Relay issue

[lowell]

Yes makes sense. I blindly followed RGs instructions and failed to simultaneously use my brain.

[Enzo]

Oh I trust RG for sure, but he did say it would be interesting to find out. A diode would indeed be cheaper than a magnet.

[nickb]

Oh I trust RG for sure, but he did say it would be interesting to find out. A diode would indeed be cheaper than a magnet.

I thought RG's suggestion was a jolly good. It just so happens that I pulled a bad FRT5 polarized 24V relay today. So...I hooked it up to a bench supply set to 24V and 20mA. Relay clicks in and pulls 10mA one way round. When the other way round it fails to operate but still pulls 10mA with a 24V drop. No diode in this specimen.

[Tom Phillips]

I'm thinking that the relay design is such that a DC voltage applied to the coil in One Direction pulls in the contacts but if the DC voltage is reversed then it repels the contacts. The current draw and voltage drop would be the same in either case.

[The Dude]

Do this experiment:
take a plain old 1N4007 diode, and clip a 410 ohm resistor in parallel with it. Oh 390 ohms is a close standard value. Now try measuring the diode. I think you will find the low resistance obscures the diode function.


In my days working on pinball machines, we drove the solenoids - the coils that worked the moving parts to slap the ball - with DC voltage and transistors. Those solenoid coils would destroy a transistor in an instant, were it not for a reverse diode across each coil. COnsidering a coil might be 550 turns of #24 wire, and so very low resistance, I had to convince them they would never detect a shorted diode with an ohm meter.

That explains the resistance measurement with a DVM. I don't see how that explains the voltage drop of 9.15V. If there were a diode in the relay and it were forward biased, you'd read a diode junction (about .7V) instead of 9.15V. I don't see how it could be as simple as a snubber diode in this instance.

[J M Fahey]

The "added magnet" may be built in and cost nothing.

Armature "should" be made of soft low carbon steel, think SAE1008 or its modern incarnations ... which nowadays are harder to find, recently one of our friends in the Pickup section was worried about unobtanium 1008 and 1012 rods for his pickups.

Higher carbon steel is abbundant and cheap because of itīs mechanical properties so everybody carries it and low carbon (magnetically good) can be easily ordered ... 500 Tons minimum batch and probably a couple Months delay.

So some bright bulb at Omron goes with the higher carbon type (which retains some magnetism) and turns a problem into a feature.

Just to make it consistent they pulse each armature (or a tray full of them) in a speaker type magnetizer ... FWIW even I could precharge , say, from 40 to 120 of them on a single "kick" which proves itīs not exactly NASA technology.

Such a relay would test symmetrical to a multimeter but not to applied current.

[Enzo]

Oddly enough it reads the same in both directions. Resistance as well as semi. 410ohms/517mv.

This is what I saw, I didn't see 9v. The 517mv.

[MarkusBass]

Lowell,

Did you noticed that the schematic in the datasheet says: Bottom View? This is a standard and I would be very surprised if suddenly one company would manufacture relays with reversed polarity. No one would use such relays.
Other datasheets of similar relays have a note: VIEWED TOWARD TERMINALS (which is the same as BOTTOM VIEW).

Mark

[The Dude]

This is what I saw, I didn't see 9v. The 517mv.

Gotcha. I was going from the first post in the thread: 9.15V dropped with the relay coil polarity reversed.