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controlling a mains-powered oven

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  controlling a mains-powered oven Jim Nagel <jimnewsm13c@abbeypress.co.uk> - 2015-09-06 15:20 +0100
    Re: controlling a mains-powered oven "gareth" <no.spam@thank.you.invalid> - 2015-09-06 17:40 +0100
      Re: controlling a mains-powered oven Andy Burns <usenet.feb2014@adslpipe.co.uk> - 2015-09-06 17:56 +0100
        Re: controlling a mains-powered oven The Natural Philosopher <tnp@invalid.invalid> - 2015-09-06 18:40 +0100
          Re: controlling a mains-powered oven Bernard Peek <{bap}@gamma.shrdlu.com> - 2015-09-07 20:16 +0000
    Re: controlling a mains-powered oven Gordon Henderson <gordon+usenet@drogon.net> - 2015-09-06 18:09 +0000
      Re: controlling a mains-powered oven mick <invalid@invalid.invalid> - 2015-09-07 08:03 +0000
      Re: controlling a mains-powered oven Alan Adams <alan@adamshome.org.uk> - 2015-09-07 09:48 +0100
        Re: controlling a mains-powered oven mm0fmf <none@mailinator.com> - 2015-09-07 19:19 +0100
          Re: controlling a mains-powered oven Kallu Wiegand <spam.only@roev.de> - 2015-09-08 21:12 +0200
      Re: controlling a mains-powered oven Jim Nagel <jimnewsm13c@abbeypress.co.uk> - 2015-11-20 14:08 +0000
        Re: controlling a mains-powered oven Gordon Henderson <gordon+usenet@drogon.net> - 2015-11-21 14:23 +0000
          Re: controlling a mains-powered oven Folderol <general@musically.me.uk> - 2015-11-21 14:55 +0000
          Re: controlling a mains-powered oven rickman <gnuarm@gmail.com> - 2015-11-21 10:50 -0500
            Re: controlling a mains-powered oven Gordon Henderson <gordon+usenet@drogon.net> - 2015-11-21 19:06 +0000
              Re: controlling a mains-powered oven rickman <gnuarm@gmail.com> - 2015-11-21 20:52 -0500
                Re: controlling a mains-powered oven Gordon Henderson <gordon+usenet@drogon.net> - 2015-11-22 10:11 +0000
                  Re: controlling a mains-powered oven rickman <gnuarm@gmail.com> - 2015-11-22 10:47 -0500
                    Re: controlling a mains-powered oven Gordon Henderson <gordon+usenet@drogon.net> - 2015-11-22 18:17 +0000
                      Re: controlling a mains-powered oven rickman <gnuarm@gmail.com> - 2015-11-22 13:51 -0500
                        Re: controlling a mains-powered oven Andy Burns <usenet.feb2014@adslpipe.co.uk> - 2015-11-22 18:59 +0000
                          Re: controlling a mains-powered oven rickman <gnuarm@gmail.com> - 2015-11-22 14:26 -0500
                            Re: controlling a mains-powered oven Andy Burns <usenet.feb2014@adslpipe.co.uk> - 2015-11-22 19:50 +0000
                              Re: controlling a mains-powered oven rickman <gnuarm@gmail.com> - 2015-11-22 15:05 -0500
                                Re: controlling a mains-powered oven Andy Burns <usenet.feb2014@adslpipe.co.uk> - 2015-11-22 20:17 +0000
                                  Re: controlling a mains-powered oven Gordon Henderson <gordon+usenet@drogon.net> - 2015-11-22 20:52 +0000
                                    Re: controlling a mains-powered oven Jim Nagel <jimnewsm13c@abbeypress.co.uk> - 2015-11-27 01:06 +0000
                                      Re: controlling a mains-powered oven Gordon Henderson <gordon+usenet@drogon.net> - 2015-11-27 18:15 +0000
                                Re: controlling a mains-powered oven Gordon Henderson <gordon+usenet@drogon.net> - 2015-11-22 20:21 +0000
                                  Re: controlling a mains-powered oven rickman <gnuarm@gmail.com> - 2015-11-22 15:40 -0500
                                    Re: controlling a mains-powered oven Gordon Henderson <gordon+usenet@drogon.net> - 2015-11-22 20:54 +0000
