Fish4Fun
So long, and Thanks for all the Fish!
AFAIK the only physical difference between an AC relay//Contactor is that a DC relay relies entirely upon the DC resistance in the coil to limit current where as an AC relay/contactor uses the impedance.
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If this is false, then I need someone to set me straight.
So, if I have a Relay designed for 24Vac @ 50/60hz, and I measure its DC resistance @ 10.8 ohms and it's inductance @ 23.78mH, then I can assume it is designed for 240-280mA via the following:
Soooooo, if I wanted to power the above relay with DC, I should use ~ 10.8 * 0.25 = 2.7V OR I should use a series resistor of ~ V/(.25 * (R + 10.8)) so for a nominal 12Vdc supply, I would need roughly a 30 ohm resistor with a power rating of at least 3W. For a 5V system, I would need roughly a 10 ohm resistor rated @ 1W.
The problem with all this theory is that it doesn't work, LOL. The relay will not work at all @ 5V, and @ 12Vdc the maximum series resistance that will still reliably operate the relay is 1.25 ohms, and it "works more like 24Vac" with no added series resistance at all @ 12Vdc.
Soooo, would somebody please '"splain to Lucy" what the physical difference between an AC relay and a DC relay really is? 'Cause obviously I am confused.
Thanks
Fish
^
|
|
If this is false, then I need someone to set me straight.
So, if I have a Relay designed for 24Vac @ 50/60hz, and I measure its DC resistance @ 10.8 ohms and it's inductance @ 23.78mH, then I can assume it is designed for 240-280mA via the following:
Code:
50hz = 3.141 x 10^3 Rad/Sec
60hz = 3.769 x 10^3 Rad/Sec
(3.141 x 10^3) * 23.78mH ==> 74.70
(3.769 x 10^3) * 23.78mH ==> 89.64
24 / (74.70 + 10.8) = 280mA
24 / (89.64 + 10.8) = 240mA
Soooooo, if I wanted to power the above relay with DC, I should use ~ 10.8 * 0.25 = 2.7V OR I should use a series resistor of ~ V/(.25 * (R + 10.8)) so for a nominal 12Vdc supply, I would need roughly a 30 ohm resistor with a power rating of at least 3W. For a 5V system, I would need roughly a 10 ohm resistor rated @ 1W.
The problem with all this theory is that it doesn't work, LOL. The relay will not work at all @ 5V, and @ 12Vdc the maximum series resistance that will still reliably operate the relay is 1.25 ohms, and it "works more like 24Vac" with no added series resistance at all @ 12Vdc.
Soooo, would somebody please '"splain to Lucy" what the physical difference between an AC relay and a DC relay really is? 'Cause obviously I am confused.
Thanks
Fish