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Fast Snubber for Solenoid Valve

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Tomas_2

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First of all, I present myself. I am an industrial engineer, 27 years old. In my free time, I´m working in a personal project. Basically it is a kind of PLC than controls 150+ solenoid valves. The PLC is a modiefied Arduino platform with many UNL 2803 ICs (each Arduino output is 40mA max and it not enough). Each UNL 2803 can handle 500/600mA (50V max). The solenoid valves are 12VDC and 500mA. I´m using two UNL 2803 in parallel (one above the other) that handles 1000/1200 mA and have some security margin.

The idea is that the solenoid valves must open and close VERY fast and at a rate of 10Hz max (approx.). Each valve is controlled individually and the actual valves I bought have a response time of approx. 10 ms to open/close. This is perfect to me and works fine. The problem is that as solenoid loads are very inductive so I must add a Snubber / Transient voltage suppression to eliminate the peak voltage produced when the solenoid is turned off. If I don’t use some kind of protection, surely I will fry the ICs of the circuit!

Actually I´m using one 1N4004 diode parallel-connected to each solenoid. This protection works fine but it has a big controversial issue: the close time is widely increased (by 2x or 3x) and makes my system not to work correctly.

I´ve been searching for some alternatives that don’t increase the close time (maybe I´m wrong!):

-RC snubber.
-Two inverse-series Zener diodes (transorb).
-Varistor / VDR (some call them MOV).
-Other one?


I will appreciate if you can help me to choose and calculate the fastest snobber possible. My electronics knowledge is quite basics so simpler solutions are preferred (sorry about that!).

The only data of the solenoid valves I use is that they are 12VDC-500mA (I don’t have the tools to measure accurately the R and L of the inductance, if it is very important to know, I can contact someone that can measure it).

Thank you very much and best regards!
Tomas
 
Hi,

the ULN28XX series transistor arrays have free wheeling diodes on chip for each output. If you connect the +12V rail to the "common" pin you should have sufficient protection of the chip.

If you want to do more I suggest to look into the BY203 (fast avalanche diode), which has a recovery time of 200ns.

I doubt the ULN28XX can handle 1.2A constantly. The data sheet just says 500mA per channel. That would be more my point of doubts.

Boncuk
 
I'd be curious as to the valves' minimum holding voltage & current. You could use a higher supply voltage through a resistor to the valve and a cap to ground. This, with the valves' low side driver would fire the valve faster, but power limit it by the resistor.
I'd also think about a different driver. There are MOSFET drivers (i.e. TC442x series) that are very fast and 1+amp current, but could get pricy.
For protection, I use reverse biased Schottky diodes (i.e. BAT54x), to both ground and supply. G.H... <<<)))
 
I've run three sims (for diode, RC and back-to-back zeners) and the fastest of those snubbers I found was back-to-back zeners, as per attached. Valve cut-off time is ~140uS, for a solenoid of assumed inductance 1mH and resistance 0.1 Ohm. We really need to know the actual valve inductance/resistance to get a meaningful result, though.
 

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Nice to read so many answers!

Boncuk:
ULN28XX do have some protective diodes but I doubt they will protect the IC from the simultaneous closing of 8 solenoids (reverse voltage of aprox 200-300V). It is a lot of energy to dissipate, I don’t know if it can handle it.
ULN2803 support´s up to 500mA (some say 600) per output but as I “doubled them”, the max amp is 1000 mA / 1200mA.

OlPhart:
I’m interested in a MOSFET opton. What advateged will I have versus de ULN´s? More info will be welcomed!

alec_t
Do you think back-to-back 1N4755 zeners will work? They cut al 43V but handle only 1,3W, hope its enough. Maybe it is possible to put more if necessary.

Thanks!!
Tomas
 
By running the diodes in parallel to the solenoid coils you are causing the collapsing electromagnetic field to slow itself down since it has to dissipate its own energy in the form of heat. If you place a resistor in series with your diode you can effectively speed up that field collapse time by dumping that energy outside the coil.

