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Relay spark problem
Relay spark problem
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Old 27th July 2007, 08:32 AM   #1
Dxvideo is offline Dxvideo  Turkey
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Unhappy Relay spark problem

Hi all,

In my LM4702 amplifier I am using a Finder 4052 series double contact relay for switching the 500VA mains transformer. The relay connected on both live and neutral line.
Anyway, my problem is, a really big spark appears between relays contacts while swtiching on and off. It also makes a big noise like (I dont know like what, but a big noise really frightening)
Does anyone know a solution for this?
Thanks in advance..
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Old 27th July 2007, 05:09 PM   #2
jackinnj is online now jackinnj  United States
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Relay spark problem
The relay contacts are like a pair of capacitor plates -- as they come together the capacitance increases -- so much so that the charge arcs over.

The solution is a QuenchArc -- you can buy or make -- basically a film capacitor with a resistor in series -- this dissipates the charge while the contact are moving into proximity.

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Old 28th July 2007, 01:15 PM   #3
AndrewT is offline AndrewT  Scotland
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Hi,
the relay should not be connected to Live AND Neutral.

A double pole isolation switch is normally used for mains isolation.
The switch contacts should normally have a large gap to ensure safe isolation.

A relay cannot usually meet this contact gap requirement. It can do on/off duty but not isolation.

The relay is usually fitted to the Live line only to do on/off duty.

If you have fitted a soft start circuit, then the time delayed relay is across the current limiting device. Again this is usually fitted to the Live line.
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Old 28th July 2007, 01:23 PM   #4
AndrewT is offline AndrewT  Scotland
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Quote:
Originally posted by jackinnj
The relay contacts are like a pair of capacitor plates -- as they come together the capacitance increases -- so much so that the charge arcs over.

The solution is a QuenchArc -- you can buy or make -- basically a film capacitor with a resistor in series -- this dissipates the charge while the contact are moving into proximity.
Hi,
the spark quencher usually works when the switch is breaking. The visible spark is due to the inductance in the load trying to continue drawing current when the switch opens. The faster the switch opens the higher the voltage that the load inductance creates in an attempt to jump across the opening gap. That is also part of the reason for the wide contact gap mentioned in the earlier post.

It is quite unusual to have a significant spark at switch on. Yes the air insulation in the rapidly closing gap can break down and allow the current to start flowing before the gap actually closes, but the time delay between initiation of this closing spark and the contact actually touching is tiny. In addition the current will tend to be delayed by the action of voltage/inductance/phase relationship and so little current will be allowed to flow in the instant of establishing the near zero resistance across the closing switch.
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Old 28th July 2007, 01:56 PM   #5
jackinnj is online now jackinnj  United States
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Relay spark problem
Quote:
Originally posted by AndrewT

It is quite unusual to have a significant spark at switch on. Yes the air insulation in the rapidly closing gap can break down and allow the current to start flowing before the gap actually closes, but the time delay between initiation of this closing spark and the contact actually touching is tiny. In addition the current will tend to be delayed by the action of voltage/inductance/phase relationship and so little current will be allowed to flow in the instant of establishing the near zero resistance across the closing switch.
I was recalling from a apnote written by Mallory. You're most likely correct.

It is interesting to noodle around this issue -- in CNC machining the small burst of energy caused one company to have holes go slightly out of round (or more acurately, perfect concentricity) as the power was switched off and the router bit removed.
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Old 30th July 2007, 09:18 AM   #6
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Sorry for late answering, I was out of the city.
Anyway,
The question is; should I use just a RC or a soft start circuit?
I will swich on / off only on one line thats ok.
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Old 30th July 2007, 09:41 AM   #7
AndrewT is offline AndrewT  Scotland
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But the point is;
the switch should not be sparking when you close. You said it did. Is it wired in correctly?
A switch does spark when breaking a circuit, but when enclosed as mains switches are, the spark is not normally visible. Have you wired it in correctly?

Go back and check what you have done.
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Old 30th July 2007, 09:45 AM   #8
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No no.... Its in general meaning.
Its sparking ONLY while switching to on position.
Thx
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Old 30th July 2007, 09:48 AM   #9
AndrewT is offline AndrewT  Scotland
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Quote:
Originally posted by Dxvideo
No no.... Its in general meaning.
Its sparking ONLY while switching to on position.
Thx
that is wrong.
Have you wired it correctly?
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Old 30th July 2007, 09:51 AM   #10
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Why wrong?
The relay is between mains and trafos input. Thats all! What more?
And IT IS sparking when its coils energized like a renegade!
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