Isolating cause of mains interference

T

Terry Pinnell

Guest
The *root* cause is plainly the set of fluorescent lights in the
garage being switched on or off (or both) via a simple relay
controlled circuit of mine . But what I'm really seeking advice about
is how to establish why that has suddenly started causing malfunction
in *another* circuit.

In my lounge I have an infra-red remote control unit I made about 25
years ago. Push buttons in the battery powered remote toggle various
lamps, TV, hi-fi, etc via relays. (Not the garage lamps, which use an
independent circuit.) It has its own DC power supply derived from the
mains. Very reliable previously. But now, every time I return from the
garage after using the light circuit, chaos reigns. Various units are
switched on and don't respond to the remote. Removing mains power from
the master unit for a few seconds restores normality (sometimes after
two attempts).

The garage unit, powered from the mains, switches 4 parallel wired
fluorescent tubes of various types if any of several buttons are
tapped.

Access to the lounge unit is difficult and so before doing that and
opening up the master unit and trying to understand my 25 year old
circuit notes I'm seeking practical tips on how I can optimise the
forensic work please.

For example, which of these is more likely?

1. The source noise from the garage lamps has suddenly increased

2. The DC supply to the remote control receiver and relay circuitry
has suddenly become noisy.

What simple tests can I make to help me isolate the cause please? My
'scope (barely portable) is in my now rarely used shed/workshop, so
I'd prefer not to be dependent on that in this context.


--
Terry, East Grinstead, UK
 
RobertMacy <robert.a.macy@gmail.com> wrote:
On Tue, 11 Mar 2014 00:47:23 -0700, Terry Pinnell
terrypingm@deletegmail.com> wrote:

The *root* cause is plainly the set of fluorescent lights in the
garage being switched on or off (or both) via a simple relay
controlled circuit of mine . But what I'm really seeking advice about
is how to establish why that has suddenly started causing malfunction
in *another* circuit.

...snip...

Time to replace the relay with a 'cheap' solid state switch. For all you
know the chatter from that aged relay has gone out to more than twice what
it used to be. And solid state relays switch at crossover and are much
more quieter, electrically speaking.
Click to expand...

I'm voting for relay problems as well- it's an old system with relays
that's starting to act weird, plus the lamps are an inductive load.

burned contacts can cause impressive arcing, and it downward spirals
pretty fast in relays and contactors.
 
On Tue, 11 Mar 2014 00:47:23 -0700, Terry Pinnell
<terrypingm@deletegmail.com> wrote:

The *root* cause is plainly the set of fluorescent lights in the
garage being switched on or off (or both) via a simple relay
controlled circuit of mine . But what I'm really seeking advice about
is how to establish why that has suddenly started causing malfunction
in *another* circuit.

...snip...
Click to expand...

Time to replace the relay with a 'cheap' solid state switch. For all you
know the chatter from that aged relay has gone out to more than twice what
it used to be. And solid state relays switch at crossover and are much
more quieter, electrically speaking.
 
Cydrome Leader <presence@MUNGEpanix.com> wrote:

RobertMacy <robert.a.macy@gmail.com> wrote:
On Tue, 11 Mar 2014 00:47:23 -0700, Terry Pinnell
terrypingm@deletegmail.com> wrote:

The *root* cause is plainly the set of fluorescent lights in the
garage being switched on or off (or both) via a simple relay
controlled circuit of mine . But what I'm really seeking advice about
is how to establish why that has suddenly started causing malfunction
in *another* circuit.

...snip...

Time to replace the relay with a 'cheap' solid state switch. For all you
know the chatter from that aged relay has gone out to more than twice what
it used to be. And solid state relays switch at crossover and are much
more quieter, electrically speaking.

I'm voting for relay problems as well- it's an old system with relays
that's starting to act weird, plus the lamps are an inductive load.

burned contacts can cause impressive arcing, and it downward spirals
pretty fast in relays and contactors.
Click to expand...

Thanks both, I'll investigate solid state relays. But presumably they
lack that one key advantage of relays: complete electrical isolation?
I have used triacs and SCRs in circuits and can't recall any
significant problems, but that was always one factor that made me a
bit uncomfortable.

Meanwhile I'm happy to report that I fixed the immediate problem. For
some reason all those years ago I'd not added a couple of important
components to the power supply section of the circuit. It's a standard
4-terminal bridge rectifier delivering 21 V followed by a 7815
regulator. A 4k7 resistor and a 1 ľF cap are recommended across the
15V output but I'd left them off. With those now soldered in, the
noisy garage circuit no longer causes havoc.

After 25 years of largely trouble-free use, I'm guessing that the
failing relays (plus some old tubes) are now causing more noise than
the previously adequate circuit can cope with. And now that I think
about it, the relays themselves (surplus stuff I used to buy) are
probably now at least 40 years old.

--
Terry, East Grinstead, UK
 
On Tue, 11 Mar 2014 07:47:23 +0000, Terry Pinnell
<terrypingm@DELETEgmail.com> wrote:

The *root* cause is plainly the set of fluorescent lights in the
garage being switched on or off (or both) via a simple relay
controlled circuit of mine . But what I'm really seeking advice about
is how to establish why that has suddenly started causing malfunction
in *another* circuit.

In my lounge I have an infra-red remote control unit I made about 25
years ago. Push buttons in the battery powered remote toggle various
lamps, TV, hi-fi, etc via relays. (Not the garage lamps, which use an
independent circuit.) It has its own DC power supply derived from the
mains. Very reliable previously. But now, every time I return from the
garage after using the light circuit, chaos reigns. Various units are
switched on and don't respond to the remote. Removing mains power from
the master unit for a few seconds restores normality (sometimes after
two attempts).

