Electrical advice - old fire alarm bell

[Perplexed]

Here are some close-up pics.

 

[PBramble]

Don't know much about them but a friend's dad had one hooked to an alarm clock. Would wake up the whole house every morning.

 

[KOPBET]

Here are some close-up pics.

Most likely is DC. Do you have any 6v or variable DC power supplies?

 

[Perplexed]

Most likely is DC. Do you have any 6v or variable DC power supplies?

I’ll be borrowing a variable DC unit in a couple days and see. Thanks.

 

[dennishoddy]

I don't know what he powered it with but my Uncle who was Assistant Fire Chief for many years in my home town had one of those on his back porch to call in the kids when he needed them at home.
Dinner, fire callout or whatever. When that bell resonated over the neighborhood, they knew it was time to beat feet to the house.

 

[Letfreedomring]

Ah just take a cordless screwdriver battery to it! The neighbors will let ya know if you get it right...

 

[Perplexed]

I was able to plug in a variable DC unit and hook up the fire alarm to that; at 6V, the striker moved, but weakly, so I tried 12V, starting at 2 amps but the overload protection kicked in so I bumped the amperage first to 3, then 4, with the same result. Finally at 12V and 5 amps, the striker started hitting with authority. My question now is - there’s a tiny spark that forms whenever the striker hits a screw that limits its backward travel. Is this what normally happens if any of you have a similar vintage fire alarm?

 

[kingfish]

Any time you have relay contacts opening and closing with a voltage potential across them, you are going to get a spark. That seems a little much for 12v, but it could just be your camera making it look brighter than it really is. Just be sure you don't have any gas leaks in the room when you set it off. ;-)

 

[travisstorma]

Probably completely normal. As the magnetic field collapses after power is removed from the coil it creates a high volt low amp spike.

You can likely put a diode across the contacts reverse biased to get rid of that. Many relay circuits have a diode built in to clamp that voltage spike from the collapsing magnetic field as it will damage electronics.

 

[Perplexed]

Probably completely normal. As the magnetic field collapses after power is removed from the coil it creates a high volt low amp spike.

You can likely put a diode across the contacts reverse biased to get rid of that. Many relay circuits have a diode built in to clamp that voltage spike from the collapsing magnetic field as it will damage electronics.

Thanks for the comments. I’d have to brush up on my electrical engineering to figure out how and where to use such a diode in this setup Do you have any recommendations on what sort of material online I could study to figure it out without a deep dive into the whole field of electronics?