Brake for 1336 II AB Drive

There's almost always 'more than one way to skin a cat.' However, without knowing details of what your brake does in the production, it's impossible for anyone to say, "yes" or "no" to your question.

its a 20% dynamic braking system that activates when the motor turns faster than the synchronous speed set by my drive, which causes a build up of dc voltage. the brake just uses up the excessive volts on a resistor and causes heat. so i was wondering if i could use a 4000watt heating element for a possible temp. job if it happens again.

the brake is on a drive that slows down and speeds up alot. were talking about 4000 to 5000 times in a 12 hour shift.

Any resistor (heater) with similar resistance and same or greater wattage works. Your manuals will state the resistance range you can use. The wattage at the upper end will match the drive wattage, for infrequent stops and light load they will be considerably smaller. The energy is partially absorbed by the thermal capaitance (grams of metal) in the resistor for the short term duty.

I have often thought it should be a water heater to pre-heat water for the washrooms.

Bonitron Inc makes (or used to make) some excellent add-on regenerative units that connected to the DC bus. With the frequent stopping cycle you quote it would pay for itself in short order in recovered energy.

Depending on the inertia you are stopping you could consider a large capacitor bank to absorb the energy and then it gets used on the restart. We used to do that with cutter knife drives with tens of cycles per minute. E = 1/2 C v^2. Calculate the nominal bus voltage energy and the energy at max bus volts, the difference is what you can absorb on a stop without tripping. You may need to modify the precharge circuit. (I am not very fond of large capacitor banks due to the extreme amount of energy they can discharge on a fault. Be sure to use adequate fusing.)

Why did the original resistor fail, do you think? Not big enough power capacity, bad control leading to too much braking energy, change of process etc?

Fit a recommended resistor with overheat protection to prevent failure - you then need to decide what to do if there's too much braking energy causing this problem.

Don't fit a spare heater unless you know its suitable, the inductance can cause a severe overvoltage leading to potential brake device failure, brake resistors are specifically low inductance.

If the main drive is VFD, you can couple DC links to recover the braking energy, discuss with your supplier.

if im not mistaken the brake is the original one that was installed over 10yrs ago. the cause for failure hasnt been deterimined yet, cause nothing i know of has changed as far as the operation or any of that sort. the only thing that may have had a hand in it was the night before we had an electrical strom brew up. on that morning i had a vfd go out on my log line and edger for no real obvious reasons. so brake could have failed due to usage over that period of time.

thanks for all the info though, i love this web site!

What is the 'brake' that's failed?

I assumed resistor but it sounds like the complete braking module including brake transistor and associated components and also the resistor(s).

Which part(s) failed as far as you know?

I don't believe you can do that on these drives. The reason is, there is a control board inside of these braking modules that monitors the bus voltage and only dumps off the excess voltage.

If you were to put a resistor across the dynamic brake terminals the resistor would always be dumping energy even when the buss wasn't high.

I believe Allen Bradley has quit making these dynamic brake modules. Here is a link to the company that now makes them.

http://www.powerohm.com/BMdefault.aspx

If he has a braking resistor now, he has the brake chopper unit. I interpreted that he is asking if the resistor itself could be swapped out with something like a heating element. But it's still a good point, we don't know that for sure.

MattJohnson, pay heed to Elroy's post; you can only replace the RESISTOR, but not the entrie DB unit, because it contains the brake chopper and control board that senses when to fire into the resistor.

Also, couple of problems with heaters as brake resistors;

They probably won't match what the VFD mfr was looking for in terms of temperature Coefficient of Resistance. Most "heating elements" are NiCh wire based, which may allow for faster heating than what the chopper components can handle.

Also, heating elements are selected by watts for heat output, not by resistance so you will need to calculate the resistance on your own to match what the VFD is requiring. I have done it, but I found out after the fact that it wasn't a good idea. My applications were never as demanding as yours however so I got away with it, you may not. 7 cycles per minute is an extremely high duty rating for the chopper unit too, regardless of what the resistor is capable of.

You might want to consider a regenerative drive instead.