Does Power Factor Matter?

[jls001]

I recently shifted house (in the same town). When I connected back my power amp in the new place, the fuse blew. Replaced it with a spare, and it blew again. Everything else (pre, TT, CDP) worked fine.

Not wanting to risk damages, I prompty took it to Sanjay Raut of AVC last Sat. To my pleasant surprise, he called me on Monday (yday) and told me that my amp is ready. When I asked him what had gone wrong, he told me probably the power factor at my new place was lagging and therefore the fuse rating of 4A was inadequate. He had put a new fuse of 5A and plugged it back. He refused to charge me though I protested.

I took home the amp last night and true to his words, it switched on without any issue.

My question: how does a lagging power factor affect the current drawn by the amp?

FWIW, the amp has a rating of 700W printed on the rear panel. I am guessing this is the full rated power.

My rather limited understanding of power factor is that if one's power factor (of the load) is lower than unity, one ends up drawing more power from the power utility, and therefore some power utilities impose a penalty on consumers with poor PF.

Joshua

 

[borg]

sanjay raut is trying to fool you, power factor is a characteristic of load and not of source(mains supply). So there is no such thing like the "power factor of new place"

May be your new place has voltage fluctuations or spikes causing the amp fuse to blow

 

[baijuxavior]

^^ True. Check the voltage in your new place. If it is very low, the amp would try to draw more current and the fuse will blow to protect the amp.

 

[malvai]

Joshua,
Sanjay is really pulling a fast one on you....
i'd recommend that you get a 4A fuse and out it back, in place of he 5A that he has put....

check the voltage in your new place and invest in a decent stabilizer...

 

[Thad E Ginathom]

"lagging power factor" had me wondering if this guy was making it up as he went along... but doesn't he just mean low voltage?

Yes, the lower the voltage, the higher the current drawn to do the same amount of work. Big stuff like AC machines can burn out whole mains supply cables like this, but --- an amplifier blow it's fuse? well, I'm dubious, but I don't know. Hasn't happened here, and we celebrate if our voltage ever reaches 200!

On the other hand... a surge could do it?

 

[borg]

i am not sure what kind of load is an amplifier.
If it is a constant power load then as the voltage decreases the current draw increases to keep the power constant. If it is a linear load then it behaves the opposite way

 

[jls001]

The voltage reads 238 to 240V on a digital multimeter. And the earth to neutral voltage is 0.7 to 0.8V.

Yes, the power factor is a function of the load (which in my case is the amp itself). Nothing inside the amp has changed from the old place to the new place:lol:. And before powering it up, I made sure all the tubes are tightly in place in their respective sockets! So power factor explanation is a non-starter. The voltage reading of 238-240V is not too far off from the usual 230V, so that shouldn't really be a problem. I have slow blow fuses (4A) purchased from the factory. Will try one of these and see if it still blows.
Joshua

 

[just4kix]

I recently shifted house (in the same town). When I connected back my power amp in the new place, the fuse blew. Replaced it with a spare, and it blew again. Everything else (pre, TT, CDP) worked fine.

Not wanting to risk damages, I prompty took it to Sanjay Raut of AVC last Sat. To my pleasant surprise, he called me on Monday (yday) and told me that my amp is ready. When I asked him what had gone wrong, he told me probably the power factor at my new place was lagging and therefore the fuse rating of 4A was inadequate. He had put a new fuse of 5A and plugged it back. He refused to charge me though I protested.

I took home the amp last night and true to his words, it switched on without any issue.

My question: how does a lagging power factor affect the current drawn by the amp?

FWIW, the amp has a rating of 700W printed on the rear panel. I am guessing this is the full rated power.

My rather limited understanding of power factor is that if one's power factor (of the load) is lower than unity, one ends up drawing more power from the power utility, and therefore some power utilities impose a penalty on consumers with poor PF.

Joshua

To go back to basic electricity principle:

Voltage is supplied while current is drawn.

What this means is that an appliance will draw the same current whether you connect it to a 5A plug point or a 15A plug point - assuming that voltage is constant. A fuse is meant to protect the appliance in case the current exceeds the recommended value.

The equation is I = V/R. The resistance of the appliance is not going to change. So in your case, there must have been a voltage surge causing more current to flow into the amp. The 4A fuse blew off protecting your device. If you replace the 4A fuse with a 5A fuse you are potentially risking the amp.

On that day, the voltage may have been higher and subsequently restored to normal. I will recommend that you use the fuse that is recommended.

The situation here is akin to replacing your house mains fuse with a higher capacity allowing more current to be drawn and risking an electric fire.

