Update to dc/dc converter install

I’m returning to this post with an update. I’m not finished with the whole project yet but I finished the dc to dc charger and battery wiring today. I labeled some of this because the wires are close to one another.

I added the Victron 712 smart monitor because why not spend more on this project.
So over the top of the two 105 ah Lion Safari batteries is the wiring for the dc to dc converter and the Progressive Dynamics 9100. Just one red positive from that to the positive bus bar.
The batteries are also wired to the buss bar and the Victron battery reader is on the far side. Oh I took this before I had that wire connected.
I also wired a Progressive Industries EMS-LCHW30 it’s the smart version so I buried it in the converter box where the old WFCO was located. I moved the incoming wire from the top of the compartment to the bottom using the same hardware and used 12 awg romex to wire to the incoming breaker and to extend the incoming power wire.
I didn’t get any pictures because it was kind of a frustrating job and I didn’t have my phone with me.
I just kept buying stuff and made this a much more expensive project than I expected. And I had most of the #2 wire. I had all red so in two places I used red for the ground but marked it with black tape. I ordered a couple of shorter more flexible #2 wire too.
This has been an expensive project. I invested because I hope to keep this newer RV another 10 years. The batteries were from Costco for about $1725 with tax and then another $912 in added equipment with 8% tax. That’s a crazy $2650 or so for new batteries. Yikes. Plus several days of installation. If I hadn’t seen that sale ad from Costco...

Item Cost
PD 9100 $189.79
Renogy DC $139
PI surge suppressor $180.61
Victron BMW 712 $206.55
Buss bars $14.97
Lugs 3/8” $13.98
Lugs 1/4” $14.07
3 ft blk/red #2 awg wire flexible $20.99
Shrink wrap $7.59
#2 to #4 wire adapters $9.99
ANL 60 amp fuse and extra fuses $21.12
1ft 12 ga cord too short $11.97
2 ft 12 ga extension cord $13.97

I’m actually thinking of screwing the charger to a piece of plywood fitted in the step battery compartment directly above the batteries. The solenoid is in the same compartment and I’m planning to use #2 wire. I was not planning to replace the wire from the chassis battery though. That would be a pain. I’m working on the wiring information for the progressive 9100 charger too. I’m not sure how close I can get it to the batteries. It’s actually not that far away at the WFCO converter about 4’. But I could reduce that if I figure out how to place it under the refrigerator. Still planning.
After reading about circuit breakers and ANL fuses, I decided a fuse was safer so I ordered a case and a couple of extra fuses. May never need to replace one but good to have.

It looks like you’ve got the connections right. The only thing I’d say is to make sure the circuit lengths as short as possible. On the input side of the Renogy unit, the circuit length will likely be quite long which will induce a voltage drop. But, by using the recommended wire size, it will be able to draw the needed amperage through the bigger gauge wires so the unit can boost the voltage on the output side.

Hopefully you can place the Renogy charger very close to the batteries it is charging, and keep the circuit length on the output side as short as possible. Inducing voltage drop on the output side would defeat the purpose of the DC-DC charger.

:):)

So here are the wiring connections for my rig. First the not very helpful Renogy diagram. I suppose it gives the general operational idea.

This is my plan for the solenoid/isolator wiring.

The negative side of the charger input is grounded under the rig with other grounds.
On the coach battery connections i add a 60 amp breaker then wire that to the coach DC and the positive battery terminal. And then wire the negative directly to the negative terminal.

Edited to add charger connections.

Thanks! That was exactly my question. I figured that the charger would be on the battery wire after the isolator and only work when the coach is running. I needed confirmation that the LG wire would read the ignition starter and pass that to the charger through D+. But of course had I been testing instead of looking for the answer at night online I may have figured it out. Nothing like hands on. Just interesting that these wiring diagrams leave out some detailed information. So glad you identified these wires.

The solenoid shown in your diagram is the isolation solenoid between the starter battery and the coach battery, correct?

The wire “LR” you’ve circled is the activation wire for the solenoid, and should be switched by the ignition. You can confirm that with a 12v test light or volt meter. With the engine off and ignition switch off, there should be no voltage between that terminal and ground. With the engine running, there should be voltage. If that’s true, that’s your switched circuit to connect the D+ wire to. The purpose of the D+ wire is to activate the Renogy charger only when the engine is running. It doesn’t carry any charging current, which is why it’s so small. It’s just to sense when the engine is running.

The wire you said is labeled LG, is actually “LC”. It’s used for current limiting only. If it’s connected to a 12v source, the output of your 40 amp charger will be limited to 20 amps. I have no idea why you’d want to do that. If you want to use the Renogy’s full charging capacity, don’t connect anything to the LC terminal.

The DC input to the Renogy could be connected to the “CABLE ASM STATER-EXT RED 2” side of the solenoid (yes, I think that’s a typo as well). That cable should be coming from the plus side of the starter battery. Ensure you’re using the recommended gauge wire for the input and output wires connected to the Renogy charger. Both plus and minus.

:):)

Here is the wiring diagram for my 25b.

Attach to CABLE ASM STATER-EXT RED 2? (I assume that is a typo for starter.)

Thanks for your replies. My rig does not have a boost switch. At least not where our Itasca had one on the dash. I’m looking for a wire that is energized with ignition to switch on the DC/DC converter. This is a Renogy 40 amp charger and a D+ wire is required from the alternator for turning on with on-board battery or ignition. “Note: requires wired to turn on DC-DC.” I believe this means that the charger is only is switched on when connected to a switched on ignition. Would attaching the D+ wire to the “boost” turn it on with ignition? Or is that wire also switched and I’m just not aware of that function on our new RV? I noticed the engine battery boost switch is an option. Otherwise would it be the + wire from the engine chassis labeled Ford battery in the photo?
The wiring diagram is unclear about the use of the small wire on the isolator. They label it LG. I don’t know if that means boost. And I’m assuming boost is the switch that allows the batteries to jump the coach battery if that is depleted.
I don’t need another switch for this device. I’m hoping it just charges like the normal alternator charge except protects the batteries from overcharge and the alternator from burning out. I just need to know exactly where to connect the 16-18 ga wire. That is recommended for the D+ connection. I wish there was a diagram that shows exactly where to connect it.

I can’t tell from your post, so I’ll just ask:

Is the input wire to the DC-DC charger switched? In other words, is it energized all the time, or does it become energized when you start the vehicle, or flip a switch manually?

If it’s already switched, then you just connect the “starter wire” (D+ Ignition) to the same source as the +DC input terminal. Unless your wanting to have total control over when the DC-DC charger is actually charging, then you would run the D+ Ignition wire from the +DC source, then through a switch, then connect it to the +DC input terminal on the DC-DC charger.

:):)

Try going to Winnebago support website with your coach vin and serial number for the wiring diagram.
Small yellow wire should go to the boost switch. should be fed from coach battery side of relay.