Variable Frequency drives, Finding the right one

[hurk27]

Ok I have a small job to put controls to a mixer.
Let me start with what the application is.

The mixer is an ex large cement truck back unloader, mounted on a frame bolted to the floor in a place that processes material for the mills, it has a 20 HP standard 9 lead motor with E class insulation, 1750 rpm's belt driven through what looks about a 4:1 ratio to a gear drive unit that has a 11:.89 ratio the gear drive has about a 6" sprocket that drives a chain around a 5' sprocket welded on the back of the mixer drum.

Motors voltage is 230/460
FLA is 57/28
plant power is 208/120 3/phase 800 amp MDP

Now I was told this setup was originally controlled by a 3-pole transfer switch (nothing surprises me:roll that would reverse two leads in one position from the other and a NEMA 3 starter.

The new owners would like to have speed control and reversing jog capability.

I have already told them that to use this motor under the rated speed we would have to add additional cooling fan independent of the motor speed, to the back of the motor, and I could not guarantee the life of this motor, they said that they didn't care as long as it got into operation and they will purchase the proper inverter rated motor at the time this one fails.

For the most part the motor will run full speed in FWD, but since in reverse is has to be controlled to empty the drum, inside the drum are flights that form a screw to back out the material.

Now the question?
I have been pouring over the details on so many VFD's I seem over whelmed.

Can any one narrow down out of the hundreds of VFD manufactures which drive can possibility do the above job with the least amount of programing, and install.

External FWD, STP, REV, And maybe a analog VR for speed control would also work, but would like to keep it simple (cost wise) to the unit to have the required functions on the unit.

Guess it's like HELP

At least who knows of any suppliers who would have a tech line to discuss which drive to use, I was trying to deal with the Drives Warehouse but ran into a dead end with them.

 

[jim dungar]

Buying VFDs is like buying a laptop or a cell phone, in all honesty it is unlikely that you can find one that does not work as far as functionality goes. So make your choice on local support.

But, you need one sized correctly. Do not make a selection based solely on the HP rating. Your drive needs to be sized to start and stop(?) a fully loaded mixer.

Across the line starting of a motor produces a whole lot of starting torque, but a VFD will not. Most VFDs are limited to about 1.1 (maybe 1.5 if you are lucky) times torque.

Can you take measurements of existing starting currents?

I would not be surprised to find you needing a 60HP drive to feed your 20HP motor.

 

[petersonra]

Buying VFDs is like buying a laptop or a cell phone, in all honesty it is unlikely that you can find one that does not work as far as functionality goes. So make your choice on local support.

But, you need one sized correctly. Do not make a selection based solely on the HP rating. Your drive needs to be sized to start and stop(?) a fully loaded mixer.

Across the line starting of a motor produces a whole lot of starting torque, but a VFD will not. Most VFDs are limited to about 1.1 (maybe 1.5 if you are lucky) times torque.

Can you take measurements of existing starting currents?

I would not be surprised to find you needing a 60HP drive to feed your 20HP motor.

What he said. With this kind of load you need to look at starting torque. A vector drive may be of some interest, as you don't get much torque at all at zero speed with a standard VFD.

 

[Jraef]

I'll echo the primary issue of local support, especially since it appears you are new to the exciting world of VFDs. VFDs have to be pretty good to survive in a tough market, so the differences are minor from a product standpoint. Look for someone with a staff specialist that can meet you at the job site if you get in trouble, if they rely on an 800# from a factory, look elsewhere.

You want a good quality Vector drive for this. Of the available major mfrs out there, I like the ABB ACS550 as the simplest setup and programming. Toshiba, Yaskawa are good too, as is Allen Bradley but for them, you will likely pay a premium (their motto seems to be "You can always find better but you'll never pay more!"). I also like the old TB Woods drives, now sold as Vacon X Series. Siemens, Schneider (Sq. D / Telemecanique), Vacon (other than the X Series) and Emerson / Control Techniques all make good drives, but the programming leaves a lot to be desired; they are what I call "systems drives" because if you have a large overall system and want to leave the programming to an Engineer, they are good but if you want to turn a shaft, you will probably be frustrated. Also-rans (meaning OK products but programming is translated from another language): Teco, LG (LSIS), Hitachi and many smaller brands are private labels of one of the above.

A few to stay clear of (just my opinion); AC Tech / Lenze / Leeson (cheap) and Delta / Automation Direct (cheapest out there). These are still not horrible, but they focus on being the cheapest options so their support sucks because they can't afford it. Baldor has good tech support but I have seen some serious QC problems with them over the years, I still can't recommend them.

