Battery grounding

zozomike

Seems I have found conflicting advice, or at least enough variation to confuse a non specialist. Should the negative of the battery bank be tied to the residential ground system?
BTW this is a 24v off grid system with a brand new GB Industrial battery I don't want to lose. The 4 ground rods that everything else is tied to are bonded together with #6 then a slab poured on top for the battery enclosure and the rebar tied to this grid. Nearby is a PTO 15kw generator which is grounded to that also.
Thanks

Cariboocoot

Re: Battery grounding

Under most circumstances the negative battery terminal should be tied to the grounding point.

If there is DC ground fault interruption it will not be.

If the inverter or charge controller's case ground is ground and tied to negative an extra ground wire may be redundant and create a ground loop.

If the inverter is of the MSW type then the most important thing is to avoid an neutral-ground bond on the AC output (make sure it does not exist anywhere within the wiring).

In short the most correct answer is to consult the wiring instructions that came with the inverter. Although they may be remiss on providing that information, in which case you do a "best guess". :roll:

One thing you can do is check for Voltage potential between battery (-) and ground when there has been no bond made. There should be none or very little.

BB.

Re: Battery grounding

When checking voltages between "unknown" connections... Use a 4 watt to 40 watt 120 VAC light bulb to get some sort of current flow.

When using a typically DMM (digital multi-meter), they have 1 MegOhms or greater resistance and you can have a bit of static charge (or an RF filter Capacitor holding a charge).

The filament lamp will discharge any static charges and, if there are any "bad circuit paths" that are actively holding a potential, the DMM will still show a non-zero (or more than a couple volts)--Or in some cases, the light will even glow.

-Bill

zozomike

Re: Battery grounding

Thanks, I see I should have been more specific. Both the VFX3524 and the Flex Max 80 are tied to the ground. No DC ground fault device exists. In the FX series manual it states " for all installations, the negative battery conductor should be bonded to the grounding system at one ( and only one) point in the system. I think that means don't bond the battery if the other components ( inverter/controller) are already bonded??

BB.

Re: Battery grounding

Normally, the DC power are floating (positive and negative) for charge controllers, inverters, AC battery chargers and such.

Where you can get into trouble is mixing in, for example, automotive accessories such as a car stereo where the chassis of the radio is also the negative return lead.

When you have a DC negative return tied to Earth Ground in two or more places, you have parallel current paths. In some cases, the earth grounding has lower resistance than the DC wiring and you can have pretty heavy current flows in the earth ground system that you did not plan on (shielded cables for antennas, etc.).

So--In a well designed DC power system, your grounding at the negative battery bus common point to the earth ground rod is not going to create any ground loops (unless there is a short circuit somewhere).

-Bill