S
Steve Evans
- Jan 1, 1970
- 0
Anyone know?
tnx,
steve
tnx,
steve
Steve said:Anyone know?
used to absorb the reverse (flyback) voltage release from aSteve said:Anyone know?
tnx,
steve
used to absorb the reverse (flyback) voltage release from a
coil when energized source is removed quickly.
the flyback voltage is in reverse of what went in and can get
very high in level which will short out things.
the trick is to place a diode across the coil connections.
the Cathode is connected to the + side and Anode to the - side
when energized, the diode does not conduct. when source is
removed quickly, the release will generate high voltage in reverse
polarity. at this point the diode will conduct and anything above the
cut off voltage of the diode will get absorb in the diode and protect
other voltage sensitive components.
The voltage isn't "absorbed" it is prevented from developing.
Steve said:On 28 Nov 2004 04:51:28 -0800, [email protected] (dB) wrote:
That makes sense. But the diverted engery has to be dissipated
somewhere. If the diodes simply in antiparallel with the source, itll
act as a short circuit on the back emf. Why doesn't that (the energy
of that reverse pulse) destroy the diode?
Someonne else said a cap and
bleed resitor can be used to store and discharge the pulses
harmlessly, but no one esle has verfified this. Can we have some
clarification, please?
From: John Popelish [email protected]
Date: 28/11/2004 17:06 GMT Standard Time
Message-id: <[email protected]>
Steve Evans said:That makes sense. But the diverted engery has to be dissipated
somewhere. If the diodes simply in antiparallel with the source, itll
act as a short circuit on the back emf. Why doesn't that (the energy
of that reverse pulse) destroy the diode? Someonne else said a cap and
bleed resitor can be used to store and discharge the pulses
harmlessly, but no one esle has verfified this. Can we have some
clarification, please?
Steve Evans said:On Sun, 28 Nov 2004 21:52:57 -0000, "john jardine"
[snip]
Tnx, john (and others). Thats a pretty comprehensive answer, i guess.
I'll ponder on it for a while. I must say your first bold
pronouncement about coils discharging harmlessly and caps desroying
had me confused, but your explanation of these pheonomena is of
considerable help!
Steve Evans said:On Sun, 28 Nov 2004 21:52:57 -0000, "john jardine"
[snip]
Tnx, john (and others). Thats a pretty comprehensive answer, i guess.
I'll ponder on it for a while. I must say your first bold
pronouncement about coils discharging harmlessly and caps desroying
had me confused, but your explanation of these pheonomena is of
considerable help!
Somebody check me on this.
AIUI a cap stores voltage and an inductor stores current,
Steve Evans said:IIrc,. they both store *charge*.
Actually the inductor stores a magnetic field, which is converted back to a
current.
People say inductors store current because there is a direct
relationship, but there is no direct relationship to charge. Charge is a
function of the number of electrons (6 * 10^18 electrons per coloumb I
think), but that parameter is not characteristic to the stored energy in
either device, and measurement of columbs only takes you farther away from
the parameters that matter.
Active8 said:Nope. Faraday's Law states that a time varying flux (which is caused
by the "field") induces an EMF.
d(Phi)
EMF = - -------
dt
Mike, can you reconcile that please with the numerous references that say
it's a current and not a voltage that is proportional to the rate of change
in a magnetic field? I don't see how it can be both.
Active8 said:Show me a law of physics that states such a proportion
mathematically. How are you going to get a current in a transformer
secondary if it's open? Same thing with a generator or motor - the
EMF or back EMF is what we talk about.
Obvious. Should have seen that. My physics is very rusty.
But I asked (3 of my messages back) if I was correct in stating that the
snubber can't see a current higher than what the coil carried before it was
turned off. What about that?
Tom said:Steve Evans said:On Sun, 28 Nov 2004 21:52:57 -0000, "john jardine"
[snip]
Tnx, john (and others). Thats a pretty comprehensive answer, i guess.
I'll ponder on it for a while. I must say your first bold
pronouncement about coils discharging harmlessly and caps desroying
had me confused, but your explanation of these pheonomena is of
considerable help!
Somebody check me on this.
AIUI a cap stores voltage and an inductor stores current,
so the result is
that when you discharge a cap you can't see a voltage higher than what you
had put into it, and when you discharge an inductor you can't see a current
higher than what it carried before discharging.