[sgiitk]

@fine69; General (not O General, since the O is just the logo) is an excellent brand, at par with Daikin, ie in the top bracket. I may add that I have been a bit unlucky. My Daikin sprung an internal leak and finally had to be repaired, and then moved to the living room. I bought a General and that too worked for about seven months when the control unit cards packed up, and were replaced under warranty.

[adimicra]

Finally, I decided to go with LG - 4 1.5 ton inverter ACs.
While browsing their Website, I found that the indoor units come in different sizes.
Is there any advantage of a bigger indoor unit if all other factors are same?
The larger indoor units are priced approximately 2000 Rs higher than the smaller ones. Not sure if that's worth the money.

[Aroy]

Originally Posted by adimicra

Finally, I decided to go with LG - 4 1.5 ton inverter ACs.
While browsing their Website, I found that the indoor units come in different sizes.
Is there any advantage of a bigger indoor unit if all other factors are same?
The larger indoor units are priced approximately 2000 Rs higher than the smaller ones. Not sure if that's worth the money.

If the larger indoor unit has larger heat exchanger area, then it is worth the cost. A larger area will increase the heat exchange rate, that is it will cool faster.

[adimicra]

Thanks, is there any way to find that out from the specifications?

[JLS]

Originally Posted by Lobogris

Everyone, including experts, claim this to be the reason for inverters saving money. However, this is incorrect. It is true that the compressor might use say six times more power at start up but that is only for a few milliseconds. Even if we grant one second of extra power, that is still minuscule. It is like running the ac an extra six seconds. If you do it 3 times an hour and for 10 hours per day, you are saving at best about 2 minutes of running time. That won't save much power. The real reason inverters can save power is that they use brushless DC motors which are about 10 to 20 % more efficient. In addition, an inverter can run at lower power. For instance a non inverter unit might be consuming say 1500 Watts and runs for 40 minutes each hour. The consumption would be 1 KW per hour. An inverter unit (in ideal circumstances) could run at say an average of 800 Watts and thus would consume only .8 KW for the hour.

......

.

I am out of touch with regards to current set of components being used in ACs and also not sure whether AC induction motors are being used or brush less DC motors are being used for driving AC compressors.

However I have a basic doubt:

In an inverter AC, first a converter will convert AC current to DC, Inverter would convert DC to AC (at a desired frequency) and that would be used to power AC induction motor, which in turn will drive compressor, and speed will be varied by varying frequency, hence the name Inverter ACs - that was my understanding.

If compressor is driven by DC brush less motor, then we need only AC to DC conversion, and inverter and frequency varying operation would not be needed.
And ACs would be called converter ACs rather than inverter ACs .
What 'inversion' operation is done in 'Inverter' ACs?

Can you please clarify the above.

Your clarification will help me to get my understanding up to date

Thanks in advance

JLS

[Thad E Ginathom]

Originally Posted by JLS

If compressor is driven by DC brush less motor, then we need only AC to DC conversion, and inverter and frequency varying operation would not be needed.
And ACs would be called converter ACs rather than inverter ACs .
What 'inversion' operation is done in 'Inverter' ACs?

I've wondered about this too, having occasionally seen claims of DC motors on non-"inverter" ACs.

My thoughts are that a non-inverter AC may contain DC parts, just like many electronic devices, but, within the realm of AC machines, "inverter" refers specifically to the the combination of a DC compressor, combined with all the technology and components that allow the speed of that compressor to be continuously variable according to cooling demand.

I think that many of our domestic devices work on DC. Our computers have power supplies that output various DC voltages, and most of the ubiquitous "wall warts" output DC --- but we don't call them inverters. I suspect that they might be rectifiers rather than inverters. Hey, perhaps our household "inverter" is a rectifier.

I am not electronically literate. I don't know the difference bewteen a rectifier and an inverter. I look forward to an explanation from our engineers here

.

[Prowler]

Originally Posted by Thad E Ginathom

I've wondered about this too, having occasionally seen claims of DC motors on non-"inverter" ACs.

I think that many of our domestic devices work on DC. Our computers have power supplies that output various DC voltages, and most of the ubiquitous "wall warts" output DC --- but we don't call them inverters. I suspect that they might be rectifiers rather than inverters. Hey, perhaps our household "inverter" is a rectifier.

Simply put a rectifier takes an alternating current (AC) input and outputs a Direct Current (DC). Usually a diode does that or a bridge of diodes does that. An inverter loosely stands for a circuitry that 'converts' a DC to AC.

An inverter AC compressor uses a Variable Frequency Drive (VFD) circuitry to drive a DC Motor.

[sgiitk]

I had a Hitachi 5* window unit pack up. The control card is shot, and he is getting it repaired. Also, he pointed out that DC motors for blowers are no longer popular since they are not reparable. AC motors seem to be coming back.

[ksameer1234]

Originally Posted by JLS

If compressor is driven by DC brush less motor, then we need only AC to DC conversion, and inverter and frequency varying operation would not be needed.

Originally Posted by Thad E Ginathom

I've wondered about this too, having occasionally seen claims of DC motors on non-"inverter" ACs.

While it is true that brushless DC motor operates on fixed voltage DC supply, that DC voltage needs to be supplied in pulses (on-off / o-max voltage) to match the speed of rotating part of the motor (strictly speaking, the rotor follows the pulses of voltage). It is for generating these pulses of voltage that the inverter is used.

The actual innovation that happened with brushless DC motors is that from working just fine with DC voltage, they now need to be fed pulsed DC voltage!! (Of course with tremendous benefits)

I am not electronically literate. I don't know the difference bewteen a rectifier and an inverter.

