Minimising EM noise from PWM switched fairly lights?

[Rick C]

On Thursday, October 24, 2019 at 1:12:43 PM UTC-4, Tim Watts wrote:

On 24/10/2019 16:37, Rick C wrote:

Why not deal with the RFI by not creating it? I'm not sure what your setup is at the moment but driving with a DC current should be pretty much as simple as PWM. You talk about adding a choke. I'd be willing to bet if you look at the resulting circuit it is a short stone's throw from being a DC/DC converter.

Drive with DC and you only need to deal with residual high frequency noise you can stop with a simple filter.

I'm one of those people who see and are very annoyed by the blinking taillights on so many cars. Cadillac was the first car I noticed it on many years ago and have always been the worst offenders with huge taillights on some of their vehicles. More recently they seem to have changed their design, either by bumping up the frequency or by using DC.

Interesting that you can't effectively google this effect because there is a distinct effect from replacement LED turn signals blinking too fast because they don't draw enough current for the blink circuit to work correctly, called hyper flashing.

Interesting idea - so I'd need a programmable bi directional constant
current drive to do that.

What? Why bidirectional? You can adapt a constant voltage drive to be a current drive very easily.

However, not really something I could use here as I'd still have to
strobe as the LEDs are in 2 sets, back to back wired on a single feed
pair of wires - hence the H-Bridge.

They are designed for AC??? This is a bit weird. I guess there's a lot you aren't telling us.

--

Rick C.

-- Get 1,000 miles of free Supercharging
-- Tesla referral code - https://ts.la/richard11209

 

[Rick C]

On Thursday, October 24, 2019 at 1:10:01 PM UTC-4, Tim Watts wrote:

On 24/10/2019 16:30, jlarkin@highlandsniptechnology.com wrote:

At a low PWM rate, say 100 Hz, anything radiated in the AM band will
be ballpark the 10,000th harmonic of the switch frequency. The energy
will be nil.

That was about as much as I understood about the whole thing

It's also misleading. The edge rate is what generates the harmonics. Even at 100 Hz, a fast edge will generate noise, in this case modulated at 100 Hz. Although it's a bit like the question "if a tree falls in a forest and there's no one there to hear it... does it make a sound?" Nobody listens to AM anymore so can you call it interference if only interferes with signals no one is receiving?

Slow down the switching edges a bit if you like. Add mosfet gate
resistors to soften the edges.

Interesting... Sadly won't be able to do that as I'm using pre built
H-Bridge modules based on the L298N

https://www.ebay.co.uk/itm/Dual-L298N/172822867116

Sorry for wimping out there ;-

I still say just use an adjustable switcher current source rather than PWM. 100 Hz is way too slow and will be perceived due to not even very fast motion.

I was watching video from my car through the front window in the rain and the wiper blades looked like they were bent from the scan rate of the video. Even at 100 Hz, various artifacts of movement are visible. They up the scan rate to 120 Hz to watch sports and on some sets they up it to 240 Hz. I suggest your flicker rate should be around 1000 Hz.

--

Rick C.

+ Get 1,000 miles of free Supercharging
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[Rick C]

On Thursday, October 24, 2019 at 11:02:36 PM UTC-4, Bill Sloman wrote:

On Friday, October 25, 2019 at 2:30:23 AM UTC+11, jla...@highlandsniptechnology.com wrote:
On Thu, 24 Oct 2019 09:57:49 +0100, Tim Watts <tw@example.com> wrote:

Hi,

This year's project is to drive 3 strings of 30V DC LED outdoor fairy
lights from Raspberry Pi's[1]


I've been on here before last year and took some greet advice with
respect to H-Bridges and found some, along with DC-DC converters that
will enable me to interface a 30V DC supply to the Pi and the Pi back to
the lights.


The only thing I am mindful of is not to inadvertantly blat out a ton of
EM noise.

So I was wondering if anyone (without guarantees of course) might be
able to offer any rule of thumb advice please?


1) I'll keep the PWM frequency as low as possible without causing
visible flickering to passing motor cars (which is sometime I can test
by driving by, road speed limit is 30mph so not super fast).

