Braking ??

stasis

Member
Join Date
Mar 2005
Location
Columbus, Ga
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Does anyone know what options are available for braking instantaneously, other than using servos? We have an older (circa 1969) RDC machine that has a 50HP DC motor & a Flexpak 3000 drive. Since parts are harder to come by, our plant manager asked about swapping this for an AC set-up. The only throwback I can see to this option is braking (like in the case of an E-stop). I'm sure most are familliar with dynamic braking, but what type of options are available for AC? The only thing I can offer is mechanical braking, but wanted to see if any of you that are more 'in the loop' technology-wise could offer any suggestions...
 
You could use DC to stop the motor, but that is a pretty abrupt stop for a 50 hp unit. An alternate for an emerggency stop would be an electric release spring applied brake on the motor.
 
We have an older (circa 1969) RDC machine that has a 50HP DC motor & a Flexpak 3000 drive.

The Flexpak is fairly new in terms of DC drives, it shouldnt be hard to repair or replace. Built in 69 it probably had a Maxpak, mogen(or similar) originally and the Flexpak replaced it in recent years.

I dont think I would replace the Flexpak, I dont see any benefits at this time.
 
Rsdoran, the drive was replaced about three years ago...couldn't get the SCR's for the maxpak cheap enough. But, since the manager said replace it...we have to. I'm not sure about the braking, but as stated, I can only see mechanical braking as an option. I'm not confident that mechanical braking will stop a 50+ HP motor (2500 RPM) efficiently, or that the costs of maintaining/replacing a mech brake will be worth it.

Tom,what do you mean using DC to stop it? So far, the alternatives are to use either a mech set-up or an AC brake mounted on the tail end of the motor...
 
VFDS offer dynamic and regenerative braking. (Note: The Flexpak 3000 is/or may be regenerative) A VFD actually uses a DC bus so it can "inject" DC into the motor for braking, there are several options including an electro-mechanical brake depending on how fast you want to stop and if you need to "HOLD" it when stopped.

The price tag on this will be up there but as I mentioned I dont see any benefits. May want to have a drive specialist come in and take a look.
 
Does the 50 HP motor have to stop or just what it is driving?

A company called Horton Industrial Products 612)331-5931 makes Clutch/Brakes that would drive the work and stop it with air or electromagnetic force by disconnecting the motor from the load.
 
Let me clarify some things I think I know

Stasis is in the paper (corrugated) business. It may depend but usually where any paper is involved there is a web (or something similar) that may require tension and a controlled stop. Corrugated paper isnt rewound in many cases so using the rewind for tension control isnt always an option. Having dealt with a GP plant right around the corner it can be demanding work.

Is RDC a rotary die cutter or dip coater?

Even though AC drives have come along way they may not always match DC drive capabilities and performance. DC drives have been around and used for ALONG time and with the advent of DIGITAL DC drives they offer even more capabilities, options and/or features.

I know bosses are bosses and always right but you may be spending money that would be better spent on upgrading another area of the machine depending on issues/problems you may be having. The cost may not be real high but its bound to be 5 digits.

I still suggest you get a Flexpak drive specialist in to verify the unit and motor are properly tuned. He may also be able to determine if there are mechanical problems that may be creating issues. It also gives you and maybe others a training class.

This is something I would take slow but if you do remove the Flexpak and DC motor when can I haul them off for you?
 
stasis said:
Rsdoran, the drive was replaced about three years ago...couldn't get the SCR's for the maxpak cheap enough. But, since the manager said replace it...we have to. I'm not sure about the braking, but as stated, I can only see mechanical braking as an option. I'm not confident that mechanical braking will stop a 50+ HP motor (2500 RPM) efficiently, or that the costs of maintaining/replacing a mech brake will be worth it.

Tom,what do you mean using DC to stop it? So far, the alternatives are to use either a mech set-up or an AC brake mounted on the tail end of the motor...

If your drive (AC or DC) is rather new you should take a look at the manual. There should be a braking feature that will stregthen the fields and cut armature current. If not you might be able to set it up with one of the paramater settings. Depending on the mass (armature & load) you might get a quick enough stop. An additional motor mounted disc brake (Like from Dings) will require an extended shaft. OR you could use a brake like this: http://www.hollisterwhitney.com/products/brakes.html

Actually a DC brake could be setup to drop very quickly and provide more precise braking control.
 
I dunno if you can tell but I like Flexpak drives

The manuals and options are here:
http://www.reliance.com/prodserv/standriv/dc/flexpak/

If the Flexpak was installed just 3 years ago and someone wants to change it I have to assume there seem to be problems with the drive. I would bet my last dollar that its not set properly for the application if that is true.

The AB/Reliance AC drives arent anything to brag about but the Flexpak (DC Drive) is a whole different ballgame. You will be hard pressed to develop an AC system that can match what the Flexpak can do.

The old Maxpaks are hard to beat but its just getting too costly to repair and maintain them these days.

I apologize if I am too emphatic on this subject.
 
The drift I get is the drive is being replaced because of parts cost or just because the manager wants to.

Options to stop a 3 phase motor.
1. Let it coast down.
2. Let VFD lower frequency to a stop
3. Tie heater across it
4. DC injection
5. Plugging (reverse motor to a standstill)
6. Mechanical brake

# 1 is longest # 5 is shortest in time.

With respect to tearing up motor # 4 is bad if done frequently # 5 can also damage motor and the conctators. However it is done on cranes.


As far as tearing up the load being driven, # 1 is least # 5 is most likely.
IF it is Emergency Stop and you NEED to do this for employee safety then that is what you do. IF you have to do E stop for machine safety then the same thinking applies but maybe you can do in controlled condition.

