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Re: Relay contact ratings.
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It could be a reference to the absence of bearings - except to the
extent that the metal axle rotates in a hole in the plastic housing. At
least, that's the situation in the one I have.

Perhaps I shouldn't be concerned about having a "genuine" part, because
the original looks about as cheaply made as it could get while still
working at all.

Sylvia.

Re: Relay contact ratings.
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That could be a problem.  Mine has a standard clock motor with metal
case and bronze-looking bearings.

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.
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Re: Relay contact ratings.

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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.

Re: Relay contact ratings.
On Thu, 08 Dec 2011 17:50:39 +1100, Sylvia Else

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---
The contacts are rated at 10A for either 250VAC or 30VDC, so 250VAC *
10A = 2500VA, and 30VDC * 30A = 300W.

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Re: Relay contact ratings.
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That makes more sense. RS Components don't help by reversing the order
of the power ratings relative to the voltage and current ratings.

Quoting power ratings seems redundant.

Sylvia

Re: Relay contact ratings.
"John Fields" .
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** Problem being, there is simply not enough gap available to break the arc
that forms if the DC ratings are exceeded.

For the type of relay in question, a permanent arc will form with DC if the
current flow is say 10 amps and the voltage across the contacts is over 40
volts.  This means there is over 400 watts of heat, mostly being dissipated
into the contacts and destroying them in a few seconds.

In the world of high powered audio amplifiers it is still common to see such
relays used to protect speakers from DC high fault currents and turn on/off
transients. In the case of former, the relay is not capable of doing the
job.



...   Phil



Re: Relay contact ratings.
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**Tapco CP500 anyone? Crap design, with useless relay protection.

--
Trevor Wilson
www.rageaudio.com.au

Re: Relay contact ratings.
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Seen that happen. Contacts weld, amp and speakers go boom.

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Re: Relay contact ratings.

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

 Conclusions are:

1. There is no readily available relay capable of breaking the voltages and
currents involved if a 1000 wpc amp goes DC.

2.  If you wire a changeover relay so it shorts the speaker and disconnects
the amp at the same time - chances are good the speakers will be OK,  but
the relay contacts will be burnt by the resulting arc to ground.  The amp
must have DC rail fuses if this is to work.

3.  A large ( ie octal base ) relay with 4mm clearance contacts PLUS a
strong magnet next to the contacts CAN
work with amps up to about 400wpc. The magnet pulls at the arc and helps
break it.

4.  A triac "crowbar" will also work but gives no on/off transient
suppression. The amp must be able to take a dead short without internal
failure and not have response down to subsonics or DC.




...  Phil



Re: Relay contact ratings.
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**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.

--
Trevor Wilson
www.rageaudio.com.au

Re: Relay contact ratings.

"Trevor Wilson"

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** 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







Re: Relay contact ratings.
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**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.

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**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.

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**Depends on what you call "affordable".

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**Funny about that.

--
Trevor Wilson
www.rageaudio.com.au

Re: Relay contact ratings.
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**Emails to you are bouncing. Is there a trick to your email addy?

--
Trevor Wilson
www.rageaudio.com.au


Re: Relay contact ratings.
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A big capacitor in series with the output :)




Re: Relay contact ratings.
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There are aftermarket universals better than the OEM part
http://compare.ebay.com/like/290638915750?var3D%lv&ltyp3D%AllFixedPriceItem =
Types&var3D%sbar

Re: Relay contact ratings.
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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.


Re: Relay contact ratings.
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parthttp://compare.ebay.com/like/290638915750?var=lv <yp=AllFixedPriceIt...
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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.

Re: Relay contact ratings.

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CD4060, CMOS logic, an R-C astable and a 14-stage divider chain in
one DIP package, but not strong enough to drive a relay directly like
an LM555 would be.

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--
⚂⚃ 100% natural

---

Re: Relay contact ratings.
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Sylvia,

Try a PICAXE 08M2 - it costs $2.50 in one off's and programs in BASIC.
Software and examples are free from www.picaxe.co.uk
It is not uncommon for people totally new to the PICAXE have had them
running programs within 30 minutes of getting their first chip.

The only stuff you need to program one is a serial port (RS232 or TTL
level) and a resistor.

--
We have failed to address the fundamental truth that endless growth is
impossible in a finite world.

Re: Relay contact ratings.

We have failed to address the fundamental truth that endless growth is
impossible in a finite world.

---
Not true; consider Moore's law.

--
JF

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