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Contactor coil: 50 Hz vs. 60 Hz

J

John S

Jan 1, 1970
0
No, that wasn't a hack as far as the diodes goes, that is a practical
design in a family of relays, We use large contactors with the dual
coil and diodes in them. You don't see this from the out side world but
they are incased in the encapsulation. Those particular types can have
DC going directly to them. It's just the way they are with obvious
reasons.




The app note is pointing equivalent power dissipation, as you
know relays will pull in at a lower current So I don't see a problem
here.


Why don't you put a few AC types on the bench and test them yourself?

I think you'd be surprised in what you find. Lab testing tells a lot
about what you can do.

The only problem I have found with this practice of using AC on DC is
that some AC units use material that has a high hysteresis and the
AC will help keep this down. They do this in cases where they don't use
the dual coil system. In DC operation, I've seen it over magnetize the
core and cause a little slow release on the contacts. But that may not
be such a big deal in most cases.

Have a good day.

Jamie

I have an Essex contactor which was removed from my old A/C outside
unit. It has a 24VAC 50/60 Hz coil. I can make some measurements on it
if anyone is interested.

John S
 
J

Jamie

Jan 1, 1970
0
John said:
I have an Essex contactor which was removed from my old A/C outside
unit. It has a 24VAC 50/60 Hz coil. I can make some measurements on it
if anyone is interested.

John S
If you have IR gun/camera, you should also do some comparisons.

Jamie
 
J

John S

Jan 1, 1970
0
If you have IR gun/camera, you should also do some comparisons.

Jamie


BTW, Jamie, if by IR gun/camera you are interested in coil temperature
rise, that can be done using the copper resistance vs temperature rise
method.

And, which comparisons are you referring to?

John S
 
J

Jamie

Jan 1, 1970
0
John said:
BTW, Jamie, if by IR gun/camera you are interested in coil temperature
rise, that can be done using the copper resistance vs temperature rise
method.

And, which comparisons are you referring to?

John S

I have IR equipment, I just thought that most people that work in this
field would at least have a small hand held unit. When doing quick
checks between induction and DC R it's a quick and dirty way to
determine the operating range of AC coil in a DC environment.

Most AC coil design i've seen try to balance between DC R and
induction, for obvious reasons.

We use one of the Humphrey solenoid valve series at work that employs
a single DIODE in series to operate the coil from the 120AC control
voltage in many different applications.

I suppose it's possible those units actually have a 240 AC coil in
them and that is done for 120 volt operation. Or say that it could be
done to help keep the valve from sticking, thus allowing it to buzz
just a little how ever, these unit runs perfectly quiet and if they're
buzzing I can't hear or feel it? Depends on the hysteresis in the core I
guess.

Have a good day.

Jamie
 
J

Jamie

Jan 1, 1970
0
The said:
YES JAMIE TAKE YOUR HUMPHREYS BABY PILLS...
YOU ARE HYSTERICAL...BOOWAHAHAHAHA!

THE HYSTERISIS CURVE IS A CHARACTERISTIC OF A WAVE FORM., NOT INSIDE
THE CORE BUT THE INPUT/OUTPUT SIGNAL.......

TRY AND HAVE A NICE WEEK
PATTYCAKE
TGITM

BOOWAHAHAHAHAHAHA !
Goes to show what you know about induction and construction of such things.

Buzz off..

Jamie
 
F

Fred Abse

Jan 1, 1970
0
THE HYSTERISIS CURVE IS A CHARACTERISTIC OF A WAVE FORM., NOT INSIDE
THE CORE BUT THE INPUT/OUTPUT SIGNAL.......

Go learn some magnetics theory (if you're capable).

You might learn to spell "Hysteresis" as well.
 
J

Jamie

Jan 1, 1970
0
NT said:
I got the time to do some googling, and the dual rated relays I found
were all rated at teh same voltage ac and dc, albeit with 2 different
currents. The dual rated ones I used were all a fair few years ago, I
remember it pretty well though, being struck at first by the dual
rating thing. I wonder if design has shifted over time. These old
relays were quite a lot bigger than the typical pcb ones of today,
which would fit with more L & less R in their coils.


NT
You must remember that a lot of viewers here are not or have not been
exposed to some of the large body and odd styles of relays made over the
years.

What I love is when one of the dual coils that have the Diodes in them
end up shorting a diode. THe unit will still work, it just makes the
contactor noisy, in some cases, very noisy, but they still work.

Jamie
 
E

ehsjr

Jan 1, 1970
0
NT said:
I got the time to do some googling, and the dual rated relays I found
were all rated at teh same voltage ac and dc, albeit with 2 different
currents. The dual rated ones I used were all a fair few years ago, I
remember it pretty well though, being struck at first by the dual
rating thing. I wonder if design has shifted over time. These old
relays were quite a lot bigger than the typical pcb ones of today,
which would fit with more L & less R in their coils.


NT

Thanks. I found the same thing as you when I googled - the dual
rated relays were all rated at the same voltage - and that prompted
my original question. Maybe Jamie has a specific reference to
an old relay that has the dual rating with the DC rating at ~1/2
the AC rating. Do you remember if the ones you wrote about
had dual coils - or was it just single coil relays rated that way?

I suppose it doesn't matter if those relays are no longer available,
but there is a fascination in trying to figure it out. I can't see
how/why they would make a relay that operates on DC at half the AC
rating. The physics says it can't be a single coil relay, unless
the manufacturer is playing fast and loose with the ratings.
I can see it if the thing has a cap across the coil and a dropping
resistor in series, but then I don't see why a manufacturer would
do that.

Ed
 
J

Jamie

Jan 1, 1970
0
NT said:
They were all single coil. With the right ratio of L and R, 24v ac and
12v dc will give the same coil current. It seems today's miniature pcb
relays are more R dominated, hence the currents are similar at 12v ac
and 12v dc.


NT
I think you're studdering today, seems like we're getting double post! :)

To add to that comment, we still have standard 24V AC coil relays that
we can use with 12VDC. With the R of the coil, its a good way to lower
the Q of the coil and remove side effects on the control line. It Just
happens to work out for many cases that you can do this.

Jamie
 
E

ehsjr

Jan 1, 1970
0
NT said:
They were all single coil. With the right ratio of L and R, 24v ac and
12v dc will give the same coil current.


NT

Thanks.

Ed
 
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