 

[askii2]

Replacing fuse with a higher rating is a commonly employed solution everywhere. That's what electricians advice us. Fuse bar bar ja raha hai to higher rating ka lelo. It works only if the original fuse was of lower than recommended rating. Higher rating fuse will actually make it useless since it'll not protect at the current level it's supposed to.

As others have adviced, I too think that the most probable reason is a voltage surge.

The other possibility is shorted speaker connection, which you restored later. Many amps have a separate protection against shorted speaker connections, so the main fuse wouldn't blow up. The amp simply shuts itself down. This is generally true only with higher cost amps.

 

[rohitt]

power= voltage*current*power factor(cos phi)
700watts= 230volts*current*1
therefore current= 700watts/230 volts= 3.04 amps

700watts=230volts*current*0.8
therfore current= 700watts/230volts*0.8= 3.84 amps

therfore as power factor goes far from unity i.e 1
the current drawn by the equipment increases.

power factor is the cosine angle between the current and voltage.
if the current lags the voltage, then the power factor is lagging.
if the current leads the voltage, then the power factor is leading.

it is possible that the power factor is lagging at ur new house, may be due to inadequate capacity of capacitor bank at the distribution transformer, more number of incandescent bulbs or induction motors connected in the particular phase.

 

[hifipal4all]

Joshua,
Sanjay is really pulling a fast one on you....
i'd recommend that you get a 4A fuse and out it back, in place of he 5A that he has put....

Absolutely right!!!

check the voltage in your new place and invest in a decent stabilizer...

Perfect solution

 

[arj]

power= voltage*current*power factor(cos phi)
700watts= 230volts*current*1
therefore current= 700watts/230 volts= 3.04 amps

700watts=230volts*current*0.8
therfore current= 700watts/230volts*0.8= 3.84 amps

therfore as power factor goes far from unity i.e 1
the current drawn by the equipment increases.

power factor is the cosine angle between the current and voltage.
if the current lags the voltage, then the power factor is lagging.
if the current leads the voltage, then the power factor is leading.

it is possible that the power factor is lagging at ur new house, may be due to inadequate capacity of capacitor bank at the distribution transformer, more number of incandescent bulbs or induction motors connected in the particular phase.

actually this thread got me reading a bit..its more than 20years since i studied power distribution !
found this interesting read www1.eere.energy.gov/industry/bestpractices/pdfs/mc60405.pdf
apparently high inductive load in your house/building/area can cause a much lower power fact0r (as low as .6) in an extreme which increases current consumption.

But i believe the power on Idle load for your amp would not be more than 300-400 W at least for regular operations (should be the class A bias)

what i am not able to understand is the fuse being a Fast Blo. as far as I know , an amp, especially tube amps with lots of transformers usually have a Slo Blo fuse as the Surge current to charge up the Transformer/capacitors are very high (5-20 times) can you confirm with AR on the kind of fuse to be used ?

 

[afj]

pl make sure you use a stabilizer

 

[omishra]

Blowing of fuse at power on is also caused due to initial current surge in power supply, transformer core saturation (if any) and power capacitor charging. Capacitors discharge slowly after kept powered off for long time (bleeding current). Transformer's primary is inductor. It's core will magnetically saturate first till it shows proper inductance (high resistance) and then caps will charge simultaneously. This draws sudden current from mains.

On lower mains voltage this current surge will be lower as higher voltage it will be higher. For this reason high power amps use slow start circuit in mains power line.

Bottom line: use proper fuse with voltage stabilizer.

 

[mkreddy]

Rohit,
You are absolutely right. Lagging power factor can cause more current drawn and there by burning fuses.
As other members said, lagging power factor is caused by the inductive loads, such as motors, AC Compressors etc..

Thanks,
Murali.

power= voltage*current*power factor(cos phi)
700watts= 230volts*current*1
therefore current= 700watts/230 volts= 3.04 amps

700watts=230volts*current*0.8
therfore current= 700watts/230volts*0.8= 3.84 amps

therfore as power factor goes far from unity i.e 1
the current drawn by the equipment increases.

power factor is the cosine angle between the current and voltage.
if the current lags the voltage, then the power factor is lagging.
if the current leads the voltage, then the power factor is leading.

it is possible that the power factor is lagging at ur new house, may be due to inadequate capacity of capacitor bank at the distribution transformer, more number of incandescent bulbs or induction motors connected in the particular phase.

