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VFD Brake unit, can a universal or different brand be used?

mmurray70

Stainless
Joined
Jan 11, 2003
I have a 7.5kw hitachi L200 VFD on a lathe and the braking needs to be pretty slow to avoid alarms. Dont think it has any internal braking and cant seem to find an external braking unit to fit.

Just curious if you can mix brands or if anybody makes a universal braking unit? The brake unit on my Fadal simply connects two wires to the +/- of the DC bus and just turns on a resistor if voltage gets too high. Seems pretty simple. Could i use a different brand? I do have connections available to the N and P terminals for the dc bus.
 
If you have the connections, yes.

You need to know the appropriate voltages, but you could just adjust it down until it works, while not tripping on a 10% high line voltage (which could burn it out).

I have done that.
 
If you have the connections, yes.

You need to know the appropriate voltages, but you could just adjust it down until it works, while not tripping on a 10% high line voltage (which could burn it out).

I have done that.

Ok great. One more question... If i buy a brake unit with smaller kw rating then drive, do i risk damaging brake unit, or do I just get less then 100% braking power before getting the high voltage alarm? Not really worried about overheating the smaller one, wont be huge load on it.

Not sure how much room I have to mount it, basically wondering if I can still get some decent gains with smaller unit. Also, I see some VFDs have it built in. Guessing some of the built in ones would have to have lower ratings then an external one due to size.
 
The units have internal braking resistors, but usually have minimal braking ability with higher momentum loads. They do spec. braking units for that model and they are available. Braking is a function of the resister value, dissipation and braking parameters. The braking resistor must be attached to the specific terminals, not the dc buss +/- if it does not have a chopper circuit. Last person that did that fried his VFD. Not familiar with your VFD unit the newer Hitachi units like the WJ200 have specific braking connection terminals and only require connection to the resistor, and with some braking units there is also a thermal sensor connection.
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Both HBR2 and HBR3 are instock, if you are looking for a factory braking resistor. I often will source them from different vendors, but you need to have a resistance value within the operating specs. for the size VFD, dissipation is a function of the degree of braking so you can go lower in watts if not frequent. Also be aware that there is significant voltage on the buss and the resistor needs to be rated as such.
 
The actual (stand-alone) bus overvoltage units are connected to the bus terminals.

There are add-on units sold by the VFD makers, for which you follow their instructions for the models they fit.

Yes lots of VFDs have it built-in. They have minimum allowed resistor values. The lower the resistance the more energy can be removed, but too low fries the brake controller.

Yes, the resistor must be one that is good for the voltage, AND good for pulsed current overloads, as well as the specified power capability. The resistor is generally overloaded on current, but the pulsing limits the average actual power level.
 
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If that's an option, it might be very effective.

Mostly, the VFD cannot brake any harder than it accelerates, unless you use DC injection (a feature of some VFDs). But while DC injection can stop a motor, it cannot "hold position" very well. A complex servoed VFD might hold position fairly well, but again, no better force-wise than it can accelerate.

Mechanical brakes can stop as fast as you want (if selected correctly) and they are very very good at holding position.
 
Thanks for all the help so far. Mechanical brake isnt really an option, i would rather buy a new inverter then go there. I dont need crazy fast stops, just would like it slightly better then it is now. Right now my top speed is 1000prm (4000 motor rpm) and its set at 1.5 seconds acceleration. Deceleration is set at 6 seconds to avoid high voltage alarms. If i could cut that in half it would be awesome.

My drive has DC braking but max starting frequency is 60hz and im way above that at high speed so that doesnt seem like a great solution.

Does anybody know anything about the Lenze braking units? Pretty sure these including the resistor and the electronics unit to switch it on and off as needed, and just connect to bus. which should be easy enough to connect to mine. something like this: https://www.ebay.com/itm/403377169625?hash=item5deb2724d9:g:EcoAAOSwNyxhyKS1

Also, this is a 10hp vfd, but im running off single phase and the motor is 7.5hp. I ran the machine off a 5hp single phase motor for last 5 years and have never ever stalled it so should be safe enough. How does this affect how I size the brake unit? Do i get a 5, 7.5 or 10hp brake unit?
 
If you want to do a test without investing $250 or $321 for the resistors, you might want to consider electric range heating elements. They are rated in the range needed and are very robust. My smaller element is 37 ohms at 220 volts, or 6 amps, 1300 rated watts. My larger element is 22 ohms, 10 amps, 2200 rated watts.

HRB2 is 35 ohms/600 Watts, so close to the 37 ohms of the smaller element. HRB3 is 17 ohms/1200 watts, 2 small elements in parallel would be 18.5 ohms. They're AC, so their peak rating is 240 * 1.41 or nominally 340 volts dc. Other series/parallel arrangements can give you other values to test.

No responsibility assumed for this very non-standard use of the heating elements. If you try it, be sure your wife will be gone for a while....
 
If you want to do a test without investing $250 or $321 for the resistors, you might want to consider electric range heating elements. They are rated in the range needed and are very robust. My smaller element is 37 ohms at 220 volts, or 6 amps, 1300 rated watts. My larger element is 22 ohms, 10 amps, 2200 rated watts.
That only works if your drive has the circuit built in to switch it on and off. Mine doesnt have that. I need to connect a braking unit which also has the switching gear, not just a resistor.

No responsibility assumed for this very non-standard use of the heating elements. If you try it, be sure your wife will be gone for a while....
No worries there, my wife left a year ago lol.
 
