Re: Relay confusion

On 2006-06-29, Roger Bourne <rover8898@xxxxxxxxxxx> 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.

relays are crude mechanical devices, get the voiltage approximately right and
they'll work after a few microseconds.

as you have noticed they are inductive and so won't respond instantly to a
voltage, and using a constant current drive can get a slightly faster
response.

similarly sized relays need a similar ammount of magnetism to operate the
contacts, to get that from a lower voltage needs less resistance:
thiker wire and fewer turns carrying more current.

total watts will be in the same ballpark.

Bye.
Jasen
.