Electrical conundrum - mains aircon in motor home

[Mary Fisher]

You need to get out more.Really.

Mary

[Andrew Gabriel]

Startup will be much more.

120W fridge/freezer compressor draws around 3kW starting (and 3kW for longer when trying to start with a locked rotor due to trying to start too quickly after stopping).

My home aircon is 1200W power consumption, and that draws over 4kW (max my power meter reads) when trying to start against a locked rotor for a few seconds before giving up and retrying after a timeout. The momentary starting load when it does start properly will be the same, but for too short a time for normal power meters to measure.

You can't combine the output of multiple AC power sources unless they are explicitly designed to sync their output waveforms (a bit like solar panel inverters).

Also, when sizing power sources for loads like this, you need to use the VA rating, not the watts rating. (A decent power meter will tell you the VA load - it will be more than the power consumption.) You probably also want a pure sine wave inverter - inductives load often don't like the stepped output which most inverters produce. (Pure sine wave inverters are now much more viable than they used to be, most being class D amplifier outputs, i.e. switched-mode power supplies at a much higher frequency to generate the sine wave output.

[David]

Good call. Perhaps I should buy a motor home? Oh, wait.......

[Roger Mills]

Yes, indeed - and a 13A fuse will stand a considerable over-load without blowing provided it doesn't last very long.

I remember doing an experiment a few years ago to see whether my 2kW Honda generator would power some device or other. [Can't remember whether it was a compressor, a table saw or a pressure washer - but it was something rated at way below 2kW]

Whatever, it was, the genny wouldn't start it - it just groaned and went into some sort of 'limp home' mode, and had to be reset by shutting it down and re-starting it before it would run normally again.

[DerbyBorn]

Get an awning and sleep outside. Enjoy the outdoors and the weather. Go sightseeing. Drink wine. Remember that the more you spend on kit, the more you loose on depreciation. Or go in a hotel with air conditioning.

[Dave Plowman (News)]

Must admit I don't share the love of AC many have. Perhaps it's because I was born in the NE of Scotland, where it's more likely cold than hot, so loved the odd hot day.

Both my cars have AC, but almost never used. I'd rather open the roof and windows and enjoy a hot day. ;-)

[David]

Self and partner can't cope with temperatures much above 30C without going into meltdown.

We don't use the aircon very often (once every year or so) but it is reassuring to have it.

Some people love high temperatures; others find that they can't cope and get very unhappy indeed.

Cheers

Dave R

[harry]

It's just not technically feasible. The grid tie inverter runs at 400 odd volts You need to have conventional AC fitted to the engine of your vehicle. The only practical solution.

[David]

As already stated I have conventional A/C fitted to the engine of my vehicle.

Additionally, the exhaust pipe exits into the awning area, so running the engine when the van is set up with the awning is not a good plan.

This is looking at ways to use the habitation A/C which is already fitted.

However the information that it requires a 400 volt grid tie inverter for a solar system does rule it out for a motor home.

Cheers

Dave R

[Dave Plowman (News)]

Very rare to have a true temperature above 30c in the UK. The inside of a car in the sun, yes. But opening the windows on the move soon cools it down to ambient.

I have used it to cool the car down before getting in.

True. But we're in the UK. ;-)

[polygonum]

Partner has issue which means she gets severe pain in higher temperatures. Usual maximum in our house is 17 degrees - much more is not acceptable.

[Bob Minchin]

Add to that, even if you provided the Grid Tie inverter with enough battery volts, you will possibly be disappointed that it will not give any output when the grid is not present.

[Dave Plowman (News)]

Oh. That must make life pretty difficult.

[harry]

Well then, the obvious solution is to re-route the exhaust system. Or dispense with the awning.

[David]

Ummm...can I tactfully point out the "Mobile" in "Mobile Home"?

This does mean that we are not tied to the UK and can visit the far flung reaches of mainland Europe.

Where (especially at some distance from the sea) the temperatures can be more extreme than those normally experienced in the UK.

Mind you, I can remember 30C plus temperatures in the UK - around 2007 IIRC.

Cheers

Dave R

[David]

I was assuming "grid tie" was code for latching onto a 240V AC supply from an external source.

Ummm...yes, the implication is that you would need an external AC source to persuade the inverter to run (otherwise the safety lock to prevent killing people repairing the grid would cut in).

Which brings me to wonder if a solar array can keep the home going if the grid is down.

This would require a reliable cut out!

Cheers

Dave R

[polygonum]

It does - not for me - but for her. Lots of places are effectively off-limits - such as theatres, cinemas, many restaurants, pubs, ... Short periods in some shops are OK (or bearable) but nothing that means a long time. Hospitals are among the worst...

[Johnny B Good]

Sounds like she may have inherited "Peace Keeper" genes from an alien encounter many generations past.

[Chris J Dixon]

In a word, no.

It is possible to set up an off-grid battery-based PV system, but a conventional setup will not run.

Chris