Looks like the drive is fairly flexible in term of whats connected for braking unit. I found a PDF on the Hitachi braking unit and they show a chart showing available braking torque based on one braking unit, or 2 in parallel, and for different amounts of external resistors plugged into each brake unit. So looks like if have a large braking unit it will slow quick, if its smaller I guess you can only slow down so fast before getting the over voltage alarm.

According to the chart from hitachi I should get 50% braking torque when using a 35 ohm resistor, 80% braking torque with a 17 ohm resistor, 100% with dual 17 ohm resistors. I found a good deal on a Lenze unit with a 21 ohm resistor so hoping this will work decent. Going to give this a shot.
 
................. So looks like if have a large braking unit it will slow quick, if its smaller I guess you can only slow down so fast before getting the over voltage alarm.

...............................
That's pretty much it. The VFD takes energy out of the motor (makes it "generate") and moves that energy to be charge in the bus capacitor. The faster the stop, the faster the voltage goes up.

You then need to remove that energy by draining current from the bus. Obviously the lower resistance removes more current, draining energy faster, and allowing a faster stop.

Energy removal is also affected by how long the resistor is connected by the controller. A 100 ohm resistor that is "on" half the time, acts like a 200 ohm resistor. Most VFDs have a "duty limit" that ensures the resistor is not over-heated.

There are other factors, but you have little or no control over them.
 
Hey guys I got the Lenze braking unit and have it all hooked up and its not doing anything at all. Im guessing the hitachi VFD throws an overvoltage alarm before the lenze brake unit kicks in. This sucks, was really hoping this would have worked.

Anything else I could be missing? Does I need to set a parameter to work with the brake unit? Maybe allowing slightly higher voltage before alarm?

Ill check what voltage is going to tomorrow, see what it actually alarms out at.
 
You may be able to set the Hitachi to a higher threshold. I have not searched the manual.

You may also be able to set the Lenze unit to a lower voltage. If so, you want to be careful.... you need the brake resistor to be set high enough that a normal high mains voltage will not trigger the brake unit. There is no way the brake unit can drag down the mains, and you do not want it to die trying.

EDIT
I looked through the parameters in the L200(2) manual, and failed to find a setting. I DID fine B130 and B131, which will allow modulating the braking to avoid a trip-off. That probably does not reduce braking time, but may give the least braking time.
 
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I just did a few tests, looks like its alarming out right around 400v, and brake unit is doing nothing at this point.

My Fadal CNC mill has an external braking unit and did a test on this for comparison, it limits voltage to 375. This would have worked perfect for me. Maybe i should run an extension cord over to the fadal and use that brake unit for both!! haha.
 
There are a few other small terminals on this brake unit. I think these are mostly for detecting alarms, but not sure on it. Is there any chance that these are used by the drive to switch brake unit on and off? Or is the switching definitely done automatically once voltage reaches a certain level?
 

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The Hitachi brake unit probably operates independently.
maximum peak voltage from 240V at high line condition is about 375V, so there is a little leeway there, but not much, between a "normal" peak voltage, and the overvoltage setting.

If the Lenze unit cannot be set in that range, you might try parameters B130 and 131 to avoid a trip-off. That won't shorten the braking time much if any, though.
 
I did a little more digging and It looks like the Lenze brake unit might have outsmarted me. It has 4 smaller terminals. 2 of them are for an over temperature alarm. Normally open and close if too hot. So wont need these to run.

I looked at the other 2 terminals, and they connect to TB 11 and 14 in the Lenze VFD. Number 11 is 12vdc supply. And number 14 is a digital output. I looked at the parameter that configures this output and one of the options is for dynamic braking option. I bet this digital output tells the brake unit when to dump power to resistors. So if thats the case I guess im screwed. Such a shame, got it all mounted up so nice and neat. Guess im right back to square one.

Just tried the B130 and B131 and got some noticeable gains! Still get over voltage alarm if i go crazy with it, but I have it set at 3.5 seconds now and its working reliably and much faster then it was. You can hear it adjusting frequency slightly as it slows to avoid the OV alarm. Strange they didnt have this listed in the manual??
 
pretty much that....

I find that you often need to know more-or-less what you are looking for, then you can go through the parameter list to find anything that looks similar.

There is a list, and somewhere in the manual there is an explanation. So anything that looks interesting, you can look up in the explanation to see if it is relevant to what you want.

That's how I found B130 etc.... I just went through the list of parameters and looked for anything that appeared to reference overvoltage or the like.
 
My read of the manual for the SMV braking resistor for models for their drives, they have a B+/B- connector, a power connection and also connections for a communication line back to the VFD's control circuitry which modulates the braking. VFD control connection 4 and 11 is neg and +12V, 13A I assume is a fault trigger and 14 is the digital COM. It may be that the braking module is VFD/brand specific. What I outlined previously was for L200 is to use just a braking resistor as the chopper circuit and controls are already in the VFD. You may be able to disconnect the control circuitry in the Lenze module and just using the braking resistor, but I could not find any information on the module you purchased. I would have just gone with the factory Hitachi braking resistor units at the end of the day.

This would also be an option, there are other variants in aluminum casings with leads, they do require mounting to a metal surface to achieve their dissipation ratings. I often will mount them at the top of the enclosure, there are also open air types on a ceramic core.
ARCOL / Ohmite HS600 25R J
 

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The only references I saw which showed connections, showed a "braking unit" PLUS a resistor. Check section 5, under "dynamic braking".
 








 
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