2) I'm thinking to pop a suitable choke inline with each string of
lights after the H-Bridge to block the higher harmonics. This is the bit
I'm not sure of. What would be a suitable number of Henrys as a function
of drive current and base frequency of the PWM?

3) Are there any inexpensive ways of doing a quick and dirty
verification of the amount of noise being emitted? I don't have a
'scope, though I could get a picoscope type unit if sticking an antenna
of some sort on it would provide useful tests???

Many thanks,

At a low PWM rate, say 100 Hz, anything radiated in the AM band will
be ballpark the 10,000th harmonic of the switch frequency. The energy
will be nil.

Not true. AM transmitters are delectable for miles. Even a small high frequency component from a radiator next door can be big enough to create problems.

Slow down the switching edges a bit if you like. Add mosfet gate
resistors to soften the edges.

Which increases the switching losses. If you slow down the edges enough, you will cook your MOSFETs.

This is a pretty bizarre design. Trying to drive separate LEDs by reversing the polarity of the power without generating EMI. It hurts too much to think what will happen if a choke is thrown into the mix. One pair of FETs turn on to drive current into the choke and LEDs, then they turn off and the other FETs turn on to reverse the current, but the current is going to continue in the same direction for a bit pushing power back into the PSU until the choke winds down and ramps back up in the other polarity.

Yeah, this is ugly. I guess it will work.

--

Rick C.

-+ Get 1,000 miles of free Supercharging
-+ Tesla referral code - https://ts.la/richard11209

 

[piglet]

On 24/10/2019 16:30, jlarkin@highlandsniptechnology.com wrote:

At a low PWM rate, say 100 Hz, anything radiated in the AM band will
be ballpark the 10,000th harmonic of the switch frequency. The energy
will be nil.

Household triac dimmers have to include filtering.

piglet

 

[gray_wolf]

On 10/25/2019 1:04 AM, piglet wrote:

On 24/10/2019 16:30, jlarkin@highlandsniptechnology.com wrote:

At a low PWM rate, say 100 Hz, anything radiated in the AM band will
be ballpark the 10,000th harmonic of the switch frequency. The energy
will be nil.

Household triac dimmers have to include filtering.

piglet

Oh god yes. When I my guitar amp, guitar business I installed a triac dimmer
just to test for pickup rejection. I told them just consider it distortion
enhancement.

 

[Martin Brown]

On 25/10/2019 06:33, Rick C wrote:

On Thursday, October 24, 2019 at 11:02:36 PM UTC-4, Bill Sloman
wrote:
On Friday, October 25, 2019 at 2:30:23 AM UTC+11,
jla...@highlandsniptechnology.com wrote:

At a low PWM rate, say 100 Hz, anything radiated in the AM band
will be ballpark the 10,000th harmonic of the switch frequency.
The energy will be nil.

Not true. AM transmitters are delectable for miles. Even a small
high frequency component from a radiator next door can be big
enough to create problems.

Slow down the switching edges a bit if you like. Add mosfet gate
resistors to soften the edges.

Which increases the switching losses. If you slow down the edges
enough, you will cook your MOSFETs.

Only if they are very weak and feeble. He just meant to avoid having
them snap hard into conduction at their maximum slew rate. The sharper
the edge is the more high frequency content it contains.

The level of interference this toy is likely to produce might well be
stopped by wrapping the outgoing wires through a ferrite ring.

This is a pretty bizarre design. Trying to drive separate LEDs by
reversing the polarity of the power without generating EMI. It hurts
too much to think what will happen if a choke is thrown into the mix.
One pair of FETs turn on to drive current into the choke and LEDs,
then they turn off and the other FETs turn on to reverse the current,
but the current is going to continue in the same direction for a bit
pushing power back into the PSU until the choke winds down and ramps
back up in the other polarity.

I presume he is trying to drive one of those multiplex strings of LEDs
which with a modest number of wires can do interesting patterns. One set
of LEDs wired each way across a pair of wires (possibly more than one pair).

> Yeah, this is ugly. I guess it will work.

It cuts down on the number of wires compared to a filament bulb setup.

