Basic question for 3-Wire Solenoid and Connecting my Flyback Diode?

Hi all,

I have a 3-wire solenoid (+12, -12 and GND) and I would like to connect a flyback diode in order to reduce the effect of the inductive current spike when the solenoid closes.

I have the GND of the Solenoid currently connected to a terminal block (with other grounds).

Can I simply connect the Cathode of the 1N4001 diode to the +12 of the solenoid and the Anode of the 1N4001 diode to the GND terminal block? Or should the Anode be connected to a ground on the solenoid/enclosure itself. Also, am I correct in connecting the cathode to the +12 side, and not the -12 side?

Thanks!

Do you have a link to the solenoid? I've never heard of a 3-wire like that.

It's the ASCO 8320P172:
http://www.asco.com/ASCO%20Asset%20Library/asco-next-gen-valves-catalog.pdf

I’m having a hard time finding any electrical details in that datasheet, where did you get that idea that it was a bipolar solenoid? There’s a lot of mechanical specs, but I couldn’t even find one drawing or table naming the wire connections.

Since it says they’re “electrically enhanced”, my suspicion is that the 3 wires are power, GND, and signal, and that the driving circuitry and protection diode are already built in.

But that’s just speculation. Where are the electrical details?

Have you measured coil resistance in both directions ?

I think it's +12V, 0V & case ground, according to link, suppression is built in.

I have a 3-wire solenoid (+12, -12 and GND)

Prove it.

It’s the ASCO 8320P172:

Bottom of page 111, third line from the bottom.

Measure the coil resistance across the two red wires and then from each red wire to the black wire.
Post the results.

It is possible it is a bidirectional solenoid , meaning the direction is reversed just like a motor by reversing the coil polarity, which means you need an H-bridge or DPDT relay to drive it in both directions. I don’t think the black wire is used to power the coil but can’t be certain until you post those measurements.

If it really uses -12V, how are you controlling that? You will need a kickback diode there as well.

It is not clear what they mean by "surges suppression" and the lack of any electrical information on the data sheet makes it impossible to determine what is going on.

It could be that one of the red wires is for the +V, one for 0V, and, as already observed, black is case ground, or pipe ground. Generally, when you have a threaded connection, and grounding is an issue, you are obliged to connect the threaded pipes together with jumper wires. This wire would be the jumper from the pipes to the pipe fittings of the valve.

Or maybe not. Get the electrical specs.

In general, 1N4001 is not a good choice for a kickback diode when a microcontroller is involved. The forward voltage drop on a standard silicon diode is about 700 mV, which exceeds the -500mV allowed at the pin of an AVR chip. A Schottky diode is a far better choice, because it has around 200mV forward voltage drop.
joe

flounder:
In general, 1N4001 is not a good choice for a kickback diode when a microcontroller is involved. The forward voltage drop on a standard silicon diode is about 700 mV, which exceeds the -500mV allowed at the pin of an AVR chip. A Schottky diode is a far better choice, because it has around 200mV forward voltage drop.
joe

The might be relevant if the device (and clamping diode) was connected directly to the controller. A solenoid like this should have at least a discrete transistor driver between it and the microcontroller. The diode isn't protecting the controller, it's protecting the driver from getting hammered by an inductive voltage spike. The driver circuit shouldn't care about the difference between 0.3 and 0.7 volts.

In general, 1N4001 is not a good choice for a kickback diode when a microcontroller is involved. The forward voltage drop on a standard silicon diode is about 700 mV, which exceeds the -500mV allowed at the pin of an AVR chip. A Schottky diode is a far better choice, because it has around 200mV forward voltage drop.
joe

The might be relevant if the device (and clamping diode) was connected directly to the controller. A solenoid like this should have at least a discrete transistor driver between it and the microcontroller. The diode isn't protecting the controller, it's protecting the driver from getting hammered by an inductive voltage spike. The driver circuit shouldn't care about the difference between 0.3 and 0.7 volts.

I completely agree. That comment about the diode and the AVR didn't make any sense. A solenoid is like any other coil (relay, motor etc). There's always going to be a mosfet (which I personally don't like to call a "transistor" despite the fact that "fet" stands for "field effect transistor") or a transistor (BJT) and the diode protects that. The AVR is only connected to the gate or the base resistor so it has nothing to do with the diode.