Power main distortion from TRIAC dimmers, what can I do to get rid of it?? - Page 1
Forum section: electronics / projects

author: SharpEars
author_rank: Unknown
timestamp: September 18, 2014, 03:44:27 pm
content: Quote:TRIAC based dimmers are very efficient. TRIAC based dimmers are relatively inexpensive. TRIAC based dimmers flood your mains with TRIAC induced phase cutting noise!The problem:I have Lutron TRIAC based phase-cut dimmers all over my house, as do many people these days. These dimmers control dozens of halogen recessed lights and are often set to the 50% position. This floods my mains with 120 Hz transient noise from the TRIACs regulating power via phase-cutting. Here is what the noise looks like (courtesy of davehouston.org):and an image of the TRIAC operation including the noise spikes (courtesy of hardforum.com):This has not been a big issue for me to date, because most devices in the home are built to be immune to power line noise.Recently, I have installed some active monitors (i.e., loudspeakers with the power regulation, amplifier circuitry and crossover circuitry built-in). These monitors do not do a good job of power noise filtering and are picking up the 120 Hz noise being generated by all of the dimmers around the house, causing their woofers to emit a light but annoying buzz at that frequency. Sadly, other than their power main noise intolerance, I love these monitors because they sound great and were reasonably priced.If I turn all of the dimmers in the house off, the buzzing from the monitors stops. The more dimmers I have set to around 50%, the worse the buzzing from the monitors gets.Other important info:The active monitors are on their own 15 amp circuit that isnot sharedwith the dimmers. However, the noise from the dimmers seems to be going beyond their respective circuits and crossing over to the circuit that the monitors are on (because every circuit in the house is on the same 200 amp main, ultimately). TRIAC phase cutting is efficient, but apparently it also floods your mains with transient noise introduced by the phase cutting that sensitive devices like my monitors pick up.The question:What I need is some sort of circuit I can build or device I can purchase that I can place between the power plugs from the active monitors and the noisy outlet to which they are connected. Power conditioners offer no help here, because although they filter out RFI (i.e., high frequency noise), they are useless for filtering out low frequency noise, such as the noise spikes that are being introduced into my power by the dimmers 120 times a second.They sell coils that can be placed in series between the dimmer and the hot connector that are supposed to reduce (i.e., smooth out the spikes) of each dimmer, but I would have to install one of these for every dimmer, of which I have many, and I would need in-wall space for these things. These coils also buzz themselves, creating a whole new problem. The possibility of replacing all of the dimmers with non-TRIAC based solutions would be expensive and quite a PITA.I am hoping that there is a circuit I can build or device I can buy that I can place between the monitor power plugs and the wall mains that can filter out or at least decrease dimmer introduced noise (Smoothing it out some so that it becomes a non-issue is also an option). The monitors need up to 1000 W of power at 120 V, by the way, so the circuit would need to be able to accommodate this kind of load.I seek your expert help in this matter, because although I understand the problem, I have no idea how to solve it. I have a basic knowledge of electronics fundamentals so feel free to get technical in your answer. However, when it comes to high voltage, I'd rather consult with you experts before building something ineffective or worse yet outright dangerous, since we are potentially dealing with some nine amps at 120 V.

author: wraper
author_rank: Unknown
timestamp: September 18, 2014, 04:26:33 pm
content: You need at least to use mains filter like this for your audio equipment outlet. All audio devices must be connected to the output of it. Also it would be best to connect the same filter (or at least half of it as it is 2 filters in series basically) to the input of each dimmer.

author: tggzzz
author_rank: Super Contributor
timestamp: September 18, 2014, 04:38:35 pm
content: You need to quickly check whether the impulsive noise is being transmitted to the monitor via the mains leads or some other route.A quick and simple technique is to put themains lead through a toroidal ferrite filter. I've used them to completely suppress the click generated by a fridge switching on/off. Seehttp://www.ukradioamateur.co.uk/full/html/c9-1-3.htmespecially figure 9.3 Ideally this is done at the interference source, but by teh amplifier would have an effect too.If that partially removes the problem then your next step would probably be a proper mains filter, specifically including common mode inductors.If you can, do an FFT on the impulsive noise. You will find that it has frequency components far above the 120/240Hz shown in your oscillogram. RF attenuators will suppress those.