--
Regards,
Martin Brown

 

[Bill Sloman]

On Friday, October 25, 2019 at 11:18:01 PM UTC+11, Martin Brown wrote:

On 25/10/2019 06:33, Rick C wrote:
On Thursday, October 24, 2019 at 11:02:36 PM UTC-4, Bill Sloman
wrote:
On Friday, October 25, 2019 at 2:30:23 AM UTC+11,
jla...@highlandsniptechnology.com wrote:

At a low PWM rate, say 100 Hz, anything radiated in the AM band
will be ballpark the 10,000th harmonic of the switch frequency.
The energy will be nil.

Not true. AM transmitters are delectable for miles. Even a small
high frequency component from a radiator next door can be big
enough to create problems.

Slow down the switching edges a bit if you like. Add mosfet gate
resistors to soften the edges.

Which increases the switching losses. If you slow down the edges
enough, you will cook your MOSFETs.

Only if they are very weak and feeble.

What kind of MOSFETs do you expect to see in a Christmas light driver?

He just meant to avoid having
them snap hard into conduction at their maximum slew rate. The sharper
the edge is the more high frequency content it contains.

Sure - we can all do the Fourier transform of a square wave. A trapezium wave loses the high frequency components that have steeper edges than the sloping bits.

The level of interference this toy is likely to produce might well be
stopped by wrapping the outgoing wires through a ferrite ring.

Do-it-yourself common mode choke.

But "wrapping" may not be the right word. You really ought to keep on threading the entire length of the string through the hole in the ferrite ring until you run out of space.

If you've got a stock of biggish ferrite rings in a bottom drawer it might be an attractive option. If you haven't, buying a pre-wound common mode choke might be a less tedious option.

And you still ought to put a capacitor between the leads on the output side of the choke - the inter-winding capacitance between the go and return wires won't be insignificant but won't get above about 1nF. 100nF would be a hundred times more effective.

<snip>

--
Bill Sloman, Sydney

 

[John Larkin]

On Fri, 25 Oct 2019 02:48:55 -0500, gray_wolf <g_wolf@howling_mad.com>
wrote:

On 10/25/2019 1:04 AM, piglet wrote:
On 24/10/2019 16:30, jlarkin@highlandsniptechnology.com wrote:

At a low PWM rate, say 100 Hz, anything radiated in the AM band will
be ballpark the 10,000th harmonic of the switch frequency. The energy
will be nil.

Household triac dimmers have to include filtering.

piglet


Oh god yes. When I my guitar amp, guitar business I installed a triac dimmer
just to test for pickup rejection. I told them just consider it distortion
enhancement.

A guitar amp doesn't (or shouldn't!) rectify RF. Any buzz from a triac
dimmer is baseband, and no reasonable filter will help that.

SCR dimmer edges aren't especially fast, and the AM band is about the
8000th harmonic of 120 Hz. Even an ideal square wave has a wimpy
8000th harmonic.

One interesting thing that a triac dimmer can do is *modulate* the
ambient RF, which could be very audible. A filter can help that.

--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[Rick C]

On Friday, October 25, 2019 at 1:11:59 PM UTC-4, John Larkin wrote:

On Fri, 25 Oct 2019 02:48:55 -0500, gray_wolf <g_wolf@howling_mad.com
wrote:

On 10/25/2019 1:04 AM, piglet wrote:
On 24/10/2019 16:30, jlarkin@highlandsniptechnology.com wrote:

At a low PWM rate, say 100 Hz, anything radiated in the AM band will
be ballpark the 10,000th harmonic of the switch frequency. The energy
will be nil.

Household triac dimmers have to include filtering.

piglet


Oh god yes. When I my guitar amp, guitar business I installed a triac dimmer
just to test for pickup rejection. I told them just consider it distortion
enhancement.


A guitar amp doesn't (or shouldn't!) rectify RF. Any buzz from a triac
dimmer is baseband, and no reasonable filter will help that.

SCR dimmer edges aren't especially fast, and the AM band is about the
8000th harmonic of 120 Hz. Even an ideal square wave has a wimpy
8000th harmonic.

