Electrical advice - old fire alarm bell

[Perplexed]

DC does not have a cycle (or frequency), only AC. You will need a ~24v power supply or a step-down transformer. Like some doorbell transformers.

I suspected that was the case. I’m learning, and so far it’s not been expensive

 

[KOPBET]

I suspected that was the case. I’m learning, and so far it’s not been expensive

That's good! Learning (the hard way) can be very expensive.

 

[LesEldre]

Read all the advice then discard all but the right one. Try YouTube.

 

[Perplexed]

Ok, here’s another one that has had me stumped for a while...

I have this antique bell with two electromagnets, and the wires from each end of the EM’s are as shown on the underside - this is the way it came to me, but I had to rewire the EM’s because the rig in the past apparently had gotten too hot and the wrap around each EM had melted. I tested each newly wound EM using a variable DC power supply, and both were good. 6V DC and 12V DC, 2-3 amps, proved to work by pulling steel objects toward them. I tested the EM’s again after linking them, and again both were good. The end caps were made from Delrin. I mounted the two EM’s directly to the frame as in the original, and tested them by connecting the DC power to the ends of the two wires. They pulled the arm of the clapper to them, as expected. Then I connected the ends of each wire as shown in the pics (A and B), using shrink tubing as an extra insulator, and I tried testing by touching the power leads to the post at A and the bracket that holds the clapper arm (B), but got nothing. No response. I tried one lead on A and then the two knurled knobs at C and D, and one lead on B and then C and D, but nothing. Now I’m wondering (1) if the bolt that holds the (A) post in place from underneath should be electrically isolated where it passes through the steel base, and (2) what the knurled knobs at C and D are for, since I can’t see how they are connected to the circuit unless a wire or two is missing that bridges C or D to either A or B. I’m assuming the two knurled knobs are for the power leads, but again, I’m not sure how they’re connected to anything else unless it’s via the steel base. I do have a multimeter, but I’m not exactly sure how or where I should be measuring resistance on this setup other than to confirm the two EM’s are connected properly to each other. Any tips from you electrical wizards would be appreciated!

 

[Perplexed]

No one know how this last alarm bell should be wired up?

 

[Perplexed]

No one know how this last alarm bell should be wired up?

Got it figured out, thanks to another alarm bell that I received yesterday that was laid out the same way. Turned out that when the alarm in question came to me, one of the wires was connected to the wrong post but I assumed it was correct. When I studied the layout of the second alarm bell, I saw the error and rerouted the wire to the correct post. Voila, it works. If anyone is interested, it was Wire “B” that should have gone to Post “D.”

 

[Letfreedomring]

How are you not having reoccurring nightmares of standing next to your locker trying to remember your combination completely naked with all these school bells going off???
Or am I just projecting my own psychosis?

 

[Perplexed]

How are you not having reoccurring nightmares of standing next to your locker trying to remember your combination completely naked with all these school bells going off???
Or am I just projecting my own psychosis?

I have a dim recollection of the alarm bell going off as we all filed underneath it to exit the grade school during fire drills. It’s a pleasant memory, so it must just be you

 

[KOPBET]

Got it figured out, thanks to another alarm bell that I received yesterday that was laid out the same way. Turned out that when the alarm in question came to me, one of the wires was connected to the wrong post but I assumed it was correct. When I studied the layout of the second alarm bell, I saw the error and rerouted the wire to the correct post. Voila, it works. If anyone is interested, it was Wire “B” that should have gone to Post “D.”

The original pictures make it unclear as how the posts at the bottom are connected to the rest of the mechanism. Can you post front and back of the second alarm bell in perhaps better detail?

 

[Perplexed]

The original pictures make it unclear as how the posts at the bottom are connected to the rest of the mechanism. Can you post front and back of the second alarm bell in perhaps better detail?

The bolts labeled “A” and ”B” in the underside pic are threaded through the base plate into the two parts labeled “A” and ”B” in the topside pic. “A” contains a bolt with a point that completes the circuit with the spring steel leaf attached to the steel clapper arm, which is in turn held in place by a pair of pointed bolts (one on top, one on bottom), all of which are held in place by the bracket (labeled “B” in the topside pic) into which Bolt “B” is threaded from underneath. Originally, the leads coming off the EM’s were attached to Bolts A and B on the underside, but I found out this morning this is wrong. The wire going to Bolt B should instead go to Bolt D, which is attached to the steel base plate.

Here’s a side-by-side pic with the “new” alarm bell which came to me wired correctly; note the base plate is made of wood, hence the strip of metal connecting the post in the lower right with the steel base on which the EM’s are mounted. It’s not easily seen in the pic, but one lead from the EM’s is attached to the top of what would be “Post A” with the pointed contact, while the other lead from the EM passes over a folded piece of insulation to the strip of metal that leads to the post in the lower left corner. The layout on this second alarm bell basically has the two posts, along the lower edge, switched compared to the two posts on the black alarm bell that are mounted on the fancy tabs. I hope this makes sense!