# Adding Braking Resistor To Teco Fm50



## hman (Aug 9, 2016)

I'm in the process of converting both my mill and lathe to 3 phase 1 ½ HP motors and Teco FM50 VFDs.  Both machines are wired up, tested, and run successfully.  I've left the decel time (F2) at the factory set 5 seconds, but would like to reduce it to near zero (safety, stopping the lathe quickly when threading to a shoulder, etc.)  So I bought and wired in the specified (100 ohms, 150 watt) braking resistor on each of them.

Now I have some questions ...

(1) How do I let the FM50 know that I've added the resistor?  There doesn't seem to be any function setting for this.

(2) How low can I set the decel time (F2) without cooking something?  

(3) Do I need to adjust any/all of the F14 thru F17 parameters?  The manual kinda describes the slowdown process, but I really don't understand what's going on here.  Among other things, it mentions "DC braking starting frequency" (F16).  Huh?  I thought frequency had to do with AC, not DC????

Any and all insights would be greatly appreciated.


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## mksj (Aug 9, 2016)

I assume you have a 2Hp (1.5kW) version. The resistor connects between the "P" and "R" terminals, you do not need to set anything for it to recognize the resistor, a braking resistor can only be used for the FM50 - 202 and 203 models at this input voltage level.  Actually the stock Teco without a braking resistor can brake at a fairly quick rate.

You cannot cook the VFD, if they brake at a rate that exceeds the ability to dissipate the regenerative voltage, then the VFD will trip (free run) and you will get an over voltage error. You do not want this to occur, no braking will be applied if this error occurs. Still, you should set your braking speed at not less than 1 second. There is just too much mass/momentum in the system to be able to stop quicker, it does not matter what you set the deceleration rate at.

The manual is clear as mud on F14-F17. I would add the braking resistor and change F2 and see how it does. You may be able to tweak F14-F17 as follows, but I have not tried these on a Teco. 
F2 = 1.0 Deceleration time (try between 1.0-1.5 seconds
F14 = 0 controlled deceleration stop (default value)
F15 = 0.0 DC braking time
F16 = 1.0 Hz braking injection frequency
F17 -= 20 (%) DC braking level


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## hman (Aug 11, 2016)

Thanks, mksj!  I tried setting the decel time to 1 second, then 0.5 second.  WOW!  It's really impressive to see the lathe chuck stop so fast.  No problems, even stopping from full speed.  Guess I won't need to mess with F14-17.


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