# Electrical conundrum - mains aircon in motor home

This first post is a place holder in part, so that I don't forget to ask the question, as I usually do once I get involved in stuff during the day.
The Motor Home has mains powered habitation air conditioning - that is an ELectrolux slug on the roof.
So for it to work you need to be on a site with mains electricity.
There is also the issue of the power surge on start-up compared to the power demand on normal running.
What I would like to be able to do:
(1) Run the A/C whilst driving - that would I assume involve an inverter which could take power through the 12V electrics buffered by the habitation batteries (unless the demand needs a direct connection to the alternator charging circuit instead of via the charge controller which charges the habitation batteries). This also allows starting the engine, firing up A/C and then stopping the engine and letting the A/C run on using the habitation batteries.
(2) Run the A/C when away from mains power - using a small Honda generator which might be able to meet most of the demand apart from start-up. I am envisaging perhaps the generator pushing power into the system whilst the A/C takes power out so that the use of habitation battery charge is slowed. This probably equates to running a UPS (that is, power in to UPS for charging, power always out of UPS for running the device) and using a small generator to keep feeding some power into the UPS during a power cut. The generator may not fully meet the power demand but it slows the rate of discharge.
This does seem to demand a lot of inefficiency, though, potentially with the generator input being converted from 240V to 12V then back again. It would be nicer if the battery 12V power could be used to boost the 240V input from the generator so that most of the power comes directly in at 240V.
Bottom line is that one way may require blending two 240V inputs into a single output, with obvious (I think) requirements to lock the wave forms of the 240V together.
If I can manage ASCII art:
12V -> 240V -> Blender -> A/C 240V -----------^
I think this is probably not realistic because you would have to prevent back flow which is why there are so many issues with combining power inputs connected to the grid. Then again, it is only like combining a solar panel and mains (but that does allow back flow into the grid).
I need to dig out the handbook for the A/C to check all the power demands, but meanwhile does this sound in any way feasible?
I know (2) could be met by just buying a bigger generator, but I bought the little Honda because I could just shoehorn it into the available storage and anything bigger is too tall/wide to fit anywhere usable.
Cheers
Dave R
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On Friday, February 26, 2016 at 10:59:10 AM UTC, David wrote:

.
r

,

Non starter. Aircon requires an immense amount of energy that you are just not going to get out of the 12V system or a battery.
You possibly could add an aircon compressor to the engine if there is space for one and all the other components of course (many engines just substitu te an idler pulley instead of the compressor if the aircon option isn't cho sen) but it would be hugely expensive.
Probably better all round to open the window when driving and sit outside i n a deckchair when camped without leccy hookup.
Philip
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On Fri, 26 Feb 2016 03:31:22 -0800, snipped-for-privacy@gmail.com wrote:

There is already cab aircon which is fine for driving along and can also cool the interior of the MH unless it is really hot - keeps the cab cool but the interior of a MH has a lot more volume than a van cab or a car.
Also does not solve the 240V issue as you would have to run the engine all the time even when you are on a powered site.
Also not good to cool the van when you are out at the beach - which seems to be one of the favourite reported usages.
Cheers
Dave R
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On Friday, 26 February 2016 11:31:26 UTC, snipped-for-privacy@gmail.com wrote:

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t not going to get out of the 12V system or a battery.

ce for one and all the other components of course (many engines just substi tute an idler pulley instead of the compressor if the aircon option isn't c hosen) but it would be hugely expensive.

in a deckchair when camped without leccy hookup.

+1
Automotive AC runs directly off the engine such is the power required.
Such AC can be retro-fitted but not cheap.
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David wrote:

To get some idea of the overall feasibility, what is the actual power demand from the aircon?
Chris
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Chris J Dixon Nottingham UK
snipped-for-privacy@cdixon.me.uk
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On Fri, 26 Feb 2016 10:59:07 +0000, David wrote:

The handbook is not entirely clear. *<shock>*
The unit is an Electrolux Blizzard B1500.
The technical data includes:
Cooling consumption 715 watts Heating capacity 800 watts.
Looking at the manual it seems that the unit is not designed to be used as a heat pump when blowing warm air (as you might expect) but has a small heating element - so from the data it looks to be an 800 watt fan heater (less a small deduction for the power to turn the fan).
The 715 watts may be the maximum start up for the compressor, or may be the average after the compressor has started.
Google isn't helping me much so far (apart from several links about the heater giving of a burning smell then stopping working) but there is one foreign link which related the "1500" in the brand name to 1.5kW. The fuse recommended is a 10 amp slow blow, so good for up to about 2.5kW, which may hint at the expected starting load.
I suppose what I really need is a power meter of some sort to accurately measure the power draw when it is fired up via the mains.
Can anyone recommend a reasonably priced meter which can do this sort of thing?
Amazon offers plug in meters from about £7 upwards - to about £55.
In this case I won't be looking for milliwatt accuracy, but who knows what I might need to check in the future.
Oh, and the generator is rated at 450 watts normal 550 watts maximum at 50Hz. It is badged as a 650W generator as this is the maximum output at 60Hz.
Assuming that the real draw from the A/C is 715W then the generator couldn't run it stand alone, but could supply a reasonable percentage of the power.
Cheers
Dave R
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Windows 8.1 on PCSpecialist box

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On Friday, 26 February 2016 12:29:55 UTC, David wrote:

That might be for 110 volt? Or it might refer to cooling capacity of 1500 watts, with electrical consumption of 715 watts, which would be a coefficient of performance (COP) of about 2 which sounds reasonable for a small heat pump.
Owain
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On Fri, 26 Feb 2016 05:17:40 -0800, spuorgelgoog wrote:

Thanks - another bit of the data says that it is 230 volts at 50Hz.
Cheers
Dave R
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David wrote:

Whatever scheme you use you need the VA requirements of the compressor NOT the watts to get an inverter or genny to power it. You also need to be able to source the Starting VA of the compressor which will be far higher than the running figure by several times.
One way to estimate pk current is to look at the rating of the fuse and knock off a little.
You will soon see the requirements are far too high for a toy genny or a battery.
Basically this is a non starter. Forget it.
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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.
--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]
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Vehicle AC is invariably driven direct from the engine - the compressor via a belt drive, etc. You'd need a massive alternator to provide anywhere near enough current. And a massive inverter.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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Dave Plowman (News) wrote:

Agreed. A big alternator will give you 2.4 Kw, nowhere near enough to start a locked compressor. Try sourcing a refigerated container heat pump and see what it takes.
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On 26/02/16 10:59, David wrote:

Is not possible.
When I took an RV across the Mojave desert, it had aircon that was powered by a little donkey engine/genny at the back that chewed petrol. Only used it in anger once, near Lake mead. There was just enough humidity to make the 40C+ temps unbearable.
It was noisy too.
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On 26/02/2016 10:59, David wrote:

As soon as we know the spec, it might be possible to assist.

For a narrow boat I installed a 3kW inverter (with surge capability), 150A alternator and 4 100Ah batteries. It can be done though challenging. I doubt you'll have the space to fit a second alternator.

Again without knowing the rating of the air con, and the size of your portable gen, we're in the dark.

You cannot "blend" 2 AC voltages.
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Snag is many motors if rated at nominally under 13 amps take a great deal more when starting. Not a problem for a normal mains supply - but an inverter or even generator may not like this.
--
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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On 26/02/2016 17:58, Dave Plowman (News) wrote:

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.
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Cheers,
Roger
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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.
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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. ;-)
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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On Sat, 27 Feb 2016 15:59:27 +0000, Dave Plowman (News) wrote:

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
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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. ;-)
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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