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robh

MicroLogix

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I do a lot of looking on E-Bay for MicroLogix controllers that might work in our plant and or we might not have but would like to play with before we would buy them brand new. I notice that there are a lot of controllers with DC inputs, but it seems that there are fewer with AC inputs. Is this because DC is used more, or the other way around and they are surplus? We use the ML 1200 & 1500 a lot and I also have noticed that most of the expandable I/O is DC as well. We use mostly AC control power, with DC power in specific applications. Just one of those things I was pondering!

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Most of our hydraulics are 120 VAC coils, but we use the 24VDC Micrologix with the Relay outputs (BWA) The reason for this is you get the high speed inputs with the 24VDC Micrologix so you can hook encoders to them. It is probably a 10 to 1 ratio on DC to AC for me Also as a trend more controls are going to 24VDC for safety purposes Edited by TWControls

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How long do your relay outputs last? Or do you isolate them with another relay? I have been using the AB slimline relays for this. They last a lot longer and are cheaper to replace! I see that now they have a wiring system for the 1200.

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No isolation relays. The older ones have 2 amp breakers on each output but found it was a waste of money. Was paying as much in breakers as the Micrologix cost and they never tripped. The newer ones we didn't put the breakers on. The 110 VAC output power going to the relay outputs is protected. I don't know how fast you pulse you outputs but our worst glancing through our programs quickly appears to be 80ms on, 220ms off pulsing a hydraulic solenoid. Hydraulic coils tend to have quite a bit of inrush. That should kill one pretty quick and never burnt an output up in 5 years. Just looked in the manual and nothing popped out about as far as how fast you can pulse them but they can take a lot of inrush. What type of load are you putting on them? Have you burnt up the relay outputs in the past? Edited by TWControls

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You name it. Mostly solenoids for hyd and air cyl pilots. I don't have the specs close at hand, but mostly small stuff. 2.9 watts, 6.8 watts @ 110 vac. Since we have started using the slim relays we have had a lot better luck. Plus it seems to be kinda comforting to some of the maintenance guys to have relays to change, and blame for problems.

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Yes you are correct the trend is towards 24 VDC controls. For a couple of reasons. The 24vdc presents less of a shock hazard to those working with and around it. 24 VDC control also is less susceptable to induced current causing false signals.

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If you need 115 vac ouputs, just add some solid state relays to your 24vdc outputs. They are very inexpension and you dont have to worry about sticking contacts from high inductance loads like coils. Most are about $15 each and can handle up to 3A. I have designed a simple motion controller from a Micrologix 1000 with a single ended encoder using the high speed counter input. It worked like a charm with an inverter. Even had position feedhold control.

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Funny you should mention that. We had a machine that would go through a few of those little cube relays a week. We finally rewired it and I took the relays out of the circuit but being in a hurry I did not remove them, I just removed the wires. What is the first thing everyone still tries when something is wrong with the machine. Yep, they change the relays. Also it is probably old school, but I prefer the relay outputs (BWA) to the FET outputs (BWB). But if you are going to use the solid state isolation relays then I don't guess it would make a difference

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TW- What application do you need your hydraulics pulsing that fast?

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Hum, it is pretty much a stamping/forming machine. But before the part is stamped/formed, a hold down comes down to hold the part in place. The hold down has the cycle I mentioned Edited by TWControls

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I see

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That's why I can't understand why your are burning up relays with 6.8 watt air solenoids. I can't say for sure with our Micrologix, but we have Controllogix doing the same thing with 2 amp fuses on the outputs. If we use a fast acting fuse they will blow during long runs. We have to use time delays so I would say we are pushing the 2 amp relays pretty hard But I won't complain about being lucky

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