Hand waving arguments. While it may be "wimpy" it is a wimpy component of a switching edge at power line voltages, over 300 volts peak in 240 VAC systems and potentially plenty of amps. Even a wimpy multiplier creates significant radiation in broadcast bands. The proof of the pudding is in the eating. Many cheap dimmers cause noise on AM radios. Hard to dispute that.

--

Rick C.

+- Get 1,000 miles of free Supercharging
+- Tesla referral code - https://ts.la/richard11209

 

[Lasse Langwadt Christense]

fredag den 25. oktober 2019 kl. 20.27.26 UTC+2 skrev upsid...@downunder.com:

On Fri, 25 Oct 2019 10:11:47 -0700, John Larkin
jlarkin@highland_atwork_technology.com> wrote:

On Fri, 25 Oct 2019 02:48:55 -0500, gray_wolf <g_wolf@howling_mad.com
wrote:

On 10/25/2019 1:04 AM, piglet wrote:
On 24/10/2019 16:30, jlarkin@highlandsniptechnology.com wrote:

At a low PWM rate, say 100 Hz, anything radiated in the AM band will
be ballpark the 10,000th harmonic of the switch frequency. The energy
will be nil.

Household triac dimmers have to include filtering.

piglet


Oh god yes. When I my guitar amp, guitar business I installed a triac dimmer
just to test for pickup rejection. I told them just consider it distortion
enhancement.


A guitar amp doesn't (or shouldn't!) rectify RF. Any buzz from a triac
dimmer is baseband, and no reasonable filter will help that.

The most likely culprit is your guitar and especially your guitar
cord.

SCR controlled stage lighting spew around audio frequency buzz.
Unfortunately, most guitars use asymmetric connections and all
metallic parts are also connected to the signal ground. The ground
signal connection is connected through the cable shield to the
amplifier signal ground and finally into mains ground.

There are typically a 10-100 pf stray capacitance between lighting,
you and (exposed) guitar metallic parts. A audio leakage current will
flow from the lights, through guitar metallic parts, through the
guitar cord into the amplifier. This leakage current will cause
voltage losses in the guitar cord shield and especially in bad
connections, both in the guitar as well as amplifier end. Any voltage
losses in this path will be directly added to the audio signal,
causing buzz.

This is particularly evident when moving around and sometimes a strong
buzz is heard, when there is a bad connection at the guitar end jack.

Using a good quality guitar cord with good shield and high quality
plugs at both ends and that the jacks in the guitar and in the
amplifier are tight and in good condition. This will reduce the ground
resistance and hence noise voltage.

a lot of the hum must be magnetic or humbuckers wouldn't work

 

On Fri, 25 Oct 2019 10:11:47 -0700, John Larkin
<jlarkin@highland_atwork_technology.com> wrote:

On Fri, 25 Oct 2019 02:48:55 -0500, gray_wolf <g_wolf@howling_mad.com
wrote:

On 10/25/2019 1:04 AM, piglet wrote:
On 24/10/2019 16:30, jlarkin@highlandsniptechnology.com wrote:

At a low PWM rate, say 100 Hz, anything radiated in the AM band will
be ballpark the 10,000th harmonic of the switch frequency. The energy
will be nil.

Household triac dimmers have to include filtering.

piglet


Oh god yes. When I my guitar amp, guitar business I installed a triac dimmer
just to test for pickup rejection. I told them just consider it distortion
enhancement.


A guitar amp doesn't (or shouldn't!) rectify RF. Any buzz from a triac
dimmer is baseband, and no reasonable filter will help that.

The most likely culprit is your guitar and especially your guitar
cord.

SCR controlled stage lighting spew around audio frequency buzz.
Unfortunately, most guitars use asymmetric connections and all
metallic parts are also connected to the signal ground. The ground
signal connection is connected through the cable shield to the
amplifier signal ground and finally into mains ground.

There are typically a 10-100 pf stray capacitance between lighting,
you and (exposed) guitar metallic parts. A audio leakage current will
flow from the lights, through guitar metallic parts, through the
guitar cord into the amplifier. This leakage current will cause
voltage losses in the guitar cord shield and especially in bad
connections, both in the guitar as well as amplifier end. Any voltage
losses in this path will be directly added to the audio signal,
causing buzz.

