NT wrote:
On Sep 9, 5:33 am, ehsjr wrote:
Jamie wrote:
ehsjr wrote:
Jamie wrote:
ehsjr wrote:
NT wrote:
On Sep 2, 8:41 pm, John Fields wrote:
Snipped a lot of repetitious, self serving nonsense.
and if the relay is
designed to operate on AC with a certain RMS current in its
coil, how
can it possibly overheat if that current is DC?
With the same current it wont, with higher curren ti will. IIRC
you
proposed using 174v rms,
No, I merely added a capacitor across the output of _your_ proposed
full wave rectified 120 VRMS 60Hz source (170V peak) in order to
get
smoothed DC closer to the relay's must-make current.
fwliw I said use diodes, you came back with a FW BR. I dont think it
matters.
---
Then show me your circuit.
Just in case you've forgotten, your suggestion was to use a 240V AC
relay using diodes and 120V mains.
---
that would be ok on your specific relay, but
not a universal solution.
???
Your proposd BR+C delivers the right i for one specific relay. For
some relays it will fry them.
---
Show me.
If you want to go get some specs of other relays, you can. This is
starting to get silly.
Worth investigating, to me. JF gave a specific relay & numbers. I
tried to find a relay to support the idea that an AC/DC relay would
be happy with DC voltage about 50% of AC rating. Can you please
provide a reference?
Meanwhile, what I did find was an ap note from Tyco entitled
"Operating DC Relays from AC and Vice-Versa" .
http://relays.te.com/appnotes/app_pdfs/13c3250.pdf
It does not agree with the DC at ~50% of AC rating idea. It uses
the example of a KR series relay coil. Their example uses a 12
volt AC relay fed by DC. The example states that the "DC voltage
cannot exceed 9.8 volts", and "should not be lower than 7.35 volts".
Thus the DC range would be ~61%(minimum) to ~81% (maximum) of the
12VAC rating.
Extrapolating, it does agree with the idea of BR+C fed by 120 for
the 240 volt relay, insofar as the DC voltage:
~146VDC min to ~194VDC max, which makes the midpoint ~170VDC.
That's very close to ~168 from the BR+C
Regarding coil ratings, I've worked with DC relays, and I've worked
with AC relays, but I haven't worked with AC/DC coil relays, so
I can't speak from experience with them, and I haven't found
anything yet specifically dealing with that, other than the
link I found to Tyco. So a specific link or links would be
most helpful.
Thanks,
Ed
You must remember that AC coil relays are wound a little different,
its not just induction here. Inter pole windings help keep the AC
coil from chattering the armature. I am sure under DC operation, this
may effect the calculations.
There are some AC coil relays that do not do this and thus the 50%
voltage for DC should come close, but then again, DC R in the coil also
plays a role in this.
Jamie
Your post contains nothing specific and does not address
my question.
I am looking for a specific link or links that shows a datasheet,
ap note, or example of a relay that NT has in mind. Do you have one?
I want specifics, like John Fields posted; the specs that NT
said you could get: "If you want to go get some specs of other
relays, you can." The specs I have been able to find so far
do not demonstrate what NT was talking about, thus my post
asking for a reference.
Ed
Don't be anal, they make relays that will do AD/DC because they have a
diode imbedded in them. The voltage ratings are the same. The coil is
actually of DC type.. They also have relays with shunt diodes built into
them, for those you need to insure the polarity is correct and are
strictly DC only.
We also deal with solenoids to operate in the same manner..
Scroll down and read about AC coils, I am sure if you're looking for
some more detailed information you can find it, but this will explain
some of the differences.
http://www.ehow.com/about_6498402_di...elay-coil.html
Jamie
I don't know how to make it clear enough for you to understand.
While I do appreciate your attempt to help, I must say it misses
the point.
I want a *specific* link to an *AC/DC* relay of the type *NT*
had in mind, or to an ap note or reference that discusses a relay
coil that is rated for *both* AC and DC as he indicated.
Do you have a link to what NT was talking about? Here's what
he said:
"The various ones I've seen that have coil 2 ratings, one for ac one
for dc, have consistently had the dc coil rating be half the ac
voltage rating."
I _do not_ need generalizations, hand waving and condescending
responses. You mentioned a relay that will "do" DC because it
has an imbedded (sic) diode and say "The voltage ratings are the
same." That is *NOT* what NT said. He talks about the dc
coil rating being half the ac rating.
Ed
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