Inverter question

[eddie]

This is the correct DIY method, but a proper inverter-charger does it better. I'll give Victron as an example but all decent brands should do this:

The 500 Multi series will detect if the incoming mains is within the correct safe range before it gets used - so too low or too high and it stops using it.
The 800 and upwards Multi series support Boost and Fade, which means it will re-process mains that is a bit too low or high into the correct voltage so it works exactly as a high-end computer UPS delivering clean power within spec regardless of what goes in!
(The 800 and upwards can also be paralleled for more power with a synchronising bus cable as an aside).

So a relay is fine, but a proper product is always better for the reasons stated above!

It was a DIY question!

 

[Ivory55]

Or for the un technically minded, get a generator. Haha

 

[GPW]

It was a DIY question!

Yes, my reply was just FYI for the technically minded.

 

[olley]

And for those with deep pockets.

 

[Lenny HB]

I hesitate to question someone so experienced, but shouldn't that be the other way round? When the relay is not energised, you want the inverter to be connected to the sockets, so that's through the N/C contacts. When the relay is energised by the EHU mains, you want the sockets to switch over from the inverter to the EHU mains, so that's through the N/O contacts.

That is the way I wired mine so the default is sockets connected to inverter, works for us as we are mainly off grid.
If I was using EHU a lot it would make sense to have sockets default to EHU and the relay powered by the inverter.

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[GPW]

And for those with deep pockets.

For those who buy Lithium batteries they are pocket change LOL.

The 500 Multi I bought was £365 IIRC (Bimble Solar), as it included autosensing changeover relay, a 240 Watt smart multi-phase charger and an indestructible 500 VA (with low 2 Watt standby) inverter in a single box I thought it was a pretty good deal

If I get an 800 for the next van (which I probably will as the Globescout doesn't come with an inverter) I would probably remove it before sale like the Gasit kits - i.e. keep it longer than the van!

 

[G-RMPS]

...I wish I’d never asked the question ;-). Took the wife to get her hair cut today!

 

[Rob Turner]

I did similar to Techno and all seems fine tbf. I added more circuit breakers so the fridge and battery charger were on different circuits.

 

[GPW]

Liking the double pole breakers, useful for when 'neutral' isn't related to earth. Looks like the RCD in the right place too!

For those (other) DIY installs of an inverter it's also worth adding in an RCD after the inverter itself, unless one electrically adds an inverter-charger between the van's original main EHU isolator switch and the RCD.

I.e. always look at the wiring and ensure there is an RCD between your appliances and your inverter, because the RCD is there to protect people from appliances, not vans from sites

 

[Lenny HB]

For those (other) DIY installs of an inverter it's also worth adding in an RCD after the inverter itself, unless one electrically adds an inverter-charger between the van's original main EHU isolator switch and the RCD.

Will only work if one side of the inverter output is grounded as inverter output is floating & isolated.

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[Richard n Ann]

Will only work if one side of the inverter output is grounded as inverter output is floating & isolated.

Some people think that stray capacitance at 50hz will be a problem though. It won't

 

[GPW]

Will only work if one side of the inverter output is grounded as inverter output is floating & isolated.

I think you are right as a path to ground is needed to unbalance the L and N to trip an RCD.

My Victron Multi has a built-in 'Ground Relay' that grounds the Neutral when on 'inverter mode' so I guess that's what it's for but no stand-alone inverter will have that.

 

[olley]

For those who buy Lithium batteries they are pocket change LOL.

The 500 Multi I bought was £365 IIRC (Bimble Solar), as it included autosensing changeover relay, a 240 Watt smart multi-phase charger and an indestructible 500 VA (with low 2 Watt standby) inverter in a single box I thought it was a pretty good deal

If I get an 800 for the next van (which I probably will as the Globescout doesn't come with an inverter) I would probably remove it before sale like the Gasit kits - i.e. keep it longer than the van!

Yes seems a good price for what you get, but for me 500w is to small.

 

[bfb]

Understood! This is an expensive solution to a daily five-minute hair-drying exercise,

Get the wife to put her head out the window whilst you drive. Job Done. Better on a sunny day though!

 

[eddie]

Most decent inverters tell you to add an RCD in the installation instructions

Sterling have RCD’s built in

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[Lenny HB]

Most decent inverters tell you to add an RCD in the installation instructions

Most self installers don't understand the technicalities of a floating output.