500 milliamps at 12 volts would mean you have a roughly 24 ohm coil resistance so the resistor in series with your diode should be between around 1 to 4 times your coil resistance.

More resistance will speed up the release time but also increase the peak spike voltage whereas less resistance will lower the peak spike voltage but unfortunately also slow down the release time.
 
Tomas, there are several potential problems to overcome with running solenoid valves on and off at 10 Hz.

The first is mechanical resonance of the internal spring and the mass of the internal parts. It may go into "pogo stick mode" and start bouncing uncontrollably.
The mechanical resonance frequency must be avoided.
Either run it much slower so it does not bounce, or faster so it may possibly be PWM controlled, but at resonance it will make a very nasty noise, be uncontrollable, and may rapidly self destruct.
Unfortunately 10Hz is about in the middle of the range where many of these small solenoid valves very often go totally nuts.
Anyhow, try it and see....

The higher the applied voltage, the faster the current and the resulting magnetic flux will build up.
There are tricks to doing this, such as pulsing the valve to a much higher voltage for a very short time, then reducing the voltage to just above where the valve will release.
Pulse and hold automotive fuel injector drivers do this, and some research into these might give you an insight into this type of driver.
Fuel injectors after all, are just solenoid valves anyway.
You can always build a custom driver circuit to suit your own specific needs.

The higher the voltage can rise across the valve during release, the faster the magnetic flux will collapse.
An inverse diode is absolutely the worst way to do it if speed of release is important.
It clamps the turn off voltage to only 0.6 volts and extends the release time hugely.
That is the purpose of snubber circuits, they allow the voltage to pulse much higher than the operating voltage to speed up release.
How high you can go depends on how much voltage your switching transistor can safely handle. MOSFETS are far better than bipolar transistors in this regard.
Try putting a reasonably high powered zener diode in series with the inverse diode across your solenoid, it will help a lot to speed up release.
Snubbers work two ways, you can either dump the inductive energy into a capacitor, and bleed it off with a resistor, or you can just clamp the voltage with a zener diode. Either way the power that must be absorbed might surprise you if continuous operation at 10 Hz is required.

However you decide to drive your valve, it is not going to open faster, or close faster than the mechanical resonant frequency, whatever that happens to be.
 
4pyros, you are right. I will show you what I should have done in the first post, this video shows what I am in process of building: https://www.youtube.com/watch?v=gusJeslMbLc&feature=related

The max operating frequency is (estimated) 10Hz in the most complex figures but as you can see, in normal operation the valves are much more relaxed and open/close at 1Hz (approx., it varies a lot). The faster the open/close, the better the resolution (imagine the shorter water line possible as a pixel). This is Japaneese design of what I would like to build, if mine works 50% of this, I will get very happy! Up to now, I have only the circuitry in work, haven’t worked with the valves or hydraulic up to the moment. I have simulated the valves with led´s and it works like a charm. I’m worried if it will work with the valves… I connected only one (119 led´s + 1 valve) and it worked Ok. The problem comes when connecting the 120 valves….

Looks like a Guy already did a VERY similar project to mine (Same electronics). He used IRF540 MOSFETS (100V max). This looks a great alternative to ULN2XXX!

Reading this pdf, https://www.electro-tech-online.com/custompdfs/2011/10/13c3311.pdf it says: "From the standpoint of physics, the suggested technique for relay coil
transient suppression is to use a reversed-biased rectifier diode and series
zener diode in parallel with the relay coil."

The question is, what reversed-biased rectifier diode and what zener to use? Suggestions are welcomed!

Also, I noted that the IRF840 supports up to 500V, in this case is it safe NOT tu use a snubber? Maybe only a small one is needed....

Thank you!!!
 
I would keep the voltage below 100 volts. I have some concern that above 200 volts the insulation inside the solenoid may breakdown.

I show a 1N5871 Zener for 100 volts. There are many choices in the 1/2 watt range. One option is to use a diode/capacitor on each MOSFET and tie all the caps to one Zener. In that case I would use a 1N5378 5 watt Zener. The cap may not be needed but where all solenoids use the same Zener the distance from MOSFET to Zener will be too large. Keep the MOSFET-Diode-Cap distance short.

