GORDIE'S NEW ELECTRICAL TROUBLE SHOOTING THREAD

[Gordie Allen]

RECAP:
After leaving Larry's we had an electrical meltdown of the frig cord (120v ac).  About 10 minutes after switching to the inverter.  Lots of smoke.  I threw the main breaker and meltdown stopped.
FACTS:
Frig was running on inverter at the time.
Most damaged line by far was the ground.  Ground plug was melted into socket.
My  house batteries connect to a Victron Multiplus true sine wave inverter.
The house batteries are supposed to be grounded through the Multiplus; however, I get zero volts on my multimeter from Multiplus to chassis.
zero volts from positive battery post to chassis
12 volts from pos to neg post on all house batteries (I have 4 in parallel)
12 volts between pos and neg lines running from house group to Multiplus.
I can't get 12 volts from any house pos source to chassis
If I hook a 12 volt motor directly to the pos and neg posts of the batteries it runs
If I ground the motor to the chassis, it doesn't run.
I've cleaned and tightened my ground connection from the Multiplus - no current flow
Multiplus charges batteries from shore power.
I have a second 120 line that bypasses the inverter and goes to the second post on my main.  That works fine when plugged into shoreline.  I moved all my breakers to that bar.
OPINIONS NEEDED!!!!!!!!!!!!

[bevans6]

My first impression is that you lost the ground connection for the batteries, and they tried to ground through the fridge cord.  Huge difference in current between 12v and 120v, the ground current would have been far larger than a fridge cord could carry.  I don't understand the "The house batteries are supposed to be grounded through the Multiplus;", my rule of thumb is everything gets independent grounds  Neutral is a different matter, of course.  If you can't get 12 volts from battery positive to chassis ground, I would say fix that with a cable equal to the largest positive voltage cable to the inverter, and get your batteries grounded properly.  You can never have too many grounds.  I would further say that something inside the Victron is fried, maybe a solenoid or breaker that makes the path to ground for the batteries.  I don't normally expect to see fuses or breakers in the path to ground, but there is some reason to put one in, in some cases.  I would expect that the Victron is going to need a service call, or a replacement.

edit: if the battery ground is through the inverter, the loss of battery ground and then the failed ground path through an inverter load is extremely plausible.

Brian

[Lin]

Not that I am saying it can't be done since I just don't know, I would certainly want my battery bank ground to the chassis anyway. 

[B_K]

Gordie this is just a thought but is there any chance a "chassis ground" got left off during the mechanical repairs?

The reason I ask is because right after that repair is when all this electrical trouble started.
  BK 

[luvrbus]

His problem is on the AC side our boat had 2 Victron Inverters the batteries were charged through the inverter only and had no other grounds except through the inverter the batteries were a direct connect to the inverter his problem is not on the DC side those send out all kinds of signals for the DC side 

I hope his inverter is still under warranty the Victron is a hard inverter to get serviced or repaired not much in the way of service yet on a Victron ours always had problems and the guys in San Diego at the marina would rip me big time I finally replaced both to sell the boat     

[Seangie]

Gordie-

Any chance the AC cord ground out on the chassis somewhere?  Or maybe if there was a short in the fridge and a metal part of the fridge was in touch with the chassis somewhere causing the 120v to ground out to the chassis DC ground?

Other questions - 
1. Does the fridge still work?
2. Were your house batteries tied to the chassis/start batteries anywhere? Or just connected straight to the inverter?
3. Did you blow a fuse anywhere along the way? (I'm assuming the negative side of your DC circuit was not fused?)

I think Brian is onto something with the 120v side and the 12v side getting connected at some point whether it was in the coach or in the inverter itself.

-Sean

Fulltiming somewhere in the USA
1984 Eagle 10S
www.herdofturtles.org

[Gordie Allen]

Right now I'm leaning towards Brian's theory and Clifford's opinion.  The only ground is through the inverter.  I'll add a second (maybe third!) chassis ground tomorrow and see if I can find a reason why I lost the Victron ground. No breakers tripped.  Big 400 amp fuse on pos side to inverter is good. Hopefully inverter isn't fried.  I'll replace the frig cord and pray that nothing else was damaged there.  Victron is about 18 mos. old.

[Zeroclearance]

Have your ruled out your fridge?   The compressor rotor could be locked or failing/hard start.. 

