Relay chatter

[Lenp]

Al,
The pole piece has a copper slug, or shading coil, which retards the buildup and /or collapse of the magnetic field. That's why the relay does not chatter on AC.

If the shading ring is removed the relay behaves as a DC relay. In old telephony relays, a slug was often installed on the pole piece, top or bottom, to offer a slow operate or slow release feature to a relay. Look closely at an AC relay, the pole piece under the armature has a copper ring of some sort, and that's it!

That being said, I feel that the interference that is affecting the DC relay may also be damped by the shading ring, by increasing the latency of the relays operation, like a parallel cap would. The relay would see the noise component of the DC signal much like the sine wave it was designed to operate with.

If you want more information about the magnetic properties that are affected when I get back to the office next week, I'll gather the dusty books and send more info.

Hey...Am I dating myself again!

Len

[haklesup]

I suppose the sudden appearance of a magnetic field around the relay could effect the operation of inductors in the RF reciever circuit causing reception to shift.

Well, its concievable even though I have never seen it.

Does the reciever have inductors and is the relay mounted in close proximity?

For whatever actual reason, I also think trying another relay may help.

[jwax]

haklesup- The IC is a PTC PT2294-M4, and yes, the receiver with inductors is packed in close (2 inches) to the motor. Also, did I mention the receiver appears to be a regenerative type? Very sensitive, as I get a 1,000 ft. range with only a short wire antenna and the keyfob.

[MrAl]

Hi again,

Len:
Ok thanks. I dont think i ever used a AC relay for a DC app.
I have used DC relay for AC apps many times, which is also
interesting since we are talking about chatter. The relay needs
a min of one rectifier diode and an electrolytic cap. If the cap
is too small there is much chatter. There also ends up being a bit
of a delay for turning off the coil due to the cap.

[haklesup]

Well, the part number mainly only turns up Chinese inventory sites. I couldn't find a datasheet. Mostly I was interested in the output current for the pin driving the relay but I'll just assume it's applied correctly.

At least the magnetic field - inductor theory is plausible. Several experiments will rule that in or out right away. Simplest would be to separate the relay from the receiver with a foot of wire and if it still chatters, that's not it. Just as easy would be to wave a permanent magnet near the receiver and see if it looses lock on the transmitter but that may prove inconclusive.

More experiments: Replace the relay with an equivelent value resistor and see (with a scope or LED or logic probe) if it still chatters. This eliminates the possibility the pin cannot drive an inductive load. and that the current of the load is not excessive.

You could also buffer the relay with a transistor creating an open collector configuration but alas that also takes up space. An opto isolator, transistor or SS relay might take the place of the mechanical relay alltogether depending on the load (relay contacts side) requirement.

[MrAl]

Hi again,

hakle:
I think he figured the problem was solved when he said we was
going to use the cap and leave it at that.

[jwax]

Not to beat a dead horse here, but the problem comes back (relay chatter) at lower battery voltages- closer to relay dropout, I suppose.
BUT- hacklesup got me thinking opto!
So, I replaced the 12 volt relay with a mini incandescent 14 volt bulb.
Leaning against it, I strapped a phototransistor. The phototransistor goes through a resistor, then a 5 volt relay coil, up to 12 volts. That relay contacts runs the motors 12 volts.
Note the incandescent. It still emits when its' supply cuts out for a few milliseconds, and the phototransistor doesn't notice. It stays happily on. Even if the delay is longer, now the 5 volt relay coil still sees adequate holding voltage because the 12 volts can drop substantially before the coil drops out.
Incandescents aren't dead yet!
Plus, the 5 volt relay is smaller than the 12, and the lamp/phototransistor is smaller than the electrolytic!
"Opto-isolation" at its best!

[zotdoc]

I guess this is off topic but can anyone tell me if this circuit was driving an incandescent load, could or would there be a similar problem with relay chatter?

[jwax]

In a word zotdoc, no.
The chatter was due to motor noise. Unless your lamp has very intermittent connections, no noise is produced, so no chatter.
My RF link works chatter-free with any load other than the motor.

