Need advice on snubber circuit

[SoCalMacDude]

I'm using a DTMF Decoder kit from Ramsey Electronics
**broken link removed**
to sense touch tones from an audio channel. I used it to drive relays to trigger pneumatic solenoid valves. Apparently the EMF from the coil turning off was blowing the big chip in the kit.

I have a new circuit design, replacing the mechanical relays with optoisolators triggering solid state circuitry (FET) to power the coils. When the TT7 kit's DTMF decoder 5V output pin goes low, the signal is sent through a 30ft. Cat5 cable to the optoisolater, which triggers the IRF830 FET.

My question is that I am concerned that the snubber circuit in this schematic may not be enough to protect everything. I was reading that a good strategy is to channel the energy to a capacitor, then discharge it through a resistor.

I'm not sure how to do that, or if it is best, or what values of components would work.

Here's my current circuit design. Any help would be much appreciated:

 

[stefano.delfiore]

I'm using a DTMF Decoder kit from Ramsey Electronics
**broken link removed**
to sense touch tones from an audio channel. I used it to drive relays to trigger pneumatic solenoid valves. Apparently the EMF from the coil turning off was blowing the big chip in the kit.

I have a new circuit design, replacing the mechanical relays with optoisolators triggering solid state circuitry (FET) to power the coils. When the TT7 kit's DTMF decoder 5V output pin goes low, the signal is sent through a 30ft. Cat5 cable to the optoisolater, which triggers the IRF830 FET.

My question is that I am concerned that the snubber circuit in this schematic may not be enough to protect everything. I was reading that a good strategy is to channel the energy to a capacitor, then discharge it through a resistor.

I'm not sure how to do that, or if it is best, or what values of components would work.

Here's my current circuit design. Any help would be much appreciated:

**broken link removed**

To be honest, I don't see any snubber in your circuit. The only components used to protect the power mosfets are the freeweeling diodes across the the coils of solenoids valves.
Do you are afraid about this problem or there is something else not visible in the schematics ?

Stefano

 

[SoCalMacDude]

That's my point! I was told that the diode was the snubber, but I am afraid to build the circuit and immediately blow another chip.

I am really looking for a suggested snubber circuit to be added here, but I am not sure exactly how to implement it, and what values of components (I assume R & C) to add that would protect it.

Your post confirms my suspicions! Now I'm REALLY worried!!!

Any suggestions?