Can some one please assist. I have a Axpert 4 Kva inverter installed in my motorhome.

No solar panels connected.

Batteries is 4 x 12 Silver calcium 105 AH batteries

What I found is between earth and neutral I get a reading of 80v (Dangerous), which cause my grid EL to trip as soon as I connect this to charge the batteries.

Any suggestion how this can be resolved would be appreciated.

Jan

8 minutes ago, Jan Pretorius said:

Any suggestion how this can be resolved would be appreciated.

Man... I am so tempted to say something derogatory about these cheap inverter/charger/changeover things that don't have a bonding relay... but in some ways I just did 🙂

I doubt it's the unbonded neutral that's tripping the RCD. When you connect it to the grid, you inherently bond it (because there is a bond on the grid side). Something else is causing an imbalance.

The proper way is to connect earth and neutral together on the output of the inverter, in other words bond them yourself. But the bond must be removed when it is connected to the grid and only applied when disconnected from the grid (a second bond will trip the upstream RCD aka EL). Which is why the better inverters (or even better models of this same inverter) does this automatically with a bonding relay.

You could also just leave it unbonded. That's called an IT earthing system. All your appliances are still earthed to the frame of the motorhome (that on which your feet stands inside), and that makes it safe (no potential difference can exist between the appliance and the floor). But it also means you need two earth faults before an RCD trips. And it means you cannot regard neutral as "safe to touch". Both your lines should then be considered "hot".

I do not know what the regulations say about mobile homes and bonding.

3 minutes ago, plonkster said:

Something else is causing an imbalance.

Indeed. I think you need to sort that out first. There must be something wrong with the neutral or earth wiring. With nothing powered up, can you see any conductivity between AC-in neutral and earth?
Same with AC-out and earth?

A fleeting conduction is OK; there are small capacitors there.

After that, the proper way to make this safe is with an external relay connecting AC-out neutral and earth. Read the manual about the "dry contact" feature. You can build this yourself, or there are commercial products that do all that and provide power for the relay. From memory, they are a little pricey, but relatively easy to install.

41 minutes ago, Coulomb said:

A fleeting conduction is OK; there are small capacitors there.

Sometimes the small capacitors, usually for EMI filtering or surge protection (Varistors tend to have a few picofarad of capacitance) can trip a sensitive RCD. But usually then the symptoms are that it trips when the inverter connects to the grid, and if you quickly reset the RCD it stays up after that. Also, it will only trip if you have any loads on the output.

If it trips all the time, even without loads on the output, then you have another problem that you have to find first.

Hi Plonkster

Thank you for the response,

Conductivity between AC-in neutral and earth?
Same with AC-out and earth?

What I did in the mean time is to measure the resistant's on my motorhome DB between neutral earth and live with the feed from the inverter disconnected. All is perfectly clean.

After that, the proper way to make this safe is with an external relay connecting AC-out neutral and earth. Read the manual about the "dry contact" feature. You can build this yourself, or there are commercial products that do all that and provide power for the relay

I've read the inverter manual regarding the dry contact (38) which can be enabled and disabled, but can find the setting on set up.

I need to check on the bonding of neutral earth later this afternoon as well as doing the reset test and see if this work. My big concern is when at a camping Site it some time not that easy to get access to the RCB. 

Do you have any spec's on the external relay you talking about and a drawing of how this should be installed if possible please. 

 

25 minutes ago, Jan Pretorius said:

I've read the inverter manual regarding the dry contact (38) which can be enabled and disabled, but can find the setting on set up.

Only available on some models with some firmware. @Coulomb knows the ins and outs of that. I'm a Victron guy. I only answer because I've had my fair share of RCD issues in the past 🙂

There is an easy answer to all this. Get a Victron Multiplus. It's all built in... 🙂

7 minutes ago, plonkster said:

I only answer because I've had my fair share of RCD issues in the past 🙂

Dude! I thought you where skipping the Axpert posts? 😜

34 minutes ago, Jan Pretorius said:

Do you have any spec's on the external relay you talking about and a drawing of how this should be installed if possible please. 

I would think that any relay with contacts rated at 230V and say 10A would do. Choose a coil voltage (5 V, 12 V, 24V) to suit a power supply that is convenient. Just put the dry contact (I think it would be common and normally open) in series with the power supply and relay coil. Common and NO on the relay go to AC out neutral and earth. If the logic is wrong, swap NO for NC either in the relay or the dry contact.

Sorry I'm not in a position for more details or drawings.

If the above makes no sense, you'll have to find one of the commercial solutions. Sorry, I don't remember where I saw one.

