relay question.
post-1442030

#### bg4533

I need a relay to use with the circuit below. It will be used to connect the secondaries of a transformer to a PSU. I am looking at the following relay. Link to datasheet

I chose the 24V relay because it will be powered by a 22VAC secondary. The MC4069 is only good upto 20VDC. I can also get the 12V version, but that might cause a more heat than I want. The relays datasheet says it has a "must operate VDC" of 16.8V. Does this mean the relay will run properly down to that voltage? Will there be any adverse effects like longer switching time?

Are there any other changes I need to make to the circuit to use it with a higher voltage?

Thanks.

post-1442076

#### Garbz

that means that at 16.8v the realy will flick even if it's not at it's 24v normal operating condition yet. Typically there's also a rating for the otherside where the relay will hold till say 2-4v before loosing contact.

You could in theory use any relay you want you just need to put a resistor in the path. Looking at the datasheets it should give you a coil rating and a operating current. Just simply substitue all that into Ohms law V=IR and then from there you can calculate how much resistance you need for each voltage. So if you have a 300R resistor and the relay runs at 30mA, you have a 9v relay. If you wish to power it from 12v you get 12 = 30E-3 * I which is 400. This means a 100ohm resistor must sit in series to the coil.

The only other thing that's important is the DC rating of the relay. Make sure the relay can handle the DC going through it's connections.