Faster DC solenoid release time
Faster DC solenoid release time
(OP)
I am looking for the fastest way to release a 12volt soleniod after it is de-energized. Every ms counts. Reducing the voltage after energizing? How? What else? Thanks!
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Faster DC solenoid release time
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RE: Faster DC solenoid release time
To get best results, you need a real serious sparky type.
In the meantime, a back- biased diode across the drive transistor or relay contacts will suck the stored energy out of the solenoid pretty quickly. You will smoke a few diodes until you find one massive enough to survive. The diode becomes a short circuit for the voltage generated by the collapsing field. It's not an application for a small signal diode.
Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA
RE: Faster DC solenoid release time
A "Catch Diode" across the coil is the slowest way to dump the current. A resistor in series with the diode will dump the current faster ( the time constant is L/R ). The voltage on the transistor will jump to the solenoid current times R.
Even faster will be a zener diode in series with the diode. The transistor will see a voltage jump equal to the zener voltage. Use a surge suppressor zener like a 1.5KExxx where xxx is voltage.
The fastest; most power FETs are energy rated for breakdown as a power zener diode. If the 1/2 LI^2 in the solenoid is lower than the breakdown power rating of the FET you can let the FET zener the solenoid
RE: Faster DC solenoid release time
RE: Faster DC solenoid release time
Any impedance across the solenoid coil when you open it, will extend the release time.
The problem is that when the driving circuitry releases the solenoid, there will be a high voltage generated. This can cause failure of the driving circuit. In order to protect the driving circuit, reverse diodes across the coil are common. This restricts the voltage to 0.6 Volt above the supply voltage. Adding a resistor in series with the diode will increase the switch OFF voltage across the switching device and speed up the switch OFF time.
My suggestion is to increase the voltage rating of the switching device as high as possible - hundreds of volts rather than tens of volts, and use overvoltage protection that only begins to conduct current close to the voltage rating of the device. Try to eliminate as much capacitance as possible and be aware of the affect of the millar capacitance of the output device. If you use a bipolar transistor, make the resistance between the base and emitter as low as possible. If you use a MOSFET, use a low value of gate source resistor. If you can apply a negative bias during switch OFF, the device will switch quicker and the solenoid will release quicker.
Best regards,
Mark Empson
http://www.lmphotonics.com
RE: Faster DC solenoid release time
You may also have more magnetic force than you need.
Barry1961
RE: Faster DC solenoid release time
RE: Faster DC solenoid release time
Can U tell us more about your application?
<nbucska@pcperipherals DOT com> subj: eng-tips
read FAQ240-1032
RE: Faster DC solenoid release time
RE: Faster DC solenoid release time
RE: Faster DC solenoid release time
Regards,
RE: Faster DC solenoid release time
flow i.e. the slope.
Could you use a voice-coil type ectuator ( electro- AND
permanent magnets ) or a faster valve?
<nbucska@pcperipherals DOT com> subj: eng-tips
read FAQ240-1032
RE: Faster DC solenoid release time
RE: Faster DC solenoid release time
RE: Faster DC solenoid release time
There is one additional item that you might want to consider regarding the “release time” of your solenoid. All of the previous posts regarding the use of a diode across the coil winding to quickly suppress the back EMF voltage (and drop-out time) in the coil during turn-off are right on target. A diode AND series resistor across the coil will improve the drop-out time of the coil. However, an additional item critical in solenoid response time is the magnetic circuit itself. I have seen several poorly designed solenoid’s (commercial and OEM) where the coil and internal magnetic circuit were not properly sized. As a result, the flux produced within the magnetic circuit eventually drove all the solenoid’s internal parts into magnetic saturation. When the current was shut off, the field in the coil quickly collapsed, however the moving part of the solenoid (the plunger) was now a small permanent magnet, and delayed the “release” of the moving parts by as much as 20 times as that as for a non-saturated circuit. One suggestion as a test to see if your solenoid has succumbed to this phenomenon, would be to place a small non-magnetic shim (say 0.015 inches of brass) in between the moving and stationary parts of the solenoid (if you can get at it without destroying the whole thing). Increasing the final air-gap in this manner will have a positive effect on the release time of the solenoid, and may help you to diagnose your problem. Hope this helps – good luck.
RE: Faster DC solenoid release time
Frank, assuming DC, how do you test the magnetic frame to ensure that it is not in saturation?
Are you saying that the frame is certainly saturated If the moving core sticks to the stop when the coil is de-energised?
Thanks & regards,