Electric Bell - AC or DC?

[Br4nd0n]

I have a 6" vibrating electric bell that is old and all "nameplate" info has deteriated. I think it's an AC bell, but I'm sure someone here can verify for me.

The bell has a black and red leads which are each connected to two separate coils and then together at the top of a small contact block which appears to do nothing other than joint these wires. One side before the contact block has a small device wired in series which I believe to be a diode. The resistance across the leads is 45K ohms and can only be read one direction.
When the plunger is activated by hand, there are no contacts that open to break the circuit which I think is required by a DC bell.

Based on this, it seems to me that this bell requires AC. Am I right to think that the alternating current in conjunction with the diode creates the wanted "chatter" of the plunger against the bell? If so, should I assume it's good ol' 120V? Searching the web, 12/24v DC and 120V AC seems to be the availability of this type of bell.

 

[iwire]

If so, should I assume it's good ol' 120V?

Well if you assume it is 120 VAC and it is not the smoke will escape.

On the other hand if you assume it is 12 volts and work up from there you may find what works without smoke.

 

[templdl]

Seems to me that you intend to replace it. As such there probably are 2 wires that it attached to. Have someone activate the PB that rings the bell and simply take your meter an measure the voltage. If the circuit is dead why would you try to find a suitable replacement when an entire new power supply is required. The important think is to assure that the wires are intact as that's the hard part, running new wires.

 

[fmtjfw]

If it is part of a fire alarm system, then it is probably DC, but I would expect a contact that would break the circuit on the bell to make it "ding" more than once. Fire alarms are usually 24VDC

The diode in fire alarm bells is there so that a reverse (non operating) voltage can be applied at all times to insure that the circuit is not broken. The voltage is switched to normal to ring the bell.

If it is a signalling bell (1 ding means "George come to the front", 2 dings means "repel boarders", ...) then it may be DC as well.

Just Guessing:roll:

 

[gar]

120724-1010 EDT

Br4nd0n:

It is probably an AC bell. Think about it. If there is no contact to break the circuit, then if you apply a DC input to a solenoid the core will move to one position and stay put until the DC is removed.

Yes, there is probably a diode. If you have a Simpson 260 and you put it on the R*10,000 range, then a higher source voltage is used for the resistance measurement than on the lower ranges. On the 260 R*10,000 range a 1N4148 reads about 6000 ohms, and an MR752 reads about 5000 ohms in the forward direction. With a Fluke 27 in the resistance position the respective readings are both about 1.2 megohm, and in diode mode the respective readings are 0.56 and 0.44 . Diode mode is essentially a voltage drop measurement.

These two diodes would be lower and higher current ratings than the diode in your bell.

The diode cuts in half the pulse excitation frequency to the bell, from 120 Hz to 60 Hz.

Momentarily try 12 V AC. If that doesn't work, then 24 V AC.

Also use an AC meter with an input capacitor to measure the voltage to the bell, but with no bell. Activate the pushbutton or other source and see what is the no-load applied voltage. The Fluke 27 in AC volts has an internal input capacitor. This removes any DC component. The Simpson 260 does not have an input capacitor in AC unless you switch to the Output position.

.

 

[iwire]

I guess we all have our own ideas but mine was that the OP had a bell in his hand from somewhere unknown and is trying to figure out the voltage.

If it was still in it's place I would assume the voltage would be evident by the wiring at the bell and what supply it was connected to.

 

[Besoeker]

How much would a new bell cost?
Just replace it.

 

[iwire]

How much would a new bell cost?
Just replace it.

You will never be a Yankee.

To foreigners, a Yankee is an American.
To Americans, a Yankee is a Northerner.
To Northerners, a Yankee is an Easterner.
To Easterners, a Yankee is a New Englander.
To New Englanders, a Yankee is a Vermonter.
And in Vermont, a Yankee is somebody who eats pie for breakfast.

Yankees are known for being fiscally conservative ....... cheap.

 

[Besoeker]

You will never be a Yankee.
Yankees are known for being fiscally conservative ....... cheap.

The Scots also. Fugal.
So I'd fit in....real good...

Slightly more seriously, we moved into our current house about six rears ago.
I fitted new doorbells at both the front and back. They are wireless, and by a long way, simpler to install than trying to wire in something mains connected.
And inexpensive.
I can select different chimes or even a voice message.
For the back door I recorded "You have a back door visitor."
Our good friend Nancy was over with us for a bit and decided to change it to a rather more earthy message about what granted the right of entry.
And entry wasn't about the back door.
Fun when we'd had a few glasses of wine.