I've often wondered about this, but never had time to do any testing. Do you do this in production or personal projects? Have any data you can share? Maybe I don't understand what goes on inside a relay. Does the coil resistance change in steady state? Does it act like an inductor in series or parallel with a resistor (or both)? Maybe someone can clarify this for me, but here's the way I look at it: Taking the original poster's 5V relay @ 80mA, the coil resistance should be 62.5 Ohm. So, if we assume the wall-wart is operating at nominal voltage (eg 9V) and the transistor saturation voltage is negligible, the coil current is 9V/62.5Ohm = 144mA. That's close to twice the specified coil current. Realistically, the voltage will probably be higher, since the wall wart is rated at 380mA and thus should not be all that loaded with 80mA. So the coil current is likely to be even higher. Ok, so we need a bigger transistor, and the saturation voltage won't quite be negligible. But still, that seems like a lot more current than specified. Did i get that right, or is there something else that's going on? Looking in a DigiKey catalog, i notice some Omron relays have a %of rated voltage for continuous operation. This goes from 110% to 200% Guess you can do it with some relays more reliably than others? > -----Original Message----- > From: Lawrence Lile [mailto:llile@TOASTMASTER.COM] > Sent: Monday, July 09, 2001 4:17 PM > To: PICLIST@MITVMA.MIT.EDU > Subject: Re: [EE]: Voltage regulation for circuits with relays, how? > > > My answer: don't regulate. Relays run fine on a wide range > of voltages. I > typically run 24 volt relays on circuits where the voltage > can range from 20 > volts to 35 volts, with 3 volts of ripple. Regulation? Schmegulation. > > -- Lawrence Lile > > > ----- Original Message ----- > From: "Peter Barick" > To: > Sent: Monday, July 09, 2001 1:17 PM > Subject: Re: [EE]: Voltage regulation for circuits with relays, how? > > > > John, > > Assuming you keep that given pwr adptr and are not running the relay > > off of the regulator, have you tried this: > > Have a high val C charged thru a low val R off the adptr. > This is used > > for the Rly and minimizes the drain at the input to the reg. > > > > Peter, PIC Newbie > > > > >>> john_fm_waters@HOTMAIL.COM 07/09/01 12:49PM >>> > > Hi All, > > > > >>I'm using a 78L05 to keep a stable 5V supply to a simple > > microcontroller > > >>circuit, the power comes from a standard home-use 9V, 380Ma power > > adapter, > > >>it works fine so far. However, I want to add a relay to my circuit > > > > >>John > > > > > > > > > ______________________________________________________________ > ___________ > > Get Your Private, Free E-mail from MSN Hotmail at > > http://www.hotmail.com. > > > > -- > > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > > email listserv@mitvma.mit.edu with SET PICList DIGEST in the body > > > > -- > > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > > email listserv@mitvma.mit.edu with SET PICList DIGEST in the body > > > > > > -- > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > email listserv@mitvma.mit.edu with SET PICList DIGEST in the body > > -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listserv@mitvma.mit.edu with SET PICList DIGEST in the body