Rectifier converts alternating current (AC) to direct current (DC), while inverter does the opposite, converting DC to AC.

[Thad E Ginathom]

Originally Posted by ksameer1234

Rectifier converts alternating current (AC) to direct current (DC), while inverter does the opposite, converting DC to AC.

Thank you to you and Prowler for sorting me out on that one.

Come to think of it, I think I knew that our household inverter was being an inverter when it was converting the DC from the battery to AC for the house. But even if I did, it was very muddled in my head, to the extent that I could not tell my inverters from my rectifiers!

[Brumby]

Originally Posted by Lobogris

This is something I need to test. My newly purchased inverter one ton ac has a sticker that lists the LRA as 25 Amps. LRA or Locked Rotor Amperage is the amount of power required to first move the compressor motor from standstill. Doesn't this mean that the inveter would also have a surge of extra current? I have also often read and heard that the inverter units start up slowly to avoid this surge but the sticker placed on the unit by the manufacturer seems to indicate otherwise. I am awaiting delivery of a energy meter and I will test this out soon.

Any AC motor takes 7-8 times the normal running current on starting (no load), which means for a motor rated at 1000W the normal running current will be around 4.5 amps, and the starting current will be 32-36 amps (no load) however the home air conditioning units usually do not have no load starting feature hence 25amps LRA is very much reasonable. All inverter units have soft starters, which means the motor starts with the lowest possible current (adjusted by the lowest possible frequency which is set by the maker) for starting and then slowly the frequency is increased as per the set load.

Originally Posted by JLS

However I have a basic doubt:
In an inverter AC, first a converter will convert AC current to DC, Inverter would convert DC to AC (at a desired frequency) and that would be used to power AC induction motor, which in turn will drive compressor, and speed will be varied by varying frequency, hence the name Inverter ACs - that was my understanding.

If compressor is driven by DC brush less motor, then we need only AC to DC conversion, and inverter and frequency varying operation would not be needed.
And ACs would be called converter ACs rather than inverter ACs .
What 'inversion' operation is done in 'Inverter' ACs?

Can you please clarify the above.

Your clarification will help me to get my understanding up to date

Thanks in advance

JLS

You are correct in your understanding about the inverters, and an inverter air con will not have a brushless DC motor for the compressor unless it has been designed for a specific purpose/feature. The blower/fan for the cooler/evaporator (or the indoor unit) will have a brushless DC motor due to three preset speeds available for the user.

The inverter converts the AC to DC using rectifiers (diodes) and then converts it back to ac using transistors/thyristors. The conversion from DC to AC using transistors/thyristors gives the flexibility of having variable frequency, hence inverters are also called as VFDs (variable frequency drives) or frequency convertors.

Regards

[Aroy]

Originally Posted by JLS

..........

However I have a basic doubt:

In an inverter AC, first a converter will convert AC current to DC, Inverter would convert DC to AC (at a desired frequency) and that would be used to power AC induction motor, which in turn will drive compressor, and speed will be varied by varying frequency, hence the name Inverter ACs - that was my understanding.
.
.
.
Thanks in advance

JLS

Here is a link to what an inverter AC is supposed to do
https://www.inventorairconditioner.c...r-conditioners

This is what I got for LG AC's



So I guess that

. Inverter transforms AC -> DC and then uses DC pulses to regulate the speed of compressor

. At least for LG their compressor motors are BLDC (brushless DC motor)

[aim120]

Inverter AC uses the incoming Ac rectifies to DC and then uses inverter to switch back to three phase AC with variable frequency and variable voltage, this is done by PWM. If you look in a oscilloscope and zoom in the wave, one will notice the even a single cycle is in steps, which is done by the PWM.

Most inverter ACs used BLDC these days because the torque is higher compared to induction motor with Variable frequency drive.
In a induction motor the windings in the stator induces emf field in the rotar creating current in the rotor which then turns the rotor. You can use a VFD to also change the frequency eg of this motors are used in Lathe,milling machines and most famously in Tesla road cars.

In a BLDC motor, the rotor has permanent magnets and the magnets are trying to catch the magnetic field in the stator. BLDC motors are also more quieter then Induction motors with VFD.

[Lobogris]

Originally Posted by JLS

I am out of touch with regards to current set of components being used in ACs and also not sure whether AC induction motors are being used or brush less DC motors are being used for driving AC compressors.

However I have a basic doubt:

In an inverter AC, first a converter will convert AC current to DC, Inverter would convert DC to AC (at a desired frequency) and that would be used to power AC induction motor, which in turn will drive compressor, and speed will be varied by varying frequency, hence the name Inverter ACs - that was my understanding.

If compressor is driven by DC brush less motor, then we need only AC to DC conversion, and inverter and frequency varying operation would not be needed.
And ACs would be called converter ACs rather than inverter ACs .
What 'inversion' operation is done in 'Inverter' ACs?

Can you please clarify the above.

Your clarification will help me to get my understanding up to date

Thanks in advance

JLS

You are correct.
The main compressor does use AC current which is converted back from DC along with frequency modulation.

[Lobogris]

Originally Posted by Brumby

Any AC motor takes 7-8 times the normal running current on starting (no load), which means for a motor rated at 1000W the normal running current will be around 4.5 amps, and the starting current will be 32-36 amps (no load) however the home air conditioning units usually do not have no load starting feature hence 25amps LRA is very much reasonable. All inverter units have soft starters, which means the motor starts with the lowest possible current (adjusted by the lowest possible frequency which is set by the maker) for starting and then slowly the frequency is increased as per the set load.

Thanks for the explanation. Even if the start up load is 36 Amps, it is for a second or two. It will have no impact on power consumption if we have a few shut downs and starts each hour.