# why does a 3/4 hp aircon consumes more than 746*0.75=560 watts?

#### edgar peace

Joined Nov 28, 2018
16
HI! I don't know if i can put this topic here but i can't find a reliable air conditioning forum. i cannot use my clamp meter to measure its current which is more accurate because i don't want to cut on the wiring. so i used a submeter and based on my computation it's almost 1000 watts. what accounts for the extra power consumption? Any input will be helpful. Thanks.

i know that 1 hp is 746 watts so a 0.75 hp is equivalent to 560 watts only.

#### AlbertHall

Joined Jun 4, 2014
11,598
It isn't going to be 100% efficient which likely accounts for the difference.

#### oz93666

Joined Sep 7, 2010
737
Universally when manufacturers describe a motor , pump or AC as 1HP it means that the input electrical power is 746W so your AC should consume 560W ....

You calculated consumption based on "submeter" ??? what's that ??? "....submetering is a system that allows a landlord, property management firm, condominium association to ..." Wikipedia

The person you by your power from has adjusted the meter to rip you off , (probably legal )...

Joined Mar 10, 2018
4,057
The clamp meter can give you current without cutting wires, and you
know the approximate line V, or measure it with clamp meter that
does not require cutting wires. Then you can compute power from that.

Regards, Dana.

#### DickCappels

Joined Aug 21, 2008
7,963
How did you determine the power consumption?

If you measured current and voltage separately and tried to compute the power, you might have omitted the power factor, which can be pretty bad for motors.

https://en.wikipedia.org/wiki/Power_factor

#### crutschow

Joined Mar 14, 2008
28,182
The clamp meter can give you current without cutting wires
It won't work if you clamp it over the wire pair.

Joined Jul 18, 2013
23,915
i cannot use my clamp meter to measure its current which is more accurate because i don't want to cut on the wiring.
If you have feed conductors that are ran as a cable, there is often spots at the final termination points where single conductors are exposed and capable of being used with a Clamp-on.
Max.

#### BobTPH

Joined Jun 5, 2013
4,034
Or just wire an additional plug and socket between the air conditioner cord and the mains socket using separate wires.

Bob

#### edgar peace

Joined Nov 28, 2018
16
HI! I don't know if i can put this topic here but i can't find a reliable air conditioning forum. i cannot use my clamp meter to measure its current which is more accurate because i don't want to cut on the wiring. so i used a submeter and based on my computation it's almost 1000 watts. what accounts for the extra power consumption? Any input will be helpful. Thanks.

i know that 1 hp is 746 watts so a 0.75 hp is equivalent to 560 watts only.
What i mean on the clamp meter is cutting the external sheath or sleeve so i can place the clamp meter around 1 wire. The current displayed multiplied by input voltage is my power consumption. About the watthour meter, the time the measurement was taken is necessary so your kwh divided by time will give you the power consumption.

Joined Jul 18, 2013
23,915
What i mean on the clamp meter is cutting the external sheath or sleeve so i can place the clamp meter around 1 wire.
You mean there is no break-out, termination point to access?
Max.

#### panic mode

Joined Oct 10, 2011
1,918
In DC circuits power is V*I
In AC circuits power is V*I•cos(angle)
In 3phase circuits power is V*I*cos(angle)*1.73

What do you think phase angle is zero?

Your calculation shows apparent power is nearly 1000VA (not Watt!). So your cos(angle) is 0.75 which is reasonable for this type of load.

#### edgar peace

Joined Nov 28, 2018
16
In DC circuits power is V*I
In AC circuits power is V*I•cos(angle)
In 3phase circuits power is V*I*cos(angle)*1.73

What do you think phase angle is zero?

Your calculation shows apparent power is nearly 1000VA (not Watt!). So your cos(angle) is 0.75 which is reasonable for this type of load.
I used a kilowatthour meter so the reading divide by length of time is in watts so for a 0.75 hp, 900 to1000 watts is still very high because the duty cycle (on time / total time) is only @ 70%. Although of course the fan consumes power 100 % of the time.
HI! I don't know if i can put this topic here but i can't find a reliable air conditioning forum. i cannot use my clamp meter to measure its current which is more accurate because i don't want to cut on the wiring. so i used a submeter and based on my computation it's almost 1000 watts. what accounts for the extra power consumption? Any input will be helpful. Thanks.

i know that 1 hp is 746 watts so a 0.75 hp is equivalent to 560 watts only.
I used a kilowatthour meter so the reading divide by length of time is in watts so for a 0.75 hp, 900 to1000 watts is still very high because the duty cycle (on time / total time) is only @ 70%. Although of course the fan is running 100% of the time

#### edgar peace

Joined Nov 28, 2018
16
Or just wire an additional plug and socket between the air conditioner cord and the mains socket using separate wires.

Bob
Yes Bob, i think i can use an extension cord (with plug or socket adapter that fits) which i can separate the wires to get the current reading. Thanks

#### edgar peace

Joined Nov 28, 2018
16
HI! I don't know if i can put this topic here but i can't find a reliable air conditioning forum. i cannot use my clamp meter to measure its current which is more accurate because i don't want to cut on the wiring. so i used a submeter and based on my computation it's almost 1000 watts. what accounts for the extra power consumption? Any input will be helpful. Thanks.

i know that 1 hp is 746 watts so a 0.75 hp is equivalent to 560 watts only.
Yes that"s it. I forgot to consider the power factor angle is at play here. So what is the typical power factor of an a/c?

#### oz93666

Joined Sep 7, 2010
737
Yes that"s it. I forgot to consider the power factor angle is at play here. So what is the typical power factor of an a/c?
It's hard to imagine the manufacture would sell an item like this without putting in a capacitor to adjust the power-factor it would cost the consumer $1,000s over the life of the product ..... First check the accuracy of your "sub meter " Thread Starter #### edgar peace Joined Nov 28, 2018 16 HI! I don't know if i can put this topic here but i can't find a reliable air conditioning forum. i cannot use my clamp meter to measure its current which is more accurate because i don't want to cut on the wiring. so i used a submeter and based on my computation it's almost 1000 watts. what accounts for the extra power consumption? Any input will be helpful. Thanks. i know that 1 hp is 746 watts so a 0.75 hp is equivalent to 560 watts only. It's hard to imagine the manufacture would sell an item like this without putting in a capacitor to adjust the power-factor it would cost the consumer$1,000s over the life of the product .....
First check the accuracy of your "sub meter "
Actually i've mistaken the term as submeter because i used it in a shop i once rented. It's actually a kilowatt-hour meter and i think it's accurate. Does traditional window type aircon include a power factor correcting capacitor? I'm not so sure.

#### panic mode

Joined Oct 10, 2011
1,918
try calculating capacitor needed to correct this power factor. it should be an eyeopener.

#### edgar peace

Joined Nov 28, 2018
16
try calculating capacitor needed to correct this power factor. it should be an eyeopener.
Again it confused me. If my household is paying my electric power provider in kilowatt hours and not in kva-hours, does it make sense for power factor correction since it will only reduce my kvar and not my true power (watts) which i am paying?

#### oz93666

Joined Sep 7, 2010
737
try calculating capacitor needed to correct this power factor. it should be an eyeopener.
It's strange that no one has brought to market an automatic power correction device ... It would sit near your meter and check your power factor , switch in capacitors to reduce your bill to the minimum possible....

#### panic mode

Joined Oct 10, 2011
1,918
sure they have.... just not for consumer market. consumers have very small loads and don't pay penalties for imbalancing grid