24VDC supply

[Mike_2545]

Hey guys,

I have some 24 volt DC 10 watt solenoid valves to drive. My 24v center tapped transformer gives me 28.8 v dc (after bridge) and I don't want to over power the solenoids so I was thinking of using a Zener diode to do the job of bringing it down.

I have some 1N970B 24v zeners on hand, rated at 400 milliwatts Max

What would you suggest?

I would be running up to 2 solenoids at once for a short duration.

Or should I just use a 7824 and forget the zener idea?

 

[crutschow]

You might check the power supply voltage with the solenoid 0.4A load. It may drop to near 24V due to transformer and diode resistance. And solenoids will tolerate be overdriven for short periods of time without damage. For example, they can run at 34V at a 50% duty-cycle, since that generates the same amount of heat as 24V at 100% duty-cycle. You just need to check their temperature after a period of time to see that they are not overheating

Otherwise the 7824 is probably the easiest solution. Using the zener would require an added transistor and other circuitry to form a series regulator.

 

[Mike_2545]

Bingo

I tested the voltage with the solenoid load attached and that brought it down to 25v.

Close enough, they will be on <10% duty-cycle.

Thanks.