Chassis (galvanic) corrosion caused by common negative on vehicle

[RGIvy]

Has anyone actually experienced galvanic corrosion caused by a common negative (neutral) using the chassis, particularly in a vehicle with a leisure battery?

I know the theory that a DC-DC (B2B) charger based on common negative using the chassis instead running negative cables could cause some corrosion. Of course, this could only occur under very high current and probably with dicey connection somewhere. Some DC-DC chargers allow pretty high continuous current

The reason I ask is I've never actually seen it happen (corrosion that is), and the alternator is grounded to the chassis via the negative strap anyway (in many vehicles).

I'm not asking about the inverter, this I'm assuming would always be connected to the battery by two short and thick cables.

 

[Spectric]

Hi

Well you probably remember that vehicles changed from being positive earth to negative earth and one reason for that was corrosion, so a common negative should not be a problem. With Galvanic corrosion this occurs anywhere between different materials that are on opposite sides of the Galvanic table, stainless steel fasteners and aluminium is one. With the vehicle chasis being positive it becomes the anode and when a copper wire is in contact with the steel body and gets wet, corrosion occurs that will dissolving the anode and in theory deposit it onto the cathode.

All these problems are overcome when the chassis is isolated from the electrical system and all negative returns are cabled. Buses are an example and here things like oil pressure switches and temperature sensors have two wires because the engine block is not connected to battery negative.

Here is some further info on galvanic corrosion A bit on Galvanic Corrosion

Canal boats can cause interesting corrosion especially when connected to on shore power. The onshore power should be provided by an isolation transformer so the live is only live with respect to the neutral and not ground, ie the water the boat sits in. If not then there is a high risk of electrolysis eating holes in the metal.

 

[mikej460]

As you can see from my Avatar I suffer from this. Defenders have aluminium door skins on steel frames so corrosion is rife with a large aftermarket of solutions including all steel doors..

 

[RGIvy]

Here is some further info on galvanic corrosion A bit on Galvanic Corrosion

Very interesting link thanks!
...and a helpful answer.
The reason I asked the question is because my motorhome has a strap from engine to chassis on LHS of vehicle, whereas the battery is on RHS with a short cable to chassis. Therefore current is flowing through the chassis. I have no corrosion or structural problems despite heavy and continuous charging currents. Various people have stated how bad this is on other forums but, without insulting them, this appears to be an educated opinion but with no actual experience.
Someone recently asked me if he could use a common-negative DC-DC charger and I said yes, then afterwards wondered if someone has actually seen structural problems caused by corrosion on a motorhome resulting from a common negative using the chassis (that's a mouthful!). I've never personally seen a problem caused by using the chassis as a negative.

 

[RGIvy]

As you can see from my Avatar I suffer from this. Defenders have aluminium door skins on steel frames so corrosion is rife with a large aftermarket of solutions including all steel doors..

We owned a few landies back in Zimbabwe and South Africa, pretty dry climate so corrosion not a problem.

 

[Spectric]

I would not worry, corrosion is just something that happens in countries with wet, damp winters and summers, but road salt is more of an issue than the polarity of your ground. When I designed wiring for special use vehicles I would often run a cable from Starter motor fixing bolt directly back to the battery and ensure the alternator return was connected to the block, not reliant on it's fixings. Using the chassis as the return path is done for saving money and weight, less wiring needed and for many applications I was involved in the chassis was not part of the electrical system, we used a fully wired 0 Vdc system.

I can understand using a Dc to Ac invertor to power some mains equipment but not a Dc to Dc charger as you have a Dc system and batteries are Dc anyway.

 

[Just4Fun]

The reason I asked the question is because my motorhome has a strap from engine to chassis on LHS of vehicle, whereas the battery is on RHS with a short cable to chassis. Therefore current is flowing through the chassis.

I have known a lot of cars with the battery in the boot (either as standar or after a modification) with current flowing through the car bodywork. Also a friend has a large motorhome in which the battery is halfway down the vehicle rather than with the engine, and I assume that uses the chassis as a conductor. I have never known these layouts lead to a problem.