Hard wiring an inverter.

Dave and Ginny

Dave and Ginny

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I've looked around previous posts but can't seem to find what I'm looking for so excuse me if the answer is there somewhere!

So I now have my nice new pure sine 300 watt inverter and I've found a spot to mount it near the leisure battery that's under where the wife sits, just next to the gas bottle locker :eek:

I want to hard wire it and I'm using a 35 amp fuse from the live to the inverter. Although the inverter has an on/off switch, I'm a bit concerned at it being live to that switch. Perhaps I'm over complicating. When laid up for a few weeks I can always take the fuse out but not ideal.

Has anyone put an extra switch in, or maybe a plug connector?
 
davidandginny said:
Has anyone put an extra switch in, or maybe a plug connector?
Click to expand...

No and no problems seen. But do use that switch, they take a fair bit of current when idling.

I fitted a short 240 extension with a neon indicator so I know when it's switched on.
 
Instead of just a secondary switch i would include a 40a relay close to the battery to isolate almost all of the wiring when turned off.
only light gauge wiring needed from relay to on/off switch and a much lighter duty (illuminated) switch.
 
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JeanLuc said:
I fitted mine with an additional relay switch and leave the switch on the inverter permanently on. Here is my report on the installation in the Resources section. (Rather like Pappajohn's suggestion.)
http://www.motorhomefun.co.uk/forum/resources/install-a-small-inverter.17/
Click to expand...

Nice article Philip, mine is pretty much the same with the exception that I have fitted a 40amp 240 volt changeover switch that I can switch between EHU/Inverter thus allowing 240 volt to be accessed from all fitted 240 volt sockets. Both EHU and inverter are isolated from each other when switched.
Also in upper left is a switched USB socket and a voltmeter that reads both Hab and main battery when they are switched via Zig unit.

image.jpg
 
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I hope that your all remembering to put a RCD on the mains output when accessing the 13 amp sockets?
 
Where do you connect the earth to on the inverter?
 
snoopey2 said:
Where do you connect the earth to on the inverter?
Click to expand...

Jonkil said:
Earth lug on the case usually. (Not always fitted)
It's the wing nut on the left centre below.
Click to expand...
Good question & perfectly accurate answer. But I wonder if that's what snoopy2 meant?

First question - what is that wing nut connected to? The case, obviously, but is it also connected to the earth line on the 23oV socket?

Second question (& I wonder if this is what snoopy2 wanted to know), if you attach an earth wire to the wing nut, what should the other end of the earth wire be connected to? There is, after all, no 'earth' as we would normally understand it in 230V terms, as our vehicle is sitting on rubber tyres.

Reading the installation instructions on the Sterling Power Products web site, the answer appears to be to connect to the neutral or -ve or vehicle body - which are all the same thing in effect as they are all connected.

As Jonkil rightly points out, not all inverters have this earthing wing nut. So do we assume that they have the 230V cable earth connection, the inverter case & the -ve battery connection already connected together inside the case?

What sparked my interest is a problem I have with my inverter. My previous inverter was a Sterling unit with a case wing nut. This was connected, albeit indirectly, to the vehicle chassis. It was indirect because it was via the -ve terminal on the battery.

My current Waco inverter has no separate earth.

The output of both units went through a plug-in RCB.

No problems at all with the Sterling unit.

No problems with anything with the Waco unit except for my laptop power supply, which immediately trips the RCB. It does this whether the laptop is plugged into the power supply output or not. It's a fairly beefy bit of kit - 19V 9.5A output, but still trips under no-load condition.

If I take the same RCB into the house & plug it into the mains, I can plug the laptop power supply into it without it tripping out.

I have tried two different RCBs, with the same effect.

So am I looking at a real fault & if so, where?
 
Hi The Caller,
There are two different types of RCD, just to make life simple. One for modified sine wave and one for true sinewave inverters. An RCD is there to protect from live to earth faults, not short circuits, they are the domain of fuses or MCB's. The earth terminal is connected to the neutral side of the live and neutral pair before the RCD, so if the RCD sees an inbalance of the current flowing in the live and neutral wires because some or all (more than 30mA) of the current is going back down the earth wire then bypass the RCD it will trip. If the earth wire is not connected to the earth terminal in the socket then there is no live to earth protection.
A modified sine wave invertor will saturate the coils in a 'normal' (type A) RCD and it will not work correctly. To find out if your circuit is correct just use the Test button, with the power on to the inverter and RCD. (No need for any load).
With the tripping of the power supply, it probaly does not have a transformer input for the mains supply. With the inverter disconnected from the mains, check with a meter on ohms. which of the output leads is connected to the earth, it should be the neutral one.

David
 
Thanks David (I think!!)

I think I have followed most of that. It certainly inspired me to do some reading about earthing, inverters & RCBs. As with most things electrical, it produced a number of different opinions, several diametrically opposed!

Tomorrow, in daylight & hopefully in sunshine rather than the current wind & rain, I'll check which of 230V ground, inverter case & 12V -ve are interconnected. I'll do the same on my old Sterling inverter as well, to see if that explains the different behaviour - I still have it, I only changed it to get a slightly higher capacity.

For those that care about these things, I see my earlier posts have consistently omitted the 'e' from Waeco. Mind you, as I discovered that they omit to tell you that they advertise their inverters at max output rather than continuous, I don't feel too bad about my omission!
 
I have two inverters, the original was a 500w one specifically to run the washing machine and was wired through a 40a relay with the inverter switch permanently on. The later addition of a 3000wPeak inverter is permanently connected to the battery bank as a 300A relay is a bit of a no no.

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TheCaller said:
Tomorrow, in daylight & hopefully in sunshine rather than the current wind & rain, I'll check which of 230V ground, inverter case & 12V -ve are interconnected. I'll do the same on my old Sterling inverter as well, to see if that explains the different behaviour
Click to expand...
Had a bit of sunshine, but I missed it. At least it wasn't raining.

Interesting results. They are wired differently.

The Sterling has the 230V neutral bonded to earth on the output, but not to either the case or the 12V -ve. The wing nut on the case is bonded to the metal parts of the case only.

The Waeco has the 230V earth bonded to both the case & the 12V -ve. There is no separate wing nut earth connection on the case. The 230V earth is not bonded to the 230V neutral (unlike the Sterling).

Now my head hurts from trying to work out the implications. :confused:
 

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