Auber PID power "conditioning?"

I have an Auber SYL-2352 in my new brew rig. I've got it wired up in kind of a temporary fashion to do some testing. I've noticed that sometimes when I cycle power to my Asco gas valve it causes the PID to kind of 'reboot', or to flash an odd temp sensor reading.

I've got the wires to the RTD away from the 120V... I'm thinking that the Asco valve causes power to fluctuate when opening or closing it. Is there a simple way to 'condition' the power to the PID to prevent this?

Thanks!

Install one of these across the solenoid coil leads http://www.alliedelec.com/search/productdetail.aspx?SKU=8450587. This will stop the voltage spike when relay contacts open, other problem could be loose connection voltage drop when solenoid coil is activated.

MOV's are for protection purposes only...they shouldn't be used to repeatedly defeat a voltage spike. They degrade with every spike and will be useless quickly. A better solution is to install a capacitor across the coil...this will help reduce the spike a bit.

I have a feeling that it's not a spike that's causing the problem though...if it happens when you power on the valve, it could be a voltage drop problem, either from a loose connection like kladue said or just a weak source. try keeping the power run as short as possible and/or beef up the wiring. What's the current rating on the valve?

Current rating on the valve is only 10.1 watts ... though it sure clanks when opening or shutting and hums a bit while energized.

Specs on it here

The other weird thing is that I can start and stop my march 809 pump, or the little giant 3-MD-HC and it doesn't give the PID any trouble... those are bigger loads, but I imagine motor loads versus the solenoid are quite different.

Thats interesting, MOV's are industry practice for AC control relays and solenoids, capacitors for small DC control relays and solenoids. AC and capacitors in paralell does not sound like a good idea for protection, capacitor would act like a load or short circuit if large enough.

A resistor in series and then a bipolar cap in parallel would make a low pass filter (wired as close to the PID power input as you could get it) that would help reduce the problem if it's voltage sag. The only issue would be making sure the filter's cut off frequency is at least 10% above 60hz so you dont damp the main AC supply.

The filter will work the same on DC as AC if you have it set up right. The filer would effectively "short" any higher frequency pull to ground, which is exactly what you want, and the resistor would act as a damper to make sure you dont run too much current, while not acting as a "short" for lower frequencies.


The only real load the filter would show to any load wired further down the AC line would be a phase difference, possibly changing the complex part of the impedance, which for a solenoid shouldn't make a big difference, if you had a 3 phase motor down the line I might worry, but a standard single phase motor like your pump, it shouldn't effect. (I'm assuming the filter would be wired only to the PID and that the PID is only switching, and not supplying the power for the solenoid).

The MOV is a good idea, because for an AC circuit it acts similar to what is called a "free wheeling diode" which will prevent the inductor in the solenoid from causing a voltage spike when it's current is shut off. The voltage spike from the inductor comes at a negative voltage from the original voltage direction at the time of disconnect, thus at DC placing a diode backwards across the coil allows the spike current to run backwards through the coil dissipating the magnetic field quickly and removing the voltage spike from the system. The MOV is the same idea but for an AC system.

The filter circuit would also reduce the impact of a voltage spike without the MOV. The filter only cares about the frequency of the spike, up or down in voltage, the MOV will only protect against an upward "absolute" upward spike in voltage. (aka if you're at -60 in your AC cycle and the spike took you to -160 very quickly, or 60 to 160 quickly, the MOV wont protect against -160 to -60 or 160 to 60) the filer circuit would reduce the effect of both, but the MOV is much better at preventing the absolute spike.

Now, an inductor acts to current as a capacitor does to voltage. Thus you never have a fast change in current over time across an inductor. Based on this, I'm going to bet that your issue is most like a voltage spike, rather than a voltage dip. Turning on a compressor motor usually causes a big load spike because at 0 RPM the motor uses the most current and has the most torque, but the instant the switch is turned on the current pull is low until the coils saturate and then pull large current. (goofy transient response I know).

but bjornbrewer (/wave at a fellow EE) is right:

Another method for suppressing voltage spikes is the transient voltage suppression diode (TVD). Although diodes do not have as much capacity to conduct large surges as MOVs, diodes are not degraded by smaller surges and can be implemented with a lower "clamping voltage". MOVs degrade from repeated exposure to surges and generally have a higher "clamping voltage" so that leakage does not degrade the MOV. Both types are available over a wide range of voltages. MOV tends to be more suitable for higher voltages, because they can conduct the higher associated energies at less cost.[2]

thus using a TVD may be your better solution:
http://en.wikipedia.org/wiki/Transient_voltage_suppression_diode

in this case, you'd want a bidirectional TVD with a breakdown voltage of about (120 * root(2) for RMS) 170v, and be able to handle a good surge amperage.