                                      Re: controlling a mains-powered oven rickman <gnuarm@gmail.com> - 2015-11-22 16:08 -0500
                                        Re: controlling a mains-powered oven The Natural Philosopher <tnp@invalid.invalid> - 2015-11-23 05:02 +0000
                                      Re: controlling a mains-powered oven Charlie <cdknospam@msn.com> - 2015-12-11 21:27 -0500
                                        Re: controlling a mains-powered oven Theo Markettos <theom+news@chiark.greenend.org.uk> - 2015-12-12 13:53 +0000
                                          Re: controlling a mains-powered oven Charlie <cdknospam@msn.com> - 2015-12-15 22:17 -0500
                                            Re: controlling a mains-powered oven Folderol <general@musically.me.uk> - 2015-12-16 10:01 +0000
                                              Re: controlling a mains-powered oven Charlie <cdknospam@msn.com> - 2015-12-19 19:47 -0500
                                            Re: controlling a mains-powered oven Stuart <Spambin@argonet.co.uk> - 2015-12-20 12:28 +0000
                                              Re: controlling a mains-powered oven Kallu Wiegand <spam.only@roev.de> - 2015-12-20 15:59 +0100
                                                Re: controlling a mains-powered oven Stuart <Spambin@argonet.co.uk> - 2015-12-20 16:26 +0000
                                                  Re: controlling a mains-powered oven Folderol <general@musically.me.uk> - 2015-12-20 17:54 +0000
                                                    Re: controlling a mains-powered oven Kallu Wiegand <spam.only@roev.de> - 2015-12-20 23:21 +0100
                                                      Re: controlling a mains-powered oven Gordon Henderson <gordon+usenet@drogon.net> - 2015-12-21 09:52 +0000
                                                        Re: controlling a mains-powered oven Andy Burns <usenet.feb2014@adslpipe.co.uk> - 2015-12-21 12:30 +0000
                                                          Re: controlling a mains-powered oven The Natural Philosopher <tnp@invalid.invalid> - 2015-12-21 12:39 +0000
                                                        Re: controlling a mains-powered oven Folderol <general@musically.me.uk> - 2015-12-21 18:28 +0000
                                                        Re: controlling a mains-powered oven mm0fmf <none@mailinator.com> - 2015-12-22 08:52 +0000
                                                          Re: controlling a mains-powered oven The Natural Philosopher <tnp@invalid.invalid> - 2015-12-22 08:56 +0000
                                                        Re: controlling a mains-powered oven Charlie <cdknospam@msn.com> - 2015-12-22 10:53 -0500
                                                  Re: controlling a mains-powered oven rickman <gnuarm@gmail.com> - 2015-12-20 13:18 -0500
                                                    Re: controlling a mains-powered oven Paul <paul@pcserviceselectronics.co.uk> - 2015-12-22 13:44 +0000
                                                      Re: controlling a mains-powered oven rickman <gnuarm@gmail.com> - 2015-12-22 10:47 -0500
                                                        Re: controlling a mains-powered oven Paul <paul@pcserviceselectronics.co.uk> - 2015-12-22 18:33 +0000
                                                      Re: controlling a mains-powered oven Charlie <cdknospam@msn.com> - 2015-12-22 11:08 -0500
                          Re: controlling a mains-powered oven mm0fmf <none@mailinator.com> - 2015-11-22 19:42 +0000
    Re: controlling a mains-powered oven rickman <gnuarm@gmail.com> - 2015-09-07 14:25 -0400
