What Watts are What?

[Dave Hounddriver]

A lot of people here have mentioned they worked with electricity and I would like to get some opinions from some of you.

A 6.5 KW Chinese, gas powered, generator once powered my entire house including a 3/4 hp air conditioner; but it would not get the 1 hp air conditioner running. (No I was not trying to run both air cons at the same time.)

On a DIY forum I have been reading it was suggested that a 3KW pure sine wave, heavy duty inverter which "surges" to 9 KW will power the same house including the 1 hp air conditioner.

Is this likely to be true?  Does the ability to supply up to 9 KW for a short time make that much difference?  On a generator, what does the 6.5 KW  rating mean?  Is that the max it will ever output?  No surging?  What would someone expect that 6.5 KW generator to put out on average?

Its a bit confusing because I use less than 20 KWh per day, (so the electric meter says), running 2 aircons so I would have thought a 6.5 KW generator would supply both aircons, but it didn't.  Why not?

[Gary D]

1 hour ago, Dave Hounddriver said:

A lot of people here have mentioned they worked with electricity and I would like to get some opinions from some of you.

A 6.5 KW Chinese, gas powered, generator once powered my entire house including a 3/4 hp air conditioner; but it would not get the 1 hp air conditioner running. (No I was not trying to run both air cons at the same time.)

On a DIY forum I have been reading it was suggested that a 3KW pure sine wave, heavy duty inverter which "surges" to 9 KW will power the same house including the 1 hp air conditioner.

Is this likely to be true?  Does the ability to supply up to 9 KW for a short time make that much difference?  On a generator, what does the 6.5 KW  rating mean?  Is that the max it will ever output?  No surging?  What would someone expect that 6.5 KW generator to put out on average?

Its a bit confusing because I use less than 20 KWh per day, (so the electric meter says), running 2 aircons so I would have thought a 6.5 KW generator would supply both aircons, but it didn't.  Why not?

I hp is 726 watts so should run both with no problem. I would expect a 6.5 kW generator to be able to supply 6.5kW continuously, unless Chinese watt are different to SI watts. The problem probably lays in the starting current of the aircon. The generstor can handle one but the second is too much for it. I assume you have tried starting one aircon at a time and not both together.

[Dave Hounddriver]

1 hour ago, Dave Hounddriver said:

it would not get the 1 hp air conditioner running. (No I was not trying to run both air cons at the same time.)

 

23 minutes ago, Gary D said:

I assume you have tried starting one aircon at a time and not both together.

Yeah, I did.  But the 1 hp I was using would just not get up to speed on the generator.  I admit that the 1 hp was an older model aircon and the 3/4 was a newer model.  Anyway, thanks for the input.  I was thinking along the same lines.  Its possible that the 1hp was just too old and the Chinese gennie was not really a full 6.5 (Its not like I had a gauge to tell me how many watts were being used that would have been too simple  )

[not so old china hand]

4 hours ago, Dave Hounddriver said:

Its a bit confusing because I use less than 20 KWh per day, (so the electric meter says), running 2 aircons so I would have thought a 6.5 KW generator would supply both aircons, but it didn't.  Why not?

A quick reminder: KWh is the number of units of electricity consumed. It gives no indication of the load from individual appliances (ie the power they require).

The power from a generator is generally specified in kVA (kilo volt amps), although marketing material may refer to kW.  For some devices (eg incandescent light bulbs) the values are the same in both units. However for devices such as motors there is a difference expressed as kW=kVA x power factor. So for a relatively poor power factor of say 0 .5 a rating of 2kVA would be the equivalent of 1kW in actual power.

An an earlier poster suggested the problem might be the starting current. A combination of starting current and a poor power factor could be the cause of the problem. On most appliances there is a plate or label somewhere that will indicate the power factor and maximum current draw.

In my experience both petrol generators and inverters are quite good at handling surge starting currents (unlike diesel gennies).

Edited October 14, 2017 by not so old china hand

[mogo51]

This was interesting information.  But even though my Dad was a Sparkie, I did not follow in his footsteps.  Its all Greek to me.

[Castaway]

Whenever I'm buying a new Aircon,  I always need to convert the HP amount into BTU's first... since determining the strength of any Aircon solely on the HP number  just rolls over my head... but the number of BTU's gives me a clear idea of the power of an Aircon unit.

[Dave Hounddriver]

10 hours ago, not so old china hand said:

However for devices such as motors there is a difference expressed as kW=kVA x power factor. So for a relatively poor power factor of say 0 .5 a rating of 2kVA would be the equivalent of 1kW in actual power.

This is getting to the heart of my query.

Reading your post and doing a little googling has me believing that all air-conditioners claiming to be 1HP are NOT using the same amount of power.  Even though they all have specs that claim they are using about 900 watts (give or take) it seems to depend on the age and efficiency of the unit, as well as whether the manufacturer incorporated a PFC (Power Factor Correction) circuit into the power supply. It would also matter if the unit was inverter or non inverter.  So it is likely that the old 1 HP I was trying to run was just too inefficient and using twice the power it should.  (Please make suggestions if it appears I am wandering off course here).

