In an earlier article I mentioned that inverters were used in other ways, this is where you see a device with a motor in it (example air conditioner, or fridge), and the manufacturer states it is more efficient because it is an inverter air conditioner, what does this mean?
I will use an air conditioner (but exactly the same principle applies to fridges), to try to explain what it means.
Before the manufacturers started to build in inverters the motor that drives the compressor was fixed at a single speed, it was either going, or stopped. Thus all the temperature control could do was start and stop the motor. To go from stopped to flat out very quickly took a large amount of power, and given that they needed to do this regularly, it makes non Inverter air conditioners very power hungry, this explains why they are hard to run from a generator.
The motor speed was fixed by the frequency of the alternating current (AC), which is 50hz (cycles per second).
Then someone said what if we could change the speed of the motor, and to do this they first rectified the AC to DC, then they used an inverter where they could vary the frequency to provide power to the motor. This small change allows the manufacturer to start the motor gradually, thus getting rid of the big pulse of power need to start it, it also allows the control system to adjust the speed of the motor to get just the right amount of cooling, thus they can keep the motor running at a slower speed.
But how much difference does it really make?
From my experience it is considerable, all of the roof top air conditioners I am aware of are non inverter devices, and they tend to be Ok when plugged in to mains power, but difficult to run on a generator, or from a battery through an inverter. They draw six amps running, and often more than twelve starting, they also tend to make a clunk when they start, and stop, and many have a vibration that is hard to ignore (especially since it is being amplified by the roof panel)
I now run a Fujitsu split system in our van, the most I have ever seen it draw is about four amps (the manufacturer states 6 amps), and it settles down to draw about an amp once the van is down to temperature. I happily run it on battery through my inverter for many hours at night.
There are many examples on the forum where people talk about problem running the air con on a 2kva generator, there has also been a case recently where someone else mentioned that they have no problem running their inverter split system on a 1kva generator.
Why don't caravan air conditionermanufacturers use inverter technology, because it costs money to develop a system, and at the moment they are getting away with selling a massively overpriced system for almost every caravan made. Why would they?
Enough of my waffle.
Peter_n_Margaret said
06:49 PM Jun 28, 2015
Variable frequency speed control is also used on the Fisher and Paykel washing machines and Breezair evaporative air conditioners.
It also results in significant reductions in power consumption when running at lower than full speed, as well as start up.
Cheers,
Peter
DeBe said
09:47 PM Jun 28, 2015
12/24V Danfoss compressors are also inverter technology as they can be run at several diferent speeds.
Woody n Sue said
09:56 PM Jun 28, 2015
That clears up a few things for me many thanks for this one no wonder people are changing to split systems
Plendo said
10:47 PM Jun 28, 2015
For people locked in to roof top air conditioners there may be a viable solution:
I found this link tonight, along with another site selling 12V split systems for use in dangerous/flash sensitive environments.
Maybe the RV air con market is about to change after all.
Hi Dave. I couldn't find anything from this link suitable. Many are car 12V systems and the 12V part is the clutch actuator only. Any chance of a better link. Sorry I did look???
Plendo said
07:06 PM Jul 4, 2015
Baz try this link.
If it does not work for you search for 12V air conditioner RV china, that should find it. I also spotted a 12V split system as well, but I am having trouble re finding that one.
Looks ok Plendo, good find, still heavy & pulls some serious amps, but at least somebody is starting to produce one.
Think it will be a long time before they reach the same level of economical power use as a domestic inverter air-con. Mine is 520w draw at 240v at start up & drops dramatically once the humidity has been removed. 24v battery's do it easy for a 8-10 hour run, be flat in no time with that rooftop.
In an earlier article I mentioned that inverters were used in other ways, this is where you see a device with a motor in it (example air conditioner, or fridge), and the manufacturer states it is more efficient because it is an inverter air conditioner, what does this mean?
I will use an air conditioner (but exactly the same principle applies to fridges), to try to explain what it means.
Before the manufacturers started to build in inverters the motor that drives the compressor was fixed at a single speed, it was either going, or stopped. Thus all the temperature control could do was start and stop the motor. To go from stopped to flat out very quickly took a large amount of power, and given that they needed to do this regularly, it makes non Inverter air conditioners very power hungry, this explains why they are hard to run from a generator.
The motor speed was fixed by the frequency of the alternating current (AC), which is 50hz (cycles per second).
Then someone said what if we could change the speed of the motor, and to do this they first rectified the AC to DC, then they used an inverter where they could vary the frequency to provide power to the motor. This small change allows the manufacturer to start the motor gradually, thus getting rid of the big pulse of power need to start it, it also allows the control system to adjust the speed of the motor to get just the right amount of cooling, thus they can keep the motor running at a slower speed.
But how much difference does it really make?
From my experience it is considerable, all of the roof top air conditioners I am aware of are non inverter devices, and they tend to be Ok when plugged in to mains power, but difficult to run on a generator, or from a battery through an inverter. They draw six amps running, and often more than twelve starting, they also tend to make a clunk when they start, and stop, and many have a vibration that is hard to ignore (especially since it is being amplified by the roof panel)
I now run a Fujitsu split system in our van, the most I have ever seen it draw is about four amps (the manufacturer states 6 amps), and it settles down to draw about an amp once the van is down to temperature. I happily run it on battery through my inverter for many hours at night.
There are many examples on the forum where people talk about problem running the air con on a 2kva generator, there has also been a case recently where someone else mentioned that they have no problem running their inverter split system on a 1kva generator.
Why don't caravan air conditioner manufacturers use inverter technology, because it costs money to develop a system, and at the moment they are getting away with selling a massively overpriced system for almost every caravan made. Why would they?
Enough of my waffle.
It also results in significant reductions in power consumption when running at lower than full speed, as well as start up.
Cheers,
Peter
For people locked in to roof top air conditioners there may be a viable solution:
http://www.alibaba.com/product-detail/Portable-small-DC-battery-powered-electric_60151989536.html?s=p
I found this link tonight, along with another site selling 12V split systems for use in dangerous/flash sensitive environments.
Maybe the RV air con market is about to change after all.
Hi Dave. I couldn't find anything from this link suitable. Many are car 12V systems and the 12V part is the clutch actuator only. Any chance of a better link. Sorry I did look???
Baz try this link.
If it does not work for you search for 12V air conditioner RV china, that should find it. I also spotted a 12V split system as well, but I am having trouble re finding that one.
http://www.aliexpress.com/store/group/DC24-air-conditioner/830189_252636887.html
Think it will be a long time before they reach the same level of economical power use as a domestic inverter air-con. Mine is 520w draw at 240v at start up & drops dramatically once the humidity has been removed. 24v battery's do it easy for a 8-10 hour run, be flat in no time with that rooftop.