For time requirement of the mechanical brake to stop let me compare to a car - depends on how hard you press the brake pedal.

THE ONLY one that will hold the motor for long term is the mechanical brake. Some DC inject or special feature with VFD can also hold the motor BUT at expense of motor damage with longer time.

I hope this answered the original question.

Dan Bentler
 
Rsdoran, the machine is a rotary die cutter. Since you are familiar enough with this type of machine, you can see my delima.

Yet, let me clarify a few things :
the machine is currently set up with a Flexpak 3000 & a 50HP DC motor, using dynamic braking.There is nothing wrong with the drive/motor set-up on the RDC now, except our second & third shift electricians couldn't troubleshoot why the drive kept blowing 125A fuses on the drive. I came in the next morning & found an SCR shorted (cooling fan went out), replaced it & the fan and got the RDC running. After the machine being down from 8:30PM Friday, until 8:00AM Saturday, the plant manager decided it was in the plant's best interest to retro-fit all the finishing machines with AC motor/drives so that it will "be easier to troubleshoot".
That aside, when running this machine at normal operation, the motor is running about 70% of it's rated RPM. When E-stopped or a jam is detected, it needs to stop then, not coast. For those that are'nt familliar with RDCs, the machine is separated by downs & stations. This particular machine has a feed table, two print downs & one drum station. Each section separates for cleaning. Each section is about 8' wide & 24-30" long and all sections are driven through an array of gears housed in one side of the machine & driven by the main motor.
I'm left with the job of coming up with an efficient way of upgrading these machines.
Using an AC drive/motor, I do not know of a way to stop the RDC without a mechanical brake, and even then I'm not sure of one that would survive long with that much stress...
 
I, like rsdoran, am a big fan of Reliance FlexPak3000's. Even tho I am no longer able to sell them, I still consider them the most usable and adaptable DC drive out there. There is nothing "old" about them.

Since statis has indicated that the DC option is out, he is concerned that powerful braking is not an option with AC.

I can assure statis that effective braking can be acheived with AC drives equal to that of DC drives. You simply need to pick the right pieces and program the drive accordingly. Assuming the right pieces including a new 50hp AC motor, you could brake the machine with up to about 300 ft-lbs of braking torque from that motor. To get that, you will need an oversize drive and either full capacity snubber braking or a four-quadrant drive. The difference is economics mainly and four-quadrant would only be justified if braking occurred frequently or nearly continuously as in an unwind stand. It doesn't sound like that kind of application so snubber braking would be the right choice.

The use of a mechanical brake presents several problems. First, the brake lining becomes a maintenance item. Second, it is very hard to adjust the decel rate which, at full application, can be very severe. Third, under varying load conditions, the decel time becomes unpredictable---short under light loads and longer under heavy loads.

Generally, it works out best to let the drive/brake system do the decel and then engage a mechanical brake if you need a holding brake. Be sure to pilot or interlock the mechanical brake with the drive Run/Stop relay to prevent the drive from trying to run into an engaged mechanical brake.
 
There is nothing wrong with the drive/motor set-up on the RDC now, except our second & third shift electricians couldn't troubleshoot why the drive kept blowing 125A fuses on the drive.

Not everyone can find a bad SCR/thyristor or IGBT, that same problem could happen with an AC Drive.

The Flexpak has an OIM that will display fault messages, a bad or inoperative SCR may show alarm error F0030-41 and state which one is bad.

CS3000 software can also be used for diagnostic and it offers an oscilloscope like option that will show an SCR not firing properly. Here is the manual for the software: http://www.reliance.com/pdf_elements/d23405.pdf

If the people were unable to properly troubleshoot the drive it is not the drives fault. An AC drive, with same scenario, may not be any easier to troubleshoot. They also use operator interfaces to display messages to assist in determining the problem, if maintenance personnel do not know how to use this information there will always be a problem.

I am not sure what the changeover would cost but its bound to exceed $10000. Why not see what it would cost for training, in the long run this may offer more benefits. Whether DC or AC drives, training will allow maintenance people to become more familiar with all the options available.

Doesnt hurt to discuss it with management, an AC drive uses similar components and could have the same kind of problem.
 
stasis said:
There is nothing wrong with the drive/motor set-up on the RDC now...the plant manager decided it was in the plant's best interest to retro-fit all the finishing machines with AC motor/drives so that it will "be easier to troubleshoot".

If you change it, you're breaking the cardinal rule of maintenance (if it ain't broke, don't fix it). I use Flexpak3000s, and a variety of AC drives. Your maintenace issue with the Flexpak is minor compared to the total maintenance costs that will be incurred with a mechanical brake.

Sounds like your plant manager is making a rash decision based on a single crisis...imagine that...That happens to me here all the time.

Our flexpaks (40hp - 200hp) don't always do the best job of reporting scr faults correctly, but our AC drives fail at least as often. The only thing to be gained by going to AC is eliminating brush maintenance and maybe getting by with a cheaper motor. But, as you clearly understand, you stand to lose some of your critical control.

We keep complete spare drives for the 40 and 50hp flexpak models, and have no trouble finding scrs for the bigger ones. You should spend a little on training your techs and leave the machine alone.

Just my opinion.
Paul C.
 
Paul, I'm of the same opinion...I like the set-up that are currently on the machines, and yes, the manager is touting the todem pole philosophy on this one (me higher, you do as told!). I'm just waiting for the AB rep to deliver the quote for one machine as this should shut them up quite quickly.

As for training the other shifts, managers balked at a drive class because of the costs....imagine that.
 

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