Relay contact ratings.

[Trevor Wilson]

"Trevor Wilson"




** Plus the telephone line - modems and TAMs drop like flies when there is
a thunderstorm.

**Quite true.

** It's an issue in many rural areas - the solution to which is fitting
varistors in the power box.

**I'm a city boy. I don't see many country products.

** Funny how microwave ovens all seem to have relays turning on the big
tranny.

**Might be something to do with the different failure modes of the two
devices.

 

[Trevor Wilson]

"swanny"
"Phil Allison"

** I have made a bit of a study of this in an attempt to find a solution.

**Mains shut down works fine in most cases, provided there is not a very
large energy storage employed. A few hundred joules should be do-able by
a serious bass driver which is normally connected to such a large amp.

 

[Phil Allison]

"Trevor Wilson"

**Might be something to do with the different failure modes of the two
devices.

** Thinking about it - it is more to do with failure mode in the oven
itself.

If a diode or high voltage cap goes west, or there is an internal short the
HRC fuse in the AC will blow.

The current surge during such events would destroy any low cost triac - but
not a relay.

Also, a relay provides high isolation from the control PCB to the AC supply.



.... Phil

 

[Trevor Wilson]

"Trevor Wilson"



** Thinking about it - it is more to do with failure mode in the oven
itself.

If a diode or high voltage cap goes west, or there is an internal short the
HRC fuse in the AC will blow.

The current surge during such events would destroy any low cost triac - but
not a relay.

**Good points.

Also, a relay provides high isolation from the control PCB to the AC supply.

**All academic now anyway. I've noticed that MOs are starting to employ
SMPS nowadays. I scored a broken, high end model from a neighbour. Lots
of IGBTs, but no relays to be seen. Naturally, the fault lies with the
IGBTs. :-(

 

[Phil Allison]

"Trevor Wilson"

**Mains shut down works fine in most cases, provided there is not a very
large energy storage employed.

** So the AC goes off when single polarity voltage on the output passes a
threshold in voltage and time - then what?

There has to be a warning LED and an auxiliary power supply to do the AC
relay control. Ideally, it should not be possible to switch the amp back on
after DC is detected.

And there still has to be relays for de thumping.

BTW

I was after a solution that could be affordably retro-fitted to any amp.

The only time a customer is willing to pay for speaker protection to be
fitted is when they see the bill for the repair of a couple of JBL 2226s
etc.



.... Phil

 

[Trevor Wilson]

Is the house (hosting the fridge) required to be fire retarded?

**Irrelvant. Whilst I don't know the specific legislation pertaining to
relays, here in Australia, ALL mains connected components (from
transformers to power leads) MUST have the requisite approval numbers
and, usually, fire retardant protection, or specific materials used in
their construction. Other jurisdictions may not have such legislation,
for whatever reason. Sylvia resides in Australia. As such, connecting
non-approved components may carry an insurance liability risk.

 

[Spehro Pefhany]

Something like the Omron G7L is properly rated for motor loads. You
could use a second relay for the heater.

Come to think of it, do you really need two contacts? If the heater is
just a few watts maybe it could be connected in series with the
compressor and shorted out to turn the compressor on.



Best regards,
Spehro Pefhany

 

[Trevor Wilson]

"Trevor Wilson"



** So the AC goes off when single polarity voltage on the output passes a
threshold in voltage and time - then what?

There has to be a warning LED and an auxiliary power supply to do the AC
relay control. Ideally, it should not be possible to switch the amp back on
after DC is detected.

**Correct. I'll email you a schematic Peter Stein used 30 years ago.
Simple, cheap, reliable and highly effective. BTW: Mains switching is
accomplished by a TRIAC.

And there still has to be relays for de thumping.

**Ah, I forgot about crappy designed amps. Perhaps another relay and
appropriate sensing will be required for that purpose. In fact, perhaps
an existing design could be utilised, using a small auxiliary power
supply and an extra relay. I guess complexity and cost needs to be
weighed up against burnt speakers.

BTW

I was after a solution that could be affordably retro-fitted to any amp.

**Depends on what you call "affordable".

The only time a customer is willing to pay for speaker protection to be
fitted is when they see the bill for the repair of a couple of JBL 2226s
etc.

**Funny about that.

 

[Trevor Wilson]

"Trevor Wilson"



** So the AC goes off when single polarity voltage on the output passes a
threshold in voltage and time - then what?

There has to be a warning LED and an auxiliary power supply to do the AC
relay control. Ideally, it should not be possible to switch the amp back on
after DC is detected.

And there still has to be relays for de thumping.

BTW

I was after a solution that could be affordably retro-fitted to any amp.

The only time a customer is willing to pay for speaker protection to be
fitted is when they see the bill for the repair of a couple of JBL 2226s
etc.

**Emails to you are bouncing. Is there a trick to your email addy?

 

[Trevor Wilson]

You are missing the point.