[chribec2]

This is a very small, battery powered device- no AC available here.
The 12 VDC relay is driven by an 18-pin DIP IC.
Without the cap across the coil, and a cap across the motor, a large battery still results in chatter. The supply voltage is not dipping- the relay drive is being chopped by RF interruptions from motor noise. The caps fix that.

I realize that this may be a little late, but perhaps, I can shed a little light on this subject. The 'motor noise' is actually
the tiny sparking going on at the commutator of the motor - said motor being VERY close to the antenna of the receiver.
Any electrical spark from any source will put out E.M.I. across the entire R.F. spectrum. The motor/antenna distance you
have is close enough to cause the chatter. The 'cap across the motor' fix is used quite heavily in the model boat and plane
arenas for the same reason. The cap across the relay coil acts as a damper for what pulses do get through. The cap/coil
combo is known as a snubber circuit. An A.C. relay coil will also work quite nicely on D.C. - but not a D.C. coil on A.C.
That is known - as previously mentioned - as a buzzer! I doubt, though, that an A.C. relay would work any better in this circuit
as A.C. relays (and squirrle cage motors, too) are designed for a very narrow frequency range - 50 to 60 hrz. It's those
dang shading coils! They provide a physical damping to the incoming A.C., and therefore, their size/frequency relationship
is critical. I hope this throws a little more light on the subject.

Phil Potter.

The earth is - oh my gosh - round

P.S. - Have you ever noticed how the city stores all the electricity during the day and then in the middle of the night when you
want to use the bathroom, they dump it on the grid just as you turn on the light??!?

[chribec2]

This is a very small, battery powered device- no AC available here.
The 12 VDC relay is driven by an 18-pin DIP IC.
Without the cap across the coil, and a cap across the motor, a large battery still results in chatter. The supply voltage is not dipping- the relay drive is being chopped by RF interruptions from motor noise. The caps fix that.

I realize that this may be a little late, but perhaps, I can shed a little light on this subject. The 'motor noise' is actually
the tiny sparking going on at the commutator of the motor - said motor being VERY close to the antenna of the receiver.
Any electrical spark from any source will put out E.M.I. across the entire R.F. spectrum. The motor/antenna distance you
have is close enough to cause the chatter. The 'cap across the motor' fix is used quite heavily in the model boat and plane
arenas for the same reason. The cap across the relay coil acts as a damper for what pulses do get through. The cap/coil
combo is known as a snubber circuit. An A.C. relay coil will also work quite nicely on D.C. - but not a D.C. coil on A.C.
That is known - as previously mentioned - as a buzzer! I doubt, though, that an A.C. relay would work any better in this circuit
as A.C. relays (and squirrle cage motors, too) are designed for a very narrow frequency range - 50 to 60 hrz. It's those
dang shading coils! They provide a physical damping to the incoming A.C., and therefore, their size/frequency relationship
is critical. I hope this throws a little more light on the subject.

Phil Potter.

The earth is - oh my gosh - round

P.S. - Have you ever noticed how the city stores all the electricity during the day and then in the middle of the night when you
want to use the bathroom, they dump it on the grid just as you turn on the light??!?

Also, I can't even read what I'm writting. E.M.I. should be R.F.I.

[Droidwerkz]

I've run into this problem before with indutrial dc relays (big , 125 amp suckers) with 40VDC coil voltage at about 1/2 amp throwing current pull. the problem we had was with the current draw being too high for the source to effectively source. the relay would pull closed, open , pull closed , and open (chatter) at 40vdc . I dont remember how we solved this problem . but i do remember that the cause of teh failure was due to the relay needing more current to close than the circuit could source. the relay would pull, heat the coil, release, pull , heat the coil, release. Have you tryed using a smaller relay?

[jwax]

Tried various combinations of batteries, relays, motors, and caps.
What worked best at the time, was an opto-isolator. The incandescent used did not respond fast enough to the digital noise drop-out of the drive signal, keeping enough light output on to keep the phtodetector "on".
Guess what though? I found a different motor, more "upscale", which doesn't need any such circuitry. Must have better shielding.
A 0.1 MFD across the motor (as is typical) does the job.
Thanks!