question

prkarls avatar image
prkarls asked

Inverter/Charger Chassis Connection Safety in Vehicle

Hi,

I’ve been working on the schematic for my conversion build but I am having a tough time convincing myself it’s safe when it comes to the inverter/charger. I’ve read several manuals, guides, and posts in this forum (and other forums) regarding this topic, but none of them give consistent information that I find to be trustworthy. If I missed the answer to this, I apologize.

The metal enclosure of the inverter/charger should be tied to the vehicle chassis. Assuming the inverter/charger contains an automatic transfer switch that connects the Neutral to the metal enclosure (chassis) when no shore power is available, a TN-S earthing system is created. This part is rather straight forward, but I am concerned about the fact that the negative terminal of the vehicle’s starter battery and the negative terminal of the house battery are also tied to the chassis. Since the Neutral is connected to the chassis, the high voltage AC is no longer isolated from the low voltage DC circuits, which I believe creates a safety issue on the low voltage side as the 12Vdc circuits are much more accessible due to the number of loads that run directly off it.

Here is a simple schematic that shows the lack of isolation (in inverting mode).

image1.png

This is based off a system schematic readily available from Victron:

https://www.victronenergy.com/upload/documents/DS-Lucians-Victron-Van-Automotive-Full.pdf


Are my concerns valid? Or am I overthinking this?


Any advice would be greatly appreciated. By the way, I am in the US.

Thanks,

Phillip

MPPT ControllersMultiPlus Quattro Inverter Charger
image1.png (257.0 KiB)
2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

2 Answers
kevgermany avatar image
kevgermany answered ·

Few points

Mains neutral is 0V, the line connection has the varying voltage.

You need to ensure external power connections are correctly wired. /Earthed/grounded. It's possible to get simple plugs that show this.

Legal requirement here to ground theains external feed to vehicle chassis.

Victron inverter chargers sense whether there's external mains or not. If there isn't, neutral is switched to chassis as well as the existing earth/ground.

There's good internal design to prevent DC/AC cross contamination. So no worries. But your AC from the inverter/charger should be wired through fast circuit breakers so that any misconnection/short breaks the circuit before injury can occur.



2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.

prkarls avatar image
prkarls answered ·

Thanks for your feedback, can you comment on the following:

You need to ensure external power connections are correctly wired. /Earthed/grounded. It's possible to get simple plugs that show this.

Can you give me a little more detail on what you mean by this (specifically the "/Earthed/grounded")?


Legal requirement here to ground theains external feed to vehicle chassis.

I'm assuming you're just referring to the ground connection from shore power?


Victron inverter chargers sense whether there's external mains or not. If there isn't, neutral is switched to chassis as well as the existing earth/ground. There's good internal design to prevent DC/AC cross contamination. So no worries.

When you state "good internal design to prevent DC/AC cross contamination," I am assuming you're referring to the circuit design within the inverter/charger. Is the circuit design that prevents to DC/AC cross contamination there to increase performance or for safety reasons?

If it's there for safety reasons, isn't it bypassed when your setup contains a separate converter for charging the house battery from the alternator that also has a chassis connection (like the Buck-Boost DC-DC Converter in the link I sent)?


I appreciate your help on this. It's possible I am overthinking this, but I just want to make sure I fully understand what I'm setting up.



2 |3000
Toggle Comment visibility. Current Visibility: Viewable by all users

Up to 8 attachments (including images) can be used with a maximum of 190.8 MiB each and 286.6 MiB total.