Brake rectifier
Brake rectifier
(OP)
Hi
Over the last 2 weeks we have had to replace the brake rectifier 3 times on a 415v 3 phase motor with 415vac/205vdc rectifier. The complete motor and brake have also been changed along with contactor.
The rectifier is fed directly from the 415v from the motor so as the motor starts the brake releases. The operation that the motor drives requires start/stop 36 times/minute.
1st question - I presume there could be a slight delay in the motor start/ brake release but could this be causing the issue of destroying the rectifier?
2nd question - Should the rectifier be connected across U1/V1 or W1 incoming to the motor or U1 and copper bar for star connection?
Any other advise would be gratefully received.
Thank you
Stuart
Over the last 2 weeks we have had to replace the brake rectifier 3 times on a 415v 3 phase motor with 415vac/205vdc rectifier. The complete motor and brake have also been changed along with contactor.
The rectifier is fed directly from the 415v from the motor so as the motor starts the brake releases. The operation that the motor drives requires start/stop 36 times/minute.
1st question - I presume there could be a slight delay in the motor start/ brake release but could this be causing the issue of destroying the rectifier?
2nd question - Should the rectifier be connected across U1/V1 or W1 incoming to the motor or U1 and copper bar for star connection?
Any other advise would be gratefully received.
Thank you
Stuart





RE: Brake rectifier
That motor is seeing quite a severe duty with that number of starts per minute. How big is it, and is it a special design?
RE: Brake rectifier
The longer the conductors from the control to the motor, the higher the cost,
But
The longer the conductors from the control to the motor, the greater the likelyhood that you will need them.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Brake rectifier
This is designed from the manufacturer of the machine (Indosa can seamer) and has run for 20+ years, only having to replace the rectifier/motor on average every 4 years. Probably state of the art 20+ years ago and I know there's alternatives available but with a cost. Just struggling to understand why this is happening so frequently now?
Stuart
RE: Brake rectifier
RE: Brake rectifier
The supply from contactor to motor are approx. 2metres.
I'm not sure how much of a delay between motor start and brake release there would be but if there was a minute delay, when the motor is trying to rotate would this increase the draw current through the rectifier and eventually result in failure of the rectifier?
Stuart
RE: Brake rectifier
You refer to neutral but this rectifier is 415v input? At current it is connected through U1 and U2 on the motor terminals. I've had a look through the internet and SEW advise U1 and star terminal in the motor for a 200vdc brake coil and 415v motor. Not sure what difference this would make?
Stuart
RE: Brake rectifier
It happens even on new equipment.
The replacement may be designed for line to neutral connection.
Does the brake have surge suppression or a free wheeling diode?
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Brake rectifier
The coil winding measure 1kOhm which appears correct. No surge suppression, not sure about the diode?
Stuart
RE: Brake rectifier
If this motor is truly running on 415V AND the rectifier was truly being 'fed from the motor' then perhaps it was tapping somehow into the the low voltage taps of the motor. I'd have to think about that and if it's possible.
More likely it's as Scotty is trying to tell you, the motor is WYE connected and the rectumfryer is supposed to be going from one phase to the neutral.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Brake rectifier
The motor comes direct from the manufacturer with rectifier already wired up?
Stuart
RE: Brake rectifier
You want to check the resistance to ground with a megger at 500 Volts or 1000 Volts test voltage. You can not get a reliable insulation resistance measurement with a low voltage multi meter.
You can tap off 208 Volts from a nine lead, delta connected motor. Nothing else comes close to 205 Volts.
Is there a series resistor?
If the replacement brake is designed for AC operation then using the rectifier will quickly burn out the brake coil.
You may want to try full voltage AC to the brake. If it releses cleanly, that is your solution.
I have seen more AC brake coils than DC brake coils. Typically designed to be connected to the motor terminals and typically designed to accept the starting voltage dip.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Brake rectifier
Definitely 6 lead motor and the coil is rated at 205vdc hence the need for the rectifier. The resistance of the coil was tested at 500v using fluke insulation resistance tester and came back just over 1kOhm. As said, the rectifier comes prewired direct from the manufacturer so not sure how it could be incorrectly connected, twice. The brake is releasing, it's the rectifier that is failing?
stuart
RE: Brake rectifier
Hi Stuart. Yes, but just because the motor comes wired to the brake doesn't mean they necessarily wired it for the correct voltage...
Got any part numbers? Like the motor? The brake make and the model you have?
A picture of the schematic associated with the brake?
Perhaps a picture into the pecker-head where the rectifier and motor leads terminate? Waross and his type :) would be all over that picture and could probably even read your fortune from it.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Brake rectifier
In the past I've had motors delivered that don't have the input connected if it requires an external source (240vac), you just presume that the manufacturer would wire this correctly but I will certainly review it and look at external supply for coil as the supply cable is 7 core with 3 taped up not being used, again, why waste money with a 7 core cable if you could install a 4 core to do the job? Thank you all for your help?
Stuart
RE: Brake rectifier
I did a little googling on brakes with 205 VDC coils..
If the rectifier is half wave, the connection is line to line.
If the rectifier is full wave the connection is line to neutral.
There has probably been a supply change from half wave rectifiers to full wave rectifiers.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Brake rectifier
RE: Brake rectifier
RE: Brake rectifier
I was mooching through this thread and thought I would throw in my 2p/2cent:
In my limited experience, motors can be supplied with "415Vac" or "230Vac" on the brake rating plate, and as mentioned, this is usually an indication of the rectifier module fitted - the actual brake coil is the same, 180Vdc - 205Vdc. the rectifier is either half-wave (415Vac) or full-wave (230Vac). One other observation I will make - I'm not convinced that the exact voltage supplied to the coil is critical, the main effect is the reaction time.
re. the OP, if the rectifier states "max. 500V", then the failure is unlikely to be caused by the supply. However, if the motor/brake is switched via a contactor, then I wonder where the back EMF from the brake coil is going when the contactor opens? It seems to me that a free-wheel diode is required on the dc side of the rectifier?
Please correct if my thoughts are wrong on this.
Thanks in advance,
Mort
RE: Brake rectifier
RE: Brake rectifier
RE: Brake rectifier
Keith Cress
kcress - http://www.flaminsystems.com
RE: Brake rectifier
RE: Brake rectifier
I just had to wrestle with a brake on a guy's bender. It wasn't disengaging correctly so of course the motor was -seriously unhappy- and the overload was getting cycled. I had to hunt down a data sheet on it and in the process stumbled over one that was a different model but pretty comprehensive. That data is out of a Lenze Brake Unit manual and I don't recall where I found it as it was a major battle since the USA site seems to ignore brakes altogether.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Brake rectifier
At 36times/min (1.66s) operations, may arise in some moments high voltage across rectifier diode; add one more diode in series or a small resistor across brake coil connected when motor power is off.