author: Richard Crowley
author_rank: Super Contributor
timestamp: September 18, 2014, 04:39:02 pm
content: Professional dimmers (such as those used in the entertainment industry) feature di/dt filters (typically a largish torrodial inductor) to limit the current rise.If you want to get into study of various design schemes:http://sound.westhost.com/lamps/dimmers.html

author: SharpEars
author_rank: Unknown
timestamp: September 18, 2014, 04:50:44 pm
content: Quote from: tggzzz on September 18, 2014, 04:38:35 pmA toroidal ferrite filter seems like an inexpensive and easy to test solution, so I will give that a go once I find an inexpensive source for the toroidal ferrite ring(s).Would something like this do:http://www.ebay.com/itm/4-x-TOROID-RING-FERRITE-CORE-EMI-RFI-CHOKE-FILTER-64-x-40-x-9mm-/331261704775?pt=LH_DefaultDomain_0&hash=item4d20bc7a47I hope that the end result of this is not the same thing that a normal power noise suppression circuit does in a distribution panel (e.g.:http://www.tripplite.com/surge-protector-isobar-4-outlets-6-ft-cord-3330-joule-leds~ISOBAR4ULTRA/), because I've tried this route and it doesn't suppress the noise issue I am having.Thanks

author: SharpEars
author_rank: Unknown
timestamp: September 18, 2014, 04:52:15 pm
content: Quote from: wraper on September 18, 2014, 04:26:33 pmCan you please describe what this circuit does?

author: tggzzz
author_rank: Super Contributor
timestamp: September 18, 2014, 05:03:39 pm
content: Quote from: SharpEars on September 18, 2014, 04:52:15 pmFrom left to right: 2*surge/overvoltage suppressor, capacitors filtering common and differential mode noise, common mode inductor, rinse and repeat. Standard EMI/EMC stuff described in many publications.Don't make your own since the detailed construction is important: just buy the whole thing.

author: Marco
author_rank: Super Contributor
timestamp: September 18, 2014, 05:16:36 pm
content: Shouldn't there be some non common mode inductors in that filter to attenuate the differential noise a bit more?Or do they just intentionally make the coupled inductor leaky to get some differential mode filtering?

author: SharpEars
author_rank: Unknown
timestamp: September 18, 2014, 05:18:38 pm
content: Quote from: tggzzz on September 18, 2014, 05:03:39 pmWhere can I buy this thing? Could you please supply me with a link or a model number?Perhaps something like this:http://www.ebay.com/itm/Schaffner-FN2070-25-08-25A-EMI-Line-Filter-/161414361541?pt=LH_DefaultDomain_0&hash=item25950bb1c5

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: September 18, 2014, 05:41:12 pm
content: Great info above. In general, you always want to kill the noise at the source, rather than try to fix the problem downstream, which is never fully effective. Modern dimmers often omit the needed filtering. Get dimmers with filters. Yes, they usually cost a bit more.

author: SharpEars
author_rank: Unknown
timestamp: September 18, 2014, 05:47:40 pm
content: Quote from: Conrad Hoffman on September 18, 2014, 05:41:12 pmShow me in wall 600 W and 1000 W dimmers that include the proper filters, do they even exist in the sense that they could fit into the space of an an electric power switch?

author: Marco
author_rank: Super Contributor
timestamp: September 18, 2014, 06:01:05 pm
content: AFAICS most of the distortion is differential ... against which those tiny ferrite chokes won't help much.Big chunks of iron are needed.

