A/C makes lights dim.

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Ravenvalor

Ravenvalor

Senior Member
Location
Piedmont region of NC
Greetings Friends,

Can someone please suggest a residential electrical system design that will prevent the lights from flickering whenever the A/C condenser starts?

Thanks and Happy Holidays,
 
G

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
101216-1039 EST

Use GE dimmable CFLs without a dimmer. These have a much more constant light output vs voltage than an incandescent with sine wave excitation. Their problem is they quit at about 100 V.

Another solution. Bring in a separate service from a different pole transformer. Obviously not realistic.

Get special lights with voltage regulating electronic ballasts.

Put electronic regulators on all incandescent lamp circuits. Also could use a large Sola, lots of money, to supply the light circuits.

Basically you are fighting large inrush current from the air conditioner and voltage drop from that current and the common source impedance to the light and air conditioner circuits.

.
 
B

broadgage

Senior Member
Location
London, England
As above, presuming that you already checked the obvious, then there is no cheap simple answer to this one.
As above, flourescent lamps on good electronic ballasts flicker far less than incandescents.
A true dual conversion UPS for the lights would solve the problem, serious money though.
 
480sparky

480sparky

Senior Member
Location
Iowegia
I would check a few things first.

Is the service sized to all the loads it serves?
Does the circuit ampacity meet or exceed the nameplate rating?
Are there any loose connections in the AC or lighting circuits?
Record the voltage at the mains as the condenser starts up.
Record the amperage at the mains as the condenser starts up.
Have an HVAC company check the capacitor in the unit.... it might be bad.
Are the fins surrounding the unit free of dirt, debris, grass clippings, overgrown weeds (ie, obstructed airflow)?
 
readydave8

readydave8

re member
Location
Clarkesville, Georgia
Occupation
electrician
Every time we've run into this problem we've not been able to do anything with wire sizes or separate panels to solve it. And then the HVAC man comes and puts a hard start kit in and solves the problem. I don't know what it is but I've been recommending to my customers that it will reduce lites flickering when compressor kicks in.
 
G

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
101216-2115 EST

Next Generation:

In my opinion and many others on this forum the KVAR or similar device is a fraud relative to its claimed power saving. You have to understand RLC circuits in an AC environment to get a handle on this.

We believe that for the most part the KVAR is a pair of capacitors.

In industrial environments power factor correction capacitors, these are just good quality capacitors with a low dissipation factor, are used to counteract some of the inductive current to motors to improve the power factor seen by the power company. Large industrial users are penalized for poor power factor.

Residential users are not penalized for poor power factor, nor do they generally produce a very poor power factor. So probably no energy saving for a residential customer, and maybe a slight increase from the small power loss in the KVAR.

I won't go into all the details of what is likely to happen with different placements of a KVAR unit, but the advertisements suggest locating at the main panel.

Many claims or descriptions in the advertisements are false or misleading.


Now to the question of this thread. I do not know to what extent a shunt capacitor in parallel with the input leads to a single phase induction motor will have on the inrush current. It is an experiment worth running. My guess is that there is not a large modification of the typical 4 to 6 times full load current for the inrush current. In other words it would not be reduced to 1 times. Also keep in mind that a 1 times change of current might still produce flicker.

At 0 RPM there is no load power being supplied, locked rotor condition. Therefore, all the input current is distributed between inductive current and I^2*R losses. If the capacitor is selected to compensate the inductive current under stall conditions, then the input current will be reduced some.


readydave8:

Can you find out what a hard start kit really is? Have you ever measured the voltage change from unloaded, compressor motor off, to minimum voltage on starting the motor? And then the same measurement with the hard start device connected? This should be done at terminals near the compressor motor, not at the main panel.

.
 
kwired

kwired

Electron manager
Location
NE Nebraska
kingpb said:
Put a one 1:1 transformer near the A/C equipment, use transformer taps to get you up 5%.
Click to expand...

How does that help? You are still demanding the same thing from the source.

Three things need to be addressed:

1. can the source handle the starting load without excessive voltage drop

2. Are conductors including service, feeders, branch circuit large enough to handle starting load without excessive voltage drop.

3. Is there a way to reduce the starting current - this would in turn have a positive impact on items 1 and 2.
 
readydave8

readydave8

re member
Location
Clarkesville, Georgia
Occupation
electrician
gar said:
101216-2115 EST

readydave8:

Can you find out what a hard start kit really is? Have you ever measured the voltage change from unloaded, compressor motor off, to minimum voltage on starting the motor? And then the same measurement with the hard start device connected? This should be done at terminals near the compressor motor, not at the main panel.

.
Click to expand...
it's always been done after I left, and sometimes not at all if the customer lost interest after I told him small flicker was not a sign of dangerous wiring.

And I agree I should learn more about this. Thank you.
 
R

R Bob

Senior Member
Location
Chantilly, VA
gar said:
101216-2115 EST

Can you find out what a hard start kit really is?

.
Click to expand...

A hard start kit is an additional capacitor added to the start circuit controlled, ideally, by a potential relay.

Under certain conditions, the compressor has to start against a high head pressure, resulting in a laborious, prolonged start.

This condition is especially true with heat pumps utilizing TXVs as metering devices.
 
kwired

kwired

Electron manager
Location
NE Nebraska
R Bob said:
A hard start kit is an additional capacitor added to the start circuit controlled, ideally, by a potential relay.

Under certain conditions, the compressor has to start against a high head pressure, resulting in a laborious, prolonged start.

This condition is especially true with heat pumps utilizing TXVs as metering devices.
Click to expand...

Most single phase hermatic compressors are PSC, a hard start essentially converts them to capacitor start - capacitor run with a potential relay used to switch the starting capacitor out of the circuit. This will result in more starting torque but should also result in higher starting current but for shorter time. The light flicker is likely less noticeable because of the shorter duration of the voltage dip.
 
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