**No, I am not, but continue....


Once they (insurance co) determined that

the fire is caused by mis-speced component, they will deny the whole
claim. They will tell you to sue the manufacturer, or whoever made
the modification. It is utterly irrespondable to use auto components
for house main.

**I believe that is pretty much what I said.

 

[Trevor Wilson]

In such socialist societies as Australia (and coming soon to the US),
you'd better use the exact replacement and have it done by a certified
technician... otherwise no insurance coverage at all.

**Idiot. EXACTLY the same situation exists in the US. And the US, like
all Western Democracies, is, in part, a socialist nation. Always has been.

 

[Trevor Wilson]

Then, why is the fire/insurance issue "**Irrelvant"?

**I never said it was. I said that the flammability of the house was
(irrelevant).

 

[Sylvia Else]

The price of the relay at the url you posted is ridiculous.

Er, yes. It was only a randomly selected item for the purpose of the
discussion about power ratings. There are indeed much cheaper relays
available that would, on the face of it, be up to the task.

Sylvia.

 

[Sylvia Else]

The price of the relay at the url you posted is ridiculous.
Surely you can get something much cheaper and equally robust.
There are relays made for appliances like air conditioners
available from Digikey for < $5.00 so it's likely you can
get something where you are for much less than the ~ $82.00 at
the RS Australia site. You might be able to use an automotive
relay. Generally their contacts are rated at 30 or 40 amps at
12 VDC, and they'll handle 240 AC nicely.

I'd never use something that isn't expressly rated for the voltages and
currents I intend to use. There's nothing about a relay rated at 12VDC
that would guarantee that the insulation is up to use for mains voltages.

Sylvia.

 

[Sylvia Else]

Come to think of it, do you really need two contacts? If the heater is
just a few watts maybe it could be connected in series with the
compressor and shorted out to turn the compressor on.

It's not just a few watts. The rating plate says that in defrost mode
the fridge draws 450 watts. That may be the initial power when the
element is cold, but even when it's hot, it's clearly going to be
drawing significant power.

Sylvia.

 

[Trevor Wilson]

I think the problem is your language.

**Very likely a misunderstanding.


You called my post irrevant

when we are agreeing on the same thing. You called JT Idiot (He may
or may not deserve it) when he is really saying the same thing: The
US is getting more socialist, like AU.

**The implication was clear.

1) That Australia was a Socialist nation.
2) That the US was not.
3) That the US was becoming a Socialist nation.

I will state again:

ALL Western Democratic nations operate as Socialist states. Every single
one. Including the US. Always has done. Ever since the US Federal, State
and local governments began collecting taxation, the US has been
operating as a Socialist nation.

What JT IMAGINES is that Australia is more socialist than Australia.
That may be true for some parts of the society and less so for other
parts. In the case of the medical system, for instance, Australia enjoys
a largely socialised medical system. Australians are very happy with
that system. The US lacks a cohesive socialised medical system. As a
consequence, some 50-odd million Americans have extremely poor access to
good medical services. Additionally, some 60% of personal bankruptcies
in the US are due to medical bills. Here in Australia, no one loses
their home so they can stay alive.

And to get the issue back on topic, the US regulatory authorities have
considerable influence of what can and can not be connected to US mains
power. In the US, however, due to the low mains Voltage, there is far
less risk to consumers than there is here in Australia.

 

[Trevor Wilson]

Why is this a bad thing? The governement won't stop you (or me) from
experimenting on the main, but would stop us from selling unsafe
products to unsuspecting customers. Otherwise, i would have sold you
a furnace with auto relays. Don't blame me for burning down the
house.

**I don't consider regulation necessarily a bad thing. LACK of
regulation is, in general, far worse.

 

[Sylvia Else]

There are plenty of relays you can salvage out of garage opener (12V),
microwave (12V) or furnace (24V). Add a micro or 555 for less than $5
and you are done. I am doing one for my furnace timer.

Not sure about getting a 555 to run at 1 cycle per six hours.

A PIC would no doubt do the job easily, but then I'd have to invest in
hardware to program it.

Sylvia.

 

[F Murtz]

A furnace relay should work: 8A @110V, 24V coil for around $10. I
use a 5V relay to activate the 24V coil, but you can also use a
MOSFET.

we use 240 volts

 

[Sylvia Else]

A clock motor has about zero torque. Takes very little friction in
the first few gear reduction stages to stop it. hardened grease can
easily do it. Just cleaning out the dried up grease can make it work.

Mine ran for another decade after I cleaned/oiled it.
Replacement was about $13, but it failed after a week. Second replacement
timer lasted years before I retired the fridge.

The symptom of failure is that the motor is making a noise. It's a
familiar grating noise that I've heard from other aging clock motors. I
presume it's the rotor rubbing against the stator, given that the rest
of the mechanism consists of nylon gear wheels, though someone may want
to advise otherwise.

Sylvia.