This is particularly evident when moving around and sometimes a strong
buzz is heard, when there is a bad connection at the guitar end jack.

Using a good quality guitar cord with good shield and high quality
plugs at both ends and that the jacks in the guitar and in the
amplifier are tight and in good condition. This will reduce the ground
resistance and hence noise voltage.

An even better solution is using stereo jacks. The cold side of the
microphones and potentiometers are connect to the R-chanel and only
potentiometer cans and exposed metallic parts are connected to the
jack ground. Using a stereo cord, the signal ground and shield ground
are kept separate up to the amplifier input jack in which the R-side
is connected to ground. This should help reducing the buzz.

An other source of buzz in stage systems can be caused by ground
potential differences "ground loop", especially if TN-C or TN-C-S
mains wiring convention is used. In these cases there might be some
ground potential between mains sockets in different part of the
room/stage. At such cases connect all audio equipment into a single
mains socket and the light equipment to an other socket. Make sure
that there are no galvanic connection between audio equipment and
audio controlled light systems (light organ). Make sure there is only
a transformer connection,

SCR dimmer edges aren't especially fast, and the AM band is about the
8000th harmonic of 120 Hz. Even an ideal square wave has a wimpy
8000th harmonic.

One interesting thing that a triac dimmer can do is *modulate* the
ambient RF, which could be very audible. A filter can help that.

 

[whit3rd]

On Friday, October 25, 2019 at 10:11:59 AM UTC-7, John Larkin wrote:

SCR dimmer edges aren't especially fast, and the AM band is about the
8000th harmonic of 120 Hz. Even an ideal square wave has a wimpy
8000th harmonic.

True, but only because the even harmonics vanish. With 10W of power,
the 8001th harmonic is down to nanowatts, but... you can pick that up with a radio.

 

[Jasen Betts]

On 2019-10-25, Rick C <gnuarm.deletethisbit@gmail.com> wrote:

On Thursday, October 24, 2019 at 11:02:36 PM UTC-4, Bill Sloman wrote:

Not true. AM transmitters are delectable for miles. Even a small high frequency component from a radiator next door can be big enough to create problems.

Slow down the switching edges a bit if you like. Add mosfet gate
resistors to soften the edges.

Which increases the switching losses. If you slow down the edges enough, you will cook your MOSFETs.

This is a pretty bizarre design.

I have a LED string like this, it was purchased retail at a big box
store. it came with a controller. I have not analyzed the waveforms
used to drive it, but I do think it messes with the AM radio.

Trying to drive separate LEDs by
reversing the polarity of the power without generating EMI. It hurts
too much to think what will happen if a choke is thrown into the mix.

a choke should be ok if the drive short-circuits the output when idle.
and the drive has sufficient idle time between opposite polarities,

--
When I tried casting out nines I made a hash of it.

 

On Fri, 25 Oct 2019 10:32:52 -0700 (PDT), Rick C
<gnuarm.deletethisbit@gmail.com> wrote:

On Friday, October 25, 2019 at 1:11:59 PM UTC-4, John Larkin wrote:
On Fri, 25 Oct 2019 02:48:55 -0500, gray_wolf <g_wolf@howling_mad.com
wrote:

On 10/25/2019 1:04 AM, piglet wrote:
On 24/10/2019 16:30, jlarkin@highlandsniptechnology.com wrote:

At a low PWM rate, say 100 Hz, anything radiated in the AM band will
be ballpark the 10,000th harmonic of the switch frequency. The energy
will be nil.

Household triac dimmers have to include filtering.

piglet


Oh god yes. When I my guitar amp, guitar business I installed a triac dimmer
just to test for pickup rejection. I told them just consider it distortion
enhancement.


A guitar amp doesn't (or shouldn't!) rectify RF. Any buzz from a triac
dimmer is baseband, and no reasonable filter will help that.

SCR dimmer edges aren't especially fast, and the AM band is about the
8000th harmonic of 120 Hz. Even an ideal square wave has a wimpy
8000th harmonic.

Hand waving arguments. While it may be "wimpy" it is a wimpy component of a switching edge at power line voltages, over 300 volts peak in 240 VAC systems and potentially plenty of amps. Even a wimpy multiplier creates significant radiation in broadcast bands. The proof of the pudding is in the eating. Many cheap dimmers cause noise on AM radios. Hard to dispute that.

