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Re: Relay contact ratings.

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   I've taken apart a lot of things and I've never seen a power relay
with 120 volt rated contacts. Do whatever you want, I'm done with this
thread.


--
You can't have a sense of humor, if you have no sense.

Re: Relay contact ratings.
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Well, I obviously can't say what you've see, but here's relay with 120V
rated contacts.

http://australia.rs-online.com/web/p/electromechanical-relays/4936458 /

Sylvia.

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Mike said _power_ relay. The one in the url you posted is a
signal relay.

Ed

Re: Relay contact ratings.
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I have checked a few from my junk box, any that are intended to switch
mains power and not signal
circuits have a 240v rating.  Many were out of junked
US made equipment and made in Japan, Mexico or Taiwan.

As they are for the world market, I would think that most would be
rated 240v.

One Japan made one that is UL rated has an inductive rating of 5a
240VAC and 0.5a at 120VDC for inductive loads.

5A 120V and 32v for resistive loads.


The contact clearance is about 1mm.





Re: Relay contact ratings.
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clock,
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switching
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Still, are you going to put your hand on your heart, and say that some
unknown relay in an appliance designed for 110VAC will be safe to use at
240VAC?

That aside, this subthread related to electronic defrost timers. They
may not be using electromechanical relays at all, but semiconductor
devices.

Sylvia.


Re: Relay contact ratings.
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No, unless there was no choice but to keep the relay or device.  In
that case, I would at least examine the contact
clearance and size and compare it to a known good relay that was
suitable, or simply use the device
to drive a relay that would do the job.


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I wouldn't EVER blindly trust a solid state device designed to switch
110v on a 240v supply, unless again you could
check the ratings of the SSR or SCR. Triac etc used, and ratings of
any associated components such as
suppressors, MOV's etc that might be involved.



You just reminded me of an actual situation where this happened.

I did come across this about 20 years ago, where a disco light control
unit in a juke box imported from the USA
ran from 120v, and ran 120v 15w bulbs that were unavailable in AUS,
and blew often.  There was an internal stepdown
transformer fitted to provide the 120v needed for the entire
machine.

They wanted to change it to 240v 25w bulbs, and I will admit they did
look a hell of a lot better in the application than the 15's that were
not very satisfactory in brightness.

We were unable to determine the specs on the triacs fitted as they
only had a OEM part number on them,
but converted it to 240v use by replacing the Triacs with BT139's and
it worked well.

They were opto  and physically isolated from the logic circuit, as
well as having a separate mains rated connector and wiring
at the opposite end of the board and outer casing so there was no
problem with the safety aspect of the modification.



Re: Relay contact ratings.

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   Really?  You think the relay can only handle 120 VAC, just because
that's what poweres the timer circuit?


--
You can't have a sense of humor, if you have no sense.

Re: Relay contact ratings.
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Unless you've actually pulled one apart, and determined the exact
specification of the relay, or semiconductor device, involved, it's only
safe to assume that it's specified to perform the particular task
intended for it. It may well be a part that's specified to handle higher
voltages, but it would be rash to assume that.

Sylvia.

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Try here Sylvia

http://www.ebay.com.au/sch/i.html?_from3D%R40&_trksid3D%m570.l1313&_nkw3D%d =
efrost+timer&_sacat3D%See-All-Categories

Re: Relay contact ratings.
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http://www.ebay.com.au/sch/i.html?_from=R40&_trksid=m570.l1313&_nkw=defrost+timer&_sacat=See-All-Categories

Strange that I didn't find them. It's not as if I didn't look.

Sylvia.

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Plenty on ebay, pretty complicated though.
You have to search for "fridge defrost timer'  :-)

Rheilly

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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.

Ed

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No, you don't want to use auto relay.  If your house burn down,
insurance will not pay.  It doesn't mater whether the part can handle
it or not.


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I'm laughing at the turn this thread took.  If she installs her
own circuit, she is modifying the thing with a non-oem part,
regardless of what parts she uses in her circuit. Thus any concerns
about fire/liability/insurance/local regulations apply.  Doesn't
matter if it's flame retardant, 240VAC rated, gold plated, whatever,
the exposure is still there.

She has already indicated she would not use an automotive relay,
so it's moot as far as her project is concerned.  But I wonder,
has anyone else here actually tested one of those relays at 240VAC?
I have, and it worked fine, but I did not test to destruction,
nor for dielectric strength or flammability.

Ed


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Yes, i have, because they are cheap or free.  I also use wire wrap
wire for 110V main, they are good FUSEs.  However, i would not use
them for unattended applicants like fridge or furnace.  And i
definitely would not advice someone asking for help on usenet to use
them.

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I would not use a 12V automotive relay to switch mains voltage,
particularly inductive loads.. coil-to-contact dielectric strength of
those POS relays is << 1kV. I like to see 4kV or so. Are the housings
required to be flame retardant?  


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

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**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.

--
Trevor Wilson
www.rageaudio.com.au

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You are missing the point.  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.


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


   Once they (insurance co) determined that
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**I believe that is pretty much what I said.

--
Trevor Wilson
www.rageaudio.com.au


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