Solenoid valve drive with a PLC
Solenoid valve drive with a PLC
(OP)
Hello,
I've got a PLC with outputs, open collector or sourcing, that's limited to driving or sinking only 100mA out each output. Of course nothing I ever need to drive needs only a measly 100mA unless its a relay.
All the solenoids in this job require about 125mA to 200mA. So I need just a wee bit more. Since the cycle time in Today's Machine Project is about 4 million cycles a year this project requires non-mechanical relays. My problem is that the only solution I'm seeing is to use Solid State Relays. The very cheapest ones I can find are $22 a piece. I don't need more optical isolation. The PLC has already provided that. All the solenoids are being driven from the same supply. All I need is to boost the lame, er... weak, PLC outputs up to about 250ma or so.
This seems like such a painfully obvious situation that someone must sell something that provides this for less than a forest of optos.. 16 channels of optos cost a minimum of $350. More than the PLC! Has anyone seen a solution for this?
I've got a PLC with outputs, open collector or sourcing, that's limited to driving or sinking only 100mA out each output. Of course nothing I ever need to drive needs only a measly 100mA unless its a relay.
All the solenoids in this job require about 125mA to 200mA. So I need just a wee bit more. Since the cycle time in Today's Machine Project is about 4 million cycles a year this project requires non-mechanical relays. My problem is that the only solution I'm seeing is to use Solid State Relays. The very cheapest ones I can find are $22 a piece. I don't need more optical isolation. The PLC has already provided that. All the solenoids are being driven from the same supply. All I need is to boost the lame, er... weak, PLC outputs up to about 250ma or so.
This seems like such a painfully obvious situation that someone must sell something that provides this for less than a forest of optos.. 16 channels of optos cost a minimum of $350. More than the PLC! Has anyone seen a solution for this?
Keith Cress
kcress - http://www.flaminsystems.com





RE: Solenoid valve drive with a PLC
Allen Bradley
Bulletin 700-SK Slim Line Relay with Plug-in Quick Connect Terminals
or any other cross for this relay will work, Phenoix contact or square d or whoever has same.
RE: Solenoid valve drive with a PLC
Keith Cress
kcress - http://www.flaminsystems.com
RE: Solenoid valve drive with a PLC
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Solenoid valve drive with a PLC
RE: Solenoid valve drive with a PLC
If I go that way I'll show you here.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Solenoid valve drive with a PLC
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Solenoid valve drive with a PLC
RE: Solenoid valve drive with a PLC
Keith Cress
kcress - http://www.flaminsystems.com
RE: Solenoid valve drive with a PLC
RE: Solenoid valve drive with a PLC
If the only requirement is to sink gobs of current from a DC relay, then the Darlington array would seem to fit the bill. The Vcesat's a trifle high, but I would think that you could gang upall 8 of them, to sink the relay. Nonetheless, there are single Darlingtons or TTL-drive n-channel MOS drivers that could fit the bill. This guy is gross overkill: h
TTFN

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RE: Solenoid valve drive with a PLC
Keith Cress
kcress - http://www.flaminsystems.com
RE: Solenoid valve drive with a PLC
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RE: Solenoid valve drive with a PLC
I have found that in addition to a diode a small ceramic cap (100 nF or 0.1 uF) in series with a 2 to 5 ohm resistor is very effective. This is sometimes called a Boucherot Cell or Zobel network. If you are going to make a small printed circuit board these are easily added.
- Stephen
RE: Solenoid valve drive with a PLC
You seem to be new in here. I think that you are giving advice with good intention. But sometimes, as you say initially, they are not needed.
Itsmoked is one of the more experienced members of EngTips. And has been so for decades - well at least one decade. If you search the fora (use well-functioning search function) before you post, you will get an idea about what has been discussed and what is well known. Do that before you answer a question. It saves embarrassment.
It is interesting that you use the term "Zobel network". It is very rarely used. Last time I saw it was in a Philips book on audio power stages. The term normally used in control and automation is "snubber" or simply "RC unit".
Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.
RE: Solenoid valve drive with a PLC