Electrical advice - old fire alarm bell

[kingfish]

I honestly would not worry that much about it. It's worked that way its whole life.

 

[Perplexed]

I honestly would not worry that much about it. It's worked that way its whole life.

Thanks. I’d just like to learn more about the workings of these fire alarms.

I can just imagine however the school principal activating that alarm to warn of a gas leak

 

[KOPBET]

There probably is high contact resistance there. I would try to burnish the contacts with a burnishing tool or a very fine grit crocus cloth.

 

[p238shooter]

Lots of comments I could throw out at 3 am after cooking fish I caught earlier in my lake. Yep, most likely was not designed to be "rung" frequently, so a little "sparking" on the contacts to degrade them was not considered very much of a problem. Adding a capaciter across will help. Not knowing other paramaters, not able to help here. Yep, if the contacts are blackened (browned) a little clean up might be necessary. This can range from a little cardboard frrom a business card sliding back and forth to using a very small file to polish them. Again, Keep in mind, this device was not set up to ring once a day at 12 pm noon. This was to be sure it rang in an emergency, ring till something in its system fails, what ever it might be.

My opinion, clean up the contacts, ring it 49-50 times, then polish up the contacts again. Interesting thread. nifty device. Reminds me, I think I have a red strobe light from the 80s somewhere in my shop. Wonder if the capacitors are still Ok. Might have to "flash" my neighborhood. Ha ha

 

[SoonerP226]

I can just imagine however the school principal activating that alarm to warn of a gas leak

In that case, I guess he'd be warning you about the explosion that's fixin' to happen...

 

[BillM]

This might be what you need:https://www.sciencedirect.com/topics/engineering/snubber-circuit

 

[Perplexed]

Thanks for the advice, folks. I figured out what I’d need in the way of a converter to get the alarm to run off household current.

On a tangent, is there a device such that, if I decide to hook up this alarm to my doorbell, someone pushing the button will cause the alarm to go off for X seconds? Right now, the alarm works only as long as current passes through it. I rigged up a temporary push button switch, and if I pushed it about as long as I’d push a doorbell button, the alarm went off just for a second or two. I’d like it to go for say 3-5 seconds; short of someone leaning against the button, is there such a device?

 

[Perplexed]

Guess no one has any suggestions per my last post. But here’s a related issue to ponder, if you wish…

I have another fire alarm bell, constructed in a similar fashion, but which has an odd behavior when I apply 6V DC. The wires coming out of the electromagnet (EM) assembly go to Posts A and B, with the interrupter contact on Post B. Yet, when I attach the power leads to these posts and apply power, the clapper is drawn to the EM and held in place with no further movement, despite the interrupter contact being broken. I can see the contact is indeed broken via a visual inspection - there’s a definite gap between the contact on Post B and the spring steel extension coming off the clapper arm. Backing the contact out some more does nothing. When I cut the power, the clapper is pulled back by the spring. If I attach the leads to Posts A and C, the alarm functions normally with the clapper repeatedly striking the bell. Post C seems to have no wired connections at all with anything else - it’s just a raised extrusion of the base with a threaded screw in the top, so I don’t see why it should have any function. Anyone know why this might be so?

 

[Snattlerake]

Thanks for the advice, folks. I figured out what I’d need in the way of a converter to get the alarm to run off household current.

On a tangent, is there a device such that, if I decide to hook up this alarm to my doorbell, someone pushing the button will cause the alarm to go off for X seconds? Right now, the alarm works only as long as current passes through it. I rigged up a temporary push button switch, and if I pushed it about as long as I’d push a doorbell button, the alarm went off just for a second or two. I’d like it to go for say 3-5 seconds; short of someone leaning against the button, is there such a device?

Timer relay module. Sorry I've not read the entire thread to know the voltages required.
Are you running A/C or D/C to the bell?

 

[Bocephus123]

Guess no one has any suggestions per my last post. But here’s a related issue to ponder, if you wish…

I have another fire alarm bell, constructed in a similar fashion, but which has an odd behavior when I apply 6V DC. The wires coming out of the electromagnet (EM) assembly go to Posts A and B, with the interrupter contact on Post B. Yet, when I attach the power leads to these posts and apply power, the clapper is drawn to the EM and held in place with no further movement, despite the interrupter contact being broken. I can see the contact is indeed broken via a visual inspection - there’s a definite gap between the contact on Post B and the spring steel extension coming off the clapper arm. Backing the contact out some more does nothing. When I cut the power, the clapper is pulled back by the spring. If I attach the leads to Posts A and C, the alarm functions normally with the clapper repeatedly striking the bell. Post C seems to have no wired connections at all with anything else - it’s just a raised extrusion of the base with a threaded screw in the top, so I don’t see why it should have any function. Anyone know why this might be so?



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That’s a nice one