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48v to 12v buck converter with common ground

The old DC converter and old 12V batteries both tied to a bus bar at the DC distribution panel. You'd have DC power at the panel from the batteries if not plugged into shore power.
If plugged in, the DC converter powered the DC loads and charged the 12V battery.
You should still be able to run your new converter to that same DC bus bar in the DC distribution panel. It just needs to be connected right there since it's such a high amp load.

You may need to be careful with alternator charging. Your old converter is gone but if traveling, the engine alternator will still be connected to the 12V system. Either disconnect vehicle charging or look into how to safeguard the new 12V competing charging system.
 
Where were the Main POS and NEG conductors attached from the old converter? I'm sure you won't need to rewire all that.
The pos and neg wires come up from the ancient converter below, and onto the pos and neg of the DC fuse panel. Also on the DC fuse panel are a couple lugs, a pos and a neg, and from those lugs run heavier cables, one goes to the chassis, and the other to the positive of the house battery, after running up to the front of the rig, through the solenoid box, then back to the house battery.
On the DC fuse panel itself are the distributions of the positive side. No bus bar for ground.
I did try to cut out all the middlemen and wire the converter to those house battery lugs after disabling the old converter and removing the wires that ran to the house battery. Nothing worked.

I've seen some where they simply insert a bus bar where the old house batteries used to be. Then connect the new converter to the new pair of bus bars.
The old house batteries ground to the chassis, so I can't do that if I want to carefully abide by the instructions. In the meantime I have sent the seller my questions through Amazon, I'll update here as I get solid info.
 
Here's some drawings that may help.
50A-OEM-RV-FACTORY-WIRING-EXAMPLE-MK01-863x1024.jpg.webp


The-DC-load-panel-PN-8023-wiring-configuration-29.png
 
Yes, your first diagram is almost exactly like mine, but my rig is 30a, and the neg from the dc dist panel goes to the chassis, rather than directly to the neg on the battery. That's the only difference I can see.
Your second diagram has a neg bus bar, mine does not.
 
Yes, your first diagram is almost exactly like mine, but my rig is 30a, and the neg from the dc dist panel goes to the chassis, rather than directly to the neg on the battery. That's the only difference I can see.
Your second diagram has a neg bus bar, mine does not.
Each DC fuse in your panel can't all just bolt down to a chassis screw. They must be tied to some kind of bus bar pair.

Better if they wouldn't call that GRD. As in the second drawing, DC negative return is better description.

If nothing else, I'd put the new converter neg return in the exact same place you removed the old converter DC -. It had to be a 35 - 55 amp converter.
 
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Each DC fuse in your panel can't all just bolt down to a chassis screw. They must be tied to some kind of bus bar pair.

Better if they wouldn't call that GRD. As in the second drawing, DC negative return is better description.
It's a magnetek 6345, here's a pic from the web that is exactly like mine:
AC comes in from the top left. AC wires go from one of the circuit breakers down to the converter below. On the lower right, the DC wires come up to the upper right panel, on the back side, where you see the rivets right above the big red and big white wires. There is also a third, the green, that comes from below as well, but then up, over and then bolted to the fuse panel. As far as I can tell with my multi meter, it is also a positive. I'm not sure why it needs to be there.

The big red goes to the battery. The big white goes to the chassis.
Also, I attached a PDF from Winnebago's schematic.

Edit: I attached a second schematic, the DC panel is right in the center of the diagram.
 

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If nothing else, I'd put the new converter neg return in the exact same place you removed the old converter DC -. It had to be a 35 - 55 amp converter.
Yes, that's what I tried this morning. I disconnected the converter from it's AC source to disable it. Then I disconnected the house batteries at the terminals, so it would then be safe to remove the cables from the DC fuse panel. It is to those points I ran the new converters 12v wires. Then I tried to flip on a few lights. Nothing. I sure wish I could just wire the damn thing to the chassis. I can't be the first one around here to run into this.
 
Yes, that's what I tried this morning. I disconnected the converter from it's AC source to disable it. Then I disconnected the house batteries at the terminals, so it would then be safe to remove the cables from the DC fuse panel. It is to those points I ran the new converters 12v wires. Then I tried to flip on a few lights. Nothing. I sure wish I could just wire the damn thing to the chassis. I can't be the first one around here to run into this.
The entire old converter did get removed?

There was absolutely no wire from the battery negative directly to the disto panel?

The battery negative terminated with a single screw to the chassis - no bus of any kind. Just a cable from negative battery post to a sheet metal screw?

Does it have more than one battery and they both go no where else than a chassis screw?

Where did the Magnetec screw in DC positive?

How many other wires went to DC panel from magnetec besides the split ground with ring terminal shown in drawings?
 