[bevans6]

It was the ground plug lead that melted, and it doesn't carry any load normally.  I looked up the Victron, and indeed the batteries are directly connected to it, positive and negative, and it provides the ground connection.  In order for the failure scenario I am thinking happened to work, the battery path to ground would have had to be interrupted inside the Victron and somehow the fridge would have to have a direct path to ground from it's chassis so the ground current from the battery would have to find a path through the inverter to the house panel to the fridge.  It now seems a tad unlikely, one would think the house panel would be grounded and the path would have stopped there.  Unless the house panel used the same Victron ground as the battery, instead of a true chassis ground.  Without knowing more about the Victron and the house panel install it's impossible to guess more.  One would think the fridge was on a breaker, which should have tripped in an ordinary over-current situation.

I'll be really interested to find out what the actual answer to this one is!  I see flaws in every scenario I can dream up to explain this.

Brian

[Dave5Cs]

Could he have a hot skin problem which would explain the ground melting the cord, Just throwing it out there.

Dave5Cs

[Gordie Allen]

Brian, and all
The 120 panel has an isolated neutral and its own chassis ground.  That ground shows continuity to the chassis.  The battery ground from the Victron appears to be open (not connected inside the Victron, so no ground).  The Victron ground wire is 0000 and has a clean, solid connection at both ends.  It also has continuity from the Victron to the chassis.   The frig is on a 15 amp breaker, which didn't trip.  My plan today is to add a direct ground from the battery pack to the chassis.  I also bought a new cord for the frig.  Hoping it still works.  I'm currently using the side of the ac panel that bypasses the inverter.  Other than limiting usage to avoid overload, are the other issues with this strategy?  I know the neutral isn't balanced.
Dave,
By "hot skin" do you mean a voltage leak to the chassis?  Would you measure this by testing chassis to shore ground?

[bevans6]

I guess I would pull the Victron out, get it on a bench and open it up to see what the path from battery ground to it's chassis ground is, and why that path is open.  It might be a fuse.  The question is - if it is a fuse, why did it blow?  If it's a breaker, you could see if it resets and then connect a battery and see what happens.  I would only do this after making sure that the Victron is out of warranty and you can't talk them into helping you out.  Have you called their support line, if they have one?  Sadly I see a Magnum in your future...

Brian

[Dave5Cs]

Gordie yes I found that mine had hot skin because the ground plug was broken off indie the power cord i was using. I used a 120 volt tester and put 1 lead in the power cord hot side and the other negative lead to the metal outside of our coach and it light up 120 volts going through the metal. Fixed the ground and it has been good ever since.

[Seangie]

Gordie - First of all, thanks for posting this and keeping up with this thread.  Its really forced me to do my homework and check my electrical connections on my bus as well.

I want to clarify some things as the word "chassis" seems to be unclear as to if its the bus chassis or the inverter chassis. 

My understanding is that a 12v system and a 120v system should never use the same ground.  And I just wanted to clarify that when you say the 120v panel is grounded to the chassis that you are indeed reffering to the inverter chassis not the motor coach?

I'm also assuming that you have your inverter tied into your electrical panel and the inverter passes power through itself into the panel when power is external and when there is no external power the inverter then begins providing inverted 120v power.

The last thing Ill mention is tying the neutral and ground together.  Most inverters do this inside the inverter.  One thing I have noticed though is that on outback inverters they sell a "mobile" version that ties the ground to neutral when there is no outside source and disconnects that tied bond when the source is external so that the ground is properly tied when an external source is applied.  Does this model of Victron inverter do the same?

Is it possible if the Victron doesn't automatically switch the neutral and ground that when it was tied to shore power something over time maybe damaged the neutral/ground bond on the 120v circuit inside the inverter which is where (maybe?) this problem originated from (and possibly why Cliff had a problem in the past with the inverter?)

Just asking questions to clarify and understand.  I've got a good understanding of electrical but I'm certainly not an electrician and am quick to get an electrician involved if its something not crystal clear to me.

Thanks again - curious to see if you can figure this one out.

-Sean




Fulltiming somewhere in the USA
1984 Eagle 10S
www.herdofturtles.org

[bevans6]

Sean - ground is ground, it's the same for everything on the bus or the house or any other thing.  In a bus situation your engine electrics use the chassis as ground, the house 12v or 24v system uses the chassis as ground and the house 120v system uses the chassis as ground.  Chassis ground is tied to the inverter, the generator and the batteries as on-board power sources, and ground from the shore supply cord is tied to chassis ground on the bus.

Brian