# Thoughts on a 1336 issue



## glen1971 (Oct 10, 2012)

So I'm having some grief with an Allen Bradley 1336 plus VFD.. It is controlled by a Modicon PLC with interposing relays on the Enable and the Start/Stop. It has been working fine up until a couple of months ago.. When it stops and they go to restart it sometimes it won't start. The PLC logic is enabling the bits that control each relay, but (for what ever reason) when it doesn't start, cycling the HOA in the field to OFF then back to Auto will make it run. The HOA is wired to DI's in the PLC... There is a 4-20 mA output from the PLC to the VFD for speed control.
I've had issues with the relays before, so I swapped them out (naturally not both at the same time) and it seemed to fix it for 2-3 starts while I was there, then a few days later it would have issues again. I checked the wiring at the relays and it looked ok. Fuses are good in the PLC, and the voltages are good at the VFD.. The VFD is not in Fault, is Enabled, but showing Stopped, until after the HOA is toggled then it ramps up and all is good...


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## backstay (Feb 3, 2011)

If the signals through the relays are really good, I would say you have a problem with the drive. Is the drive old? I remember 1336s from my industrial days 15 years ago.


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## Cow (Jan 16, 2008)

Have you tried pulling all the wires off the digital inputs and manually placing a jumper across the start/enable terminals? If it takes off, you know it's not a drive issue.


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## John Valdes (May 17, 2007)

Sometimes the macro has a reset function that requires the drive to be stopped (open the stop terminal) to be able to start again. Maybe thats why you must cycle the HOA switch before it will work again. 
Its in the two-three wire operating mode if i remember correctly.
I don't remember what type of drive i had this issue with, but one programming correction was all that was required.


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## JRaef (Mar 23, 2009)

Cow said:


> Have you tried pulling all the wires off the digital inputs and manually placing a jumper across the start/enable terminals? If it takes off, you know it's not a drive issue.


Quick and dirty troubleshooting technique. Start with where the problem ISN'T.

Yes, the 1336 is really old, and in fact no longer supported by A-B (they stopped making them in 1998, supported them until 2014 but the components no longer exist). Still, if the drive is not faulting, it's probably good. You might want to start thinking of a migration plan however. AB was offering a kind of a "bounty" for replacing 1336 drives with newer versions, where you got a discount on the replacement drive but I they stopped last year.

On issue with the 1336 was that the Digital I/O on it is internally supplied TTL logic level, i.e. 5VDC, so very low energy. That means if you have interposing relays, as it appears you do, they must be suitable for TTL level signals, because if you get even the slightest amount of resistance in the circuit you lose the signal. So that usually means you must use what are called "Reed Relays" that have the contacts sealed in glass tubes to prevent contamination, or at the very least, gold flashed bifurcated contacts. If you have plain old cheap ice cube relays, they won't last long. Its not that the contacts wear out, its that with very low energy on the contacts, a film can build up on the contact surface and eventually add too much resistance. When you have more energy on the contacts, opening them causes a slight arc, which burns away that film. But at 5VDC, it doesn't happen.


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## Cow (Jan 16, 2008)

JRaef said:


> Yes, the 1336 is really old, and in fact no longer supported by A-B (they stopped making them in 1998, supported them until 2014 but the components no longer exist). Still, if the drive is not faulting, it's probably good. You might want to start thinking of a migration plan however. AB was offering a kind of a "bounty" for replacing 1336 drives with newer versions, where you got a discount on the replacement drive but I they stopped last year.


My local AB distributor is still sending off my 1336's for rebuild. I have two customers left who still have them. I just installed a freshly rebuilt one a week ago and then gave them two more to rebuild yesterday. Obviously, it's not very cost effective compared to the price of a new drive in the same size but I don't have much choice when it's four 1336's in a master slave setup each driving six dairy milking carousels that pretty much never stop. I've been waiting years to replace these things....


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## JRaef (Mar 23, 2009)

Cow said:


> My local AB distributor is still sending off my 1336's for rebuild. I have two customers left who still have them. I just installed a freshly rebuilt one a week ago and then gave them two more to rebuild yesterday. Obviously, it's not very cost effective compared to the price of a new drive in the same size but I don't have much choice when it's four 1336's in a master slave setup each driving six dairy milking carousels that pretty much never stop. I've been waiting years to replace these things....


Well AB is still repairing them if they can get the parts, but that's the problem now. Many of the components no longer exist, the companies that made the components no longer exist in some cases, and the back stock AB kept of a lot of those is now depleted. Most of the repair shops are scavenging old units to get parts, so the repaired drives are being repaired with old parts from other dead drives. 