author: ajb
author_rank: Super Contributor
timestamp: September 18, 2014, 06:01:33 pm
content: If you're mostly just running the lights at 50%, why not use lower wattage bulbs? That will cut down on the problem substantially, because not only will the currents be lower, but you won't be switching them at peak voltage. You'll also get improved energy efficiency--all else being equal, a 100W incandescent bulb running at 50W produces less useful light than a 50W bulb running at 50W. This is because the 100W bulb is running at a lower temperature and therefore its emission has shifted toward the red end of the spectrum and proportionally less of it falls in the visible range. Running halogen bulbs at lower power levels also tends to diminish their lifespan, since the halogen process is not as effective at lower temperatures, so the filament erodes more quickly.

author: bookaboo
author_rank: Frequent Contributor
timestamp: September 18, 2014, 06:20:39 pm
content: Rather than polish a turd why not look into a good quality dimmable LED setup?

author: SharpEars
author_rank: Unknown
timestamp: September 18, 2014, 06:32:24 pm
content: Quote from: ajb on September 18, 2014, 06:01:33 pmBecause half theperceivedlight output of a 75W bulb would require 75W*22.5% actual(corresponding to 50% perceived)=17 W PAR38 halogen bulb which does not exist, especially given the fact that I have very specific bulbs in terms of light angle falloff, etc...

author: SharpEars
author_rank: Unknown
timestamp: September 18, 2014, 06:34:07 pm
content: Quote from: bookaboo on September 18, 2014, 06:20:39 pmBecause then I will be playing the horrid LED CRI game and paying five times as much (per bulb). We have cheap power here (<$0.05 per kW/hr) and the lights, being dimmed as much as they are and being only on for a couple hours each day in the evening aren't costing me much power wise, thanks to those noisy but efficient TRIAC dimmers (I've gone full circle I know and there is much irony in my dilemma).

author: SeanB
author_rank: Super Contributor
timestamp: September 18, 2014, 07:04:46 pm
content: If you are using 50W 12V downlighters you can get the lower light output simply by using 20W lamps instead. Not commonly stocked at retail outlets but always available from lighting distributors. About 20% less light but uses 40% of the power.Older light dimmers had a large toroid inside the housing to do the interference reduction, but these were cost cutted out years ago as they were both a significant cost to add and made the unit too large to fit in some standard housings if there were more than 3 wires present or more than one conduit into the box.

author: eneuro
author_rank: Super Contributor
timestamp: September 18, 2014, 07:36:24 pm
content: Quote from: tggzzz on September 18, 2014, 04:38:35 pmWhen used simple dimmer circuit, but with RC snubber and had radio tuned to AM LF RF below 1MHz, switching 230VAC iron to limit its heat power to <25% in this simple radio it was significant audio change when was turning dimmer phase potentiometerI thought it might be RF noise from this circuit 5m away from radio, but maybe its 230VAC noise tooQuote from: Richard Crowley on September 18, 2014, 04:39:02 pmIn this trailing edge dimmersthey say:QuoteAnd it is not true while... my AC mosfets switch easy switches AC mains 230VACI used 1000Vds 3Ohm RDSON mosfets and it works fine and power losess with 40W bulb are about 0.2W on those 2 mosfets so they are air coldI'm using galvanic optoisolated 0.5A gate driver with photocoupled MCU pins to drive this thing.I can turn on/off 230VAC mains at any time, so these other types of dimmers are quite interesting to test and implement

author: SharpEars
author_rank: Unknown
timestamp: September 18, 2014, 08:57:17 pm
content: Quote from: SeanB on September 18, 2014, 07:04:46 pmThese are not LV lights, these are 120V 75 W lights times several dozen and three 600 W dimmers plus one 1000 W dimmer controlling the lot, and all this stuff across three 15 amp circuits. Even that is only counting the lights that are usually on, not all dimmers/lights I have that can be on, at which point things just become obscene.Also, it is sad that the coils you referred to were removed from dimmers, because they would have at least reduced my problems by smoothing those 120 Hz spikes. Initially, they were removed and sold separately. Now, Lutron discontinued them and you have to fish to find them and I have nowhere to put them, in any case, because where would they go - the switch boxes are full already with the switches?