The garage unit, powered from the mains, switches 4 parallel wired
fluorescent tubes of various types if any of several buttons are
tapped.

Access to the lounge unit is difficult and so before doing that and
opening up the master unit and trying to understand my 25 year old
circuit notes I'm seeking practical tips on how I can optimise the
forensic work please.

For example, which of these is more likely?

1. The source noise from the garage lamps has suddenly increased

2. The DC supply to the remote control receiver and relay circuitry
has suddenly become noisy.

What simple tests can I make to help me isolate the cause please? My
'scope (barely portable) is in my now rarely used shed/workshop, so
I'd prefer not to be dependent on that in this context.
Click to expand...

Don't waste the time. Often an ounce of filtering at the source of
the noise is worth a ton of effort at the affected circuit.

A snubber across the switch will likely get it. 100 ohm resistor and
..01 uf cap (in series) is a good bet. Cap has to be low inductance
ac rated or DC X3 times the line voltage and not an electrolytic - the
resistor is there to lower the Q of any resonant circuit that may be
present otherwise - so the transient doesn't "ring" and become an RF
transmitter.

That's what I use on the fluorescent's since it fits the switch
housings - and another on the audio amp for the computer because
switching it off would reset the computer.

In the case of my electric cooking range/oven it was easier to just
wind a pi filter for common mode rejection. It prevents all of the
range element switches and oven switches from interfering. (interfere
with the modem when I was on dial up). Large ferrite core, with a
pair of coils of 2 turns #8 awg stranded around it, and a 1 uf (what I
had in the junk box) 300 vac cap across the 240 VAC line, and mounted
close to the power cord connections.
 
Terry Pinnell <terrypingm@deletegmail.com> wrote:
Cydrome Leader <presence@MUNGEpanix.com> wrote:

RobertMacy <robert.a.macy@gmail.com> wrote:
On Tue, 11 Mar 2014 00:47:23 -0700, Terry Pinnell
terrypingm@deletegmail.com> wrote:

The *root* cause is plainly the set of fluorescent lights in the
garage being switched on or off (or both) via a simple relay
controlled circuit of mine . But what I'm really seeking advice about
is how to establish why that has suddenly started causing malfunction
in *another* circuit.

...snip...

Time to replace the relay with a 'cheap' solid state switch. For all you
know the chatter from that aged relay has gone out to more than twice what
it used to be. And solid state relays switch at crossover and are much
more quieter, electrically speaking.

I'm voting for relay problems as well- it's an old system with relays
that's starting to act weird, plus the lamps are an inductive load.

burned contacts can cause impressive arcing, and it downward spirals
pretty fast in relays and contactors.

Thanks both, I'll investigate solid state relays. But presumably they
lack that one key advantage of relays: complete electrical isolation?
I have used triacs and SCRs in circuits and can't recall any
significant problems, but that was always one factor that made me a
bit uncomfortable.
Click to expand...

The rectangle puck style ones are isolated. There can be small amounts of
leakage on the load side when "off", and they act funky if you run them
way under voltage. I just think of them as wall switches that light up
when they're "off".

Meanwhile I'm happy to report that I fixed the immediate problem. For
some reason all those years ago I'd not added a couple of important
components to the power supply section of the circuit. It's a standard
4-terminal bridge rectifier delivering 21 V followed by a 7815
regulator. A 4k7 resistor and a 1 ?F cap are recommended across the
15V output but I'd left them off. With those now soldered in, the
noisy garage circuit no longer causes havoc.

After 25 years of largely trouble-free use, I'm guessing that the
failing relays (plus some old tubes) are now causing more noise than
the previously adequate circuit can cope with. And now that I think
about it, the relays themselves (surplus stuff I used to buy) are
probably now at least 40 years old.
Click to expand...

SSRs off ebay will probably be cheaper than even surplus replacement
relays.
 
On Tue, 11 Mar 2014 19:39:24 +0000, Terry Pinnell wrote:

Meanwhile I'm happy to report that I fixed the immediate problem. For some
reason all those years ago I'd not added a couple of important components
to the power supply section of the circuit. It's a standard 4-terminal
bridge rectifier delivering 21 V followed by a 7815 regulator. A 4k7
resistor and a 1 ÂľF cap are recommended across the 15V output but I'd
left them off. With those now soldered in, the noisy garage circuit no
longer causes havoc.
Click to expand...

Be thankful to have managed as long as you did without the R and C.

I should be so lucky...

--
"Design is the reverse of analysis"
(R.D. Middlebrook)
 
On Tuesday, March 11, 2014 12:47:23 AM UTC-7, Terry Pinnell wrote:
The *root* cause is plainly the set of fluorescent lights in the

garage being switched on or off (or both) via a simple relay

controlled circuit of mine .

In my lounge I have an infra-red remote control unit I made about 25
years ago. Push buttons in the battery powered remote toggle various
lamps, TV, hi-fi, etc via relays. (Not the garage lamps, which use an
independent circuit.) It has its own DC power supply derived from the
mains. Very reliable previously. But now, every time I return from the
garage after using the light circuit, chaos reigns.
Click to expand...

At a guess, you'd benefit from replacing the ballast in the fluorescent
fixture, preferably with a good modern electronic unit. It'll change
the frequency of any interfering signal, at the very least.
 
You must log in or register to reply here.

Welcome to EDABoard.com

Sponsor

Back
Top