Hello,

I am making a circuit which controls two relays and there is a timer to prevent the first relay from being on for more than an hour.

I need some design critique and part selection help.

Will this circuit work?

Values for:

R10, R11, Q2 and Q3.

I have attached a jpeg image.

THanks for looking and responding!

 

Any plain old NPN transistor in a to-92 package will do if it can stand at least 35 volts. The resistors should give the transistors a tenth of the current that the relay coils require.

 

I am sorry, I don't have time to review your circuit in detail right now, but I noticed that you show the relays connected directly from +24V to ground, and the transistor also connected between the +24 volts and ground. If the transistor ever tried to turn "on" fully, it would try to short the power supply.

I suggest you get this corrected before building the breadboard.

 

I am sorry, I don't have time to review your circuit in detail right now, but I noticed that you show the relays connected directly from +24V to ground, and the transistor also connected between the +24 volts and ground. If the transistor ever tried to turn "on" fully, it would try to short the power supply.

I suggest you get this corrected before building the breadboard.

I totally missed connected the transistors. I realized it after I submitted it lol.

 

i corrected the shorting transistors.

 

Schem looks much better--use the ubiquitous 2N4401

 

Schem looks much better--use the ubiquitous 2N4401

Thank you so much.

Is there anything specific I should be looking for when selecting an AND GATE IC?

 

I noticed my relay one flicking off and on very fast before quitting.

Can I not connect the two outputs of an AND gate to make an OR? Do I have to use and OR instead?

My transistors also blew. How do I calculate Rb? Should I use two transistors to turn on the 24VDC Relay? (one NPN and one PNP)?

I was using PN2222A transistors.