author: NiHaoMike
author_rank: Super Contributor
timestamp: September 18, 2014, 11:02:49 pm
content: Use a diode to get half power?

author: David_AVD
author_rank: Super Contributor
timestamp: September 18, 2014, 11:43:55 pm
content: Seems like you should find out how the noise is getting into the powered speakers. Is the noise there when you disconnect the audio input to the speakers?

author: Richard Head
author_rank: Frequent Contributor
timestamp: September 19, 2014, 06:32:09 am
content: Whenever you have an interference problem there are a couple of choices you have. You can kill the noise at the source (better) or you can harden the equipment being interfered with.I suspect in your case it'll be easier to harden the equipment being interfered with as there is generally very little extra room inside the dimmer space to add a suitable filter.Incidently, the filter posted by Sharpears is totally unsuitable as it contains no differential mode filtering. Like Marco pointed out, the inductor will have to be a large iron cored type with a large inductance and current rating. The reason is that the inductor has to smooth out the massive current transitions (20A @ 1500W!), not just the steep edges. The only way is with a large inductor/cap L or Pi-network.If you opt to harden the equipment being interfered with you can probably get away with a much smaller filter as the current draw will be much lower. I expect you could probably get away with just a single strategically place capacitor in the active speaker module.

author: rs20
author_rank: Super Contributor
timestamp: September 19, 2014, 08:16:07 am
content: Quote from: eneuro on September 18, 2014, 07:36:24 pmYou've got two MOSFETs there, each of which is only seeing/switching DC. A clever arrangement reminiscent of an SSR, that exploits the (generally not very good*) body diodes in the MOSFETs to, in effect, rectify the current.Almost all MOSFETs have body diodes, and can onlyswitchcurrent flowing against the body diode. Current can flow the other way, but it doesn't count because you can't switch/control that current.* The body diodes of the SK1119, which I'm guessing is what you have there, have a forward voltage of 1.9 Volts. You could certainly make your circuit dissipate less heat if you added discrete diodes to "replace" the body diodes.

author: eneuro
author_rank: Super Contributor
timestamp: September 19, 2014, 09:10:16 am
content: Quote from: rs20 on September 19, 2014, 08:16:07 amIt does not matter, while this PCB as marked on its connectors can switch 230VAC mains and there are NO mosfets body diodes loses when this switch is ON-RDSON bypasses themI use SS495A Hall current sensor capable to monitor up to 25Amax current under load with 100mV/A response from sensor, which is maximum grid nominal current at home one phase 230VAC mains.Quote from: rs20 on September 19, 2014, 08:16:07 amIf I wanted to switch higher load and higher average current I can put a few such AC mosfets switches in pararell as well as use mosfets with lower RDSON if needed.

author: rs20
author_rank: Super Contributor
timestamp: September 19, 2014, 09:19:58 am
content: Quote from: eneuro on September 19, 2014, 09:10:16 amNot sure if trolling, but the same can be said of the Richard's PCB. Just because a PCB with MOSFET can switch AC, does not mean that the statement "MOSFETs can switch AC" is true in any sense relevant to Richard's post. A single MOSFET, placed inline on an AC line, will act as a diode, even if you set V_GS to zero. That's a fail.Quote from: eneuro on September 19, 2014, 09:10:16 amIf RDSON*I is less than one volt, then most of your dissipation will be in the body diode, so RDSON is irrelevant here. Paralleling multiple body diodes has hardly any effect on the voltage drop of a body diode, since diodes have an exponential response. You'd be much better off using a single smaller, cheaper, lower Vf diode than multiple FETs in parallel. Also, the body diodes in a FET, unlike the FET itself, will undergo thermal runaway when paralleled, so what you propose is really a very bad idea.