In addition remember that quite a few 100/120 Hz harmonics will fall
within an AM receiver 9 or 10 kHz IF bandwidth, not just the 8000th.

 

On Fri, 25 Oct 2019 10:32:52 -0700 (PDT), Rick C
<gnuarm.deletethisbit@gmail.com> wrote:

On Friday, October 25, 2019 at 1:11:59 PM UTC-4, John Larkin wrote:
On Fri, 25 Oct 2019 02:48:55 -0500, gray_wolf <g_wolf@howling_mad.com
wrote:

On 10/25/2019 1:04 AM, piglet wrote:
On 24/10/2019 16:30, jlarkin@highlandsniptechnology.com wrote:

At a low PWM rate, say 100 Hz, anything radiated in the AM band will
be ballpark the 10,000th harmonic of the switch frequency. The energy
will be nil.

Household triac dimmers have to include filtering.

piglet


Oh god yes. When I my guitar amp, guitar business I installed a triac dimmer
just to test for pickup rejection. I told them just consider it distortion
enhancement.


A guitar amp doesn't (or shouldn't!) rectify RF. Any buzz from a triac
dimmer is baseband, and no reasonable filter will help that.

SCR dimmer edges aren't especially fast, and the AM band is about the
8000th harmonic of 120 Hz. Even an ideal square wave has a wimpy
8000th harmonic.

Isn't the harmonic amplitude simply inversely proportional to
frequency ?

>Hand waving arguments. While it may be "wimpy" it is a wimpy component of a switching edge at power line voltages, over 300 volts peak in 240 VAC systems and potentially plenty of amps. Even a wimpy multiplier creates significant radiation in broadcast bands. The proof of the pudding is in the eating. Many cheap dimmers cause noise on AM radios. Hard to dispute that.

The 8001th harmonic would have 37 mV, spreading through the house
mains wiring, radiating all around. Older equipment without mains
filtering could also suffer directly through their power supply.

The nasty thing about bad SCR dimmers is that while the output
waveform is very dirty, but the same dirty current is drawn through
the dimmer from the feeding mains system, causing strong audio
frequency magnetic fields in the house wiring. In addition, this dirty
current produces voltage drops in both the phase as well as neutral
connector, thus, any equipment connected to the same line will get a
varying voltage. Depending on house wiring conventions used, this may
also insert dirt into protective ground and possibly into signal
grounds, causing all kind of buzzing effects in audio.

 

[Bill Sloman]

On Saturday, October 26, 2019 at 3:08:50 PM UTC+11, upsid...@downunder.com wrote:

On Fri, 25 Oct 2019 10:32:52 -0700 (PDT), Rick C
gnuarm.deletethisbit@gmail.com> wrote:

On Friday, October 25, 2019 at 1:11:59 PM UTC-4, John Larkin wrote:
On Fri, 25 Oct 2019 02:48:55 -0500, gray_wolf <g_wolf@howling_mad.com
wrote:

On 10/25/2019 1:04 AM, piglet wrote:
On 24/10/2019 16:30, jlarkin@highlandsniptechnology.com wrote:

At a low PWM rate, say 100 Hz, anything radiated in the AM band will
be ballpark the 10,000th harmonic of the switch frequency. The energy
will be nil.

Household triac dimmers have to include filtering.

piglet


Oh god yes. When I my guitar amp, guitar business I installed a triac dimmer
just to test for pickup rejection. I told them just consider it distortion
enhancement.


A guitar amp doesn't (or shouldn't!) rectify RF. Any buzz from a triac
dimmer is baseband, and no reasonable filter will help that.

SCR dimmer edges aren't especially fast, and the AM band is about the
8000th harmonic of 120 Hz. Even an ideal square wave has a wimpy
8000th harmonic.

Isn't the harmonic amplitude simply inversely proportional to
frequency?

It is for square waves. For triangular waves it's inversely proportional to the square of the frequency. For Dirac spikes it is independent of the harmonic number.