 

[ptonsparky]

Local support for drives is a pretty limited feature in this area. AB is good but as stated you pay upfront and sometimes again. I have only used one ABB and I did think it was the easiest of the more feature inclusive drives. I would not worry about braking or slowing the drum with the drive. Just let it cost to a stop, then reverse it. May need a motion detection of some sort. Some of the drives have a constant torque setting vs one for fans & pumps. The SQ D were more a pia but the 800# walked us right through the problem area. Just state your a virgin up front.

I have used small Automation Direct drives. Cheap, simple and good to learn on. I bought a small one that would take 1ph in and used it in my shop for some years. It is now on my submersible well.

Working with VFDs has put a new level of fun in the job.

 

[hurk27]

Buying VFDs is like buying a laptop or a cell phone, in all honesty it is unlikely that you can find one that does not work as far as functionality goes. So make your choice on local support.

But, you need one sized correctly. Do not make a selection based solely on the HP rating. Your drive needs to be sized to start and stop(?) a fully loaded mixer.

Across the line starting of a motor produces a whole lot of starting torque, but a VFD will not. Most VFDs are limited to about 1.1 (maybe 1.5 if you are lucky) times torque.

Can you take measurements of existing starting currents?

I would not be surprised to find you needing a 60HP drive to feed your 20HP motor.

Thanks Jim, as yes this is an area where I'm kind of little green in, and back when I was more into motor controls, soft starts were just coming out, and VFDs were a promise of the future, and I have been doing some crash course reading to try to learn all the ins and outs with the basic needs of the installation in mind, to give the customer the right options for the right price.

Tomorrow I will be going to the plant and will see if we can do a temp hook up to test the amount of torque needed, with the large gear reduction I wouldn't think it would be a lot, since the motor can be turned by hand fairly easily. I think the belts provides more of a resistance then the actual load of the mixer.

What he said. With this kind of load you need to look at starting torque. A vector drive may be of some interest, as you don't get much torque at all at zero speed with a standard VFD.

Thanks Bob
Most of the newer VFD's I have been reading about are sensor-less vector drives, and everything does point in this direction. the main questions I had were in the ease of installation and field programming which were very well pointed out in the next post below.

I'll echo the primary issue of local support, especially since it appears you are new to the exciting world of VFDs. VFDs have to be pretty good to survive in a tough market, so the differences are minor from a product standpoint. Look for someone with a staff specialist that can meet you at the job site if you get in trouble, if they rely on an 800# from a factory, look elsewhere.

You want a good quality Vector drive for this. Of the available major mfrs out there, I like the ABB ACS550 as the simplest setup and programming. Toshiba, Yaskawa are good too, as is Allen Bradley but for them, you will likely pay a premium (their motto seems to be "You can always find better but you'll never pay more!"). I also like the old TB Woods drives, now sold as Vacon X Series. Siemens, Schneider (Sq. D / Telemecanique), Vacon (other than the X Series) and Emerson / Control Techniques all make good drives, but the programming leaves a lot to be desired; they are what I call "systems drives" because if you have a large overall system and want to leave the programming to an Engineer, they are good but if you want to turn a shaft, you will probably be frustrated. Also-rans (meaning OK products but programming is translated from another language): Teco, LG (LSIS), Hitachi and many smaller brands are private labels of one of the above.

A few to stay clear of (just my opinion); AC Tech / Lenze / Leeson (cheap) and Delta / Automation Direct (cheapest out there). These are still not horrible, but they focus on being the cheapest options so their support sucks because they can't afford it. Baldor has good tech support but I have seen some serious QC problems with them over the years, I still can't recommend them.

I appreciate your response as this was kind of area I was lost in, kind of the deal like you know all cars will go down the street, but which ones provides the ease of operation and learn ability, reliability, and service support, I have downloaded the PDF's from ABB and they look good, and I have a call into there tech support which should give me a call back tomorrow.

All in all life is a learning game, and I'm trying to offer expanded abilities to broaden my options for gaining work, and as a learning tool to further my knowledge into more areas.

I want to thank you for the replies and as this progresses I will have other questions or feed back.

 

[hurk27]

Local support for drives is a pretty limited feature in this area. AB is good but as stated you pay upfront and sometimes again. I have only used one ABB and I did think it was the easiest of the more feature inclusive drives. I would not worry about braking or slowing the drum with the drive. Just let it cost to a stop, then reverse it. May need a motion detection of some sort. Some of the drives have a constant torque setting vs one for fans & pumps. The SQ D were more a pia but the 800# walked us right through the problem area. Just state your a virgin up front.

I have used small Automation Direct drives. Cheap, simple and good to learn on. I bought a small one that would take 1ph in and used it in my shop for some years. It is now on my submersible well.

Working with VFDs has put a new level of fun in the job.