 

[Richard n Ann]

Most decent inverters tell you to add an RCD in the installation instructions

Sterling have RCD’s built in

It's just to cover their arses. It won't do any harm I suppose, except to your wallet.

 

[GPW]

Yes seems a good price for what you get, but for me 500w is to small.

It's not 500W it's 500VA (It's a power factor thing ). Into a tricky load perhaps 350W, 700W peaks.

At home you generally get a 100A fuse so you have 20kW available, 500W out of a 12V battery is 500 / 12 = 41 Amps, which if done often would require a battery bank of 200Ah to manage well.

(Battery lifetime is shortened by drawing higher currents, 20% of the Ah rating is about where you need to be, 40 x 5 = 200 Ah.

In a single box Victron go up to 1200W IIRC and you can parallel up to 3 of them. Maybe start with an 800 and add another 800 later to get 1.6kW. Then if you still want more a 3rd to 2.4kW.
But to support 2.4kW you'll need some serious battery, for the odd 15 minute blow-dry I'd be looking for wet cells at 50% of capacity so that's 2 * 2400 / 12 = 400 Ah.

Another option for 2.4kW would be to use 48V devices so the current is 2400/48 = 50A, again for a 50% lbattery load that's 4 x 100 Ah batteries, but the cables can be rated for 50 Amps instead of 200 Amps.

BTW when you see inverters on eBay of 2000W for £50 they are not real, the waveforms and safety won't be as good, power will be lower than the label and when you switch them on in my view there's a reasonable chance of them going 'fzzzt' and becoming door-stops or large paperweights. Inverters are extremely complex pieces of electronics and the complexity jumps as the power rises. Hair drying is one area where a Honda 2kW suitcase generator may be the cheaper, easier option

 

[olley]

For the layman like me 500w is a good enough idea of what it can produce, getting technical about VA is just you flashing your knowledge off.
I have an 1800 watt, sterling modified wave inverter, running from 3 x 180AH batteries so fine for the short durations it get used near full power. Another reason for a large inverter which is now rarer than it used to, is low EHU of only 4-5 amps unlike the 10 or 13 we can usually get, by switching the EHU to the 50amp charger only, I can power things from the inverter without fear of knocking the EHU trip out or flatting the batteries. Admittedly this is not an everyday occurance.
As for a genny, the RV has a 5000VA unit built in.

 

[GPW]

getting technical about VA is just you flashing your knowledge off.

Thanks, I try my best to accumulate knowledge!
Few AC loads are purely resistive, although most cheap inverters appear to be designed to power large resistors: the easiest load . If a maker quotes both VA and W it shows you that they know the difference and have designed for difficult loads.
Once I bought a cheap 1000W modified sine wave, it refused to run a 95W TV but would have a reasonable (but weird sounding) stab at running a hoover at low power!! I sent it back.

I have an 1800 watt, sterling modified wave inverter, running from 3 x 180AH batteries so fine for the short durations it get used near full power. Another reason for a large inverter which is now rarer than it used to, is low EHU of only 4-5 amps unlike the 10 or 13 we can usually get, by switching the EHU to the 50amp charger only, I can power things from the inverter without fear of knocking the EHU trip out or flatting the batteries. Admittedly this is not an everyday occurance.
As for a genny, the RV has a 5000VA unit built in.

Stirling make some excellent stuff, I'll have to get more familiar with their range.

When on EHU the Victron Multi will back off the charging current draw to let more of the EHU power through when needed. The bigger 800VA upwards models also use the inverter to boost the power when needed so they add their power to the EHU when you load it too much., so you get a max of EHU power + 800VA/1200VA etc.

I think I know why most campervans come without inverters in at all, it starts to get very complicated very fast and people's electrical needs are quite variable!

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[DABurleigh]

Can an inverter be installed in such a way that it uses the exising van wiring to distribute the 240v to existing sockets, rather than plugging stuff directly into the inverter box. I have an EBL, two leisure batteries, no solar. I am considering a beefy inverter, say 2kw. Cheers...Keith

Keith,

Check-out the Fun inverter guide here:
https://www.motorhomefun.co.uk/forum/resources/inverter-guide.7/

Dave