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#23667 - 03/24/03 04:31 PM noisy music system
bill woods Offline
Member

Registered: 11/21/01
Posts: 45
i had a question from a customer today that i couldn't answer. what would cause a loud static popping noise on the speakers of a sound system every time a clothes dryer door opens and closes? i'm at a total loss. anyone have an answer for this?

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#23668 - 03/25/03 07:07 AM Re: noisy music system
SvenNYC Offline
Member

Registered: 08/19/02
Posts: 1685
Loc: New York City
The dryer door pushes a small safety switch inside the cabinet (to start and stop the drum).

The switch is probably arcing and its electromagnetic pulse gets transmitted over the air (picture a spark gap transmitter and a crystal set).

This is more noticeable when you're listening to an AM radio and someone -- even in the next apartment -- switches on a gas stove with electronic ignition "tick tick tick tick"

Just electrical interference, I guess. A quick solution might be to move the stereo away from where the dryer is and plug it into a different circuit.

They might want to change that dryer switch too...it could be reaching the end of its useful life.

Just a thought.

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#23669 - 03/25/03 07:13 AM Re: noisy music system
sparky66wv Offline
Member

Registered: 11/17/00
Posts: 2339
Loc: West Virginia
Sven, sounds good to me!

(Did you receive the old switch from me yet?)

_________________________
-Virgil
Residential/Commercial Inspector
5 Star Inspections
Member IAEI

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#23670 - 03/25/03 07:55 AM Re: noisy music system
SvenNYC Offline
Member

Registered: 08/19/02
Posts: 1685
Loc: New York City
Hi Virgil,

Yesss! I DID!! Thanks! Got it this past Saturday

Weird looking thing, I didn't realize it was made out of ceramic - first time I've ever seen something like that (all the switches I've ever seen had plastic housings -- even the old ones).

I didn't email you but I wrote you a normal letter back instead - put it in the Post on Monday night.

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#23671 - 03/25/03 02:46 PM Re: noisy music system
Scott35 Offline

Broom Pusher and
Member

Registered: 10/19/00
Posts: 2724
Loc: Anaheim, CA. USA
Just an FYI,
If you can "bypass" the switch with a ceramic Capacitor, that would suppress the surge responsible for the "Pop".

Bypassing the switch means to connect a Capacitor in parallel with the switch.

Would need a cap that was able to tolerate the heat of the dryer.

Check the "Electrical Theory Area" later on, and I'll post some simple figures for this situation in there.

Scott35
_________________________
Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!

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#23672 - 03/25/03 04:29 PM Re: noisy music system
NJwirenut Offline
Member

Registered: 09/15/01
Posts: 816
Loc: Bergen County, NJ
If you are going to attempt a bypass capacitor installation, be SURE to use only AC line rated ceramic caps, with the proper UL classification markings. The AC line is subject to high voltage spikes, and the cap's dielectric needs to be able to withstand these, and if they DO fail, not to do so explosively.

I might consider doing something like this on my own appliance, but unless you are experienced in and insured for appliance repair, the potential liability issues would keep me from doing any internal "design modifications" on someone's dryer...

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#23673 - 03/27/03 12:39 AM Re: noisy music system
luciuskwok Offline
Junior Member

Registered: 12/21/02
Posts: 3
Loc: Philadelphia, PA
EMI can usually be reduced by using quality shielded cables and connectors on the sound system, including the speaker wires. The audio cables act like antennae, picking up radio noise from other appliances, local radio stations, etc.

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#23674 - 03/27/03 12:46 AM Re: noisy music system
iwire Offline
Moderator

Registered: 01/05/03
Posts: 4343
Loc: North Attleboro, MA USA
I would look to see if any of the audio cables are running close and or parallel to the dryer branch circuit.
_________________________
Bob Badger
Construction & Maintenance Electrician
Massachusetts

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#23675 - 03/27/03 01:56 PM Re: noisy music system
pauluk Offline
Member

Registered: 08/11/01
Posts: 7693
Loc: Norfolk, England
Just one point to add:

When fitting a noise-suppression capacitor across switch contacts, it's a good idea to include a small resistor in series, otherwise the contacts closing directly across the capacitor can result in excessive arcing.

Typical values are about 0.05 to 0.1uF with a series resistance of 50 to 100 ohmns.

It's possible to buy a "snubber network" which has the RC combination fitted into a single package for direct connection across the switch. Such devices will be suitably rated for 120 or 240V AC,

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#23676 - 03/27/03 04:16 PM Re: noisy music system
Bjarney Offline
Moderator

Registered: 04/10/02
Posts: 2561
Loc: West-Southern Inner-Northeast ...
http://ftp.automationdirect.com/documentation/d4user/ch2.pdf page 25 discusses snubber-component selection.

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