I was kind of thinking the same thing to avoid the breaking resistor and feed back on to the DC buss, most mixers would be kind of like a front loader washing machine, the product in it, would tend to want to stop the drum since it always sits in the bottom, the overall load would or should be linear except if large chunks of solids were to be put into the drum, but the mouth of the drum should block that from happening, the torque load will fluctuate a little as the drum turns with product, but not to any extent, this is because of the design of the flights inside the drum in FWD will just turn over till the product spills back down to the next flight which might create a little torque change but I don't see it as being much.

I have (as I allways do) analized many angles to this install, just knowing which ones are the important ones is the key, thats where you guys great minds come in

 

[hurk27]

I want to thank everyone for their responses, as I should have posted here first before trying the thread through all the company's and suppliers out there that was making this such a difficult drive to line up, and I want to thank jraef for the post about ABB, they were great, pricey but worth it in my book, there tech support is about the best I have dealt with, and the went out of there way to give me the pointers to watch, and even a cell number to call if I have any problems or questions.

now this is the way company's should respond to potential customers.

I'm doing a trial temp full line voltage startup tomorrow, to test a few parameters such as start up current, in rush, and thermo after 15 min.s of running, after I had given Jim @ ABB the info on the existing motor he feels it will be one of the best as a standard rated motors that I could have used for this, of course a 200 volt motor would have been better for the 208 service, but he feels the 208 shouldn't be a problem if the torque ratings come back low as he thinks it will with the gear reductions it has. this motor is a US motor all aluminum case with 2" high heat sink fins which will be great at dissipating more heat when the motor is run at lower speeds, the windings are E-class so they should be good to go, and I'm going to do some meggering to make sure there in good shape, motor looks fairly new and in great shape.

I will keep ya posted as it goes and might even snap a few photo's as it progresses.

Again Thank's everyone.

 

[iwire]

Can they load a sample batch in the unit for testing?

 

[jim dungar]

Can they load a sample batch in the unit for testing?

They had better.:grin:

The highest starting torque requirements will be as the operation is moved from mixing (forward) to emptying (reverse), when it is full of wet product which is at a standstill.

 

[hurk27]

Well we did the test run today wired to a simple manual motor starter.

Used peak hold on my amp probe, to capture a inrush of 215 amps, and saw a start up current peak of about 110 amps, but the full run amps was only 13-14 amps, we loaded the drum to a full load of what they would normally run (about 1 ton of material), and the load current went up to about 21 amps, start up current went to about 146 amps, or about 3x the FLA of the motor, the inrush was still at the 215 amps.

We checked the RPM of the drum and it made about 5.75 revolutions in one minute, as I suspected with this kind of gear reduction theres really not much in the way of torque seen by the motor, and the motor is quite over sized for this job, as a 10 hp motor would have been fine on it.

So while emptying the drum, we notice the material doesn't really come out that fast, and really easy to control, and speed was not an issue.

So after all this we realized that a simple start stop for FWD and a Jog button for REV control is all that is needed, I also suggested a key switch to prevent operation when not authorized, as well as a mushroom stop button at the load/unloading end of it, other areas around the mixer will be guarded off, to prevent access, I did stress all the safety points to them that needed to be addressed and they agreed. and since they were the ones who suggested speed control, all was not in vain, so my time on the research will still get billed.

Thanks again.

I asked about taking some photos of it, but they were not to liking of the idea, company policy I guess, so I didn't push it.

 

[Cow]

So after all this we realized that a simple start stop for FWD and a Jog button for REV control is all that is needed

If your pushbuttons won't be in the same cabinet as the VFD we usually use them to seal in an ice cube relay with a seperate 120v control circuit. Set your drive up for a 2-wire start/jog and just run the drive's 24VDC inputs through the relay contacts. I prefer to do it this way just to keep the drive's 24VDC right around the drive rather than running way out into the field to pushbuttons where the wiring may eventually short out.

I'm a fan of AB myself, but mostly because I'm familiar with them. I could probably say the same for ABB too, if that's what I learned on...

Getting familiar with the menu structures and how the drive manufacturers label their different operations and settings is half the battle for me. It REALLY cuts down on the programming time once you're familiar with them.

 

[Cmdr_Suds]

This sounds like a "Constant torque" application as opposed to a "variable torque" application Make sure the salesman sizes the drive accordingly. variable torque is for centrifical pumps and fans. Also, if the motor is located any distance from the drive panel and it is going to have a safety disconnect, I would highly recommend interlocking it to the drive so that it shuts off the drive and that the drive has to be manually restarted. I have seen too many drives killed when the owner uses the safety disconnect as a remote start/stop station.

 

[hunt4679]

Check automation direct for vfd's we have installed about 30 or so at the chemical plant i work at and have no problems what so ever for 1/3 the price