Inverter grounding to batt or chassis

[pauldub]

I'm looking for some input regarding the ground (negative, not neutral) connection for my 1800 watt inverter. I need about 10 of wire to run it back to the battery or I can ground it to the motor home frame with less than 2' of wire. I suspect that the frame will provide a lower resistance return to the battery than any reasonable size wire; however, not knowing the resistance of the frame, it hard to be certain. Thoughts?

[BFL13]

More like that here--same wording in many places--looks like Go-Power inverters are Magnum? Or they have the same manual writer! (GP converters are PowerMax)

https://gpelectric.com/wp-content/uploads/2018/05/78158_MAN_ISW_RevD.pdf

[jharrell]

BFL13 wrote:
I think you are right from reading the manual where they use "chassis". It is true they all use the frame but separately, sort of.

See page 12 diagram. There is a "system" ground to the frame AND the neg from the battery to the inverter neg intake. Also there is an inverter chassis ground (equipment ground) to the frame.

Also something in there about the accessories like the monitor ending up as the neg path if you are not careful.

http://www.magnum-dimensions.com/sites/default/files/MagDocs/64-0089%20A%20Owner%20Manual%2C%20MSH30...

Diagram on page 26 makes it very clear:

[jharrell]

Delete

[time2roll]

pauldub wrote:
OP here. I'll have half my battery bank on the curb side of the motorhome and the other half on the street side. To wire the batteries in a balanced fashion will take extra wire length. This is most of my motivation to ground the inverter DC return directly to the frame. I'll use a tin plated lug which is galvanically compatible with the steel frame. I can also use a chrome plated bolt so that the bolt will be galvanically compatible with the steel and tin.

If you tie to the frame then both banks have a direct connection to the ground... you will need a like separate connection to the positive side to keep the connections balanced.

I don't think the frame negative power connection really helps you.

Do you have 12v or 6v batteries?

[MEXICOWANDERER]

All cross pieces running from side to side on the chassis are RIVETED to the frame rails and they are not welded::The easiest and most secure way to BRIDGE across the frame rails is at the engine -- the common denominator for a buss:: short lengths of 0 single aught wire can easily pass 500 amps without excessive voltage drop::I have installed systems up to 4,000 watts without the need to run a negative wire forward to the house batteries::A hole clearanced for a 3/8" bolt is fine:: Shine the steel frame rail bright:: Bolt the cable lug to the frame rail and DOUBLE NUT lock it::I use black RUSToLEUM bed liner paint over the completed work and it should last for thirty years or so even with road splash:: Spray the bedliner a few inches up the cable -- covering heat shrink tubing etc.

If you are afraid of corrosion of the fasteners, choose Silicon Bronze which will not corrode ever. It even beats 316 stainless steel.

[BFL13]

I think you are right from reading the manual where they use "chassis". It is true they all use the frame but separately, sort of.

See page 12 diagram. There is a "system" ground to the frame AND the neg from the battery to the inverter neg intake. Also there is an inverter chassis ground (equipment ground) to the frame.

Also something in there about the accessories like the monitor ending up as the neg path if you are not careful.

http://www.magnum-dimensions.com/sites/default/files/MagDocs/64-0089%20A%20Owner%20Manual%2C%20MSH30...

My Vector inverter manual has a special warning about the neg intake from battery and the inverter's chassis ground too.

Do not connect this (inverter's) chassis ground wire to the negative DC input terminal--it goes to a "solid electrical ground" ie the RV frame

[2oldman]

BFL13 wrote:
IMO this refers to the chassis of the inverter and not to the frame of the RV

Imo it refers to the chassis of the coach. Would you try to use the same grounding path for the inverter negative as the small grounding cable from its chassis? I don't think so.

I don't know why this is even an issue. Are we trying to save a few bucks on cable?

[BFL13]

2oldman wrote:

jharrell wrote:
My Magnum inverter ...manual (snip) specifically says not to use the chassis as DC negative, in their words:Do not attempt to use the chassis in place of the battery negative connection for grounding.
The inverter requires a reliable return path directly to the battery."

Ahh.. why believe the manual? 🙂

IMO this refers to the chassis of the inverter and not to the frame of the RV

[2oldman]

jharrell wrote:
My Magnum inverter ...manual (snip) specifically says not to use the chassis as DC negative, in their words:Do not attempt to use the chassis in place of the battery negative connection for grounding.
The inverter requires a reliable return path directly to the battery."

Ahh.. why believe the manual? 🙂

[MEXICOWANDERER]

No OEM frame laterals I know of are not riveted. Keep it in mind in salt ice areas.

[BFL13]

pauldub wrote:
OP here. I'll have half my battery bank on the curb side of the motorhome and the other half on the street side. To wire the batteries in a balanced fashion will take extra wire length. This is most of my motivation to ground the inverter DC return directly to the frame. I'll use a tin plated lug which is galvanically compatible with the steel frame. I can also use a chrome plated bolt so that the bolt will be galvanically compatible with the steel and tin.

I have a diagram a member from back then posted in 2011, but the dropbox has expired. He had a similar situation with two battery banks separated like that in his MH. (two sets of 6v pairs and a 2000w inverter/charger with an 80 amp charger)

For the neg side from each set he ran a wire to frame ground. On the positive sides wires to a 1,2, both switch, from that switch to the inverter pos intake. Inverter neg intake from frame ground.

[MEXICOWANDERER]

Except when people melt them while holding the key, and (get this) pumping the gas pedal.

A GEAR REDUCTION starter motor will take less than half the amperage to crank the engine.

And the frame has nothing at all to do with a negative battery cable that is connected to the engine block for use by starter motor and alternator.+

[beemerphile1]

Battery negative connects to the chassis so everything that connects to the chassis also connects to the battery negative.

Attach to the chassis at the nearest convenient point.

Grind the steel to bare metal, make the connection, and then spray liberally with automotive undercoating.

[jharrell]

My Magnum inverter has a separate ground lug that the manual says specifically to tie to chassis. The manual also specifically says not to use the chassis as DC negative, in their words:

"Do not attempt to use the chassis in place of the battery negative connection for grounding.
The inverter requires a reliable return path directly to the battery."