Re: Relay confusion

Roger Bourne wrote:

Hello all,

Today I was introduced to the wide world of magnetic relays (for SPDT
switching applications)... .Push a current through the coil of the
relay--> creates magnetism --> makes the mechanical METAL switch flip
position, and TA-DAH you have an SPDT with practically nil "switch on"
resistance capable of passing high currents (in the As).
The problem that I have with relays is to do with their data***
contents. Now I am more or less familiar with inductors; their
inductance varies with frequency alongside their series resistance but
their inductance+serires resistance is more or less constant at low
frequencies.
How is it then that the [coil inductance + the coil resistance]
caracteristics vary with the rated voltage of the coil (I assume that
the rated voltage is the voltage drop accross the inductor used to flip
the switch) in order to maintain a steady power consumption?
What I am missing ?
Does the "L+ ESR" of the coil really increase/decrease with its voltage
drop ? Seems odd.

I know that I must be not understanding a fundamental principle, since
various datasheets all have the same varying coil inductance w.r.t.
their rated voltage.

This "pseudo-problem was discovered" when scouring randomly-chosen
relay datasheets in order to find how relays are typically driven. Are
there ICs out there whose task is to drive relays. I.e. they source a
steady current of lets say 50 mA to one of the relay coil's terminal
while the other coil terminal is tethered to a power supply node ? A
typical digital control signal will simply not do the trick. Is there a
typical approach for driving relays?

All manners of feedback will be appreciated.

Kind Regards -Roger

not exactly sure what your looking for but how ever.
maybe its the pull and holding currents your looking at?
relays require more current to get the contacts toward the
magnetic core than it does to hold it there.
as the contact arm gets closer to the core the magnetic
field becomes stronger! thus once it's fully on it may only
require half the current to hold it on than what it did to
get it started.
in fuel injected engines you have what is called a
Peak and Hold injector which in it self, is a magnetic actuator..
more current is applied to get it to the full open position and
then less current is needed to hold it there ! in logic this
could be stated as hysteresis;



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