Air Con on an Inverter

[DDJC]

We have a Truma Aventa aircon fitted. We also have a 4000w inverter.
The inverter was supplied as being intended to power the Truma air con.

The aircon works fine when plugged in to the mains, but I can't get it to do anything on the inverter. Engine running obviously.

Can anyone think of an obvious reason why it won't start on the inverter?

 

[hilldweller]

Plug something else into inverter to test it.

 

[Langtoftlad]

Engine running cuts 12v system?

 

[thebriars]

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.

 

[DBK]

According to the A/C spec it draws 4.2A at 230V when cooling, which is about 1000W. The 2400W figure is cooling performance but it consumes less power than this as it is a heat pump. This means it will draw around 80 to say 90A from the batteries. With a 60A B2B fitted and suitable wiring I guess it is almost sustainable for a few hours but it will flatten the batteries eventually. A bigger B2B is needed but I don't know if you can get them larger - but I haven't looked. (Edit: I think you can get 100A B2Bs but check your alternator output.)

Test if the inverter will run something like a hair dryer. If it does and the A/C still won't run check if it is quasi-sine wave as the A/C may have electronics in it which need pure sine wave.

Aventa comfort - Inform now

Truma Aventa comfort cools your vehicle and heats it on cooler days. Find out more about this economical roof-mounted air conditioning system.

www.truma.com

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[HandyAndy]

As others have already stated, you need to test the inverter with increasing loads of a known quanity and keep increasing until it cuts out to know it's true maximum and to also find out if it's square wave, modified sine or pure sine.
On top of that you've not mentioned either the size of your battery bank or the size of your alternator. Without this info it's virtually impossible to give you anything other than speculation.

 

[Onemanandhisdog]

make 12v roof mounted air con units if you wanted to change it.

 

[Richard n Ann]

?If your going to run the engine just put the cab AC on ?

 

[thebriars]

According to the A/C spec it draws 4.2A at 230V when cooling, which is about 1000W. The 2400W figure is cooling performance but it consumes less power than this as it is a heat pump. This means it will draw around 80 to say 90A from the batteries. With a 60A B2B fitted and suitable wiring I guess it is almost sustainable for a few hours but it will flatten the batteries eventually. A bigger B2B is needed but I don't know if you can get them larger - but I haven't looked. (Edit: I think you can get 100A B2Bs but check your alternator output.)

Test if the inverter will run something like a hair dryer. If it does and the A/C still won't run check if it is quasi-sine wave as the A/C may have electronics in it which need pure sine wave.

Aventa comfort - Inform now

Truma Aventa comfort cools your vehicle and heats it on cooler days. Find out more about this economical roof-mounted air conditioning system.

www.truma.com

Even 80-90 amps is far too much current for 2 100ah lead acid leisure batteries linked together, and at that sort of current their lifespan will be very limited. Plus the fact the batteries will be fully dischared in less than 2 hours. Also remember at those currents there will be a significant voltage sag. As for running the engine, at idle the alternator current will be low.

Frankly running a roof mounted air con through an inverter is a total non-starter. You will have to use hook up.

 

[EuroTrotters]

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.

As stated, that is the cooling capacity in watts.

I run a Truma unit that consumes 600w @ 240v with a large Victron inverter. Copes no problem

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[Camping Gaza]

make 12v roof mounted air con units if you wanted to change it.

Here is another, supposedly used only 80 amps 12v when cooling (still a lot tho)

https://www.roadpro.co.uk/product/0...ing/airva-12v-2-9-kw-air-con-unit-c6301/C6301

 

[thebriars]

As stated, that is the cooling capacity in watts.

I run a Truma unit that consumes 600w @ 240v with a large Victron inverter. Copes no problem

600w at 12v = 50amps, more if you include losses.

1. What sort of batteries are you using.
2. What is the total Ah of your batteries
3. How long can you run the aircon on that?

 

[EuroTrotters]

Hi,

I use Trojan gel batteries 2 x 105ah

But I only use the a/c on hook-up or with the engine running.

If I am on longer hot journeys, I run the a/c and fridges via a generator on the move.

I don’t use it on battery, it would not last and kill the batteries.

The Trojan batteries are the best I have ever had

 

[EuroTrotters]

Genny sits on bike rack

 

[DDJC]

Hi thanks for the replies. I should have been more clear. I won't ever be using it on battery. My question was that when I am running the engine, with the inverter activated, is there any obvious reason why the AC won't work?