The entire old converter did get removed?
No, just disconnected from it's AC input and it's battery output/input.
There was absolutely no wire from the battery negative directly to the disto panel?
The white wire in the pic was disconnected, so at that point, yes.
The battery negative terminated with a single screw to the chassis - no bus of any kind. Just a cable from negative battery post to a sheet metal screw?
It's a bus bar welded to the frame, where all the lead acid batteries ground, as well as the wire from the DC panel.
Does it have more than one battery and they both go no where else than a chassis screw?
Two batteries, all to the bus bar welded to the frame.
Where did the Magnetec screw in DC positive?
To the red wire in the pic, or more accurately, to the back side of the panel where the red wire is screwed in.
How many other wires went to DC panel from magnetec besides the split ground with ring terminal shown in drawings?
Just the red pos, and the green which also appears to be pos.
 
No, just disconnected from it's AC input and it's battery output/input.
Yuck, Converter is integrated into the distribution panel.
The white wire in the pic was disconnected, so at that point, yes.
I must have missed the white wire pic. Disconnected prior to you attempting this?
It's a bus bar welded to the frame, where all the lead acid batteries ground, as well as the wire from the DC panel.
There it is. That's a major amp load point to tie in DC negative return.
To the red wire in the pic, or more accurately, to the back side of the panel where the red wire is screwed in.
Was there also a heavy red wire screwed into the front side of the panel? I suspect this is where both battery and converter supply DC+ In your drawing, it's labeled "aux batt" Do you have a generator with a starter onboard?
Just the red pos, and the green which also appears to be pos.
It looks like those two terminals on the right side may be your connection points for the new converter. That's basically the bus bar. I'd check to make sure they're the correct polarity they seem.

Don't get too hung up on the whole "chassis" thing. It looks like most everything is tied to the chassis. That's ok.
What the manufacturer is likely cautioning is a high amp 12V negative return on some spindly little high resistance wire. They want you to tie into something robust with low resistance like a battery cable or bus bar. Just because there's a connection to chassis doesn't mean you're connecting to it. You're connecting to a low resistance heavy conductor. 60A 12VDC is some serious current. Those heavy amps will choose to return on a least resistance path. Unless you force them to take a skinny wire to get back home. Then they'll bring the heat.

Think of the DC side of your inverter. Did you run heavy cable directly to bus bars and make them equal lengths? We wouldn't want to run a small negative return cable bolted to some sheet metal back to the negative side of the inverter. Pretty much same principle here. Both POS and NEG DC cables can carry close to the same current.
 
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Yuck, Converter is integrated into the distribution panel.

I must have missed the white wire pic. Disconnected prior to you attempting this?
No, I disconnected it so i could run the buck converter to that screw lug as a test this morning. As I said, everything has been working fine.
There it is. That's a major amp load point to tie in DC negative return.
That was never in question. I've been saying everything goes to the chassis. The problem is that the buck converter's instructions say NOT to. That is the whole point of this thread.
Was there also a heavy red wire screwed into the front side of the panel? I suspect this is where both battery and converter supply DC+ In your drawing, it's labeled "aux batt" Do you have a generator with a starter onboard?
Yes, the red and white wires go from the dc panel to the battery, which makes it both an input and an output.
It looks like those two terminals on the right side may be your connection points for the new converter. That's basically the bus bar. I'd check to make sure they're the correct polarity they seem.
Yes, I know. I tried it. It didn't work. Because the new buck converter is not connected to the chassis.
Don't get too hung up on the whole "chassis" thing. It looks like most everything is tied to the chassis. That's ok.
Yes, I know. I've always known that. It seems you needed to be convinced of that. Sorry if that sounds ungrateful, I'm not.
What the manufacturer is likely cautioning is a high amp 12V negative return on some spindly little high resistance wire. They want you to tie into something robust with low resistance like a battery cable or bus bar. Just because there's a connection to chassis doesn't mean you're connecting to it. You're connecting to a low resistance heavy conductor.
The instructions clearly state not to connect to the chassis. I can't go ahead and do so based on the above reasoning.
60A 12VDC is some serious current. Those heavy amps will choose to return on a least resistance path. Unless you force them to take a skinny wire to get back home. Then they'll bring the heat.
Yeah, no kidding. Which I why I need clear answers from somebody who actually knows the answers. Which I why I made the post.

While I appreciate your help, all the time and effort you've given me to understand my situation, my questions are still unanswered.

Why can't I connect this thing to ground as stated clearly by the instructions? Could be multiple things. I need to know why specifically. Hasn't anyone on here already gone through this?
What workarounds exist to allow me to safely do so, if any?

I'm not going to just go for it and have a nasty surprise somewhere.
Sorry, tired, hoped to square this away today.
Hopefully I'll get good answers from the seller, but I'm not keeping my hopes up.
 
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