author: bookaboo
author_rank: Frequent Contributor
timestamp: September 19, 2014, 01:21:15 pm
content: Quote from: SharpEars on September 18, 2014, 06:34:07 pmWow that's cheap power, where do you live?

author: TMM
author_rank: Frequent Contributor
timestamp: September 19, 2014, 01:31:33 pm
content: Somehow i think you are going to be fighting a losing battle to reduce an audible noise through your speakers to inaudible levels just by a passive mains filter going to your audio equipment.Either get rid of the offending dimmers or work out how you can drastically increase the PSRR inside your audio equipment.

author: SharpEars
author_rank: Unknown
timestamp: September 19, 2014, 01:32:31 pm
content: Quote from: David_AVD on September 18, 2014, 11:43:55 pmYes, it is power line noise. It is independent of all inputs (the noise is present when the inputs are disconnected), it is not ground related because the monitors have a two prong connection) and if I wrap foil around the speaker, it is the same (i.e., not RF pickup induced).

author: SharpEars
author_rank: Unknown
timestamp: September 19, 2014, 01:36:32 pm
content: Quote from: TMM on September 19, 2014, 01:31:33 pmI can't get rid of the dimmers (too much money invested, my wife loves how "they look/function" and convenience/efficiency). I can't modify the monitors, because that will void their warranty and I am very disinclined to "dive inside." So, my sole solace is to do power conditioning at the point of power entry into the monitors. That is effectively the advice I am looking for - preferably inexpensive advice consisting of either something I can buy (whole package) or something I can build.

author: SharpEars
author_rank: Unknown
timestamp: September 19, 2014, 01:46:09 pm
content: Hey guys, what if I wire one of these puppies in series with a monitor?LM-DBC12/24-600 - 12V/24V,600Whttp://www.waclighting.com/product/1374Will it do the job?Or, I can save money, buy a 4" ferrite ring and 14 AWG magnet wire and wind it myself. I just don't know how many winds I need...

author: TMM
author_rank: Frequent Contributor
timestamp: September 19, 2014, 01:52:22 pm
content: If it is the high frequency content (spikes), a passive mains filter like has been previously posted will be effective at preventing it coming down the power cord but likely all the wiring and lights in your house are spewing out RF at a 120Hz repetition rate and the speakers will still pick it up, just like the buzz you get through your speakers when someone receives a phone call. You can shield the amplifier circuitry all you want but you can't shield the front of the speaker driver so the speaker's voice coil will still act as a nice antenna to pick up all kinds of RF interference.If it is low order harmonics on the mains you are pretty much stuffed. You can't filter it passively without bulk iron and probably a fair amount of loss at the mains frequency. The PSRR of the amplifier is not adequate and it needs to be modified.

author: rs20
author_rank: Super Contributor
timestamp: September 19, 2014, 02:05:05 pm
content: When all else fails, power an AC motor from mains, use it to drive an AC generator, then power your monitors off the output of the generator.On a vaguely more serious note, a double-conversion UPS is one expensive solution, although the "modified sine" output of your typical UPS might cause even more problems than a dimmer.

author: G7PSK
author_rank: Super Contributor
timestamp: September 19, 2014, 02:28:28 pm
content: Get a power conditioning transformer and run all the audio equipment from it, something along the line of these.http://docs-europe.electrocomponents.com/webdocs/0e15/0900766b80e15aa5.pdfhttp://www.emersonindustrial.com/en-US/egselectricalgroup/products/control-power-solutions/power-protection-conditioning/power-conditioning/Pages/default.aspxhttp://www.solahevidutysales.com/power_conditioning.htmhttp://uk.rs-online.com/web/p/product/7079839/?grossPrice=Y&cm_mmc=UK%7CShopping-_-Google+PLA-_-Sollatek%7CPower+Conditioners-_-7079839&kpid=&kpid=7079839&istCompanyId=f7e7b05b-2daf-4c0e-8825-3633baf8113b&istItemId=xwilllili&istBid=tzit&gclid=CjwKEAjwqO-gBRCEyp2Fufm0lBASJAAZrX-5K_PJckDzA5upoOgw7tRJjhYmrfZhZpn0bOvWXR-XwBoC5ePw_wcB

author: rs20
author_rank: Super Contributor
timestamp: September 19, 2014, 02:43:28 pm
content: G7psk, the first and fourth links seem to just be variacs and don't claim to clean up waveform distortion/harmonics? 2nd link looks good though.