For more nearly real square waves - also known as trapezium waves - the amplitude rolls off faster for the higher frequency content which has faster edges than the the sloping bits.

As soon as you round off the corners to get something that might be a real square wave that part of the high frequency content decreases even faster.

Hand waving arguments. While it may be "wimpy" it is a wimpy component of a switching edge at power line voltages, over 300 volts peak in 240 VAC systems and potentially plenty of amps. Even a wimpy multiplier creates significant radiation in broadcast bands. The proof of the pudding is in the eating. Many cheap dimmers cause noise on AM radios. Hard to dispute that.

The 8001th harmonic would have 37 mV, spreading through the house
mains wiring, radiating all around. Older equipment without mains
filtering could also suffer directly through their power supply.

The nasty thing about bad SCR dimmers is that while the output
waveform is very dirty, but the same dirty current is drawn through
the dimmer from the feeding mains system, causing strong audio
frequency magnetic fields in the house wiring. In addition, this dirty
current produces voltage drops in both the phase as well as neutral
connector, thus, any equipment connected to the same line will get a
varying voltage. Depending on house wiring conventions used, this may
also insert dirt into protective ground and possibly into signal
grounds, causing all kind of buzzing effects in audio.

Back when switching power supplies first got popular, they contaminated entire mains supplies.

I was part of the Nijmegen University science faculty workshop back then, and one of my colleagues got stuck with the job of monitoring how bad it was..

We'd had a lot of informal feedback from researchers whose more sensitive electronics had been suffering from this effect, and put mains filters where it helped. But personal computer power supplies were one of the bad offenders, and every office had at least one personal computer, and lots of researchers weren't enthusiastic about paying for anything better.

--
Bill Sloman, Sydney

 

[Rick C]

On Saturday, October 26, 2019 at 12:08:50 AM UTC-4, upsid...@downunder.com wrote:

The 8001th harmonic would have 37 mV, spreading through the house
mains wiring, radiating all around. Older equipment without mains
filtering could also suffer directly through their power supply.

The nasty thing about bad SCR dimmers is that while the output
waveform is very dirty, but the same dirty current is drawn through
the dimmer from the feeding mains system, causing strong audio
frequency magnetic fields in the house wiring. In addition, this dirty
current produces voltage drops in both the phase as well as neutral
connector, thus, any equipment connected to the same line will get a
varying voltage. Depending on house wiring conventions used, this may
also insert dirt into protective ground and possibly into signal
grounds, causing all kind of buzzing effects in audio.

There is a group here in Virginia who have found potentially life threatening electrical ground problems near water. They have measured voltages in the water near docks that can cause a swimmer's muscles to spasm allowing the swimmer to drown.

These guys have traced the problem to similar currents in the neutral that is then carried on the protective ground. Seems the motor startup transients on the lines can swim upstream much as you are talking about.

--

Rick C.

++ Get 1,000 miles of free Supercharging
++ Tesla referral code - https://ts.la/richard11209

 

[Tim Watts]

On 25/10/2019 13:17, Martin Brown wrote:

On 25/10/2019 06:33, Rick C wrote:

Yeah, this is ugly.  I guess it will work.

It cuts down on the number of wires compared to a filament bulb setup.

2 wires in this case.

Happened I wanted some low voltage outdoor lights with guaranteed mains
separation, ungrounded ("SELV" in British parlance).

The type came with a controller and it it was clear they were 2 sets of
reverse wired LEDs. Son wanted to have a go with a Pi to do our own
patterns (and have Wifi access to them).

And here we are.

The project is simple and safe enough, just wanted not to be an anti
social git and recalled switching squarewaves generates a ton of
harmonics

 

[Tim Watts]

On 25/10/2019 06:25, Rick C wrote:

On Thursday, October 24, 2019 at 1:12:43 PM UTC-4, Tim Watts wrote:
On 24/10/2019 16:37, Rick C wrote:

Why not deal with the RFI by not creating it? I'm not sure what your setup is at the moment but driving with a DC current should be pretty much as simple as PWM. You talk about adding a choke. I'd be willing to bet if you look at the resulting circuit it is a short stone's throw from being a DC/DC converter.

Drive with DC and you only need to deal with residual high frequency noise you can stop with a simple filter.

