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 > DC-DC Charging ?

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BFL13

Victoria, BC

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Posted: 02/21/21 11:02am Link  |  Quote  |  Print  |  Notify Moderator

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.


1. 1991 Oakland 28DB Class C
on Ford E350-460-7.5 Gas EFI
Photo in Profile
2. 1991 Bighorn 9.5ft Truck Camper on 2003 Chev 2500HD 6.0 Gas
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Gdetrailer

PA

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Joined: 01/05/2007

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Posted: 02/21/21 12:00pm Link  |  Quote  |  Print  |  Notify Moderator

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..

BFL13

Victoria, BC

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Posted: 02/21/21 12:35pm Link  |  Quote  |  Print  |  Notify Moderator

"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--[emoticon] -- 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.

pianotuna

Regina, SK, Canada

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Posted: 02/21/21 02:25pm Link  |  Quote  |  Print  |  Notify Moderator

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.


Regards, Don
My ride is a 28 foot Class C, 256 watts solar, 556 amp hours of AGM in two battery banks 12 volt batteries, 3000 watt Magnum hybrid inverter, Sola Basic Autoformer, Microair Easy Start.

BFL13

Victoria, BC

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Posted: 02/21/21 02:59pm Link  |  Quote  |  Print  |  Notify Moderator

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.

Gdetrailer

PA

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Posted: 02/21/21 03:29pm Link  |  Quote  |  Print  |  Notify Moderator

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..

[image]

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..

MEXICOWANDERER

las peƱas, michoacan, mexico

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Posted: 02/21/21 04:07pm Link  |  Quote  |  Print  |  Notify Moderator

Easy as pie to check quiescent draw in the chassis battery but you need to follow directions [emoticon]

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.

pianotuna

Regina, SK, Canada

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Posted: 02/21/21 04:26pm Link  |  Quote  |  Print  |  Notify Moderator

Hi BFL13,

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

StirCrazy

Kamloops, BC, Canada

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Joined: 07/16/2003

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Posted: 02/22/21 06:55am Link  |  Quote  |  Print  |  Notify Moderator

BFL13 wrote:

Is everyone getting one of these things? [emoticon]

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


2014 F350 6.7 Platinum
2016 Cougar 330RBK

BFL13

Victoria, BC

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Joined: 02/15/2006

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Posted: 02/22/21 08:16am Link  |  Quote  |  Print  |  Notify Moderator

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. [emoticon] People do that somehow, but I gave up. Didn't need it anyway.

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