Re: Relays - plea for help!

[Raymond <Reb.barnett@xxxxxxx>]

Thanks for all the replies!

I've ordered the RC network recommended by Keith, and I'll try that
tomorrow evening along with a bulb (to provide a larger load) in series.
If that doesn't solve the problem, I'll run the wiring out of the boiler
and I'll just have to build a little housing for the bits, then do some
more head scratching when the dust from the kitchen has settled.

Ray.

> -----Original Message-----
> From: jtankard@xxxxxxx [mailto:jtankard@xxxxxxx]
> Sent: 12 October 1999 10:57
> To: REB.Barnett@xxxxxxx
> Subject: [ukha_d] Re: Relays - plea for help!
>
>
> Nigel,
>
> The off state current is a bit high, I have the Crydom data
> sheets, they do
> parts with off state draw of only 0.1mA.
>
> Can you bring the tails out to a convenient spot which will
> allow you some
> time to sort this problem ? also remember that the boiler should be
> protected with a fuse, SSR can deliver for a short period of time
> considerable amounts of current, you also need some form of
> isolator should
> any work need to be done on it you have to remember about the leakage
> current. My lighting gadget has a mechanical relay in series
> which opens
> after a short period without a triac firing this
> automatically protects the
> circuit, it also means that should the triac fail (they
> usually go closed
> circuit) that I can still switch it of by stopping firing the triac.
>
>
> John
> jtankard@xxxxxxx
>
> > -----Original Message-----
> > From: Raymond [mailto:Reb.barnett@xxxxxxx]
> > Sent: 12 October 1999 10:17
> > To: 'ukha_d@xxxxxxx'
> > Subject: [ukha_d] Re: Relays - plea for help!
> >
> >
> > Cheers Nigel.
> >
> > The SSR in question is from Maplin, page 624 of the catalogue,
order
> > code MG35Q. The specs suggest 3-32v DC input, and a
> 24-280VAC output.
> > 'Min current', which presumably means minimum sink from the
> mains side
> > for it to switch on properly, is 100mA. Max off state
> leakage is 15mA.
> >
> > I'm pretty sure the input on the boiler draws little if no
> current, and
> > is used solely for switching a bigger relay somewhere else
> on. I thought
> > that the min current spec for the SSR might mean the SSR would
never
> > switch on if the boiler draws less than 100mA from the input, but
> > presumably, by the same token, the boiler might have to
> draw 100mA for
> > the SSR to successfuly switch off?
> >
> > Just to clarify, the SSR can switch the boiler on fine, but it
can't
> > switch it off properly.
> >
> >
> > Ray.
> >
> >
> > > -----Original Message-----
> > > From: nigel.orr@xxxxxxx [mailto:nigel.orr@xxxxxxx]
> > > Sent: 12 October 1999 10:01
> > > To: REB.Barnett@xxxxxxx
> > > Subject: [ukha_d] Re: Relays - plea for help!
> > >
> > >
> > > At 09:27 12/10/99 +0100, you wrote:
> > > >The problem is as follows. With the SSR connected in
series or in
> > > >parallel to the existing timer control, I can
> successfully switch the
> > > >hot water/ CH on. However, when I turn the SSR off, I
get a high
> > > >frequency clicking from one of the relays buried inside
the
> > > boiler, that
> > > >does not sound healthy.
> > >
> > > It does sound like the boiler control isn't pulling enough
> > > current, so the
> > > resistance of the SSR is too high to let the relay fire or
> > > open the valve
> > > directly.  It would be worth measuring how much current the
> > > boiler actually
> > > draws when it fires.  The pump will probably be a couple of
> > > amps, but the
> > > boiler relay (or valve) might be a tiny amount.
> > >
> > > >volts output from the SSR. With the SSR disconnected,
> the existing
> > > >control timer seems to hold the boiler input at approx.
> 60v, but this
> > > >seems to drop to zero if it's left off for long enough.
> > >
> > > That might be a 'phantom' reading, just mains induced on the
> > > cables.  It
> > > does sound quite high, usually you get something around 10V.
 Try
> > > connecting a mains light bulb across it and see what the
> > > voltage is now, or
> > > if the bulb lights- I would guess the voltage will drop and
> > > the bulb will
> > > stay off, but I might be missing something.
> > >
> > > >My only guess is that the SSR never completely switches
off,
> > > or pulses
> > > >voltage, but I'd of thought the multimeter would have
> spotted that.
> > >
> > > It's definitely spec'ed for AC?  If it was 1/2 wave
> > > rectifying the power,
> > > the relay or valve would buzz at 50Hz.  I presume you
> don't have easy
> > > access to an oscilloscope ;-(
> > >
> > > >Consequently I can think of two solutions: to wire a
load
> > > (low wattage
> > > >lamp) in series with the output from from the SSR, to
> > > determine if it's
> > > >because the boiler represents too low a load to cause
the
> > > SSR to switch
> > > >off (because nothing to sink current from the SSR?).
> > >
> > > If it was never switching off, I would expect it to work
> fine, but the
> > > boiler wouldn't switch off.  Try connecting a bulb in
> > > parallel with the
> > > boiler and see if that solves the problem, by increasing the
> > > minimum load
> > > seen by the SSR.  What is the part number of the SSR, and
> > > where did you get
> > > it from?  I can skim through all the specs and see if
> > > anything leaps out
> > > (though SSRs _aren't_ my speciality!).  Could it be that the
> > > boiler valve
> > > is too inductive for the SSR to cope with?  That may or
> may not mean
> > > nothing to you, but it might jog Keith D's memory as I'm
sure
> > > he'll have
> > > some ideas too ;-)
> > >
> > > >more logically bin the SSR and simply use a relay
> between Comfort and
> > > >the boiler.
> > >
> > > Well that should work, if all else fails!
> > >
> > > You could also ask on uk.d-i-y if you have usenet access (or
via
> > > www.deja.com).  Someone there might have more experience of
> > > what you're
> > > attempting!
> > >
> > > Nigel
> > >
> > >
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