Air Con on an Inverter

[EuroTrotters]

Hope you find this helpful...
I have a Dometic roof mounted Aircon & associated/matched Dometic Inverter, with
3 x 100 amp Leisure Batteries & 4 Solar panels on the roof (each with its own individual Victron Solar controller) all fitted by Eddie’s great team at Vanbitz on my 2016 Swift Bolero.

When travelling in hot sunny weather I can run all day with the Dometic roof mounted Aircon running and importantly- arrive with 100% FULLY charged batteries! Plus an ice cold interior.

But on arrival, it is absolutely essential to switch the Aircon off before stopping the engine, unless I am immediately hooking up to the mains, to prevent the batteries from being rapidly depleted.

Note as part of the installation Vanbitz fitted new heavy weight cables between the vehicle battery & alternator circuits and the Inverter & Leisure batteries circuits.

The size of your alternator plays a big part in that. Do you know what the output of the alternator is ? eddievanbitz

 

[CaptainPaul]

Im watching this thread with interest too, as i have tried just about every conceivable solution known to man and never had any success in running an A/C unit on anything other than mains power, i have a 4000 pure sine inverter connected to 2 x100amp batteries and lots of solar panels too, the boss can run a hairdryer on it and i believe it will run a microwave but i have never had any success with the AC going off grid, i even toyed with the idea of an onboard 'silent' gas built in generator but upon demonstration at the factory that installs them i found them slightly noisier than a Honda suitcase generator! but i await with baited breath anyone who has solved this problem

 

[EuroTrotters]

Im watching this thread with interest too, as i have tried just about every conceivable solution known to man and never had any success in running an A/C unit on anything other than mains power, i have a 4000 pure sine inverter connected to 2 x100amp batteries and lots of solar panels too, the boss can run a hairdryer on it and i believe it will run a microwave but i have never had any success with the AC going off grid, i even toyed with the idea of an onboard 'silent' gas built in generator but upon demonstration at the factory that installs them i found them slightly noisier than a Honda suitcase generator! but i await with baited breath anyone who has solved this problem

Ie solved this problem.

what size is your alternator ?
What make, model and type is your inverter ?
Do you have a B2B charger ?
What is the power consumption is your a/c ?

 

[Carpmart]

Sorry but you’ve no chance. On occasion, I do run mine off the onboard generator and the load the aircon pulls is pretty significant, you’d never be able to supply that from batteries.

 

[funflair]

Im watching this thread with interest too, as i have tried just about every conceivable solution known to man and never had any success in running an A/C unit on anything other than mains power, i have a 4000 pure sine inverter connected to 2 x100amp batteries and lots of solar panels too, the boss can run a hairdryer on it and i believe it will run a microwave but i have never had any success with the AC going off grid, i even toyed with the idea of an onboard 'silent' gas built in generator but upon demonstration at the factory that installs them i found them slightly noisier than a Honda suitcase generator! but i await with baited breath anyone who has solved this problem

We can run our Dometic 2200w freshjet air con off the inverter and batteries, from memory I would say that it draws about 60 amps and that is intermittent as its only the compressor that takes the big power the rest is just the circulation fan, a decent bank of solar can go a good way towards running it and our LiFePO4 batteries would last all day.

So yes success.

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[CaptainPaul]

Ie solved this problem.

what size is your alternator ?
What make, model and type is your inverter ?
Do you have a B2B charger ?
What is the power consumption is your a/c ?

I would have to look all that info up to be honest, although the inverter is a Waeco (Dometic) 4000 sine wave, aircon is a Dometic freshjet 2000 ( i think) lol van is out in the shed so would need to double check but I'll get back to you when i find out, thank you

 

[Odd-no-more]

My Duetto Ice had an inverter to run the air con whilst driving, we also used it for up to an hour from the lesure battery with no problems

 

[EuroTrotters]

I would have to look all that info up to be honest, although the inverter is a Waeco (Dometic) 4000 sine wave, aircon is a Dometic freshjet 2000 ( i think) lol van is out in the shed so would need to double check but I'll get back to you when i find out, thank you

The other thing you will need is healthy batteries

 

[CaptainPaul]

Yea batteries are good, i was into boating for many years where bad batteries can be life or death, i use Trojan batteries which are hard to beat, but I'll get back to you with the other info thanks again

 

[funflair]

The Dometic web site used to have the full spec of power required in heating and cooling mode but the new improved web site doesn't show it or if it does I can't find it.

On the Freshlight 2200 page it shows power requirement in cooling mode as 950watts so a nominal 80A from your 12v but as I said before it is cyclic and dependent on the fan speed so a lot less than that per hour.

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[Midnightflyer]

4000w inverter? That's going to draw some 350amps on full power. Thus a 100ah battery will last 15 minutes.

Going back to the aircon, on cooling it uses 2400watts. That equates to 200amps on 12v.
Allowing for losses, a 100ah battery would last about 20 minutes before fully depleted (and almost certainly ruined!). Add to that the start up current is 28amps (at 240v) and it becomes obvious why it won't work. Engine running is not going to make the slightest difference with those currents.