    Re: controlling a mains-powered oven Dr J R Stockton <reply1500@merlyn.demon.co.uk.invalid> - 2015-09-07 21:10 +0100
      Re: controlling a mains-powered oven The Natural Philosopher <tnp@invalid.invalid> - 2015-09-07 23:49 +0100
        Re: controlling a mains-powered oven Alan Adams <alan@adamshome.org.uk> - 2015-09-08 09:04 +0100
          Re: controlling a mains-powered oven rickman <gnuarm@gmail.com> - 2015-09-08 05:32 -0400
            Re: controlling a mains-powered oven Folderol <general@musically.me.uk> - 2015-09-08 18:21 +0100
              Re: controlling a mains-powered oven Jim Nagel <jimnewsm13c@abbeypress.co.uk> - 2015-09-08 19:03 +0100
                Re: controlling a mains-powered oven Folderol <general@musically.me.uk> - 2015-09-08 19:11 +0100
                Re: controlling a mains-powered oven rickman <gnuarm@gmail.com> - 2015-09-08 14:15 -0400
                Re: controlling a mains-powered oven The Natural Philosopher <tnp@invalid.invalid> - 2015-09-08 22:27 +0100
                Re: controlling a mains-powered oven Theo Markettos <theom+news@chiark.greenend.org.uk> - 2015-09-09 14:05 +0100
                  Re: controlling a mains-powered oven Gordon Henderson <gordon+usenet@drogon.net> - 2015-09-09 13:10 +0000
                    Re: controlling a mains-powered oven Theo Markettos <theom+news@chiark.greenend.org.uk> - 2015-09-09 15:46 +0100
                      Re: controlling a mains-powered oven Rob <nomail@example.com> - 2015-09-09 16:08 +0000
                        Re: controlling a mains-powered oven Gordon Henderson <gordon+usenet@drogon.net> - 2015-09-09 19:14 +0000
                          Re: controlling a mains-powered oven Folderol <general@musically.me.uk> - 2015-09-09 21:00 +0100
                            Re: controlling a mains-powered oven Gordon Henderson <gordon+usenet@drogon.net> - 2015-09-09 21:59 +0000
                          Re: controlling a mains-powered oven Theo Markettos <theom+news@chiark.greenend.org.uk> - 2015-09-09 23:58 +0100
                            Re: controlling a mains-powered oven Gordon Henderson <gordon+usenet@drogon.net> - 2015-09-10 06:17 +0000
                      Re: controlling a mains-powered oven rickman <gnuarm@gmail.com> - 2015-09-09 23:48 -0400
              Re: controlling a mains-powered oven Alan Adams <alan@adamshome.org.uk> - 2015-09-08 19:02 +0100
        Re: controlling a mains-powered oven Gordon Henderson <gordon+usenet@drogon.net> - 2015-09-08 11:23 +0000
          Re: controlling a mains-powered oven mm0fmf <none@mailinator.com> - 2015-09-08 12:41 +0100
          Re: controlling a mains-powered oven Ahem A Rivet's Shot <steveo@eircom.net> - 2015-09-08 12:58 +0100
            Re: controlling a mains-powered oven Gordon Henderson <gordon+usenet@drogon.net> - 2015-09-08 13:26 +0000
              Re: controlling a mains-powered oven Ahem A Rivet's Shot <steveo@eircom.net> - 2015-09-08 14:50 +0100
                Re: controlling a mains-powered oven Gordon Henderson <gordon+usenet@drogon.net> - 2015-09-08 14:24 +0000
                  Re: controlling a mains-powered oven "A. Dumas" <alexandre@dumas.fr.invalid> - 2015-09-08 17:17 +0200
        Re: controlling a mains-powered oven Dr J R Stockton <reply1500@merlyn.demon.co.uk.invalid> - 2015-09-08 22:05 +0100
    Re: controlling a mains-powered oven Gordon Henderson <gordon+usenet@drogon.net> - 2015-12-20 10:15 +0000
    Re: controlling a mains-powered oven David <wibble@btintenet.com> - 2016-02-20 14:37 +0000
      Re: controlling a mains-powered oven Rob Morley <nospam@ntlworld.com> - 2016-02-20 14:53 +0000
      Re: controlling a mains-powered oven David <wibble@btintenet.com> - 2016-02-20 16:33 +0000
        Re: controlling a mains-powered oven Paul <paul@pcserviceselectronics.co.uk> - 2016-02-21 21:50 +0000

