When current flows through relay coil it creates the necessary magnetic field which then opens or closes the relay contacts.
Coil resistance is thus very crucial because if its too high it will limit the current and the relay may not work at all.
Is there any other reason as to why relay coil resistance is important?
Also how does relay coil resistance apply to electrical design?
thanks
Some relay families have many different option (AC coil, DC coil, different number of contact, different material of contacts, etc.). Some coils wound with many turns of fine wire and have quite high resistance. On one occasion, when I took resistance across the coil with a multimeter, I had OL. After some extra time spent, I grabbed another model multimeter, and it shown something around 15k. Either the first Fluke had batteries frozen, or whatnot. Any way, the finer wire, more resistance has coil, higher volts it's rated for, and less current per volt will flow. The field is obtained rather for having thousands of turns of wire around core. Coils having wire of larger gauge would have less resistance, fewer turns, higher current, and lower coil voltage. So for some relays will be listed in catalog with different coil voltages, e.g. 28 V, 24 V, 12 V, etc. Others, with heavier gauge wire may be listed for operating current of coil, not voltage. They too will have a voltage drop across the coil, but again, they can be listed by current thru coil necessary to operate the realy.
Probably those who design circuits can answer better, when it's more advantageous to have relays with voltage coils, and when it's better to use current (by the way car starter is an oversized example of current-coil relay...600A, etc.)
Since transmitted power is product of voltage and current, the same power can be achieved either by raising voltage or by increasing current. Power transmissions use prefer higher voltage, as increasing current will require heavier gauge conductors > more copper > more bucks. I don't see the same reasoning being true for miniature relays, as fine wire costs more than heavy wire per unit of weight. I guess, there may be some other considerations as what type of coil to use (besides the available voltage).