #4 charge wire will be on the Renogy pos input terminal and also jumped via manual switch to the ignition terminal.

What back feed can there be? The charger is one-way from 7-pin to camper battery.

[pianotuna]

BFL13,

The 7th pin may back feed from the trailer when the engine is running. I don't think that is too productive for presenting 14.7 to the house batteries. A simple dc rated switch on the 7th pin feed wire would solve the issue.

[BFL13]

"One line to charge the RV from the vehicle when ignition is on and one from RV to charge the vehicle from the RV.."

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".

At home parked for a while, I have a maintenance charger that holds at 13.4v forever, plugged into 120v and also the camper is plugged into 120 for the converter to float the camper batts.

With the Renogy, all I am doing is putting it between the camper batts and the camper's 7-pin, which stays connected to the truck's.

Instead of the ignition on/off trigger as designed for it, I will have 12v to it and I can put a switch on that line so my ignition trigger will be manual instead of automatic. Otherwise I would have to undo the 7-pin when parked

Your relay idea would make that auto instead of manual.

If I only had the trickle charger on the engine batt and left the Renogy on (no relay) I could float the camper batts too without plugging the camper's shore power in for the converter, BUT-that would make the voltage at the camper batts 14.7--EXCEPT the Renogy has a three-stage profile where it stays in Absorb for three hours and then drops to 13.x, so I suppose that would work...Except--:) -- leaving the camper fridge on 120v while home before a trip wouldn't be possible.

So--all same routine as now, except for my manual switch on the "ignition wire" to play with.

[Gdetrailer]

BFL13 wrote:
I like the always live 7-pin on my Chev. When the camper is on, and parked for a long time, the shore power to the camper converter floating the camper batts also floats the truck batt.

With the 5er it was not an issue since the 7-pin is disconnected when you un-hitch and move the truck away.

Without that, I need another maintenance charger for the truck batt. I have to use a second charger for the Ford Class C to keep the engine batt up when parked a long time.

Since I don't want to mix batt types now, I have to use a separate charger for the truck batt anyway. With the Renogy installed there is no choice, so separate charger for the truck still needed.

Sounds like your going to need two separate charge lines, or some complex relay switching to make what you want to do work.

One line to charge the RV from the vehicle when ignition is on and one from RV to charge the vehicle from the RV..

Relays will use power when activated, Bosch cube styles are around 250ma-350ma (3W-4.2W). Not much concern for the vehicle side when ignition is on but it is a drain on the camper side when vehicle is not running..

Have to be careful about using "solenoids" several styles of those, some designed for intermittent duty (like starting) some are designed for constant on use and some are a ratchet style that uses a impulse to the coil to switch on/off.

One of the downsides of automotive (starting or constant) solenoids is the coil draws more current than a relay which needs to be accounted for..