A different inverter with another problem.

Installed a new inverter , Siemens V20 , 11 kw to a benchsaw which , in the past had many  problems with the mechanical brake.

It was decided to replace the star delta setup with an inverter.

Ordered the V20 11KW inverter after seeking advice from the supplier.

With all Parameters for the motor set as shown below , following a factory reset.

Volts – 400

HZ – 50

RPM – 2910

PF – 0.82

Amps – 17.8

KW -  9.25

Min Frequency – 50Hz

Max Frequency – 50 Hz

Acceleration Time 10 Secs

Deceleration Time 10 Secs.

When trying it today I had the following error

Accelerates OK

Deceleration – Alarm Code A911 Shows on display , initially braking then freewheeling to a stop.

VDC_max controller active.

First two times I started and stopped the motor , deceleration was ok.

I would appreciate some advice please.

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Split from Siemens V20 Inverter Issue - Speed Not Reaching Set point HZ.

Thanks very much your reply.

I tried changing the deceleration time in stages to a maximum  of 35 seconds.

When deceleration was set to 10 sec initially , it would brake successfully when the display showed the A911 alarm , motor stopping in about 18 seconds.

It would do this several times in a row.

Then , when starting and stopping the motor again , it would brake initially , then freewheel to a stop , with the P1121 setting still 10 secs.

Increased the P1121 setting to 30 secs , intending to reduce it in stages if the setting made braking successful.

I still had the A911 alarm at this setting , the display then showing 0000 and the motor freewheeling to a stop.

Various P1121 settings were tried with similar results.

Sometimes would brake correctly , other times A911 alarm , then freewheel.

It didn't seem to make any difference if the seconds were set at 10 secs or 30 secs , sometimes braking at 10 secs was successful , yet when increased to 30 secs braking failed with the A911 alarm.

Is it possible a braking resistor would cure this , somewhat , intermittent problem and how is a braking resistor value chosen ?

Any further advice would be appreciated.

Are you saying the mechanical brake would get applied at different times and no matter what time during the motor deceleration, still it would fault and sometimes the motor would end up coasting and no mechanical brake engagement would happen?

Is the mechanical brake capable of stopping the load all by itself?
If it is, then you need the braking resistor to allow the drive and motor energy to dissipate and avoid alarms - and coasting.

The mechanical brake engagement needs to be controlled by the drive and configured so it engages that physical brake except when spinning on purpose.  Like when taking the OFF1 (run command) from high to low which should initiate ramp down at the configured ramp down rate (and/or time) and once below certain threshold it engages the mechanical brake.

When the motor faults, you might want to use the fault output as another method of engaging the mechanical brake.

SalsMaint

Thanks very much your reply.

I tried changing the deceleration time in stages to a maximum  of 35 seconds.

When deceleration was set to 10 sec initially , it would brake successfully when the display showed the A911 alarm , motor stopping in about 18 seconds.

It would do this several times in a row.

Then , when starting and stopping the motor again , it would brake initially , then freewheel to a stop , with the P1121 setting still 10 secs.

Increased the P1121 setting to 30 secs , intending to reduce it in stages if the setting made braking successful.

I still had the A911 alarm at this setting , the display then showing 0000 and the motor freewheeling to a stop.

Various P1121 settings were tried with similar results.

Sometimes would brake correctly , other times A911 alarm , then freewheel.

It didn't seem to make any difference if the seconds were set at 10 secs or 30 secs , sometimes braking at 10 secs was successful , yet when increased to 30 secs braking failed with the A911 alarm.

Is it possible a braking resistor would cure this , somewhat , intermittent problem and how is a braking resistor value chosen ?

Any further advice would be appreciated.

There is no mechanical brake on the motor.

The inverter was installed as the original brake failed too often .

Replacement brakes were changed 3 times by maintenance staff , previous to me installing the inverter.

Do you have the Siemens specified DC brake connected to the V20?  If so, you might consider asking Siemens Support for an alternative DC brake that can absorb more energy.

There are companies that provide "equivalent" DC braking resistance but signficantly greater electrical braking power (by using similar DC resistors in series / parallel configuration to yield equivalent Ω).  Just be sure not to exceed the max DC braking power for your drive (which is why you ask Siemens Support for that detail).  Then you tell one of those composite DC braking vendors the maximum power to absorb and the equivalent DC braking Ω, and then wait for them to make and ship it.

SalsMaint

There is no mechanical brake on the motor.

The inverter was installed as the original brake failed too often .

Replacement brakes were changed 3 times by maintenance staff , previous to me installing the inverter.

Many thanks for all the information , you have been very helpful.

I will look into the DC Braking idea first .

Thanks for supplying details of the braking resistor required.( If I need to go down that route )

Just one thing , unless I have worded my query incorrectly , there is no mechanical brake fitted , the braking solely dependent on the inverter.

Mechanical brakes are for holding loads while a motor (typically a servo motor) is powered off and the load will fall if not held in place mechanically.

A non regen VFD without a braking resistor is capable of slowing down a motor with load attached, but not at the same rate that it can accel/decel with the motor.

Let's say the motor can accel/decel the attached load from 0 to nominal speed in 5 seconds.  The standard DC braking resistor may require 15 seconds to slow the load without faulting the drive on overvoltage.

SalsMaint

Many thanks for all the information , you have been very helpful.

I will look into the DC Braking idea first .

Thanks for supplying details of the braking resistor required.( If I need to go down that route )

Just one thing , unless I have worded my query incorrectly , there is no mechanical brake fitted , the braking solely dependent on the inverter.

Tractor

Hi

I can see a suitable resistor for an 11kW inverter V20, Frame size D as: 6SE6400-4BD16-5CA0. This is Dynamic Braking, see P1237 for braking duty, 5 to 100%, this is provided to protect the resistor from overheating.

This will provide stability for the ramp down.

The resistance 56 Ohms is important if you go elsewhere for a resistor, ensure it is suitable for 'braking'. The shock application of PWM* power to the resistor requires this to be wire wound, with good heat dissipation.

This will provide reliable stopping without using the mechanical brake, which should be only used for 'holding' the load stationary. The V20 can give you a relay output to energise this when the load has stopped , so the brake should last forever.

Note: do not energise the mechanical brake coil directly from the V20, Voltages generated by the collapse of these coils is massive, use an interface relay.

Note, Note: Ensure the mechanical brake can only be applied to a stationary load, in order to avoid the brake being applied 'before' the inverter has completed its ramp down. This would trip the V20 with overload.

Have you had a look at DC Braking??

P1230 enables this, with further parameters through to P1234, the 'effort or Heat' in this case is dissipated within the motor, and does not require a resistor.

Not as effective as 'Dynamic Braking' but worth a try.

*PWM, Pulse Width Modulation, this is what the inverter supplies to the resistor, gives the resistor a bit of 'stick', best if it is wire wound.

Hope this is 'food for thought' on a Friday afternoon.

Tractor

 Many thanks for the information.

The 56 ohm resistor has been ordered and I will update you when it is fitted.