To put it bluntly, you've not a prayer of running an aircon off 12v unless you tow a trailer stuffed full of batteries, and some incredibly thick wiring connecting it all up.

Absolutely correct it's the simple science of electrics, get yourself a 5Kva generator to power that or change the Air Con for a 12 Volt system HOWEVER these will cane your batteries. My best advice is to get used to the heat when 'Off Grid'

 

[AndyVW]

The benefits of truck chassis...... Roof aircon is a Colman Mach, when running comp. uses 1200 amps, and it cycles a lot so is not continues. inverter 2000watt Viltron, will only function when engine is running, and only supplies 220V to AC.
It has a 24 volt supply direct from truck via two 220amph batts and a 160amp alternater, works perfectly.

 

[autorouter]

Absolutely correct it's the simple science of electrics,

No it's not correct. You missed out the dark arts of the heat pump. It produces 2400W of 'cooling power' using a heat pump that uses 4.2A at 240V, ie 1008W. As DBK has already pointed out.

However 1008W is still 84A at 12V, so you'd need 84 x 5 = 420Ah of lead-acid-type battery to power it properly, or 200Ah of lithium. And it wouldn't last long even with that large battery bank.

The bottom line is, for that aircon you need about 1000W for several hours, and that needs EHU, an engine powering an alternator, a generator or a house-sized solar array.

 

[Richard n Ann]

No it's not correct. You missed out the dark arts of the heat pump. It produces 2400W of 'cooling power' using a heat pump that uses 4.2A at 240V, ie 1008W. As DBK has already pointed out.

However 1008W is still 84A at 12V, so you'd need 84 x 5 = 420Ah of lead-acid-type battery to power it properly, or 200Ah of lithium. And it wouldn't last long even with that large battery bank.

The bottom line is, for that aircon you need about 1000W for several hours, and that needs EHU, an engine powering an alternator, a generator or a house-sized solar array.

Yes the dark arts have horrified many an electrician on fitting the supply... "effing hell mate! How much power does your AC unit take!? I need to order a bigger breaker!"

 

[chrish]

I had exactly the same issue, and as suggested in an earlier post, the air con was connected to a circuit that was only energised when on EHU.
The mains fuse box had a separate MCB breaker for the air con which was fed directly from the EHU, whilst the 13 amp sockets are fed from the inverter circuit.
What I did was to put a relay that was energised by the d+ (engine running) to feed the aircon from the 13 amp socket (inverter fed) circuit.
This works a treat for me with a 3000 Watt inverter .
You do need to make sure that the MCB that feeds the air con, does not supply other appliances like the fridge or heater.

I used a relay with a manual override function (I think they call it a test function) so that I could run the Air con without the engine running.

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[autorouter]

Another relevant point - the steady-state average power requirements. Once the MH is down to the desired temperature, the power required to maintain it is governed by the outside temperature, the effectiveness of the insulation and how often you open the doors. The aircon cycles on/off to remove any excess heat coming in. How long and often it cycles depend on how much heat comes in. Better insulation, external screen insulating blinds and parking in the shade helps. Solar panels have a double benefit of providing shade producing power.

 

[MobyDick57]

Whilst in Portugal when is was hot, I noticed that a number of motorhomes had decided to cover their roof lights with latex caps. Which helped defeat the sun heating the interior of their vans. They were especially efficient when their roof vents were open. Most of our roof is covered with solar panels, which also helps keep the van roof cool, because they are in the shade of the panels. We have found this combination very effective, so not bothered with aircon

 

[EuroTrotters]

Yea batteries are good, i was into boating for many years where bad batteries can be life or death, i use Trojan batteries which are hard to beat, but I'll get back to you with the other info thanks again

I use Trojan too

 

[eddie]

Dometic supply a DC kit, which allows the inverter to draw simultaneously from the engine and leisure batteries, constantly monitoring the voltage in both. Should the engine battery volt start to drop, the system disconnects the engine until it recovers, if the voltage continues to drop it turns the AC off automatically

We’ve installed dozens and dozens of the over the years when people really want AC on the move

Personally we use the dash AC and if it’s really hot for Shadow our dog, we push the button and start the generator, but it can be done

Dometic DC Kit DSP-T 12 - DC extension kit for FreshJet series, 12 V

Dometic DC Kit DSP-T 12 - This clever kit enables the air conditioner to run off the 12 V vehicle battery even while driving. The kit includes a charging current distributor with low-voltage protection, which ensures optimal energy efficiency and saves precious battery power.

www.dometic.com

 

[Lenny HB]

, i have a 4000 pure sine inverter connected to 2 x100amp batteries

Thats crazy I'm surprised your batteries haven't committed suicide, for that size inverter you need at least 600 ah of batteries even that would be pushing it.

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[AndyVW]

I use Trojan too

Me Too .. (for leisure) 4 years old now,