If you're really worried about the life of the MOV get a high joule ratted one or write several of them in parallel (as suggested on the wiki page).

As Bjorn said, if the problem is at turn on and causing a low voltage, then the problem is most likely a high impedance in the supply wire, beefing it up may solve the problem, and making it shorter will help too, or you could run the solinoids on completely different circuits from the PID using the PID to control a switch that then turns the power on/off for the solenoid. I could see this as the case if the solenoid is having trouble closing and pulling a lot of current once the inductor is charged but the solenoid is not moving (like a compressor motor). Most compressor motors have a big cap in parallel before the motor to smooth out the voltage drop when it first turns on.

The real question is, does it have its problem when the solenoid is shut off, or turned on? If you can figure out a way to answer that question, then the solutions are in all the posts above.

-devon BSEE

-free wheeling diode:
http://en.wikipedia.org/wiki/Free_Wheeling_Diode
- MOV: http://en.wikipedia.org/wiki/Varistor

A simple snubber will work put 0.1uF 500V disc capacitor in series with a 100 ohm resistor 1/2 watt non inductive resistor. What you are seeing is dv/dt caused by the coil in the solenoid valve.

Guy BSEE

What Deven said. Snubber to reduce the voltage spike...MOV to eliminate huge voltage spike at risk of self sacrifice.

Paul MSEET (<- I have more letters in mine!)


PS...we still don't know what's causing the problem though...voltage spike, or voltage sage/surge.

diatonic said:

Current rating on the valve is only 10.1 watts ... though it sure clanks when opening or shutting and hums a bit while energized.

Specs on it here

Click to expand...

diatonic said:

The other weird thing is that I can start and stop my march 809 pump, or the little giant 3-MD-HC and it doesn't give the PID any trouble... those are bigger loads, but I imagine motor loads versus the solenoid are quite different.

Click to expand...

small motors only draw about 3-5x running current to start. Solenoids are more. It's only 10.1W holding, but the pull in current is going to be higher...sometimes 5-10x as high. however, that still isn't enough to cause problems with a high impedance source.

Thanks for the great info guys. I did some testing last night. I energized & de-energized the valve 7 time while the PID was on. It only happens when I turn off the valve, de-energizing the coil. In 7 cycles it only happened twice.

Wiring should be okay. It's all 16ga copper with lever nuts for connections.

The low impedance motors usually do not give as big a spike as the high impedance relays and solenoids do, but MOV's will work quite well in this application as the energy snubbed is not large and there will not be that many cycles.

kladue is correct if there are not many cycles that it will see. Try a .1uF cap (film type, 600V) and 150+volt MOV in parallel with the coil...that should take care of it.

An important concept to note is the capacitor's ESR (Equivalent Series Resistance). It should be as small as possible (like the value Bjornbrewer suggested). It is better to use few paralleled capacitors than only one for the same capacitance. Low ESR capacitors are ceramic capacitors and tantalum electrolytics. Aluminium electrolytic capacitors should be special low ESR types.

Why is it better to use a few caps in parallel?

A real capacitor is like a small parasitic ideal resistor, small parasitic ideal inductor, and ideal capacitor that is in series with each other.

If you put this RCL series in parallel, the R and L decrease (since resistance and inductance decrease when paralleled) and the C increases making it closer to an ideal capacitor. THat is why (I assume you know that the resistance limits current while the inductance limits rate of current change both of which are do not help in smoothing out the voltage spike).

This is also the reason why you have to use small capacitors to pass or filter higher frequencies in real life- because larger capacitors have larger parasitic inductance, and at high frequencies this inductance blocks the signal from ever getting to the capacitance in the first place making the capacitor useless at that frequency regardless of how big it is. An ideal capacitor would always pass higher frequencies better than lower frequencies, but this is not the case in real life.

So the trick is to know the main frequencies of the spike you are trying to filter and pick a capacitor that is as large as possible, while balancing out the parasitic inductance and resistance (after all, a capacitor with very little parasitic inductance and resistance that is has too small a capacitance for the job won't do too much good either)

Take a look at some impedance graphs for real capacitors. The parasitic inductance and capacitance create a frequnecy point where the impedance is lowest, and the impedance increases on either side of this frequency/

http://www.murata.com/emc/knowhow/pd...-1/12to16e.pdf

So the effect is that a a larger capacitor will have lower impedance at low frequencies than a smaller capacitor but the smaller capacitor will actually have a point at a higher frequency where it's impedance dips below the large capacitor (and in many cases, this is the frequency you are trying to filter out, rather than all the lower frequencies that the large capacitor is better at).

Travis - BSEE, PE

now you're just showing off Travis. Damn PE's.