PLC inductive load & input questions from actual experience?

[mjwalsh]

I know some of my fellow operators have actual hands on PLC experience as it applies to latching on the following:

---6.5VA dog wash 24VAC solenoids
---13 watt 24VAC Asco Solenoid
---Usual 24VAC coils on the more commonly sold Car or Dog Wash magnetic contactors in Car Wash Catalogs
---Laurel Electronic 24VDC shelf tripper motors

All of the above motors have inductive loads. In general: Do they require diodes to protect the output solid state relays of most PLCs? From actual experience are some of these items safe to run directly from the PLC output? I am aware of the voltage specs & ranges so that general configuration would be OK.

2nd question: Would the Mars bill acceptors or Slugbuster 2 or 3 coin acceptors all require 24VAC input specifications? By 24VAC i am referrring to the output pulse that would be read by the PLC input?

Thanks

 

[MEP001]

I've used PLCs for nearly 10 years for solenoid controls and have never had a single output failure.

 

[mjwalsh]

MEP001,

Is the pulsed output from the Mars & the Slugbusters 24VAC or 5VDC??? I am trying to order the right type of modules, ports or contact banks etc on the PLC. The PLC people need to know if it is dc or ac & the voltage etc.

 

[MEP001]

Slugbuster is 24VAC - the Mars with the $5 enable harness can be wired as a pulsing relay with whatever voltage you input. Some brands of coin acceptors (GinSan, IDX) can be wired the same way.

 

[mjwalsh]

Mep,

Thank you for very helpful information. At our new dog wash we will want the Mars to also accept 10s & 20s. Does this require a specific harness or specification which will in turn allow for whatever voltage?

 

[Randy]

The coin pulse for a Slugbuster coin acceptor is a constant 8 volts DC on the blue wire. When a coin is accepted the 8 volts goes to ground for 50 mil sec.
The Mars validator is a constant 5 volts DC when a bill is accepted it drops to ground for 10 mil sec, if the validator is programmed for a short pulse. A long pulse is 50 mil sec.
For your Dog wash you want to use an AE2602U3 validator.

 

[mjwalsh]

It appears like the more commonly available Mars AE2612U3E will also pulse properly for a PLC & I assume the suffix E means that it comes with a harness to splice into. I suppose that a Mars MDB validator could also work but I would have know a bit more about what is transmitted through the wires of the Mult Drop Bus version. With a MDB version it would be interchangeable with the MDB compatible vending machine validator which would make it more versatile as a backup component.

 

[RykoPro]

In general: Do they require diodes to protect the output solid state relays of most PLCs? From actual experience are some of these items safe to run directly from the PLC output? I am aware of the voltage specs & ranges so that general configuration would be OK.

You should always protect the PLC output relays with the properly sized breaker(s). Normally you would group 16 or so outputs together and distribute the load equally between 5 amp breakers. We use a "push in to reset" type of breakers.
Thanks,
Mark

 

[JIMT]

You should always protect the PLC output relays with the properly sized breaker(s). Normally you would group 16 or so outputs together and distribute the load equally between 5 amp breakers. We use a "push in to reset" type of breakers.
Thanks,
Mark

RykoPro,
Please explain what you mean. I have breakers or fuses on the input power to an output board but no fuses or breakers on the output side of each relay of the PLC.
Thanks,
JIMT

 

[mjwalsh]

I am looking at the specs of some PLCs & some modules have "short circuit proofing" built in. Instant shut down if over 1 amp is detected.

 

[MEP001]

If there's to be any load on the output of a PLC, I use a relay instead of a fuse. I can get a good Omron relay for $4 - cheap insurance to prevent burning up an output that can't be repaired or replaced.

 

[RykoPro]

The coil of the Omron relay is now the load. The relay provides isolation from the device but if the coil of the Omrom shorts, you have no protection. It all depends on the PLC being used and if it provides its own protection. The Mitsubishi's and Omron's Ryko has used for many years do not have internal protection.
For example:
Ryko uses 5 amp circuit breakers to protect 16 outputs at a time (cheaper than one Omron relay per output). This is on the VT 2000 tunnel wash that has many outputs. On the old Voyager that used the Omron C-20, they used 8 amp circuit protectors for 14 outputs. You must add up your loads and then decide how to split it up and what size protection you need. This seems to work well since the only PLC's I have replaced in the past 18 years working on hundreds of different Ryko washes were due to water damage.
Thanks,
Mark

 

[RykoPro]

The Omron C-20 actually has internal output relays that can be replaced by simply removing the cover and pulling the relay from its plug in base. The trick is knowing which relay controls what output. The only was to tell is from the traces on the board (I am not sure the is physically possible) or to use the diagram I have saved for many years.

 

[RykoPro]

RykoPro,
Please explain what you mean. I have breakers or fuses on the input power to an output board but no fuses or breakers on the output side of each relay of the PLC.
Thanks,
JIMT

As stated by MJWALSH, your PLC may have its own circuit protection. Most PLC's I have worked on do not and will require protection of the internal relays of the PLC from any load put on them. It is cheap protection since as I stated before, you can group many outputs together on one breaker. I would go with a breaker rather than a fuse.
In a system with many outputs grouped together, when the circuit protector trips, you will then need to isolate the shorted device. We normally remove all loads and add them back to the circuit one at a time until the protection device trips. You can go the other way too, remove one device at a time until the protector stops tripping. I prefer the first method since it has less of a chance damaging the protective device (if you use fuses, you will need a handful to diagnos the problem using the second method).

 

[RykoPro]

If there's to be any load on the output of a PLC, I use a relay instead of a fuse. I can get a good Omron relay for $4 - cheap insurance to prevent burning up an output that can't be repaired or replaced.

I re-read your post and may have misinterpreted your answer. I realized you may have meant an Omron overload relay. Sorry if I was wrong in thinking you meant a control relay.
Thank you,
Mark