# Odd one i came across a few weeks back



## gpop (May 14, 2018)

Allen Bradley 75hp powerflex powering a 50hp booster pump.

Got a call that the booster wouldn't make 200 gpm. Operator tried 100% manual and the flow topped out at 180gpm. (been running that way all night)

Went to the drive and it was reporting over amp-decelerating then it would ramp up a few hertz and repeat. Drive said that the amp reading was around 36 amps.

My first thought was someone had been fat fingering in the vfd menu so I checked and fla was set at 62 amps.

Seemed odd. I just happened to have my fluke t5 on me and the cables were easy to get to so I put one cable in the loop and it read higher than the drive was reporting. I placed all 3 in the loop and it read the same.

I turned to walk away when I got the WTF that's not possible.

Well it turns out that it is possible to loss a output leg on the drive with no alarm or warning. 

In a booster situation where the pump is being turned even when the vfd is turned off. If you start the vfd because the rotor is already turning and has direction the drive seems happy to go ahead and run on 2 legs. The drive seems to gets a little confused on the amps but there no complaining or alarms.

The problem ended up being a spark catcher on the C leg of the disconnect between the vfd and motor had dropped in front of the knife so only A and B closed. (yes it has a enable contact in the disconnect and that was closed even with the jammed knife)

Just goes to show that its better to go back to basics rather than ruling out what shouldn't be able to happen.


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## LARMGUY (Aug 22, 2010)

Absofreakinlutley!

There is ALWAYS a cause. YOU, just have to find it.


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## JRaef (Mar 23, 2009)

That’s because the PF750s are designed to be able to be used to power single phase devices such as resistive heaters, so it doesn’t have a fault for output phase loss. But to use it that way, it needs about a 67% de-rate because it’s hard on the DC bus in terms of causing ripple. So the drive likely went into Current Limit in order to facilitate that single phase load.


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## gpop (May 14, 2018)

JRaef said:


> That’s because the PF750s are designed to be able to be used to power single phase devices such as resistive heaters, so it doesn’t have a fault for output phase loss. But to use it that way, it needs about a 67% de-rate because it’s hard on the DC bus in terms of causing ripple. So the drive likely went into Current Limit in order to facilitate that single phase load.


Learn something new every day.
Might have to break out the manual and see if there's a parameter in there for load loss.


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## paulengr (Oct 8, 2017)

Got to be one of the 1400+ settings in that drive.


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## gpop (May 14, 2018)

looks like its set under utilities 240 something and its done on the bit level. By default its off. (wouldn't have guessed off by default)
Will have to check when im back at work just to be sure im looking at the correct manual (700 series I think).

Ive been so spoiled over the last 10 years using abb where everything is in in English and easy to navigate it all most feels unfriendly having to re-read the ab manual.


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## paulengr (Oct 8, 2017)

gpop said:


> looks like its set under utilities 240 something and its done on the bit level. By default its off. (wouldn't have guessed off by default)
> Will have to check when im back at work just to be sure im looking at the correct manual (700 series I think).
> 
> Ive been so spoiled over the last 10 years using abb where everything is in in English and easy to navigate it all most feels unfriendly having to re-read the ab manual.



It depends on the HIM module you have. AB sells roughly 3 different models for each drive series. Some have English, some have English and a speed pot and similar controls, and some just flash numbers at you. Other manufacturers are the same way. But if you run drive tools or in this case connected components, you get everything through your laptop although depending on the model some require a "cobra head" adapter to connect to it.


The 750 series replaced the 70/700 series. The 70/700 series are "kitchen sink" drives...every bit of I/O and you can even have an on board PLC stuffed in them, and competed against the 40/400 series which were the same drive minus all the extras. Customers railed against the obscene (even for AB) pricing on the 70/700 drives so eventually AB knew they had to do something. They more or less discontinued the 4, 40, 400, 70, and 700 series over time and introduced the 750 series which is essentially the 70/700 series with even more features (and settings) but it's modularized so you install just the options you actually need which brought the price down. This put them without a "low end" drive for machine builders so eventually they relented and introduced the 525.


I just cringe every time I have to mess with one because AB support around here in the Raleigh area is TERRIBLE but their stupid territory rules force me to deal with it. I've done much better supporting Schneider, ABB, and even (ugh!) Cutler Hammer.


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## gpop (May 14, 2018)

I have drive explorer which works fine for what I need to do even if it is no longer supported. 

I have nothing against ab drives now but years ago it was a different story. The end of the 1336 and beginning of the powerflex was a nightmare for the people using remote I/O. Add to that the poor packaging, technical support and the fact I felt cursed due to "failed on start up" issues abb seemed like a god send. 

Working in south florida where lightning is a ever present threat and having around 100 drives on site you tend to prefer the easiest drive to install with the least amount of headaches. 

I still dread loosing a 1336 knowing I have to upgrade to powerflex and reprogram the ladder logic because no one thought of adding a 16 bit emulator to the 20comr4 card. 

As we upgrade the plc's (plc-5 to control logixs) we are removing remote I/O and going back to hardwiring so these may be the last ab drives we use. (carnt complain really if you consider how old some of these drives are).


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## wilburwm (Jul 31, 2018)

In my company, we run multiple sets of load wires in the same raceway. We always use shielded VFD cable though.

I am curious about the "They more or less discontinued the 4, 40, 400, 70, and 700 series over time and introduced the 750 series..." comment. We use the PF 70 series quite a bit. Most of the models are still listed as active by Rockwell.


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## MDShunk (Jan 7, 2007)

wilburwm said:


> I am curious about the "They more or less discontinued the 4, 40, 400, 70, and 700 series over time and introduced the 750 series..." comment. We use the PF 70 series quite a bit. Most of the models are still listed as active by Rockwell.


