surge protection

randy

Supporting Member
Join Date
Apr 2002
Posts
158
We recently received a piece of equipment, which is controlled with a MicroLogix 1500 w/ expandable I/O modules. On one of the output modules there are several solenoid valves that are attached to it. The rating for each solenoid valve is 1.2 amp. The rating for each output is 2 amps. There is no surge suppression on any of the outputs and no fuse protection. We are experiencing problems with the outputs failing. Since the ratings for the output and field devices are so close coupled with no means of protection should I add low current relays to control these devices with the output from the PLC? I would also still add the surge suppression and fuse protection.

Thanks

rmonroe
 
You didn't mention if these units are AC or DC, but if you are direct-connecting to the valves, you really NEED some flyback protection. A diode in DC, a varistor in AC. These are low-cost components, and should be simpler to add than a bank of relays.

Incidentally, if you did add relays, you STILL need flyback protection. The kickback from a discharging coil can be immense, even with a low-power relay.

TM
 
Thanks TM

Does AB offer a terminal that has the varistor or the diode built into it?

rmonroe
 
I dont think A-B has such an animal, but check your valve manufacturer. Most have plugs that come with options, like indicator lights and flyback protection built-in. You can install these on the valves yourself.

Failing that, you can order normal field-assembly plugs for your valve type and install the discrete component right into the plug, across the screw terminals. You can get both diodes and varistors from Newark.

If your valves are direct-wired (no plugs) you can either open the access panel to the valve bank and install them inside (convenient, but not recommended - tends to get overlooked while troubleshooting) or install them in your electrical panel at the terminal strip. To do the strip, it helps if the terminals are the 2- or 3-level type, so you can go from the output signal to the common with little trouble.

Lastly, if the valves are direct-wired to single-level terminals (pain-in-the-butt), replace the terminals. You can get them dirt-cheap from automationdirect.com , add some jumpers and a common bus, then install the protection. This is alot of work, but probably the cheapest route, too.


TM
 

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