A/C kicks on... whole house "dims"

[laramie]

Hey all, thanks for taking the time to help. Here's the scenario; we have a large residential project we completed some time ago. The homeowner is complaining that when the (4) A/Cs kick on, the lights in the entire house go dim. There is a 400A 120/240V service on the house, and a total of 3 subpanels. THe ACs are run from a remote subpanel on a 2nd floor. This has gone as far as a) the utility company has come and set a new transformer outside, b) the breaker feeding the sub panel has been relocated from the lighting breakers, c) ampereage and voltage have been measured and found to be within limits..

We're out of options. Would a voltage regulator/stabilizer, and/or a power conditioner help? If so, where would i find one that can effectively monitor an entire house? I imagine this would be a common problem in factories, hospitals, etc... how do they deal???

Any help would be appreciated!

 

[charlie b]

. . . when the (4) A/Cs kick on, the lights in the entire house go dim.

Do you mean that all four start at the same time? If so, the only way to avoid that problem is to install a controlling device that prevents more than one from starting at the same time. A “DCS” (I think that stands for “distributed control system,” but this is outside my area of expertise) might resolve this problem. Or perhaps the correct term is "BMS," for "Building Management System."

The only other thing I can think of is to upsize the wires to the subpanel that feeds the A/C units. It is possible that the voltage drop is not occurring along that feeder, but is rather occurring within the utility transformer. If that is the case, there is little else that I can think of for you to do.

 

[winnie]

There will _always_ be some change in supply voltage, and thus change in light output, when additional load is applied. You _cannot_ entirely eliminate this. The best you can do is minimize it to acceptable levels.

Part of what you need to do is educate your customer; if they are seeing a bit of flicker, not enough to really be a problem, but enough to worry them, then your best solution may be to get them to understand that there will always be _some_ flicker, even in a correctly designed and functioning system.

First you must determine what the parameters of 'unacceptable' voltage drop are in this case. Are the lights flickering with perhaps a 1% voltage drop when the AC cranks on? For most applications this is acceptable, but it might be esthetically displeasing to the customer. Fixing something like this could take lots of money.

Next thing to figure out: what aspect of the load is causing the unacceptable voltage drop. Is it the 'start up' surge that causes a momentary flicker of the lights? Or is it the continuous loading that makes the lights dim for an extended period.

If it is a start up flicker, then perhaps some sort of load modification, eg. a 'soft start' might do the trick.

Next you need to determine what part of the system is the major cause of the voltage drop.

Is it voltage drop at the transformer? The service lateral? The panels? Of course, each component will add its bit of drop; you need to figure out if one component is dominant so you know where to focus your efforts.

Next you have to go and make some design decisions. There will always be voltage drop; you have to figure out how to minimize it acceptable.

-Jon

 

[laramie]

Thanks..

Thanks..

Thanks for your input..

I believe the ACs do start at the same time, which i agree, i should be able to rectify by utilizing some sort of load management system.

I know they did put "soft start" motors in the condensers already, and unfortunately this particular customer doesn't care about cost- they want the problem fixed. I'm assuming again, that some sort of voltate stabilizer for this application could be upwards of $20K, and the customer is willing to pay that. THey just want it resolved.

 

[petersonra]

Thanks for your input..

I believe the ACs do start at the same time, which i agree, i should be able to rectify by utilizing some sort of load management system.

I know they did put "soft start" motors in the condensers already, and unfortunately this particular customer doesn't care about cost- they want the problem fixed. I'm assuming again, that some sort of voltate stabilizer for this application could be upwards of $20K, and the customer is willing to pay that. THey just want it resolved.

I vote for some 20 second timers that allow the A/C units to start in sequence rather than all at once.

personally, I would be upset at whoever designed it this way in the first place.

 

[dbuckley]

I'm assuming again, that some sort of voltate stabilizer for this application could be upwards of $20K, and the customer is willing to pay that. THey just want it resolved.

Nowhere near that much, unless you want to run the whole house off it, and then you are back to the same problem. You want a unit to run only the lighting loads, but that requires segregated wiring, which could be a bit hard to backfit. Alternatively, you could fit a reg by each panel.

A while back I got pricing a unit by Salicru, which was (from memory) 6KVA, and it was a few grand, nowhere near $20K.