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[DBK]

Hi thanks for the replies. I should have been more clear. I won't ever be using it on battery. My question was that when I am running the engine, with the inverter activated, is there any obvious reason why the AC won't work?

If the inverter is of a suitable spec the A/C should work for a short while when the engine isn't running. Starting the engine will just delay the inevitable unless you have a humungous B2B and an alternator which can provide a suitable current. My guess on the latter would be one capable of 150A or so which would leave a bit of capacity spare.

 

[Robert Clark]

I’m guessing that the inverter has been wired to the 220v sockets only and not to the air con

 

[DDJC]

I’m guessing that the inverter has been wired to the 220v sockets only and not to the air con

Good answer, it fits the symptoms exactly because Mrs DDJC's hairdryer works on the inverter (engine running). I'll look into that. Might be a switch somewhere that I haven't played with yet. Thanks much

 

[DDJC]

If the inverter is of a suitable spec the A/C should work for a short while when the engine isn't running. Starting the engine will just delay the inevitable unless you have a humungous B2B and an alternator which can provide a suitable current. My guess on the latter would be one capable of 150A or so which would leave a bit of capacity spare.

Inverter is weird science to me. This is what I have got:

Maximum Continuous Output: 2000 watts
Surge Capacity (Peak Power): 4000 watts
Optimum Efficiency: >85%
No-Load Current Draw: < 1amp
Wave Form: Modified Sine Wave
Input Voltage: 10-15V DC
Output Voltage: 230V +/- 10v

 

[DDJC]

But what is a B2B?

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[Robert Clark]

But what is a B2B?

A Battery to Battery charger

 

[Robert Clark]

Sterling Power

Sterling Power is a market leader for battery to battery chargers, inverters, pro combi charger inverters, mains chargers.

www.sp-shop.co.uk

 

[DBK]

Inverter is weird science to me. This is what I have got:

Maximum Continuous Output: 2000 watts
Surge Capacity (Peak Power): 4000 watts
Optimum Efficiency: >85%
No-Load Current Draw: < 1amp
Wave Form: Modified Sine Wave
Input Voltage: 10-15V DC
Output Voltage: 230V +/- 10v

The problem could be the modified sine wave. Some things won't run on what is effectively a square wave form.

But what is a B2B?

Battery to Battery charger. They make the alternator work much harder to charge leisure batteries much faster than normal.

If the inverter was sold to you as suitable then I think you need to challenge the supplier and get your money back if it proves unsuitable.

 

[Campervan_man]

You can always fit a 13A plug to your Air Con Unit if just the sockets are wired in to your inverter.
Some air con units have a 10A fuse in the roof space which will blow before the plug fuse, check the specs and fit a lower rated fuse if appropriate in the 240V plug.

 

[EuroTrotters]

If the inverter is of a suitable spec the A/C should work for a short while when the engine isn't running. Starting the engine will just delay the inevitable unless you have a humungous B2B and an alternator which can provide a suitable current. My guess on the latter would be one capable of 150A or so which would leave a bit of capacity spare.

Truma suggest a 120ah alternator as a minimum .

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[autorouter]

Maximum Continuous Output: 2000 watts
Surge Capacity (Peak Power): 4000 watts

The continuous output of 2000W should be fine, because the steady-state power is 4.2A x 240V = 1008W. However the startup surge is 28A x 240V = 6720W. which is quite a bit more than the inverter surge capacity of 4000W. It's only a very short surge, so you may possibly get away with it if the battery supply holds up. Is this a new problem, or has it never worked on 12V?

 

[pappajohn]

I think they will have either sorted it or abandoned the idea.... The thread is almost 2 years old.

 

[DDJC]

No I think they will have either sorted it or abandoned the idea.... The thread is almost 2 years old.

No still watching !!

Resigned to a couple of things.
1. The solar panel extends the use of the aircon by about fifteen minutes before the battery carks from full charge.
2. Far easier to use EHU.

 

[Christyler]

Inverter is weird science to me. This is what I have got:

Maximum Continuous Output: 2000 watts
Surge Capacity (Peak Power): 4000 watts
Optimum Efficiency: >85%
No-Load Current Draw: < 1amp
Wave Form: Modified Sine Wave
Input Voltage: 10-15V DC
Output Voltage: 230V +/- 10v

So it's a 2000w inverter, supposedly, is it by any chance a no name Chinese unit. If so that's your problem. It's probably only capable of 500-600w in reality. A proper inverter, like a victron will solve your problem. With the inverter anyway. You may also need bigger battries.

 

[Chris Sykes]

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.

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