ECN Forum Forums General Topics of the Trade Voice - Data - Video Discussion interrupter bell and adusting the contacts

I have an extra bell attached to the doorbell that goes out to my workshop. It's the old style ringer bell. It stopped working so I checked the transformer and the wiring run and all connections. I've got it narrowed down to the bell itself. After cleaning some crud off the contacts it still isn't working. I can hear the electro magnet activate, but it seems there is a crucial gap between the contact and contact arm. With some experimenting I can get it to work, but I would be interesting to know what the gap should be. Should I see 0 ohm between them when the button is open?

Wikipedia bell diagram

It should be zero ohms or very close to it across the points with the circuit open. The contacts energize the coil when the button is pushed, it starts the armature moving towards the bell. before it hits the points open and the circuit de-energizes but inertia keeps the weight going until it dings. When it comes back the circuit is re-energized and the cycle repeats.

The adjustment is simply where it seems to work best.

Just a slight clarification...

The Ohm Meter should show a very low reading (from Zero Ohms, to possibly 100 Ohms), when the Circuit is CLOSED
i.e.: The Armature (Ringer/Arm) is at rest, and the Ringer/Arm is at the "Normal Not Energized" position.
The Contact on the Armature will be Closed in this state.

The Contact opens when the Armature makes contact to the Core/Coil Assembly (or slightly prior to making contact to the assembly).
With the Contact OPEN, the Ohm Meter should read Infinity / Off-Scale.

The Bell's operation is similar to an Automobile Horn's operation.

This type of Bell may be used on AC, as well as DC Systems.

FYI, the Ringer from an older Telephone Set oscillates the Armature via the 30 Hz, 100-105VAC Ringer Current from the Telco's CO.
In the Non-Energized State, the Armature is centered between the Two Bells.
With the Ringer Current applied, the Armature is driven Side-To-Side by the Alternating Magnetic Fields produced in the Core/Coil Assembly.
Since AC is applied to the Ringer, no Cutout Contacts are used or necessary.
If filtered DC was used, a Cutout Contact would be necessary.

-- Scott

I supposed it depends on what you mean by closed. I was referring to the door bell button "opening" the circuit.

With no current flowing a meter should see a short on the bell contact.

Just semantics.

Haligan, did you get this figured out?

0 ohms was it. However it seemed to not work if the gap was too large. I would suppose there are ohmmeters out there that can read down several decimal places. Something like .005 ohms.

Thanks gents.