Cuba made that work for cars for a few decades, I suppose it can continue for a while, but you might consider having a plan in place...

I'm working with a pharmaceutical company on this issue right now. They have hundreds of 1336 drives in "validated" machinery (meaning FDA approval) so changing anything on those machines practically takes an act of Congress. But what we do is build a panel with a replacement on it that will drop right into the same box, same wire numbers, everything the same, then applying for the validation even when the old one is still running. So when a drive goes down, they are replacing it with another "in kind" validated drive in less time than it takes to get the old one repaired.


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## glen1971 (Oct 10, 2012)

Thanks for the replies! I guess I'm gonna go with getting a newer drive and see if that does it.. I'm still baffled as to why cycling the HOA (to the PLC) will make it run, if it's already being told to run by the PLC (interposing relays)...

The control on the drive is 120 volt (taken from the line side supply).. There is also one other DI in the drive that has to be satisfied before it will run, and that one is hard wired to the control power supply fuse..


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## John Valdes (May 17, 2007)

glen1971 said:


> Thanks for the replies! I guess I'm gonna go with getting a newer drive and see if that does it.. I'm still baffled as to why cycling the HOA (to the PLC) will make it run, if it's already being told to run by the PLC (interposing relays)...
> 
> The control on the drive is 120 volt (taken from the line side supply).. There is also one other DI in the drive that has to be satisfied before it will run, and that one is hard wired to the control power supply fuse..


Once again. If the drive is in 2 wire mode, the stop input must be toggled off then closed again before the drive will accept the start input.
Are you sure no one has changed some parameters?


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## glen1971 (Oct 10, 2012)

John Valdes said:


> Once again. If the drive is in 2 wire mode, the stop input must be toggled off then closed again before the drive will accept the start input.
> Are you sure no one has changed some parameters?


Not that I know of.. If anything maybe helping to ride through power bumps, but the issue was happening before that...


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## John Valdes (May 17, 2007)

glen1971 said:


> Not that I know of.. If anything maybe helping to ride through power bumps, but the issue was happening before that...


I would look at the macro for operation and make sure its in three wire mode if thats what you are using.
If its in two wire mode and wired for three wire mode, it makes sense that turning the HOA switch to off then back on will let it run.
Let us know as I want to know for sure myself!

ps....I have seen on some drives a single parameter that will enable you to use two wire mode without interrupting the stop circuit.


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## glen1971 (Oct 10, 2012)

John Valdes said:


> I would look at the macro for operation and make sure its in three wire mode if thats what you are using.
> If its in two wire mode and wired for three wire mode, it makes sense that turning the HOA switch to off then back on will let it run.
> Let us know as I want to know for sure myself!
> 
> ps....I have seen on some drives a single parameter that will enable you to use two wire mode without interrupting the stop circuit.


So I did some more lookin on site and it looks like it is on 2 wire control.

I changed out the inperposing relay bases, in the event they are weak from the 15+ years of vibration in the PLC cabinet.

When we went to restart the site, both inputs from the PLC (enable and the stop command) were true. But the drive tripped on an overvoltage fault (05).. Switching the HOA to Off, removes the Stop DI to the drive and clears the fault. Turning it back to Auto restarts the drive.. When I did some measuring the line to ground was high (130 vac) at the drive input, and 220 vac phase to phase.. 
Once the compressor's VFD (1557) was at speed and running normally the voltages were back to around 120/208... I thought of one change as I left site that might be our culprit.. We did an engineered change to "Accel Time 3" on the 1557 from 14 to 21 seconds.. I am wondering if this change is causing the spike to the 208 volt bus and causing our grief?? The 1557 is running a 1,000 hp, 2,300 volt recip gas compressor.


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## John Valdes (May 17, 2007)

Next time it will not start, push in any "stop" button anywhere on the machine that is connected to the "stop" input terminal. 
If opening then closing the "stop" circuit" allows the drive to run, its a parameter that must be changed.
I am trying very hard to remember which parameter it was and what drive it was on.

oh.....hold on. I think it was the enable input that required switching. Look at the parameters again.
Make sure the enable input is true when you cannot restart the drive. If the enable input is open, then hitting a "Stop" button may be the only way the close/reset it.

I hope I'm making some sense here Glen.