If all this is true, then it would seem that the only two ways to check if a particular 1 HP Aircon unit will run off a particular inverter or generator is to (One) go supreme overkill to be sure you have double the power the aircon should require or (Two) get the inverter or generator that you have calculated will work, then plug it in, give it a try, and hope for the best,.

Further reading suggests that modern, non inverter split aircons should have a power factor of approximately .8 so I will make that assumption.  The specs suggest that my aircon consumes about 870 watts.  Other reading suggests that the available power when the compressor cuts in needs to be up to 5 times the amount of power normally consumed.

Getting back the opening post, I mentioned a 3KW pure sine wave, heavy duty inverter which "surges" to 9 KW.  We have learned that the 3 KW will provide 3,000 x .8 = 2400 watts of actual, usable power to the air conditioner.  It is enough to run the air conditioner but what about that start up surge?

The air conditioner will require "up to" 5 times the power for start up.  The inverter will surge up to 3 times the normal, steady current.  What are the odds that surge will last long enough to supply the start up power for the compressor motor?  I really want to buy this huge inverter and play around with it but only if there is a reasonable expectation that it will do the job I am buying it for.  It will be fun.  If it works I will enjoy playing around with it.  But I'd like a little reassurance that it will do the job before putting out the cash.

Here's an idea that someone might be able to help me with.  My aircon plugs into a wall outlet.  Is there a device that will plug into the wall, between the socket and the aircon plug, that will allow me to read how much current it is drawing at that instant?  If so does anyone have a link to one?

Oh my goodness, thank you google, I think I found what I want on Amazon and its cheap and it ships to Philippines.  someone please tell me this is the answer.  Can I plug this in, turn on the aircon, and see how many watts it is drawing?  Sure looks like it:

https://www.amazon.com/TS-836A-Energy-Voltage-Electricity-Monitor/dp/B00E945SJG

 

Edited October 15, 2017 by Dave Hounddriver

[Gary D]

24 minutes ago, Dave Hounddriver said:

This is getting to the heart of my query.

Reading your post and doing a little googling has me believing that all air-conditioners claiming to be 1HP are NOT using the same amount of power.  Even though they all have specs that claim they are using about 900 watts (give or take) it seems to depend on the age and efficiency of the unit, as well as whether the manufacturer incorporated a PFC (Power Factor Correction) circuit into the power supply. It would also matter if the unit was inverter or non inverter.  So it is likely that the old 1 HP I was trying to run was just too inefficient and using twice the power it should.  (Please make suggestions if it appears I am wandering off course here).

If all this is true, then it would seem that the only two ways to check if a particular 1 HP Aircon unit will run off a particular inverter or generator is to (One) go supreme overkill to be sure you have double the power the aircon should require or (Two) get the inverter or generator that you have calculated will work, then plug it in, give it a try, and hope for the best,.

Further reading suggests that modern, non inverter split aircons should have a power factor of approximately .8 so I will make that assumption.  The specs suggest that my aircon consumes about 870 watts.  Other reading suggests that the available power when the compressor cuts in needs to be up to 5 times the amount of power normally consumed.

Getting back the opening post, I mentioned a 3KW pure sine wave, heavy duty inverter which "surges" to 9 KW.  We have learned that the 3 KW will provide 3,000 x .8 = 2400 watts of actual, usable power to the air conditioner.  It is enough to run the air conditioner but what about that start up surge?

The air conditioner will require "up to" 5 times the power for start up.  The inverter will surge up to 3 times the normal, steady current.  What are the odds that surge will last long enough to supply the start up power for the compressor motor?  I really want to buy this huge inverter and play around with it but only if there is a reasonable expectation that it will do the job I am buying it for.  It will be fun.  If it works I will enjoy playing around with it.  But I'd like a little reassurance that it will do the job before putting out the cash.

Here's an idea that someone might be able to help me with.  My aircon plugs into a wall outlet.  Is there a device that will plug into the wall, between the socket and the aircon plug, that will allow me to read how much current it is drawing at that instant?  If so does anyone have a link to one?

Oh my goodness, thank you google, I think I found what I want on Amazon and its cheap and it ships to Philippines.  someone please tell me this is the answer.  Can I plug this in, turn on the aircon, and see how many watts it is drawing?  Sure looks like it:

https://www.amazon.com/TS-836A-Energy-Voltage-Electricity-Monitor/dp/B00E945SJG

 

That meter looks like it will do the job and is giving you the running current, what it won't do is give you the surge current. It mentions max power, not sure what that means.

[Dave Hounddriver]

15 minutes ago, Gary D said:

what it won't do is give you the surge current.

Is there a meter that will give the surge current?  Because it seems the maximum surge is the main focus of any power system.

[Jack Peterson]

18 minutes ago, Dave Hounddriver said:

Is there a meter that will give the surge current?

Not to sure about a surge current but our engineers from Polaris had a hand held Probe that told them just what power was going into the Unit,

It was because of this device that they would not commissioned the Unit until I had the Transformer installed so  guess it would be the same on your problem