DC-DC Charging ?

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.

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.

"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.

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..

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.

pianotuna wrote:
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.

Schottky diodes do not drop .7V..

They do drop some voltage but they typically have about .3V-.4V drop unlike Silicone diodes which typically drop .6V-.7V.

However, consider this, adding a diode in front of a DC-DC converter, that small .3V-.4V drop no longer is of any issue since the DC-DC converter will boost the voltage, overcoming any voltage loss on the input side.

The only downside with DC to DC conversion is the input current will go up some to compensate for the voltage loss..

Although personally since OP has a GM, they really NEED to add a relay to the charge line so the charge line is ONLY active with the ignition on.. A $2.00 40A "Bosch style" cube relay is all it takes. A relay in the charge line eliminates the possibility of accidentally discharging the vehicle battery when the vehicle ignition is off.. Shame on GM for being such cheapskates (a TWO DOLLAR RELAY FOR GOODNESS SAKES), Ford and Ram are way ahead of GM for this feature.

"I think it is important not to have a second connection between the house batteries and the truck via the 7 way plug."

It would not matter IMO. The 7-pin would be at lower voltage than from the Renogy so the battery would just ignore it.

I expect when using the Renogy to have solar and Renogy in parallel at the same voltage so they add their amps (but the main reason to have the Renogy is for when not enough solar with overcast skies.)

On shore power I could have the adjustable voltage converter on too, so that's three chargers at once all set to the same voltage.

I will not have any problem running this thing when parked idling the 2003 Chev truck. I did that before when I was doing the inverter trick. It made no diff idling at higher revs either.

Truck voltage fell off with too much inverter load so you have to watch for that. The dash voltmeter quivers pointing up at 14v, then collapses down to the left when you add more load. You can keep doing it until you see that happen. That tells you what your loading limit is. I could run the 35 amp charger but not the 55 amper off the inverter so somewhere between that is my limit. (Also turn off the auto climate etc.)

I imagine it would be the same trying to run a higher amp Renogy than what your limit is in your truck.

The manual does say something about working the alternator too hard, so it is up to the individual to figure out what applies to his own truck.

Hi noteven,

I think BFL13 got the 20 amp unit--that is what I chose, too.

pianotuna wrote:
You convinced me to get one, too! Thanks for finding what, for me, is the right size for the right price.

I bought the Renogy unit and found the size to be quite enormous. Too big for my mounting space so i returned it.

I already have heavy gauge wiring in place as shown here

I'm working on installing a Victron DC to DC Charger.

I ran 2 x 6v golf car batteries and charged them through a diode isolator in our camper outfit in the 2000's. Dodge diesel with 160amp alternator. I connected with an Anderson plug and used big cables. "Charge wire" disconnected in the 7way camper cord.

Never did get around to doing a solar spend on that camper - we didn't sit for much more that 3 or 4 days, temps at just below freezing or above, no inverter/AC loads, outside doing stuff all the time, never ran out of DC power. If batteries got a bit low in cold weather I would start the 300hp Cummins generator. We weren't full time but trips lasted 7 to 30 days a couple times a year.

The DCDC charger is a more sophistimicated version of what I had before, adjustable for different batteries, controlled output. Near as I can figure.

I think it is important not to have a second connection between the house batteries and the truck via the 7 way plug.

When sizing wiring and connectors for the Renogy "40 amp" unit I have, I think the literature states input current is 1.3 times what output is so 40amp output will be running 60amp on the input side. I see Marinco trolling motor connectors rated at 70amp.