Using a relay board to power a solenoid that draws .4 amps. Relay board is powered from USB. ATX breakout works fine energizing the solenoid but board powers off when solenoid de-energizes. Tried snubber diode, big electrolitic cap, 14V MOV. I even tried shorting the poly fuse, no dice. Any ideas?
hi , the robot that runs this forum treatened me with expulsion if i didn't post within 24 hrs of registering.
I don't have any questions/answers at this stage , but i hope this will pass the test.
Hi superUnkown, you could add a 100nF ceramic cap parallel to the relay coil.
Hope this will help
Similar to Vimark, but lose the diode and add a Resistor in series with the Cap and preferably use a Metallised Paper Cap with a 250V X2 rating. Worst case, you could use a Metallised Poly cap with the same rating. Alternatively you can buy the Cap / Resistor as a single device. The Resistor should be a Carbon or Metal film, not a wirewound and at least 0.5W and use one between about 47 and 200 Ohm - I'd suggest 100 Ohm for a start.
If this helps but doesn't eliminate the problem, try a 470nF (0.47uF) cap and a 47 Ohm Resistor.
If that works, try putting the diode back in as well, but it may be too sharp a cut-off and could actually increase the problem. In that case you could again try the bigger 0.47uF cap.
Oh, and put the RC close to the load.
Thanks! I'll try the RC. But why would this work, but not a snubber diode? What do you think is actually causing shut down? Is it the ATX breakout board or is it the power supply? Is it the inductive spike or some sort of RF voodoo?
From my experience similar to this case, we've provide a small relay that in turn switch a contactor to switch on/off a whole videoke room (consist of 0.5 hp aircon, tv and a videoke machine). PC controls and its microcontroller (connected via usb) went off when the contactor+relay is turned off. Out of a few days scratching our heads on what's going on, we've decided to place an 0.47uF 500V Mylar Cap in parallel to the relay switch (not parallel to the coil). So far problem were gone.
I believe that huge current surge rushes when contactor discharges affects the controller and the PC. In your case it could be the current surge from the solenoid and not RF related.
tried with various values of ceramic and electrolitic caps. Changed resistor values too. No change, ATX board shuts down when solenoid de-energizes. Guess next thing is to head down to the store on Tuesday (thanksgiving holiday here on Monday) to buy some faster response caps?
rooted thru junk bin and got few 200V poly caps .22uF. ran 2 in para. no dice. ran 2 in para w/ resistors (various). no dice.
So, we are all in agreement, the inductive voltage spike is what is causing the board to shut down?
Rookie mistake! I removed the 4007 and installed a 5817 schottky on the ATX terminals. No dice. Then I thought "I don't see what difference it'll make, but I might as well TRY the diode close to the solenoid". (The soleniod leads are only 24" long.)
BINGO! Works like a hot damn!
Thanks guys!
You nailed it! :) Kill the problem from its root. Nice work.
The difference is that there is 2 x 24" of antenna (and inductor) hanging between the Diode clamp and the Solenoid and lot of energy racing down those wires that is changing at a great rate of knots (a dirty great spike).The Diode is a crude, but often effective way to clamp it (in the reverse direction), but it's also a bit like stopping a car by using a solid brick wall, it's a very sudden stop with a big hit of energy and only in one direction, so ringing still occurs in the other direction until the energy dissipates. The idea of the RC is to reduce the Rate of Change (Dv/Dt) in a more controlled manner and dissipating the energy in the Res as it goes - a more elegant solution and is effective with the Diode also.
Cool! Thanks for the thorough explanation, it's not voodoo after all! Now I *really* want a scope.
Yep, it's no more Voodoo than a Car Ignition Coil is when the points (or electronic equivalent) opens, that's how they can generate 10-20kV odd from a 12V battery. A common 12V relay coil can, depending upon the unit, generate a 300V kick or more. Just think of it like letting go of a stretched rubber band. If all that stored energy is let go at once, it packs quite a wallop.