High cycle DC injection braking
High cycle DC injection braking
(OP)
A customer has a small high cycle indexing conveyor with a 1.3 second cycle. Almost all the braking with be done with decel but they are thinking of using DC injection braking to insure the motor comes to a complete stop. This is a 1/50th hp, 3 ph motor on a 300:1 high efficiency gearbox.
The load is very small and the only inertia is the rotor and input pinion.
I am trying to get an idea of how often I can lightly DC injection brake without burning the winding and how I can tell if the winding is about to burn. Will the motor case get hot before the winding burns?
Is this something doomed to fail no matter how lightly we DC injection brake?
Any ballpark guesses on what we can get away with?
Barry1961
The load is very small and the only inertia is the rotor and input pinion.
I am trying to get an idea of how often I can lightly DC injection brake without burning the winding and how I can tell if the winding is about to burn. Will the motor case get hot before the winding burns?
Is this something doomed to fail no matter how lightly we DC injection brake?
Any ballpark guesses on what we can get away with?
Barry1961





RE: High cycle DC injection braking
I have done "fine feed" with rapid cycling small induction motors on-off. Didn't need to brake them, though. Those motors lasted for many years and were removed when the plant eventually was rebuilt.
If you do not use more than rated current and switch the DC off at stand-still, I think that you may get overheated motors - but mostly because the fan doesn't run all the time. Rotor heat is usually the weak point when fast cycling, but I don't think it would be with motors as small as yours.
I would try adding some friction to the motor output shaft instead of using DC braking. Or, I would use a small 12 or 24 V DC motor (have a look at Bosch) and short the armature (possibly with some small resistor) to get a fast stop.
Gunnar Englund
www.gke.org
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RE: High cycle DC injection braking
The parameters in the VFD deal with percent torque but I have no idea what the efficiency of DC braking is.
Also the Fluke web site is down now.
Barry1961
RE: High cycle DC injection braking
Keith Cress
kcress - http://www.flaminsystems.com
RE: High cycle DC injection braking
BTW: Where did you find a 0.02 HP three-phase motor? And a VFD that suits it?
A DMM will probably not work beacause the cycle time is too short for a stable reading. Use a DC clamp and a scope or recorder if you really need to verify what's going on.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: High cycle DC injection braking
Barry1961
RE: High cycle DC injection braking
The chopper is usually alredy included.
What make are drive and motor?
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: High cycle DC injection braking
Keith Cress
kcress - http://www.flaminsystems.com
RE: High cycle DC injection braking
RE: High cycle DC injection braking
It is an AB PowerFlex and a Brother gear motor. Brother and Sumitomo both make very strong high reduction, high efficiency gearboxes down to 1/50th hp in 3 ph. They are just single voltage at 1/50th, 230 V or 460 V. I have used these on several brands of inverters and they seem to perform well.
You do have to have an output filter when running on 460 V even with short motor leads or there is a very good chance the windings will go in a month. You also need to have a OL parameter that is scaled for 1/10th amps.
Sumitomo and Brother both get the motor from the same manufacturer in Japan but I can't remember the name.
I have an application where sometimes I back drive a 750:1 right angle brake gear motor. Brother has an option for a light spring set brake for this to protect the gears. The back driving torque of this gear motor is 130 in-lb which is near it's 148 in-lb continuous rating.
FYI on the 1/50th, sort of "slippy" for a 3 ph.
208 V 1610 rpm .13 amp
230 V 1650 rpm .13 amp
460 V 1700 rpm .12 amp
Barry1961
RE: High cycle DC injection braking
I think that is all you need.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: High cycle DC injection braking
I have done my best to convince the customer not to do the DC injection braking and am hoping they will not need it.
Thanks for all the help!!!
Barry1961
RE: High cycle DC injection braking
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: High cycle DC injection braking
I think the motor will be too small to really use the vector performance of the drive.
If this doesn't work too well, try setting the VFD to standard V/F (scalar)control. The actual size of motor may work in your favour due to the inefficiency of a motor at this rating. Braking torque will be dissipated in the motor first with a low eff.
The PF 70 below 30Hp also has a built in brake resistor for light duty braking, so this would also serve to provide additional dumping rather than dc braking.
RE: High cycle DC injection braking
In past applications I did not have much luck generating torque quickly in V/F mode. In a recent application with a Mitsubishi E700 it took about .5 second to reach 100% FLT in V/F mode. I tried raising the voltage boost with not much effect. The way I got torque quickly was in Vector mode and adjusting the anti-slip parameter. I am guessing that a major part of the anti-slip is adding hertz in proportion to the amount of slip measured. Using a two-step acceleration or minimum starting hertz might be able to mimic this but I hope the AB can do the work in Vector.
Barry1961