Inductive load

[geochurchi]

Hi All, we are trying to power some restored RR crossing bells from a 12 VDC power supply and the power supply burned out, I doubt it was due to the load, some suggested that we can’t do that with an inductive load, any thoughts?
Geo

 

[ronsimpson]

I think there is not a problem with inductance in the load. The Bell probably pulls too much power.

 

[AnalogKid]

12 V across 10 ohms is only 1.2 A. A more likely cause is the back EMF spike when the contacts open. There is an R-C snubber in there, but this thing was designed way before switching or other regulated supplies. A fast diode directly across the coils, like a Shottkey or a tranzorb, would be better protection. However, this now makes the device polarity-sensitive. Placing the diode across the power supply output still lets the spark happen across the timer contacts, but should be enough protection and it doesn't force polarity sensitivity onto the device.

ak

 

[geochurchi]

Here is the spec on the bell, it states 600 to 700 ma.

 

[ChrisP58]

What are the details of the power supply that failed?

 

[geochurchi]

I have no idea about the power supply, it was gone before I got involved.
Geo

 

[Pommie]

Do you have access to a multimeter? If so, can you measure it's resistance?

Mike.