I'm one of those people who see and are very annoyed by the blinking taillights on so many cars. Cadillac was the first car I noticed it on many years ago and have always been the worst offenders with huge taillights on some of their vehicles. More recently they seem to have changed their design, either by bumping up the frequency or by using DC.

Interesting that you can't effectively google this effect because there is a distinct effect from replacement LED turn signals blinking too fast because they don't draw enough current for the blink circuit to work correctly, called hyper flashing.

Interesting idea - so I'd need a programmable bi directional constant
current drive to do that.

What? Why bidirectional? You can adapt a constant voltage drive to be a current drive very easily.

Because the LEDs are in 2 pairs of sets, alternating down the string,
wired in reverse parallel on a single pair of wires to allow for chaser
patterns and alternating blink effects.


I need alternating drive at 30V peak for this particular type

 

On Sat, 26 Oct 2019 00:48:28 -0700 (PDT), Rick C
<gnuarm.deletethisbit@gmail.com> wrote:

On Saturday, October 26, 2019 at 12:08:50 AM UTC-4, upsid...@downunder.com wrote:

The 8001th harmonic would have 37 mV, spreading through the house
mains wiring, radiating all around. Older equipment without mains
filtering could also suffer directly through their power supply.

The nasty thing about bad SCR dimmers is that while the output
waveform is very dirty, but the same dirty current is drawn through
the dimmer from the feeding mains system, causing strong audio
frequency magnetic fields in the house wiring. In addition, this dirty
current produces voltage drops in both the phase as well as neutral
connector, thus, any equipment connected to the same line will get a
varying voltage. Depending on house wiring conventions used, this may
also insert dirt into protective ground and possibly into signal
grounds, causing all kind of buzzing effects in audio.

There is a group here in Virginia who have found potentially life threatening electrical ground problems near water. They have measured voltages in the water near docks that can cause a swimmer's muscles to spasm allowing the swimmer to drown.

I remember that story. Apparent they could not get the shore grounding
electrode, the marina metallic parts and water properly bonded
together (equipotential bonding
https://en.wikipedia.org/wiki/Electrical_bonding). Normally it is
required that there shouldn't be "dangerous voltage differences"
between objects that should be grounded. What is considered dangerous,
might be different for swimmer in water and people on dry land.

If everything else fails, install a 240/240 V isolation transformer or
a new pig in the pole close to the marina and connect the secondary
center tap to a grounding electrodes on the ground, in the water as
well as the metallic parts of the marina.

>These guys have traced the problem to similar currents in the neutral that is then carried on the protective ground. Seems the motor startup transients on the lines can swim upstream much as you are talking about.

I was referring to TN-C-S wiring convention
https://en.wikipedia.org/wiki/Earthing_system
Distribution transfers are wired as TN-C with the start point (or
center tap of 120/240 V) is connected with a single PEN connector to
the houses. For ungrounded loads and ungrounded sockets this is all
that is needed. However for grounded sockets and plugs with
non-polarized sockets, the shared PEN conductor has to be split into
PE and N connections.

The latest point in which this has to be done is in the grounded
socket itself, in which a short jumper connects the PE and N
connections together. After this point the socket and equipment cord
use separate PE and N (TN-S).

Due to the voltage losses in the shared PEN conductor due to the load
current, the N (and hence also PE conductor) has a slightly different
potential. If two grounded equipment are connected to two separate
grounded sockets, the equipment chassis potential may vary by a volt
or two. Now, is an unbalanced signal cable shield is connected to the
corresponding equipment chassis, a strong current may flow, causing
all kinds of hum issues.

The separation of PEN to PE and N can also be done earlier, e.g. in
the main distribution panel and all in-house wiring use separate PE
and N wires and all PE connectors are at the same potential (unless
there is a ground fault) and hence no potential difference between
equipment chassis and no hum issues. This is a TN-C-S configuration.

However, if two buildings with separate TN-C to TN-S splitting points
are connected together, there are again ground potential issues and
hum problems. Balanced signals and grounding cable shields only at one
end helps. The other end of the cable shield can be grounded through a
resistor or a capacitor (to provide RF grounding only).