 

[winnie]

If the customer is willing to pay that much, consider the following design point:

Do your best to segregate out the 'sensitive' loads, including the lighting.

The fact of the matter is that most loads don't care about even a significant voltage drop. You don't want to waste money regulating the voltage to an electric range, for example.

Here is an off the wall idea:

Convince the AHJ that two separate services are permitted. This is something of a stretch, but is arguably permissible under 230.2(D). Because it would be a stretch you'd better get the AHJ on side prior to any installation.

_Then_ convince the POCO to supply two _separate_ transformers for these two services.

Put all sensitive loads on one service. Put the large intermittent high power loads on the other service.

Now the only shared component between the air conditioners and the lights would be on the primary side of the transformers. Transformer impedance, service lateral resistance, and main disconnect resistance would be removed as a common voltage drop between the two devices.

Not cheap, but probably cheaper than some sort of active voltage regulator of similar capacity...Plus it would put the additional losses on the POCO side of the meter.

-Jon

 

[ghostbuster]

I agree, staggered starts will certainly cure approx.+50% of the problem if not more .We have noticed however the new energy efficient lighting and electronic dimming systems are way more susceptible to momentary voltage sags.Does this house have any of these "state of the art "lighting systems??

 

[brian john]

I did a search for Salicru, they site would not load but the site info was for a UPS, an online 5 kva should cost more that $2,000.00, an off line UPS may not resolve the issue as the VD is within the limits of most UPS's.

As little as 3 VAC (about 2.5% of nominal voltage) drop at the service is noticable at the lights. It may be less than 3 VAC, in the cases where I was involved we measured 3 Volts when pupms started. What we did at one property was; recircuit the panels with all single phase motors on one L1 all lights on L2, this did nothing for 240 VAC loads but did minimize the problem from refrig, and Sewage injector that ran every 10 minutes (some sort of sewage recirculator to prefilter the waste prior to making it to the septic field).

The home owner SWORE she had never seen a light flicker, prior to buying this house and was in the process of trying to sue the developer. He hired me to ascertain whose problem it was.

 

[stickboy1375]

Try installing Hard Start kits in the AC units....

http://www.kickstartoem.com/#

(Quote from website)
Is it true that installing a Kickstart? hard start device on an air conditioning unit in the home can prevent the lights from dimming whenever the unit starts up?
Absolutely! By allowing the unit to start more efficiently through power factor correction, Kickstart? hard start devices are an effective tool in preventing lights from dimming and enhancing overall power quality in the home.

 

[dbuckley]

I did a search for Salicru, they site would not load

Sorry, should have provided a link, try this link.

They still haven't got their English sorted out, I note... heres a rough translation to save you the trouble

The RE Series has a transformer with multiple taps, each of which is connected electrically to a solid state switch. These switches are governed by a PCB with a built-in microprocessor, which controls the output voltage and, depending on its level, selects one tap or another in order to obtain the optimal voltage level with the pre-programmed accuracy. It has a servo-system that compares the output voltage instead of controlling the input voltage.

They may speak Italian, but the regulators are good.

Found the quote too; the RE6009-2T 6KVA was about 4.5K USD.

 

[robbietan]

if the lights have a wye-delta scheme for 'soft start', the timing for the next ac to run must be after the first ac has gone over to 'delta' scheme. otherwise, the problem wont go away.

 

[petersonra]

if the lights have a wye-delta scheme for 'soft start', the timing for the next ac to run must be after the first ac has gone over to 'delta' scheme. otherwise, the problem wont go away.

Since the OP indicated this was a residence, I doubt that is an issue, especially since he said something about a 240/120 service.

 

[hillbilly]

"unfortunately this particular customer doesn't care about cost- they want the problem fixed".

Yea....that does complicate things.
You said that the POCO replaced the transformer.
Did they replace the service drop/lateral?
steve

 

[wirenut1980]

How long is the secondary run from the transformer to the meter? I have found that given a reasonable distance (<300'), upsizing the secondary from the transformer to the meter will do little to quell the voltage flicker. The majority of the impedance will be in the transformer.

I also agree that providing a delay between startup of these A/C units will be the cheapest solution, and may satisfy the customer. Usually anything below 2% flicker will not be noticed.