author: G7PSK
author_rank: Super Contributor
timestamp: September 19, 2014, 02:47:26 pm
content: If you read how it operates it contains a multi tapped autotransformer that is controlled by a microprocessor.

author: SharpEars
author_rank: Unknown
timestamp: September 19, 2014, 03:17:32 pm
content: Quote from: rs20 on September 19, 2014, 02:05:05 pmYes, a (very expensive) double conversion UPS would probably do the job (and introduce more noise into the room from its fan(s) than the buzz coming from the monitors).I'm more inclined to buy a 4" ferrite ring and magnet wire and start winding. I just don't know if that will amount to anything useful.

author: eneuro
author_rank: Super Contributor
timestamp: September 19, 2014, 07:47:52 pm
content: Quote from: rs20 on September 19, 2014, 09:19:58 amWere do you see single mosfet in AC mosfets switch?This is not my idea but found it sometime ago thereIRF.com: Using mos-gated power transistor in AC switch applicationsWhile photovoltaic isolators they suggest to driver those mosfets in AC switch are quite expensive and provide not too big gate current, I've made my own gate driver and using transformer 230VAC->12V now can easy drive such switch.BTW: Yes cheap SK1119 1000Vds mosfet is used there with RDSON 3 Ohm and 1.9Vdsf body diodes.When I put 3 of them in pararell (so 6 in AC mosfets switch needed), and prrovide Vgs voltage 12V this switch is fully ON, so when we have 3 resistors in pararel, we get 1 Ohm resistance in half of this AC mosfets switch, so let us assume its body diode has 1.9Vdsf, than current needed to be above 1.9V at 3 Ohm resistance is around 0.63A. While we have 3 such mosfets in pararell in half part of this switch, then total current passing this half of the AC mosfets switch will be 3*0.63A= 1.9A which means we drive output power about 400W in the case of 230VAC and still those mosfets RDSON "shorts" them and its body diodes are below its 1.9VdsfIt is clear that putting a few mosfsts in pararell on each part in this AC mosfets switch helps lower its total RDSON.Single AC mosfets switch shown on this image (bottom) is air cold when driving 40W 230VAC light bulb and have to be while we get only 40W/230VAC= 0.174A (in more detiled calcs mosfets RDSON has to be used) current, when mutipply by 3 Ohm RDSON we have: 0.523V on half of this AC mosfest switch, which gives around 1V accross whole switch and this is what I've got when made measurementEven using cheap noname multimeter will give you this result and it is confirmation of calculations provided above when 40W 230VAC light bulb was usedSo, make real circuit, make measurements if you do not know how to calculate those thingsI've did such circuit and made measurements which fits into theory behind it and those prototype PCBs are shown in image providedUpdate: SimplyFalstadsimulation of AC mosfets switch in pararell with 3 Ohm resistors simulating its RDSON and 1.9Vf diodes modeled shows that current flow after warm up ONLY via resistors when 100W 230VAC light bulb load is connected, so it look slike guys from IRF knows what they are talking aboutIn this case we have 100W/230VAC= 0.435A average current divided by 0.707 we have about 0.615Amax, so each of 3 mosfets in half AC mosfet switch conducts only 1/3*0.615= 0.204A, so 0.614V drop on 3 mosfets in pararell, so whole AC switch should have about 1.2V voltage drop @ 100W load 0.435A current which gives around 0.5W losess in this AC mosfets switch

author: David_AVD
author_rank: Super Contributor
timestamp: September 19, 2014, 09:06:29 pm
content: Quote from: SharpEars on September 19, 2014, 01:32:31 pmThey must be dodgy speakers if they can't handle some noise on the mains supply.