The Zener could connect to the supply or ground. I now think supply might be better.

A 1N4003 is slow, will work, I would use a faster 1N4935 or UF4003.

If capacitors are used I have a thought that before the first solenoid operation the voltage on the zener will be low and thus the first operation may be slow. (connect zener to supply will help this) You could pull up on the zeners with a 100K resistor to 50 or 100 volts will solve this if it is a problem.
 

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Tomas; You may what to look into Solenoid Driver chips like the L294 Switch-Mode Solenoid Driver IC. Thay are vary fast. Andy
 
The speed problem is not just the solenoid driver but the snubber.
Often the solenoid driver puts 12 volts across the coil but the snubber holds 0.7 volts across the coil for a long time. A snubber that limits at 24 volts, (-12V across the coil) will be much faster.

To even get faster a solenoid driver could put 50 volts on the coil for 10mS then drop back to 12 volts. On release the snubber will limit at 100 volts.
 
The speed problem is not just the solenoid driver but the snubber.
Often the solenoid driver puts 12 volts across the coil but the snubber holds 0.7 volts across the coil for a long time. A snubber that limits at 24 volts, (-12V across the coil) will be much faster.

To even get faster a solenoid driver could put 50 volts on the coil for 10mS then drop back to 12 volts. On release the snubber will limit at 100 volts.

All of which is very true.
But it comes back to the mechanical resonance of the solenoid being a limiting factor to how fast it can respond.

Even if you can reach full steady state on, or zero current dump in microseconds, it will be of absolutely no use if the solenoid itself mechanically resonates at 5Hz to 10Hz which is fairly typical.
 
The question is, what reversed-biased rectifier diode and what zener to use? Suggestions are welcomed!
As I'm sure has been stated already, if you have a larger voltage across the snubber, you will have a faster decay in the coil current: LI = TV, so Time = Inductance*Current/Voltage.

The ULN2803 ICs have integrated clamp diodes designed for exactly that; you don't need to add external clamps. You can put a 45V or so zener on the clamp diode common pin to increase the clamping voltage & therefore reduce the current decay time.
 
To even get faster a solenoid driver could put 50 volts on the coil for 10mS then drop back to 12 volts. On release the snubber will limit at 100 volts.
Thats what the driver chips do.
 
You may what to look into Solenoid Driver chips like the L294 Switch-Mode Solenoid Driver IC
According to the Farnell website that IC is no longer manufactured.
 
To even get faster a solenoid driver could put 50 volts on the coil for 10mS then drop back to 12 volts. On release the snubber will limit at 100 volts.

Thats what the driver chips do.
What?? No the driver is built to put 12 volts on the coil, for on. And to turn off it puts -0.7 volts on the coil until it releases. To speed things up we are talking about -50 to -100 volts to turn off. I expanded that, why not put 50 volts for turn on, +12 to hold, then -100 for turn off and 0 volts to hold off.
 
Hey folks!

I have been working in the prototype of the "Water Printer". The electronics works like a charm with 0.1 ms precision. Valves open/close time is 6ms, fast enough for me.

Finally I use common 4004 diodes, I tested a lot of zenner diodes and they are pretty much the same (5 ms open/close time), as 4004 are cheaper, I used these.

Here you can watch some videos of the first beta, a lot of work remains....

Any suggestions are welcomed!

https://www.youtube.com/watch?v=OoJ6TRb85JQ

https://www.youtube.com/watch?v=O-kkP-_2Kdo


Best regards,
Tomas
 
What?? No the driver is built to put 12 volts on the coil, for on. And to turn off it puts -0.7 volts on the coil until it releases.
Ron;
Looking back at this I think we had a misunderstanding.
Most of the solenoid driver chips would start with a higher voltage and current then go to a holding voltage.
It was all made into the chip so you would not need a micro to do the timing.
If you google solenoid driver chip you will find some.
The L295 is still avalible.
Andy
 
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