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#10163

In article <ddnu50F3r0tU1@mid.individual.net>,
   Kallu Wiegand <spam.only@roev.de> wrote:
> My suggestion would be a Solid-State-Relais.

Yes, of course, but you will still generate less of an arc than if the
contacts open at Max volts. Zero crossing is easy enough to detect and
anticipate so you cut the relay holding current a few milliseconds before
zero.

-- 
Stuart Winsor

Tools With A Mission
sending tools across the world
http://www.twam.co.uk/

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#10164

On Sun, 20 Dec 2015 16:26:54 +0000 (GMT)
Stuart <Spambin@argonet.co.uk> wrote:

> In article <ddnu50F3r0tU1@mid.individual.net>,
>    Kallu Wiegand <spam.only@roev.de> wrote:
> > My suggestion would be a Solid-State-Relais.
> 
> Yes, of course, but you will still generate less of an arc than if the
> contacts open at Max volts. Zero crossing is easy enough to detect and
> anticipate so you cut the relay holding current a few milliseconds before
> zero.

A relay capable of of safely breaking that kind of current takes upwards of
15mS to fire, so you would be (variably) about 3/4 the way though a complete
mains cycle.

-- 
W J G

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#10166

Am 20.12.2015 um 18:54 Folderol wrote:
> On Sun, 20 Dec 2015 16:26:54 +0000 (GMT)
> Stuart <Spambin@argonet.co.uk> wrote:
>
>> In article <ddnu50F3r0tU1@mid.individual.net>,
>>     Kallu Wiegand <spam.only@roev.de> wrote:
>>> My suggestion would be a Solid-State-Relais.
>>
>> Yes, of course, but you will still generate less of an arc than if the
>> contacts open at Max volts. Zero crossing is easy enough to detect and
>> anticipate so you cut the relay holding current a few milliseconds before
>> zero.
>
> A relay capable of of safely breaking that kind of current takes upwards of
> 15mS to fire, so you would be (variably) about 3/4 the way though a complete
> mains cycle.

A (theoretical) solution would be a propper treshold. If that 
dammned^hbad mechanical part wouldn't alter its behavier in such a short 
time! Some thousend switchings and the timing is far from good and ever 
changing.

-- 
Have a nice day!

Kallu

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#10167

In article <ddoo06Falt1U1@mid.individual.net>,
Kallu Wiegand  <spam.only@roev.de> wrote:
>Am 20.12.2015 um 18:54 Folderol wrote:
>> On Sun, 20 Dec 2015 16:26:54 +0000 (GMT)
>> Stuart <Spambin@argonet.co.uk> wrote:
>>
>>> In article <ddnu50F3r0tU1@mid.individual.net>,
>>>     Kallu Wiegand <spam.only@roev.de> wrote:
>>>> My suggestion would be a Solid-State-Relais.
>>>
>>> Yes, of course, but you will still generate less of an arc than if the
>>> contacts open at Max volts. Zero crossing is easy enough to detect and
>>> anticipate so you cut the relay holding current a few milliseconds before
>>> zero.
>>
>> A relay capable of of safely breaking that kind of current takes upwards of
>> 15mS to fire, so you would be (variably) about 3/4 the way though a complete
>> mains cycle.
>
>A (theoretical) solution would be a propper treshold. If that 
>dammned^hbad mechanical part wouldn't alter its behavier in such a short 
>time! Some thousend switchings and the timing is far from good and ever 
>changing.

And a practical solution is to use an SSR that does all the zero crossing
for you without pissing about with mechanical relays, timings and other
rubbish that went out with the arc.

Gordon

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#10168

Gordon Henderson wrote:

> use an SSR that does all the zero crossing
> for you without pissing about with mechanical relays, timings and other
> rubbish that went out with the arc.

I'd have thought you'd have a snubber to prevent that :-P

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#10169

On 21/12/15 12:30, Andy Burns wrote:
> Gordon Henderson wrote:
>
>> use an SSR that does all the zero crossing
>> for you without pissing about with mechanical relays, timings and other
>> rubbish that went out with the arc.

                                   ^^^^

Oh very good...



-- 
the biggest threat to humanity comes from socialism, which has utterly 
diverted our attention away from what really matters to our existential 
survival, to indulging in navel gazing and faux moral investigations 
into what the world ought to be, whilst we fail utterly to deal with 
what it actually is.

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#10171

On Mon, 21 Dec 2015 09:52:47 -0000 (UTC)
Gordon Henderson <gordon+usenet@drogon.net> wrote:

