AC or DC Solenoid Coil Info

[TrainGuy]

I acquired a seven-segment display that uses solenoids to power the segments. Not sure if they are AC or DC, nor the operating voltage. The voltage I can figure out by experimenting, but I don't know if I should be applying AC or DC. Any suggestions on how I can find out which is correct? Thanks.

 

[lord loh.]

Solenoid? I never heard of such a thing...

If you are inducing current with a magnetic field, it has to be AC. Is that what you are doing?

Could you post a picture? I would like to see it.

Thank you.

 

[Nigel Goodwin]

A solenoid is basically an electro-magnet, obviously in this application it's used to mechanically move the segments.

They can be either AC or DC, and are VERY different for the different types. If you apply DC to an AC solenoid it will overheat and burn out (assuming same the voltage).

I would be inclined to try DC first, and see how warm they get.

EPE did a PIC project a few years back using mechanical displays, if I can find the article I'll look up what they used - from very vague memory, I seem to recall it might have been 48V DC?.

 

[lord loh.]

So there is no light emission??? Just move some coloured objects using EM force to give a figure ???

Could I have a picture? What exactly is it called?

 

[zevon8]

If it is of the "flip-disk" type the applied voltage is only needed briefly. Basically the disks are metal plates either permanently magnetized or have a small magnet attached to them. When the solenoid is powered the disk will flip to align with the solenoid. They are operated as a matrix with parallel address lines and vertical columns.

These were quite common for outdoor tote-boards and similar, used in train stations, airports, etc.

They have seen a bit of a revival, using retroreflective disks and led's in the corner to illuminate the disc. 3M makes them for traffic control signs. At my work we have sold some as finished units, never really got to look inside. The appeal is that they only need power to setup the sign, and low power for the illuminating led's, compared to making the whole display from led's.

 

[TrainGuy]

I guess a couple photos will help a lot. As long as a solenoid has power applied, the segment mechanically moves and covers the hole in the mounting plate. When the power shuts off, the segment springs back and there is no longer anything covering the hole. This is part of a 1960s vintage piece of equipment that railroads used to display axle counts at a wayside defect detector (I have only one of the three digits).