14 minutes ago, The Terrible Triplett said:

Dude! I thought you where skipping the Axpert posts? 😜

It's been a bit slow the last few days... I had to answer a few others! 🙂

Hallo Coulomb

Please confirm if the attached drawing is what you referring to as how to wire this external relay?

13 minutes ago, Jan Pretorius said:

Please confirm if the attached drawing is what you referring to as how to wire this external relay?

Yes, except you should use the inverter output, not the grid supply. If there is no grid, you want the relay to be on.

My concern is when you on grid the inverter output will still be available meaning I create a second bond while on grid correct?

2 minutes ago, Jan Pretorius said:

My concern is when you on grid the inverter output will still be available meaning I create a second bond while on grid correct?

But then the dry contact will be open.

So this is more what you we referring to as per drawing below?

Sorry checking now both Dry contact and external relay should be NC, so once grid is connected the dry  contact will  energise the coil meaning the external relay contact will open up to get rid of the earth neutral bond while on grid?

Wrong again Dry contact NC and external relay should be NO

2 hours ago, Jan Pretorius said:

So this is more what you we referring to as per drawing below?

Yes.

Thanks I’ve just tested the system again with no load as I switch the inverter on and then switch on the load all seem to be perfect now no RCB trip and only 8V measured between load earth and neutral. Thanks for the help hope the power stays on.

Sad news after 3 hours with no main RCB trip it started again when reset it last for a few seconds and then trip again any suggestions what this could be?

3 hours ago, Jan Pretorius said:

Sad news after 3 hours with no main RCB trip it started again when reset it last for a few seconds and then trip again any suggestions what this could be?

I had a similar problem. Turned out to be the earthing of the house. Now I have a TN-C-S setup.

A secondary issue, only in Multigrid cases, do not use any surge protectors on the inverter circuits.

44 minutes ago, The Terrible Triplett said:

A secondary issue, only in Multigrid cases, do not use any surge protectors on the inverter circuits.

Anywhere where the bonding is messed with, and you have surge- and EMI stuff, sensitive RCDs can trip. The way I understand it, and this might well be wrong, but many of these filters form a triangle, with one between live and neutral, and then two more between live and earth, and neutral and earth. This forms a natural voltage divider, so the moment you remove the earth/neutral bond your supply lines will drift so that they settle roughly halfway on either side of earth (so that is why you see 80V or so). If you now put the bond back in (eg by reconnecting to the grid), the energy in these devices (80V times however many Coulombs are in the capacitor at that instant) has to be discharged, and this causes a small transient spike through the RCD.

The older Multigrid tests its relay in a manner and at a frequency that causes multiple such transients, which makes it worse.

Anyway, my method remains the trial and error method, combined with an earth leakage clamp meter (borrow one, a cheap one costs about 4k). Find the appliance (or the multiplug, many multiplug has surge protectors in) that's causing the leakage. Remember that all houses have standing leakage, usually a few milliamps. As long as it remains below 15mA (preferably much lower!) and you avoid transients, RCDs can sustain this.

5 hours ago, Jan Pretorius said:

any suggestions what this could be?

If it happens with no load, then it has to be a problem with the inverter. Else, it's more likely a load. So run for a few hours no load, then gradually add loads.

I find that freezers are frequent culprits; they ice up and when it gets to the wiring, leakage to earth ensues and the RCD has to trip.

If it's inside the inverter, either repair under warranty or if you're electronically inclined, replace the Y capacitors and surge devices. I found suitable replacement part numbers on the AEVA PIP-4048MS and PIP-5048MS topic.

[ Edit: also, if there is a whole lot of dust on the PCB, that can get conductive when the humidity is high, so blowing out excess dust might help. ]

Edited April 24, 20197 yr by Coulomb

Hi

Currently the only load is my fridge freezer, will do the test with no load and see if this will help at all.

What is the view if I add a 230v to 230V isolation transformer on the grid side?

 

 

1 hour ago, Jan Pretorius said:

What is the view if I add a 230v to 230V isolation transformer on the grid side?

It's done often with boats. For two reasons actually, when you are sailing the world, your shore supply might not be 230VAC. You might be in some backwater American harbour with a measly 110V. Pffft. So a transformer that can also step up the voltage (or for some, in reverse, make 2 x 110V legs from a single 230VAC line), that is really helpful.

But other than this, there is also the issue of earthing. If you earth the hull of the boat to the shore supply, you change the land, water, and the hull of your boat into a battery (where your boat is the one plate), and galvanic corrosion results to the hull of the boat. So they are also used to avoid this (although there are other ways as well).

So on a technical level, it seems like a brilliant idea to me.

On a financial level... you do know what a 2KW isolation transformer costs? 🙂

We’ll I need to look at options, see you recomend Victron inverter would this solve my problem?