> In article <ddoo06Falt1U1@mid.individual.net>,
> Kallu Wiegand  <spam.only@roev.de> wrote:
> >Am 20.12.2015 um 18:54 Folderol wrote:
> >> On Sun, 20 Dec 2015 16:26:54 +0000 (GMT)
> >> Stuart <Spambin@argonet.co.uk> wrote:
> >>
> >>> In article <ddnu50F3r0tU1@mid.individual.net>,
> >>>     Kallu Wiegand <spam.only@roev.de> wrote:
> >>>> My suggestion would be a Solid-State-Relais.
> >>>
> >>> Yes, of course, but you will still generate less of an arc than if the
> >>> contacts open at Max volts. Zero crossing is easy enough to detect and
> >>> anticipate so you cut the relay holding current a few milliseconds before
> >>> zero.
> >>
> >> A relay capable of of safely breaking that kind of current takes upwards of
> >> 15mS to fire, so you would be (variably) about 3/4 the way though a complete
> >> mains cycle.
> >
> >A (theoretical) solution would be a propper treshold. If that 
> >dammned^hbad mechanical part wouldn't alter its behavier in such a short 
> >time! Some thousend switchings and the timing is far from good and ever 
> >changing.
> 
> And a practical solution is to use an SSR that does all the zero crossing
> for you without pissing about with mechanical relays, timings and other
> rubbish that went out with the arc.
> 
> Gordon

Hmmm "that went out with the arc." :(


The only proviso I'd make is that if you are doing fast switching, use the
mains itself as your switching time source. That way you can ensure you don't
inadvertently create any DC offsets with odd numbered half cycles.

-- 
W J G

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#10178

On 21/12/2015 09:52, Gordon Henderson wrote:
> And a practical solution is to use an SSR that does all the zero crossing
> for you without pissing about with mechanical relays, timings and other
> rubbish that went out with the arc.

Absolutely. So that's two of us who understand switching AC loads.

[toc] | [prev] | [next] | [standalone]

#10179

On 22/12/15 08:52, mm0fmf wrote:
> On 21/12/2015 09:52, Gordon Henderson wrote:
>> And a practical solution is to use an SSR that does all the zero crossing
>> for you without pissing about with mechanical relays, timings and other
>> rubbish that went out with the arc.
>
> Absolutely. So that's two of us who understand switching AC loads.
>
The switch that put the R in AC..


-- 
the biggest threat to humanity comes from socialism, which has utterly 
diverted our attention away from what really matters to our existential 
survival, to indulging in navel gazing and faux moral investigations 
into what the world ought to be, whilst we fail utterly to deal with 
what it actually is.

[toc] | [prev] | [next] | [standalone]

#10185

On 12/21/2015 4:52 AM, Gordon Henderson wrote:
> And a practical solution is to use an SSR that does all the zero crossing
> for you without pissing about with mechanical relays, timings and other
> rubbish that went out with the arc.

The fly in the ointment is that SSR's are more susceptible to things 
like line transients. As to relays, even SSRs may use a reed relay to 
eliminate voltage drop across the solid state devices. So they aren't as 
obsolete as you think.

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#10165

On 12/20/2015 11:26 AM, Stuart wrote:
> In article <ddnu50F3r0tU1@mid.individual.net>,
>     Kallu Wiegand <spam.only@roev.de> wrote:
>> My suggestion would be a Solid-State-Relais.
>
> Yes, of course, but you will still generate less of an arc than if the
> contacts open at Max volts. Zero crossing is easy enough to detect and
> anticipate so you cut the relay holding current a few milliseconds before
> zero.

"Less"???  With a resistive load opening the contacts at the zero 
crossing will create no arc since current is in phase with voltage and 
so also zero.  I believe the arc is largely created by inductive loads 
because of the large voltage spike caused by the large dI/dt, no?

-- 

Rick

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#10182

In article <n56r88$28s$2@dont-email.me>, gnuarm@gmail.com says...
> 
> On 12/20/2015 11:26 AM, Stuart wrote:
> > In article <ddnu50F3r0tU1@mid.individual.net>,
> >     Kallu Wiegand <spam.only@roev.de> wrote:
> >> My suggestion would be a Solid-State-Relais.
> >
> > Yes, of course, but you will still generate less of an arc than if the
> > contacts open at Max volts. Zero crossing is easy enough to detect and
> > anticipate so you cut the relay holding current a few milliseconds before
> > zero.
> 
> "Less"???  With a resistive load opening the contacts at the zero 
> crossing will create no arc since current is in phase with voltage and 
> so also zero.  I believe the arc is largely created by inductive loads 
> because of the large voltage spike caused by the large dI/dt, no?

1/ No load is PURELY resistive. The other parts may be small but not 
   always neglible with higher power loads.

2/ Contacts take TIME to move apart and most relays that you will see 
   have air gap, and at 1 mm mains voltage can arc, that is why there
   are creepage and clearance DISTANCES involved with dealing with 
   voltages generally above 50V AC and 36V DC.