Glen. You indicate cycling the HOA switch fixes the problem. Don't go off in another direction. The issue is in the wiring and or programming. Its not a voltage issue from what you have told us.
Stick with that circuit until you SEE whats wrong.


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## glen1971 (Oct 10, 2012)

John Valdes said:


> Next time it will not start, push in any "stop" button anywhere on the machine that is connected to the "stop" input terminal.
> If opening then closing the "stop" circuit" allows the drive to run, its a parameter that must be changed.
> I am trying very hard to remember which parameter it was and what drive it was on.
> 
> ...


John... Thanks for your help! Another set of eyes can help to refocus and find a possible overstep or over thinking of what's going on...

I believe it is a voltage spike, after seeing and measuring yesterday, that is causing the issues now.. The overvoltage fault is driven from a spike on the DC bus to above it's limit. When the drive faults and the operator cycles the HOA to "Off" it will clear the alarm, and when it is put into "Auto" the Stop input and Enable inputs are already true, so it will start..

Doing some more reading there are 4 inputs that need to be true for the drive to start.. 
1) Enable - It is controlled from a relay in the PLC
2) Start - It is hard wired from the control power, so it will never lose power (unless the control fuse blows)
3) Auxillary - It is hard wired from the control power, so it will never lose power (unless the control fuse blows)
4) Stop - It is controlled from a relay in the PLC.

The HOA is run to 2 PLC inputs, and then the logic in the PLC controls the Enable and Stop. The Enable is energized as soon as the station is reset and ready for a start. The Stop is energized as soon as the compressor starts up.

The voltages spikes and "Overvoltage Fault" I saw occur when the Compressor Contactor on the VFD pulls in. After the motor is up to speed, the voltages settle out...

One of our fixes involved replacing the relays, one at a time, and that seemed to fix their associated problems (ie - Not Enabled when the relay was seeing 24 volts).

There is a power factor capacitor and harmonic filter on site that engages, and we are looking at the possibility that when we changed the motor Accel time, we may have an created an unexpected issue.

Not sure if it's relevant, but the 2,300 VFD supply and the 208 volt bus are fed out of the same transformer...


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## JRaef (Mar 23, 2009)

> ... The voltages spikes and "Overvoltage Fault" I saw occur when the Compressor Contactor on the VFD pulls in. After the motor is up to speed, the voltages settle out...


Are you referring to an AC compressor being used to cool the 1557?

If that's the case it's not unheard of, especially if the compressor contactor is using a line voltage coil as they often do. I've had that happen, and I solved it by just putting a surge suppressor on the contactor coil. People don't realize how nasty that inductive spike is when you close a line voltage coil. It causes SCRs to self-commutate (turn themselves on) briefly when they are not supposed to. 1336 drives used SCRs instead of diodes on the front end rectifier, that might explain it.


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## John Valdes (May 17, 2007)

I guess I'm confused. I thought cycling the HOA switch fixed the issue?


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## glen1971 (Oct 10, 2012)

JRaef said:


> Are you referring to an AC compressor being used to cool the 1557?
> 
> If that's the case it's not unheard of, especially if the compressor contactor is using a line voltage coil as they often do. I've had that happen, and I solved it by just putting a surge suppressor on the contactor coil. People don't realize how nasty that inductive spike is when you close a line voltage coil. It causes SCRs to self-commutate (turn themselves on) briefly when they are not supposed to. 1336 drives used SCRs instead of diodes on the front end rectifier, that might explain it.


Sorry no... The contactor I was referring to is on the 1557 VFD.. The 1557 runs a sour gas compressor, and the 1336 in question runs a motor for an aerial cooler for part of the process..


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## glen1971 (Oct 10, 2012)

John Valdes said:


> I guess I'm confused. I thought cycling the HOA switch fixed the issue?


It is confusing for me too, trust me.. I was under the original assumption that was the case, but like I say after some investigating I found that it resets the fault on the drive, which was caused by the "overvoltage" condition... Cycling it toggles the stop command to the drive, clears the fault and when returned to Auto starts the drive...


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## JRaef (Mar 23, 2009)

glen1971 said:


> Sorry no... The contactor I was referring to is on the 1557 VFD.. The 1557 runs a sour gas compressor, and the 1336 in question runs a motor for an aerial cooler for part of the process..


Ah, so it's the line contactor that's ahead of the drive then. That will be a vacuum contactor, and they have a line voltage coil too. It's actually DC through a rectifier and if you have the IntelliVac controller or it, that has surge suppression built in. But at this age, the surge suppressor may have failed.


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