 

[arj]

Joshua, cen you check this thread out..
AudiogoN Forums: Audio Research Classic 60 & 120 owners
this talks of a fuse blowing due to wrong tube Bias (for an AR power amp)
also this..
Audio Research Classic 60 (ARC 60) - Valve Power Amp - AVForums.com

I recently shifted house (in the same town). When I connected back my power amp in the new place, the fuse blew. Replaced it with a spare, and it blew again. Everything else (pre, TT, CDP) worked fine.

Not wanting to risk damages, I prompty took it to Sanjay Raut of AVC last Sat. To my pleasant surprise, he called me on Monday (yday) and told me that my amp is ready. When I asked him what had gone wrong, he told me probably the power factor at my new place was lagging and therefore the fuse rating of 4A was inadequate. He had put a new fuse of 5A and plugged it back. He refused to charge me though I protested.

I took home the amp last night and true to his words, it switched on without any issue.

My question: how does a lagging power factor affect the current drawn by the amp?

FWIW, the amp has a rating of 700W printed on the rear panel. I am guessing this is the full rated power.

My rather limited understanding of power factor is that if one's power factor (of the load) is lower than unity, one ends up drawing more power from the power utility, and therefore some power utilities impose a penalty on consumers with poor PF.

Joshua

 

[Thad E Ginathom]

rohitt, thanks for the explanation. As a mathematical duffer, I probably will never understand it, but at least, now, I know that "power factor" exists.

 

[borg]

power= voltage*current*power factor(cos phi)
700watts= 230volts*current*1
therefore current= 700watts/230 volts= 3.04 amps

700watts=230volts*current*0.8
therfore current= 700watts/230volts*0.8= 3.84 amps

therfore as power factor goes far from unity i.e 1
the current drawn by the equipment increases.

power factor is the cosine angle between the current and voltage.
if the current lags the voltage, then the power factor is lagging.
if the current leads the voltage, then the power factor is leading.

it is possible that the power factor is lagging at ur new house, may be due to inadequate capacity of capacitor bank at the distribution transformer, more number of incandescent bulbs or induction motors connected in the particular phase.

Once again power factor is a characteristic of load and it is technically incorrect to say "power factor is lagging in your new house causing a fuse blowout in a particular equipment"

If a person has lots of reactive loads in house causing heavy draw of current then that may cause his main fuse to blow out not the fuse of a particular equipment


Incandesecnt bulbs are resistive in nature and so dont create any low powerfactor issue

The issue here is the blown fuse of OP's AMP and it is not possible for the AMP to suddenly have a low power factor at new house and draw more current and blow its fuse. There are many reasons for fuse blow out and "low power factor at his new house " is definitely not the reason

In any reactive load( inductive or capacitive), examples Motors,SMPS of your pc(if there is no pfc builtin) there will be a phase shift between the applied voltage and drawn current, meaning the power is not consumed all the time of the 50hz cycle, This is the reason why the term power factor come into play with AC loads

In this type of loads for the same amount of power consumed the current drawn is more , and this extra current will cause extra losses in the distribution system.
that is why there is rules against making equipments with unusually low power factors.

 

[dillihifi]

Hi guys,

Well I would like to put my two cents here. Power Factor exists and can be both lagging and leading (it is basically the angle between Voltage and Current phasors). Now the power factor is dependant on the load attached to the circuit / the phase from which power is drawn and may not only depend on your own load. If power factor is lagging as is generally encountered this can only be put right by installing shunt capacitors but using a stabilizer is not going to work. Power is a product of Voltage, Current and cosine of the angle between them. Generally loads are calculated at 0.8 Pf anything lower will tend the equipment to draw more current to get the required power. In domestic connections generally no penalty is levied.

Equipment at not made with low or high pf. The phase shift exists because of the load (which comprises of resistive + inductive + capacitive) and is the phasor sum of these things therefore pf comes into play. Fuse of a particular equipment can blow it is, generally it is dependant on the fuse rating and the current drawn. Power not consumed during the entire 50Hz cycle (I do not understand ????)

Next coming to the equipment the amp in question which has a fuse of 4A it means that the Amp is a full class A and consumes around 750Watts going by the calculations.

 

[anuragn]

Its more than 17 years since I studied two subjects of electrical engg and I have forgotten most of the fundas. I may be wrong, but I feel that power factor comes into play only when there is an interaction of power with an equipment.
An equipment cannot "inject" a lead or lag into the power line, nor can a power line have a power factor of its own (I may be wrong here, pl correct me if yes).
Hence, to say that one area has different power factor than another sounds incorrect. This is my 2 cents.