Having had to replace many a mains switch or relay due to arced contacts
eroding or becoming insulated.

Even power grid switches that are immersed in oil have characteristic
pops, bangs and bubbling for switching on or off, causing some oil to 
avaporate and similar.

-- 
Paul Carpenter          | paul@pcserviceselectronics.co.uk
<http://www.pcserviceselectronics.co.uk/>    PC Services
<http://www.pcserviceselectronics.co.uk/pi/>  Raspberry Pi Add-ons
<http://www.pcserviceselectronics.co.uk/fonts/> Timing Diagram Font
<http://www.badweb.org.uk/> For those web sites you hate

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#10183

On 12/22/2015 8:44 AM, Paul wrote:
> In article <n56r88$28s$2@dont-email.me>, gnuarm@gmail.com says...
>>
>> On 12/20/2015 11:26 AM, Stuart wrote:
>>> In article <ddnu50F3r0tU1@mid.individual.net>,
>>>      Kallu Wiegand <spam.only@roev.de> wrote:
>>>> My suggestion would be a Solid-State-Relais.
>>>
>>> Yes, of course, but you will still generate less of an arc than if the
>>> contacts open at Max volts. Zero crossing is easy enough to detect and
>>> anticipate so you cut the relay holding current a few milliseconds before
>>> zero.
>>
>> "Less"???  With a resistive load opening the contacts at the zero
>> crossing will create no arc since current is in phase with voltage and
>> so also zero.  I believe the arc is largely created by inductive loads
>> because of the large voltage spike caused by the large dI/dt, no?
>
> 1/ No load is PURELY resistive. The other parts may be small but not
>     always neglible with higher power loads.

Arguing that there is parasitic effects is without value unless you can 
show they have some impact on the issue.


> 2/ Contacts take TIME to move apart and most relays that you will see
>     have air gap, and at 1 mm mains voltage can arc, that is why there
>     are creepage and clearance DISTANCES involved with dealing with
>     voltages generally above 50V AC and 36V DC.

And the AC waveform takes TIME to ramp up the voltage to a point where 
it is remotely likely to arc.  By that point the gap more than prevents 
any current from flowing.  I would guess you are thinking about the 
distance to interrupt a current which is not what's going on at this point.


> Having had to replace many a mains switch or relay due to arced contacts
> eroding or becoming insulated.
>
> Even power grid switches that are immersed in oil have characteristic
> pops, bangs and bubbling for switching on or off, causing some oil to
> avaporate and similar.

Yep, because the timing is not being controlled.

-- 

Rick

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#10189

In article <n5br5b$moj$1@dont-email.me>, gnuarm@gmail.com says...
> 
> On 12/22/2015 8:44 AM, Paul wrote:
> > In article <n56r88$28s$2@dont-email.me>, gnuarm@gmail.com says...
> >>
> >> On 12/20/2015 11:26 AM, Stuart wrote:
> >>> In article <ddnu50F3r0tU1@mid.individual.net>,
> >>>      Kallu Wiegand <spam.only@roev.de> wrote:
> >>>> My suggestion would be a Solid-State-Relais.
> >>>
> >>> Yes, of course, but you will still generate less of an arc than if the
> >>> contacts open at Max volts. Zero crossing is easy enough to detect and
> >>> anticipate so you cut the relay holding current a few milliseconds before
> >>> zero.
> >>
> >> "Less"???  With a resistive load opening the contacts at the zero
> >> crossing will create no arc since current is in phase with voltage and
> >> so also zero.  I believe the arc is largely created by inductive loads
> >> because of the large voltage spike caused by the large dI/dt, no?
> >
> > 1/ No load is PURELY resistive. The other parts may be small but not
> >     always neglible with higher power loads.
> 
> Arguing that there is parasitic effects is without value unless you can 
> show they have some impact on the issue.

You claimed with less definition

    "I believe the arc is largely created by inductive loads
     because of the large voltage spike caused by the large dI/dt, no?"

And you moan about my comment when mains cable often has 100pF per metre
capacitance (L or N to E), every connection and cable has its own 
capacitance and inductance. Some of the magnetic field of the coil of a 
relay is also in the contacts.

Show that an oven has NO parasitic effects. Especially with the several
Amps of I to create a dI (at on or off time).

