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Power PMAC Advised Power On/Off Sequence


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The Power Brick AC includes an 'Advised Power On/Off Sequence' in the Power Brick AC User Manual. I've been unable to locate a similar sequence for the Power PMAC. Does one exist and if so where? If not, would someone mind posting it here for future reference. Thank you.
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When you say "Power PMAC", are you referring to a UMAC?


The main concern with Power On/Off is that the amplifier in the Power Brick series is never powered or used before the logic is online and that the soft start circuitry has time to complete its tasks. For just a Power PMAC CPU, this is not a concern, since there is no "amplifier/bus power".

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When you say "Power PMAC", are you referring to a UMAC?


The main concern with Power On/Off is that the amplifier in the Power Brick series is never powered or used before the logic is online and that the soft start circuitry has time to complete its tasks. For just a Power PMAC CPU, this is not a concern, since there is no "amplifier/bus power".


Apologies for not being more concise. We have a Power PMAC in a UMAC chassis with 2 Axis interface boards and 4 amplifiers. I'd like the sequence for power on/off of the whole enchilada.

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The power on/off procedure is generally going to be amplifier specific and depends on what features it has and how logic and bus are powered.


The main rules we have are:


1) Never allow the amplifier bus to be powered when the logic is not. If they are two separate connectors, always make sure that the logic connector is connected first and disconnected last, and do not just reset/power cycle the amplifier by pulling out the logic power connector while the bus power is still applied.


2) Never quickly cycle bus power. The amount of time that you must wait between removing and re-applying bus power varies from one amplifier to the next, but there will be a recommended time usually stated in the manuals. As an example, I believe five minutes would be sufficient on any of our amplifiers, but do not just use this as a fact for your specific hardware, always check the manual to confirm the recommended minimum time for that exact hardware.


3) Do not enable an amplifier as soon as bus is applied. The delay required is usually less than a second (and should also be in the manual), but trying to enable the motor at the exact instant that bus power is applied can damage hardware depending on the specific timing of some signals/voltages.


4) If you are using a larger and older amplifier, do not try to do a harsh deceleration (such as a quick closed-loop stop or reversal of derection) and then remove bus power during the deceleration. This is rarely an issue, shouldn't come into play for any of our UMAC amplifiers, and often can be minimized or negated by using a shunt resistor which should be available for any amplifier that could face this problem, but if I want to be complete, it should be noted.


Assuming you are using one of our UMAC-based amplifiers, I do not believe we have any with external bus/logic connections, instead all being powered off of the backplane. Similarly, the CPU would take long enough to boot that any concerns about enabling the amplifier too quickly should be moot in that case (unless they are in different racks/have different power supplies). As such, the only real concern is that you should not remove the AC power and then quickly replace it into the UMAC rack without waiting some amount of time determined by the manual for that amplifier.


A generalized procedure would look something like:


Power ON:

0) If the amplifier recently had its bus power disconnected, wait for it to fully discharge before attempting to power it back on. If the CPU is not powered, apply logic power and allow it to boot.

1) With bus power disconnected, apply logic power to the amplifier.

2) If applicable, issue any reset or configuration commands to the amplifier.

3) Apply bus power to the amplifier, then wait some amount of time for it to energize and reach equilibrium.

4) Enable amplifier.


Power OFF:

0) Stop motors, or make sure they are at least not rapidly accelerating/decelerating. This may not be critical depending on the size of the amplifier/motors.

1) Disconnect bus power and kill the motors if they had previously been enabled.

2) Wait for the amplifier to discharge.

3) Disconnect logic power.


(Again, I've probably said it about 10 times already, but to stress--consult the manual for your specific amplifier for the specific details)

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Your question implies you are using either MACRO or Direct PWM D-T drives. If not, then the power on/off is somewhat irrelevant as most manufacturers provide adequate protection internally, sometimes in the form of a 'drive ready' contact. However it is always good practice to provide control power first and then bus power.


I follow this sequence:

1) Panel power ON

2) Logic ON to PMAC

3) Output from PMAC PLC enables logic to drive. This ensures PMAC is fully booted. Rumor at one time was that a corrupt StrobeWord could be communicated to the drive if PMAC was not fully awake before drive logic is applied.

4) Wait until I can read undervoltage or line fault from amplifier, or IGBT temp if in enhanced mode, or see some noise from current sensors.

5) Enable line supply for bus

6) Wait a few seconds & Safety relay energized. This last step is unfortunately somewhat uncontrolled as the E-Stop circuit might be set at nearly any time during the boot sequence. And certainly during normal operation.


Power OFF:

1) Stop motors and kill all axis

2) Power down bus

3) kill logic supply

BUT... this is somewhat fantasy as it is not uncommon for a main disconnect to be opened on a piece of equipment and an orderly sequence of bus first and then logic only happens if the logic supply has suitable capacity and low enough load to outlast the bus. Not usually reliable.


- In the manual for the Direct PWM drive it is advised to use a Wye-Delta transformer. I think they mean a Delta-Wye.

- Highly recommended to order the drive with the X4 'Safety Relay' connector and use this for E-Stop applications rather than power down the bus.



- As many problems as have been encountered over the years, why is it STILL up to the user to provide basic boot protection/sequencing ?

- Why is the bus not exposed for load sharing on all drives, not just the 20 & 30 amp versions (pin 1&3 of regen connector) ?

- Safety Relay could be standard rather than an option.

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Thanks again to both of you.


One last question: we are using 3U042 and 3U081 direct PWM drive amps. Unfortunately, our 3-phase bus power is not controlled by PPMAC IO pins but rather externally via a 120v relay switch. I'm considering changing this so that we control our 3-phase bus power via PMAC/UMAC IOs so that we can enable/disable from startup PLCs directly.


Thus my question is, is it possible to directly monitor the bus voltage *after* it has been disabled (on shutdown) and/or *before* it is reenabled on startup to determine if the Amp Capacitors have sufficiently discharged? According to the manual we can get this information via the Adc strobe words, but it isn't clear if it is still monitored or accurate after bus voltage has been terminated.


Thanks for all your help.

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