Edit to add: A bad service neutral will exasperate flicker considerably. But you mentioned that measurements were taken and looked to be in order. How much flicker is showing up at different places along the circuit, i.e at the meter, at the main panel, at the subpanel, at the A/C unit?

 

[brian john]

Did a job with light flicker yesterday, I ahve attached the disturbances as well as a text print out of the voltage and current levels.

This house had an unusual number of incadescent light firtures 150+, and 7 HVAC units. This house had a 200 amp service that was upgraded to 600 amp, appears the utility left the 200 amp triplex in use, about 150" changed to 250 AL undereground 150, plus what appears tro be a 30 KVA pole mounted transformer (300 feet away).


MIN VAC MAX VAC MIN CURRENT MAX CURRENT
PRE START UP 122 122 30 30
START UP 115 122 30 175
START UP 115 115 169 176
START UP 115 121 43 166
RUNNING 121 121 42 46
RUNNING 121 121 45 45


I have graphics to post with this but have not figured out how to include, any help would be apprciated.

 

[Wednesday]

Before you spend to much money on any fix, install hard start kits on the A/C condensing units. Like stickboyz mentioned in his reply.

The hard start kits will allow the compressor to start a little quicker and more smoothly, they basically add capacitance to the compressor motor which which shift the phase wiring and provide a more out of phase relationship which will assist with quicker startup of the A/C compressors.

Some compressors can draw more than 8 times normal full load amperage on startup, They have more moving parts to them a typical motor and this along with cold temperatures can really create problems for any single phase service regardless of the amperage size.


I would speak to the installing company of the A/C's and ask them to install Hard Start Kits and possibly crankcase heaters if you are in a colder environment.

The compressor motor is just like your car engine trying to start on a cold day.

Typical trade pricing for a crankcase heater and hard start kit is $100.00 - $150.00 for each compressor along with an 1 hour labor per unit. This is a cheap way to improve the A/C units and also see if this will help or alleviate some of the dimming or light flickering.

Hope this helps.

 

[ServiceTech1/c]

I agree with winnie. You must first determine if there is a volt drop sufficient enough to cause harm. You must be able to inform the customer of the inevitable flicker. I believe all AC units manufactured today come with the soft start kits installed in them. As far as the utility company requirements, find out what percentage of voltage drop is allowable. My company has determined 5% to be adaquate. The standard delivered product is 120V, so 5% of 120v up is 126v max allowed and 114v min allowed. This standard is practical, low volt is just as damaging as high volt. If the utlity replaced the tx, that sure is no indication the problem does not reside on their side. So, as winie suggested, do a complete quality survey, get your facts and resolve that issue.

 

[winnie]

A slight expansion of what I was saying:

Educating the customer doesn't necessarily mean 'convince them to accept a particular level of flicker'. If they simply don't like the level of flicker that they are seeing, and are willing to put the cash out to fix it, then go make money on giving the customer what they want.

Educating the customer means getting them to understand the parameters of the fix, and getting them to adjust their requirements. If they really require _no_ flicker, then you will need to go far outside of the box of normal fixes. If they require less flicker than the utilities own standards, then the fix will be more expensive than otherwise. But if the utility provides +-5%, and they want +-2%, then there are still ways to get there.

As ghostbuster notes, some electronically controlled lighting systems are very susceptible to line voltage variation. On the hobby side of things, I build lights for my bicycle riding; these are battery based systems, and one of the tools that I use is something called a 'lightbulb voltage regulator'. http://www.cs.indiana.edu/~willie/lvr.html Basically this is a dimmer circuit for battery powered lights that uses some feedback in order to regulate the output to a constant stable level. Normally one sets up the supply voltage to be greater than the lamps nominal operating voltage, and then 'dims' to normal (but now regulated) output.

As a question for the vast number of ECs here:
Do any of the dimmer manufacturers sell _regulating_ dimmers that will hold the light output constant even as the supply voltage changes? Have you used any such items?

-Jon

 

[RayS]

Well, I was going to speculate about having a separate feed from the utility for the AC loads as a possibly option, but Wirenut in post 15 mentioned that the xfmr impedance may overshadow the line losses.

If the client really is troubled by this, and wants to pay for this, a constant voltage transformer (I.E. SOLA) or a rack of electronic voltage regulators (I.E. Furman) may be a solution.