> > 2/ Contacts take TIME to move apart and most relays that you will 
see
> >     have air gap, and at 1 mm mains voltage can arc, that is why there
> >     are creepage and clearance DISTANCES involved with dealing with
> >     voltages generally above 50V AC and 36V DC.
> 
> And the AC waveform takes TIME to ramp up the voltage to a point where 
> it is remotely likely to arc.  By that point the gap more than prevents 
> any current from flowing.  I would guess you are thinking about the 
> distance to interrupt a current which is not what's going on at this point.

As contacts are known to bounce on relays and switches from 1 to 20ms 
and you assume it takes ZERO time to separate contacts.
 
> 
> 
> > Having had to replace many a mains switch or relay due to arced contacts
> > eroding or becoming insulated.
> >
> > Even power grid switches that are immersed in oil have characteristic
> > pops, bangs and bubbling for switching on or off, causing some oil to
> > avaporate and similar.
> 
> Yep, because the timing is not being controlled.

Right a very simple knowledge then.


-- 
Paul Carpenter          | paul@pcserviceselectronics.co.uk
<http://www.pcserviceselectronics.co.uk/>    PC Services
<http://www.pcserviceselectronics.co.uk/pi/>  Raspberry Pi Add-ons
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#10187

On 12/22/2015 8:44 AM, Paul wrote:
> In article <n56r88$28s$2@dont-email.me>, gnuarm@gmail.com says...
>>
>> On 12/20/2015 11:26 AM, Stuart wrote:
>>> In article <ddnu50F3r0tU1@mid.individual.net>,
>>>      Kallu Wiegand <spam.only@roev.de> wrote:
>>>> My suggestion would be a Solid-State-Relais.
>>>
>>> Yes, of course, but you will still generate less of an arc than if the
>>> contacts open at Max volts. Zero crossing is easy enough to detect and
>>> anticipate so you cut the relay holding current a few milliseconds before
>>> zero.
>>
>> "Less"???  With a resistive load opening the contacts at the zero
>> crossing will create no arc since current is in phase with voltage and
>> so also zero.  I believe the arc is largely created by inductive loads
>> because of the large voltage spike caused by the large dI/dt, no?
>
> 1/ No load is PURELY resistive. The other parts may be small but not
>     always neglible with higher power loads.
>
> 2/ Contacts take TIME to move apart and most relays that you will see
>     have air gap, and at 1 mm mains voltage can arc, that is why there
>     are creepage and clearance DISTANCES involved with dealing with
>     voltages generally above 50V AC and 36V DC.
>
> Having had to replace many a mains switch or relay due to arced contacts
> eroding or becoming insulated.
>
> Even power grid switches that are immersed in oil have characteristic
> pops, bangs and bubbling for switching on or off, causing some oil to
> avaporate and similar.
>

Back in the 70's, one of my favorite and now mostly illegal power 
switches was a Mercury switch that used a movable piston and a pool of 
Mercury. Very high reliability, with a small gotcha!
A fault big enough to rupture the containment tube could spread Mercury 
and vapor all over the place. At the time, a fair number were used to 
control heating elements in the industrial ovens and Mold machines.

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#10005

On 22/11/2015 18:59, Andy Burns wrote:
> rickman wrote:
>
>> Gordon Henderson wrote:
>  >
>>>>>>> I'm only sampling the data every second - the PID control loop is
>>>>>>> running
>>>>>>> 10 times/sec.
>>>>>>
>>>>>> I'm not sure why you would run the two at different rates.  Do you
>>>>>> know
>>>>>> why?
>>>>>
>>>>> Yes. I wrote the program, so I know exactly why.
>>>>
>>>> Can you explain?
>>>
>>> Yes.
>>
>> Ok
>
> I suggest if you'd had less of the "aggressive know-all" attitude, he
> might have done so ...
>

I got fed up with his aggressive know-all attitude a while back and 
plonked him.

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#9561

On 9/6/2015 10:20 AM, Jim Nagel wrote:
> Has anybody used a Pi to control a mains-powered device?  I'm looking
> for some tips.
>
> The electronic controller of our electric double oven is no longer
> reliable -- temperature varies far too much, according to the
> independent external thermometer I bought.  Rather than spend £200 to
> replace the controller, I fancy using a Pi instead.  It could live
> inside a nearby cupboard door, with a nice big screen at eye level
> instead of the present little thing for which I have to don specs.
>
> Seems to me the Pi's job would basically be to read a temperature
> sensor in each oven (smaller upper one and larger lower one) and
> trigger relays (or nowadays maybe thyristors?) to switch various
> heating elements on and off accordingly. (That's top and bottom
> element in each oven plus a fan element in bottom oven.)
>
> Would this be feasible?  Anybody done it already?

