FlameZum 1500/3000 Inverter

[RDMETimmy]

Peoples. Really scratching my head on this one. Wired up as per labelling and my camper sockets showed reverse polarity via my LAP socket tester. Rechecked all my connection in case senility had kicked in but everything correct. Disconnected inverter 240v output and put LAP directly on to inverter socket and it registered no earth! Checked my cabling again including grounding the extra earth all fine but still getting no earth...

Decided to put a plug on rather than hard wire and tested again... guess what.. same fault on sockets... neutral live polarity issue according to my LAP Tester.

Wanted to protect inverter socket i fused the battery input and it blew 30A fuse when I switched on camper microwave. 750w draw 500W microwave.. I am fairly technically competent with 30 years as electronic engineer but this is beating me...

Any reasonable suggestions?

 

[merl]

In a domestic system Earthing typically involves connecting the neutral and earth together at various points in the supply and also a connection of this earth/neutral to Planet Earth. Because 'Earthing' a system involves this connection to planet Earth then there cannot be an earth potential on an enclosed system within a MH running on it's own enclosed inverter unless you physically add a secondary cable to an earth stake pushed into the ground. You will however gain an earth when you connect the van to a conventionally earthed supply via a EHU lead. Socket testers typically display 'No Earth' and/or reverse polarity because of this.

Amps = Watts divided by volts.
750(W) divided by 12(V) equals 62.5A but this doesn't take wiring or inverter losses into account and assumes 12V at the battery terminals.
Depending on battery type/condition/SOC, inverter efficiency, wiring etc your 750W load from the microwave will draw approximately 60-80A from your 12V battery hence a 30A fuse will rupture.

 

[alwaysared]

What Merl said

A search on Google (other search engines are available) shows that lot's of people get this problem on Swift vans because their Sargent control unit has a reverse polarity warning light

Regards,
Del

 

[Geek]

So I'm clear: Are you saying that the electrics work OK on hookup and on the inverter?

If the wiring causes your LAP tester to say it is reverse polarity, what is it telling you?

In domestic wiring, one wire (usually the blue one) is connected to a neutral with which is more or less the ground voltage at your local substation.

The same connection is used by a separate wire, usually green and yellow. This is meant to be connected to the case of the appliance. It is also connected to the conductive bits of your house, to make them the imported 'earth' voltage.

A third wire (usually brown) is connected through a transformer to be about 240V AC away from earth.

Because you are electrically connected to the green and yellow wire, if you touch the blue wire you shouldn't get much of a shock (though a safety device might notice and cut the power anyway).

It is different in a motorhome with an inverter. Neither the brown nor the blue wires are connected, directly or indirectly, to the earth anywhere. They float independently.

The body of the van should be (but possibly isn't) connected to the green and yellow wire, which will be connected to the appliance casing.

If you touch either the blue or the brown wire, you should not get a shock. Don't touch both at once!

Because neither leg is connected to any earth, the idea of 'reverse polarity' is a bit moot. And testing for it is a joke.

With a hookup connected to an external supply, it's quite a lot more complex. Especially when it's a 13A plug through the letterbox into a house with PME wiring on a TNCS supply. That is very much outside the scope of this comment.