Relay with magnets

Netlist · 17th June 2006, 08:49 AM

This is an output relay from a Stage Accompany SA900C.
Can anyone tell me why the two magnets are glued to the sides of the relay?

/Hugo

dnsey · 17th June 2006, 09:01 AM

At a guess, it's to convert it into a 'bistable' relay. That way, a pulse of one polarity will switch it one way, and one of the opposite polarity the opposite. Saves having the coil permanently energised.
'Proper' versions are available, but are fairly expensive - this looks like a cheap bodge

AndrewT · 17th June 2006, 09:08 AM

Hi,
if it's a bodge, then it's a clever bodge.

I am envious of these later thinkers.

Netlist · 17th June 2006, 09:50 AM

Thanks.
The coil however is permanently energized and only one of the two contacts is used.

/Hugo

jacco vermeulen · 17th June 2006, 10:20 AM

The magnets make the relay switch off faster.

(Stage Accompany used high quality parts in those years. e.g : retail price of the Siemens B32521 MKT on the pic was around $0.25 in production years of the 900C, SA could have used a lot cheaper cap)

johnnyx · 17th June 2006, 11:07 AM

I suspect that the magnet increases the sensitivity of the coil, so that less current is needed to operate it. This makes sense if the relay is normally permanently energised.
Some high sensitivity relays have built-in magnets; the polarity of the coil must be observed, and will not operate if the polarity is reversed. I've been caught out by this when checking relays.

Netlist · 17th June 2006, 11:58 AM

Quote:

Originally posted by jacco vermeulen
The magnets make the relay switch off faster.

This sounds like a plausible explanation. After all, we want it to switch off as fast as possible. The principle escapes me though.
It's an EMC Soprel 011.51-22-001 but I can't find any info with Google.

Quote:

Originally posted by johnnyx
I suspect that the magnet increases the sensitivity of the coil,

The magnets are located near the contact points and the strongest magnetic field is exactly in line with them, not with the coil. Which doesn't mean your statement is incorrect.
The two washers I inserted take the natural position as seen in the picture.
If I try to move them, they always return to that same point.

/Hugo

jacco vermeulen · 17th June 2006, 12:39 PM

Quote:

Originally posted by Netlist
sounds like a plausible explanation.

Not plausible, it's an old trick.
Ed Wijnker is SOAphobic, like a couple overhere. Stage Accompany amplifiers "were" pretty expensive. The SA1600 i had went in protection mode far to easy.

EMC= Electro Moderna Components
Soprel is the factory.
Seulement pour les potes Belges:
http://www.efacec.pt/presentationLay...ocal=13&area=1

Netlist · 17th June 2006, 02:09 PM

Merci Jacco. Is that a division of ACEC or in any way related to it?
(Logo)

I reassembled the amp and it sounds like its build.
Clear and detailed mids and highs, well balanced sound and good control of the bass. I didn't measure but the 285W/ch is probably rather conservative.

/Hugo

ralphs99 · 17th June 2006, 02:49 PM

Hi Hugo,

The intention of the magnets is to help the relay switch off a bit faster as Jacco has suggested.

It's a technique that is used in high voltage switching. The magnets pull the arc formed as the relay opens towards the magnets because of the plasma's negative charge. As the plasma formed by the arc is now curved rather than straight across from contact to contact, is breaks slightly sooner.

This is significant where thousands of amps are being switched as it saves a lot of contact material being vapourised. Whether it's of any real use for an audio power amp where the arc length is a fraction of a millimeter is debatable.

Another technique for breaking the arc is to blow the arc out of the gap between the contacts with compressed air. I haven't seen this technique use for audio amps however!

Cheers, Ralph.

17th June 2006, 10:20 AM	#5
jacco vermeulen diyAudio Member Join Date: Oct 2004 Location: At the sea front, Rotterdam or Curaçao	The magnets make the relay switch off faster. (Stage Accompany used high quality parts in those years. e.g : retail price of the Siemens B32521 MKT on the pic was around $0.25 in production years of the 900C, SA could have used a lot cheaper cap) __________________ Not so much,.......if it says "ZM" in the corner.

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17th June 2006, 09:01 AM	#2
dnsey diyAudio Member Join Date: Mar 2004 Location: Shropshire, England	At a guess, it's to convert it into a 'bistable' relay. That way, a pulse of one polarity will switch it one way, and one of the opposite polarity the opposite. Saves having the coil permanently energised. 'Proper' versions are available, but are fairly expensive - this looks like a cheap bodge

17th June 2006, 09:08 AM	#3
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi, if it's a bodge, then it's a clever bodge. I am envious of these later thinkers.

17th June 2006, 11:07 AM	#6
johnnyx diyAudio Member Join Date: Jan 2004 Location: manchester	I suspect that the magnet increases the sensitivity of the coil, so that less current is needed to operate it. This makes sense if the relay is normally permanently energised. Some high sensitivity relays have built-in magnets; the polarity of the coil must be observed, and will not operate if the polarity is reversed. I've been caught out by this when checking relays.

17th June 2006, 02:09 PM	#9
Netlist diyAudio Moderator Emeritus Join Date: Jan 2003	Merci Jacco. Is that a division of ACEC or in any way related to it? (Logo) I reassembled the amp and it sounds like its build. Clear and detailed mids and highs, well balanced sound and good control of the bass. I didn't measure but the 285W/ch is probably rather conservative. /Hugo

17th June 2006, 02:49 PM	#10
ralphs99 diyAudio Member Join Date: Jul 2006	Hi Hugo, The intention of the magnets is to help the relay switch off a bit faster as Jacco has suggested. It's a technique that is used in high voltage switching. The magnets pull the arc formed as the relay opens towards the magnets because of the plasma's negative charge. As the plasma formed by the arc is now curved rather than straight across from contact to contact, is breaks slightly sooner. This is significant where thousands of amps are being switched as it saves a lot of contact material being vapourised. Whether it's of any real use for an audio power amp where the arc length is a fraction of a millimeter is debatable. Another technique for breaking the arc is to blow the arc out of the gap between the contacts with compressed air. I haven't seen this technique use for audio amps however! Cheers, Ralph.