set up VFD dynamic brake

I would try not to use DC braking.

DC braking is not the same as using your brake resistor.

Your normal braking is done by decreasing frequency below the motor's RPM. This makes the motor act as a generator, which produces extra DC voltage, which the drive dumps into the resistor.

Are you saying just hook up the brake resistor and reduce decel time, no other program changes? Seems to easy to be true.

Karl

My understanding of the DC braking, is that you set it to cut in when you have a load that must be held in position between the decel starting and the motor brake engaging, like with a loaded dumbwaiter. if the motor is just ramping down to a stop, and the driven equipment won't try to move the motor before the brake engages, or if it doesn't matter if things drift a touch between slow and stop, you do not need DC.

Stuart

This would be my suggestion, yes. Pick decel time so that the lathe can decelerate at highest RPM, without tripping on overvoltage.

Very well said.

DC braking is more like a mechanical brake, in that it holds the motor.

I would have to concur with Iggy. Your equipment would have to be designed to withstand the sudden stopping. And I do mean sudden.

In another life, I programmed high speed check reader sorters that used DC to stop the motors in the sorter. There could be up to 5-6 motors all required to go from full speed to stopped in just a few milliseconds when a paper jam was sensed. Quite a noise!

You need to determine how quickly you want to motors to stop and see if restive loading will do the job. Take into consideration any drive belts and what they are driving. How will they react to rapid or sudden stops?

Good luck, Paul

I see dc braking used in tool changer arms on older VMC's and in stopping the tool carosel. Both things you want to stop at precise positions.

I don't see any reason to use it on the lathe.

Wes

OK, I mounted the brake resistor and gave it a try, very little if any improvement in braking. In contrast, on my mill and CHNC, the braking improvement was dramatic. These were with Hitachi and I made some program changes to enable braking. My guess is something is missing here on this motortronic drive. Any suggestions?

Karl

So, what happens if you run the lathe at medium speed, like 300 RPM, then turn off electricity (so that there is no electronic braking) and time the stopping time with a stopwatch. Then set the VFD to stop it in 1/2 of that time and measure it using stopping. See if you get an improvement, that would tell you if your VFD is working.

The VFD is definitely working. I got an 8" adjust true chuck for this lathe. Much heavier than my 6". I have found I have to slow down to 1500 RPM before stopping or I get an over voltage KO on stop. When this happens it coasts for 10+ seconds. If it don't KO it stops in 4 seconds and you can see the VFD slowing it down. Adding the resistor hasn't helped this issue much if at all.

Karl

OK, so the VFD is working, but adding a resistor makes no difference?

Did you cover the basics, such as is that the right sized resistor, is it plugged in correctly, is the resistance as specified (maybe it is open?)

Yep

I'm slightly off on the ohm spec. it calls for 40 ohms, I tested 35. Should be close enough. The manual just calls for connection to terminals P and R. That looks good. What voltages should i see here on decel and is it AC or DC? I could do some checks this way.

Karl

Should be something like 300 volts DC, give or take.

be careful.

I just re-double checked everything. page 14 in the manual gives the resistor size - 40 ohms. page 15 shows the power terminals. My 205 unit is line 1.

With no power, i get 35 ohm between pins P and R, the power resistor teminals. same reading accross the resistor. (Duh, there's just wire between these check points)

With the VFD running I get 13-14 volts AC. During stop its up to 30 - 40 volts AC.(not DC)

My conclusion is this brake resistor is not enabled. I'm still hooked on thinking it needs programming. Or, you got another idea?

Karl

Page 7 of 76 in the PDF manual at the top says

"The CSD Series unit offers an optional function called dynamic braking. Dynamic braking, in adjustable frequency drives, allows the motor to produce 100% braking torque for a 10% duty cycle for four-quadrant operation (like DC regenerative drives). With dynamic braking, the regenerative energy from the motor is dissipated by switching the dynamic braking transistor to shunt the regenerative current from the DC bus capacitors through the braking resistor (See Figure 1 - 3). This circuit is optional in the CSD drive line, please contact the factory if your application requires dynamic braking."

Your drive may not have the chopper circuit installed as an option to use the braking resistor.

:( BUMMER! I had never read that paragraph. This unit is out of production, safe to assume I can't upgrade anymore.

Thanks for pointing out my problem.

Karl

I have a 5 HP VFD for sale with brake resistor

Even if the drive does not have dynamic braking, it sounds like it supports DC braking. Contrary to the other posters, there is no "Brake" attatched to the motor. The drive applies a DC current to the windings. This will create a braking action. It is essentially driving the motor at Zero HZ, This is similar to driving the motor at a speed faster than it is going, it WANTS to STOP with DC applied ot it. can you try bumping up Fn55, the magnitude of DC braking?

It appears that Fn53 might leave the DC braking on a little longer than the Deccel time. I am completely speculating now.... But that may be so that it will continue to apply DC braking after it is Commanded to stop, so that any coasting is impeded.

Let us know what happens next.

If someone has the same model with that option, it shouldn't be hard to duplicate. They may use the same module on other models, too.