Grounding?

[GlennWest]

Since I am doing away with factory battery system, do I need to ground to chassis? 

[Kirk W]

You still need to have a return path to the battery. In 12V-DC that return is the chassis. To do away with the chassis ground you would need a major rewire of the RV.

Edited December 25, 2019 by Kirk W

[GlennWest]

My 12v system will be untouched except for the factory batteries. My new system is 48v with a step down convertor supplied 12v tied into the same location my factory converter was. So I shouldn't need to add a ground on my new system right? 

Edited December 25, 2019 by GlennWest

[oldjohnt]

14 minutes ago, GlennWest said:

So I shouldn't need to add a ground on my new system right? 

Glenn here's the deal:

1) On many typical RV or automotive 12 Volt applications the frame/chassis is used merely as a current return path/conductor versus having to run the current through wire or cable. That's why the battery - post is bonded to the frame/chassis (for current return path) so to power the starter (which uses its case/frame as the - conductor) so you only have to run one huge cable.

2) If you have a 48 volt battery bank and a 48 to 12 VDC Converter, you now have 12 VDC + and - to power 12 Volt appliances. So if you run two wires to those 12 volt appliances  you don't need to use the frame/chassis as a return current path.

 So long as your converted (48 to 12) 12 volt source has + and - wires of adequate ampacity to power loads you don't have to use the frame/chassis as an alternate current path.  

NOTE When using alternate 120 VAC energy sources such as an Inverter or a Genset and they are wired and configured as a Separate Derived Source they use a Bonded (NOT Floating) Neutral which is bonded to the RV frame/chassis but that's a whole other subject.

Your engine battery uses frame as a return current path so it remains in place. ALSO if any part of your RV's 12 Volt System uses the frame/chassis as a current path and you don't instead run  two + and - wires to it, a frame/chassis Ground is required.

I will go out on a limb NOT knowing your system or any specs and take a pure "guess" your 48 Volt Lithium battery bank is floating off frame/chassis and after the 48/12 DC Converter (if ??? it replaces the normal 12 VDC House Battery Bank) if the original system bonded the house battery bank - to frame/chassis  you could bond the Converters - to frame chassis the same as before. This assumes your 48/12 Converter TOTALLY replaces the factory 12 VDC battery system ????? If there are still necessary remaining  frame return paths  you need to bond the - to frame, or else run two wires and eliminate the frame return

 DISCLAIMER I had to do this in a hurry as its about time for the parks Christmas Dinner and I haven't thought it through yet so I may modify it later. Absent any specs or data of your new or original 12 VDC system and wiring I may be wrong as rain so hope someone can correct any mistakes grrrrrrrrr my bad for being in a hurry...……...  

Merry Christmas

John T

[GlennWest]

Just trying to cover all bases so no mistakes here. Thanks.

[oldjohnt]

5 hours ago, GlennWest said:

Just trying to cover all bases so no mistakes here. Thanks.

You're welcome, if the original 12 VDC House battery bank bonded the NEG to frame chassis AND THERE REMAINS REASON TO DO SO (I can know absent specs and diagrams) such as something ??? used the frame for current return, the 48/12 Converter 12 VDC - output could likewise be bonded. However, if all the 12 VDC appliances and loads following your remodel have a proper current return path I don't see its necessarily required.   

John T   

[GlennWest]

My Chinese dc/dc convertor shares the negative for input and output. So negative for 48v and 12v negative to frame on same post..Is this all right? 

[oldjohnt]

Glenn, if the Converter and the Converters specific instructions and wiring diagrams (or how it comes from the factory) call for connecting their common Negative (48 v - and 12 v - ) that's all well and good and how it needs wired DO AS THEY SAY NOT ME.

  HOWEVER, whether or not that common Negative ALSO needs bonded to the Frame/Chassis is a separate issue to which my response above remains unchanged.

1) If any 12 VDC load or device uses the Frame/Chassis as a current return path in lieu of two wires (+ and -) supplied to them, the 12 VDC - obviously needs bonded to the Frame/Chassis. It cant work without two + and - feeds be it a piece of wire or the frame used as the  - conductor.

2) If NOOOOOO 12 VDC loads or devices use the Frame/Chassis as a current return path and they all have two wires (+ and -) fed to them in lieu of the Frame/Chassis, those loads or devices will "work" since they have the two necessary 12 VDC  + and - feeds.      

3) If the factory original 12 VDC house battery configuration (which you are replacing with the Converter) had the - bonded to the Frame/Chassis, I don't envision a problem (but cant say not having specs or diagrams) if the 12 VDC Converter has its - bonded to the Frame/Chassis.  

4) Typically an RV house battery has its - bonded to the Frame/Chassis and there may or may not be good reasons OTHER THEN the above loads and devices discussion for that to be so, IN WHICH CASE SURE BOND THE NEGATIVE TO FRAME/CHASSIS on same post as you asked.   

NOTE AND CAUTION: There may well be factory original house battery 12 volt configurations whereby the truck battery provides a degree of charge current back to the trailers 12 volt house battery when towing AND IT RELIES ON THE FRAME/CHASSIS FOR THE - CURRENT PATH (IE trailer battery - is bonded to frame) !!!!!!!!!!!!!!!  BUT CAUTION !!!!!!!! I don't envision you wanting to connect the truck battery to the Converters 12 VDC like you would if the trailer had its own normal 12 volt battery and you wanted to charge it from the truck when driving.

IE  if your truck and trailer is now wired (usually via the 7 pole round RV plug) so the truck and trailer batteries are connected and you now have instead only the 48/12 Converter, I would disconnect any such circuit !!!!!!!!!!!  

Despite what my opinion is (absent any specs or wiring diagrams mind you) DO WHAT THE MANUFACTURER SAYS, although I question any connection from the truck battery back to the trailers 48/12 Converter 12 Volt output  so take a good look at that...

Happy New Year

John T 

Edited December 27, 2019 by oldjohnt

[Sehc]

Negatives on dc circuits are smart and they find their way back to the right battery.

[GlennWest]

Thanks. Just seemed strange to me.

[Kirk W]

2 hours ago, GlennWest said:

Thanks. Just seemed strange to me.

Electricity of any type must find a path to return to the source. DC circuitry is somewhat less complicated than AC and with low voltages there is no safety issue do chassis grounds are standard. In an AC power the need for a return is the reason that cords have two wires. 

[oldjohnt]

12 hours ago, GlennWest said:

Thanks. Just seemed strange to me.

 Glenn, you're on top of this. As long as any 12 VDC loads or appliances have their needed  + and - voltage feed, be it a wire or the RV frame as one of the conductors,  sure they will work. If there is a need or reason for the 12 VDC source (be it a Battery or Converter) to be bonded to the RV frame AS IS TYPICAL in regular 12 volt house battery configurations, there's no problem. Your 48 to 12 DC Converter sharing a common Negative does not surprise me.

Of course, as far as your 120 VAC Inverter or Genset being configured as a "Separate Derived Source" are concerned, their use of a Bonded (non floating) Neutral  plus bonding to the RV frame is correct and proper.

Happy New Year

John T  Live dry camped at a Bluegrass Festival in Arcadia Florida