Good afternoon, I have a 6 volt analog clock in a car. The clock has points in it. Where the points brake contact arcing occurs. This in-turn damages the points contact area. I am looking for an electronic circuit that will eliminate or reduce the arc. Can anyone help?
thanks
Ross

 

hi W.
Welcome to AAC.
A common fix can be s diode or resistor/capacitor 'snubber' across the contacts or the coil driving the contacts.
Do you have a photo or sketch of the clock you could post?
E

 

What part of the do you need a photo of?
points,coil?

 

Hi.
The contacts that are arcing maybe controlled by a mechanical cam wheel or an electrically operated relay, depending upon the clock design.
A photo may show us which type of operation.
E

Update:
Connect a 10nF capacitor and a 47R resistor in Series across the two arcing contacts.

 

Ok, i will have more info tomorrow. It’s points are opened by a coil I think.

 

Thank you for your help

 

Since this is in a car, the circuit would be switching DC. The arc may be caused by a back EMF from the device the contacts are switching. A diode across the switching contacts should suppress the arcing. Make sure the diode is on the external device side of the wiring. Even better, put the diode across the external device wiring as close to the device as possible.
Since we don't know what the clock contacts are switching, that is my best guess.

 

Hi.
The contacts that are arcing maybe controlled by a mechanical cam wheel or an electrically operated relay, depending upon the clock design.
A photo may show us which type of operation.
E
Update:
Connect a 10nF capacitor and a 47R resistor in Series across the two arcing contacts.

 

Hi.
The contacts that are arcing maybe controlled by a mechanical cam wheel or an electrically operated relay, depending upon the clock design.
A photo may show us which type of operation.
E

Update:
Connect a 10nF capacitor and a 47R resistor in Series across the two arcing contacts.

 

Since this is in a car, the circuit would be switching DC. The arc may be caused by a back EMF from the device the contacts are switching. A diode across the switching contacts should suppress the arcing. Make sure the diode is on the external device side of the wiring. Even better, put the diode across the external device wiring as close to the device as possible.
Since we don't know what the clock contacts are switching, that is my best guess.

 

Thanks for your help. I haven’t played with electronics for over 30 years so I am pretty rusty. What size Diode?

 

Be sure if you use a diode for arc suppression that you connect it correctly. If the battery is negative ground connect the cathode to the positive feed for the relay. You state that the clock is 6vdc. If it is being powered by 12Vdc, this is a problem and my explain why you are drawing an arc. Some older (really older cars) used 6 volt batteries and were positive grounded.
How old is this clock? Looks like it may have been designed for a 6 Volt system???

 

Yes, it is a 6v clock. I have put a 12v to 6v reducer just for the wipers and the clock. The rest of the car is now 12volt. Can you draw me a drawing just to be sure I fully understand please. What about the diode, how will I know I have one that will carry the correct volt and amps?

 

Zener Diode or Schottky Diode ?

 

Use a 1N4007 general purpose diode.



Note the diode has a band on one end. This is the cathode, the other end is the anode. A diode will conduct when the Anode is more positive than the Cathode by about 0.5 volts. And will pass a maximum of 1Amp.



The idea is to connect the diode across the inductive load (the coils of the relay) with the cathode connected to the positive supply of the relay's coil and the anode connected to the negative side. The diode will NOT CONDUCT normally, but when the coil of the relay is disconnected, then energy stored in the relay's coil will release in the opposite direction to which it was energized. This is called a CEMF voltage spike. CEMF stands for Counter Electro Motive Force. Electro Motive Force is just another name for voltage and Counter means opposite polarity.



This CEMF is proportional to how much current was flowing in the coil and is inversely proportional to how fast the current is removed. CEMF can be quite high and disruptive as you can imagine .



The purpose of the diode is to limit the CEMF spike to less than 1volt, thus avoiding the problem of a high voltage negative voltage spike damaging the activating component (transistor or relay or ??) with a negative voltage overload, and/or arcing)

 

Thank you very much. hope this will fix the problem.