Stick around and you'll figure out that Paul has some wisdom to convey, but a lot of what he says seems to be pulled out of the clear blue sky. 

It is true that the models he spoke of aren't really used for new builds these days by integrators and panel builders that like to keep up with the times, but they're still quite available.

I won't be sad when 4, 40, and 400 finally are obsoleted. They're junk from the day they are installed, in my opinion.


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## JRaef (Mar 23, 2009)

wilburwm said:


> In my company, we run multiple sets of load wires in the same raceway. We always use shielded VFD cable though.
> 
> I am curious about the "They more or less discontinued the 4, 40, 400, 70, and 700 series over time and introduced the 750 series..." comment. We use the PF 70 series quite a bit. Most of the models are still listed as active by Rockwell.


 When there is a large installed base, Rockwell doesn't simply make older products obsolete the way smaller companies (and a few very large ones) do. All of those VFD models are still valid, but are referred to as "Active Mature", meaning they will no longer spend any money developing or improving the product. There are 4 official stages for Rockwell product life:


*ACTIVE:* Most current offering within a product category.
*ACTIVE MATURE:* Product is fully supported, but a newer product or family exists. No further product development or improvement.
*END OF LIFE:* Discontinued date announced – actively execute migrations and last time buys. Product generally orderable until the discontinued date.
*DISCONTINUED:* New product no longer manufactured or procured.


There is an unofficial final stage, Obsolete, wherein the parts to _repair_ them are no longer made. That's where the old 1336 drives are now.



But so long as the parts are still available, they will offer them for sale. 



What they do however is raise the prices on them once there is a newer model available, making it expensive to keep using the older models. The PF70s in particular were not raised for a while after the PF750s were released because the 750s were not available in 240V for a long time. But that recently changed, so now the PF70s will go up too.


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## paulengr (Oct 8, 2017)

The 4 was made in response to the low end Altivars and Chinese drives. It’s a cheap drive something you would put on a low end piece of equipment for maybe fan control. It was made for the $100 drive market. If you wanted a cheap diode front end, no filtering, V/Hz one chip controller kind of drive, that’s what it was. In a way it was a bad marketing decision because the people that focus on price alone don’t buy AB drives.

The 70s were so high priced they almost priced themselves out of the market when they were introduced. The 70s are like the “kitchen sink” model. Meaning except for the cassette ports it had everything in one drive. For the 750
series AB took the basic power end and modularized the rest of the drive so you just buy what you need extra of. That got the 70 price down to something very competitive.

When you had a more basic need like fan/pump drives, the 40/400 fit well. It was targeted towards OEM/machine builders ala the 525 of today but the niche was more of a fan/pump drive. I could never figure out why they didn’t market it for what it was.

The machine builders weren’t happy though paying for a “big” drive for tight machine control but forced into the 700S or maybe the 70 which was even more crazy expensive. So the 751/753/755 fit that niche too. But I’ve seen 500s used as “amplifiers” on a tire assembly machine as part of a servo system.

It took a while to absorb the whole 70 product range with various 750 series models. So unlike the whole Powerflex introduction where they tried to immediately downplay the 1336s the migration towards the 750 series was slower but unlike 1336/70 the 750 series kind of sold itself unless you wanted a one drive does everything solution. There are still some limitations. Like you can get a Controllogix PLC on board or on a cassette in the 70 chassis but not in the 750 series at least last time I ran into that. You can’t get RIO in communication cards either. There are probably more things I’m forgetting.

As explained to me by an AB drives engineer when I bought two 7000 series 1750 HP AB VFDs (over the Toshiba that has been around for over a decade) when AB develops a new power stack/drive they get the chip vendor on a 20 year contract. 10 years of new sales, 10 years of mature product support. They target a 100,000 hour operating life for all components. That’s about 11 years. So if you buy inside the first ten year window you should be able to get service, parts, and replacements for at least 10 years, maybe 20 if you bought at the beginning of the cycle. If you continue to buy drives in the second ten year window, you’re getting towards the end of product life. After that they will service/support as long as they can but the chip vendors are off the hook so it might not last long. A TMEIC engineer described the same thing and they have a nice PowerPoint. See page 43:

http://www.wmea.net/Technical Papers/GE Medium Voltage Drives.pdf

Just like Intel comes out with a new CPU chip line about every 5 years, power semiconductors have a new chip line about every 10 years. I don’t know what drives it but 10 years or 100,000 hours is a magic number.

As an end user given this scenario and thinking that down time is money I’d want my drives in the first 10 years. I might not want year one (debugging) or year 10 but years 2-8 are the best. That way I can just swap drives or parts when it breaks once or twice.before it needs to be retrofitted to a new model.

As an equipment builder considering the cost to redesign things I want to wait a little for the debugging phase (year 2) then continue to buy drives as long as I can without running into my own warranty window so well into years 11-20 even if I’m ultimately screwing my customers in terms of long term support past warranty. If I wait too long though I’m selling drives perpetually in years 11-20 because I’m waiting too long to adopt the new one and I don’t want to stretch it out so far I’m using obsolete drives (warranty trap) then jumping to year 1 just to skip a whole generation.

My company is a distributor for a couple different VFD manufacturers. We’ve seen this same pattern play out across the board. Schneider just came out with the 300/600/900 line in the past year or two. Teco just obsoleted everything but the E5xx/F5xx/A5xx lines in the past year and they just got away from the MA7200 line in the last upgrade/obsolete cycle. Only LSIS (aka LG), private branded by multiple vendors seems pretty quiet right now.



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## tmessner (Apr 1, 2013)

Been there done that. We could tell when the underground broke feeding a small well vfd. It would go out on overload because of the increased load on 2 lines instead of 3.


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