William At MyBlueRoom
New Member
I've seen both used in schematics. On a small signal < 12V relay coil would a cheap 1N4148 work fine for back EMF?
Follow along with the video below to see how to install our site as a web app on your home screen.
Note: This feature may not be available in some browsers.
William At MyBlueRoom said:I've seen both used in schematics. On a small signal < 12V relay coil would a cheap 1N4148 work fine for back EMF?
GizmoWizard said:Depending on a lot of different variables, the back EMF from this type of relay can briefly reach several hundred volts. The 1N4148 has about a 75-volt rating, the 1N4001 is 100 volts. Stick with a 1N4004 to 1N4006 (or equivalent).
GizmoWizard said:William At MyBlueRoom said:I've seen both used in schematics. On a small signal < 12V relay coil would a cheap 1N4148 work fine for back EMF?
Depending on a lot of different variables, the back EMF from this type of relay can briefly reach several hundred volts. The 1N4148 has about a 75-volt rating, the 1N4001 is 100 volts. Stick with a 1N4004 to 1N4006 (or equivalent).
neon said:nigel you still don't get it if the diode has a low saturation voltage {reverse} to you it will breakdown and go south to mexico for a vacation and the voltage will not be .7v or whatever but a short. god you guys still learning i supose. imagine a 75 volt spike and 20ma figure it out the power and you will get the an answer fast. learn my friend.
I'm afraid it is you that does not understand.neon said:nigel you still don't get it if the diode has a low saturation voltage {reverse} to you it will breakdown and go south to mexico for a vacation and the voltage will not be .7v or whatever but a short. god you guys still learning i supose. imagine a 75 volt spike and 20ma figure it out the power and you will get the an answer fast. learn my friend.
Yes. Back-to-back zeners across the coil will suppress the spikes.Do you have to be concerned with the back emf on an AC solenoid
Usually un-needed, but it would depend on the coil inductance since the coil current is out of phase with the AC input and may be relatively high when the AC voltage crosses zero.What is switching the valve, a triac? If so, it turns off at a zero-crossing of the AC input, so usually no suppression is needed.
What is switching the valve, a triac? If so, it turns off at a zero-crossing of the AC input, so usually no suppression is needed.
Yes. Back-to-back zeners across the coil will suppress the spikes.
I have taken apart a sprinkler valve timer which uses triacs and it had no suppression. The inductance of the solenoid coil likely is quite small. It is wound with tiny wire, so mostly the coil resistance limits the coil current.