Interesting.  Some time back when the rPi was just a gleam in the eye of 
the developers, I conversed with someone about just such a controller. 
It would have a number of isolated SSR outputs as well as isolated 
digital inputs and several thermocouple inputs.  That was when I learned 
that a thermocouple doesn't measure temperature, it measures a 
difference in temperature and the temperature of the cold junction has 
to be subtracted out (or added in depending on how you look at it).

If there were much interest in this unit I would be happy to build a 
few.  The original design was for a BeagleBone, but would be easy to 
adapt to an rPi.  I don't recall if it used I2C or SPI, but could easily 
be bit banged if nothing else.

-- 

Rick

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#9563

In comp.sys.raspberry-pi message <b201e7fe54.jim@abbeypress.net>, Sun,
6 Sep 2015 15:20:49, Jim Nagel <jimnewsm13c@abbeypress.co.uk> posted:

>Seems to me the Pi's job would basically be to read a temperature
>sensor in each oven (smaller upper one and larger lower one) and
>trigger relays (or nowadays maybe thyristors?) to switch various
>heating elements on and off accordingly. (That's top and bottom
>element in each oven plus a fan element in bottom oven.)

If, rather than switching things on and off every few seconds or
minutes, you alter the point in each mains half-cycle at which the mains
is applied to the elements, you _may_ increase the life of the elements.

-- 
 (c) John Stockton, nr London, UK.   E-mail, see Home Page.    Turnpike v6.05.
 Website  <http://www.merlyn.demon.co.uk/> - w. FAQish topics, links, acronyms
 PAS EXE etc. : <http://www.merlyn.demon.co.uk/programs/> - see in 00index.htm
 Dates - miscdate.htm estrdate.htm js-dates.htm pas-time.htm critdate.htm etc.

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#9564

On 07/09/15 21:10, Dr J R Stockton wrote:
> In comp.sys.raspberry-pi message <b201e7fe54.jim@abbeypress.net>, Sun,
> 6 Sep 2015 15:20:49, Jim Nagel <jimnewsm13c@abbeypress.co.uk> posted:
>
>> Seems to me the Pi's job would basically be to read a temperature
>> sensor in each oven (smaller upper one and larger lower one) and
>> trigger relays (or nowadays maybe thyristors?) to switch various
>> heating elements on and off accordingly. (That's top and bottom
>> element in each oven plus a fan element in bottom oven.)
>
> If, rather than switching things on and off every few seconds or
> minutes, you alter the point in each mains half-cycle at which the mains
> is applied to the elements, you _may_ increase the life of the elements.
>
I haven't ever even met someone who has had an oven element go in the 
last 30 years....


-- 
New Socialism consists essentially in being seen to have your heart in 
the right place whilst your head is in the clouds and your hand is in 
someone else's pocket.

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#9566

In message <msl493$35c$2@news.albasani.net>
          The Natural Philosopher <tnp@invalid.invalid> wrote:

> On 07/09/15 21:10, Dr J R Stockton wrote:
>> In comp.sys.raspberry-pi message <b201e7fe54.jim@abbeypress.net>, Sun,
>> 6 Sep 2015 15:20:49, Jim Nagel <jimnewsm13c@abbeypress.co.uk> posted:
>>
>>> Seems to me the Pi's job would basically be to read a temperature
>>> sensor in each oven (smaller upper one and larger lower one) and
>>> trigger relays (or nowadays maybe thyristors?) to switch various
>>> heating elements on and off accordingly. (That's top and bottom
>>> element in each oven plus a fan element in bottom oven.)
>>
>> If, rather than switching things on and off every few seconds or
>> minutes, you alter the point in each mains half-cycle at which the mains
>> is applied to the elements, you _may_ increase the life of the elements.
>>
> I haven't ever even met someone who has had an oven element go in the
> last 30 years....

I've had two go in the last 2 years. Awaiting the repair mine as we 
write.


-- 
Alan Adams, from Northamptonshire
alan@adamshome.org.uk
http://www.nckc.org.uk/

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