author: rs20
author_rank: Super Contributor
timestamp: September 19, 2014, 10:00:00 pm
content: Quote from: eneuro on September 19, 2014, 07:47:52 pmAh, I stand corrected... I forgot that a MOSFET can be modulated between dropping Rds * I and Vf in the reverse direction.My overarching point stands: to switch AC with a MOSFET, you need to overcome the MOSFET's intrinsic inability to do so on its own. One solution is anti-series FETs, another is a bridge rectifier.

author: David Hess
author_rank: Super Contributor
timestamp: September 24, 2014, 10:42:19 am
content: Quote from: Marco on September 18, 2014, 05:16:36 pmThey are usually deliberately designed to have high leakage inductance so they function as both a common mode and differential choke.As far as the original question, I would filter the power lines *at* the dimmers despite their number because once the conducted interference is in the power line, it will radiate everywhere and be more difficult to control.Also, active power conditioners and online UPSes usually share the neutral between input and output so they will not reduce common mode noise. Some older ones split the neutral so might help here.

author: Seekonk
author_rank: Super Contributor
timestamp: September 25, 2014, 03:10:31 pm
content: I used to work for a company that made RC snubbers along with other products. We had a customer that had 50 German opto sensors (won't mention the name) that had a line operated phase triggered power supply. As you can imagine, they would all trigger on at about the same time. I had him try two RC networks at each unit. That worked for him. Guy with a three phase bag sealer also had false triggering problems and they worked there. Have this theory that once upon a tome there was a lot of old fashioned light bulbs out there putting a nice dampening on all the noise dumped on the power line. Now all that junk just bounces around. It doesn't go away until you can turn it into heat with some terminating resistance.

author: macboy
author_rank: Super Contributor
timestamp: September 26, 2014, 02:06:23 pm
content: Quote from: David_AVD on September 18, 2014, 11:43:55 pmThis is a very good point. The noise may be RFI being that is transmitted by all those conductors, and being picked up by your audio interconnects. In that case, filtering the AC at the monitors won't help.I always have a good stock of snap-on ferrites. I try these first, and they help or fix the problem often enough. Try some on both the power and signal cables going to the monitors and the source(s) feeding them. If there is room to loop the cable a couple times or more, that is even better (google image search "snap ferrite loop").

author: Richard Crowley
author_rank: Super Contributor
timestamp: September 26, 2014, 03:31:57 pm
content: The interference is coming from the OUTPUT of the dimmer on its way to the LOAD, the dimmed lamp(s).The interference is caused by the sharp risetime of the power being turned on, mid-cycle by the thyristor (Triac or SCR).There may also be some noise going back out of the mains INPUT to the dimmer, but that is secondary.The solution (which has been used maybe since before some of you were born) is to put dI/dT limiting on the output.This is accomplished with a rather large inductor. In modern times, this is typically a torrodial coil.Note further that in some cases the filament of the lamps themselves "sing", shocked into vibration by the steep leading edge.So the dI/dT limiting inductors also serve the purpose of reducing "filament sing".

author: eneuro
author_rank: Super Contributor
timestamp: September 26, 2014, 07:29:12 pm
content: Quote from: Seekonk on September 25, 2014, 03:10:31 pmWhat about such halogen light bulbs?Three such halogens and we have 4.5kW dump loadJust will be testing smaller J-78 60W/150W halogens (they are cheap about 1$ each) put pararell to 230VAC AC mosfets switch with 30Amax currents in pulses <10ms shifted in phase between 90*deg-180*deg, driving a huge transformer primary in spot welder and will see what happends if I miss right moment to switch this circuit off in the case of zero crossing bad detection?I have Hall sensor based mains current sensing with 100mV/1A, so it should be easy to find right moment to switch OFF this AC mosfets switch.