ThatShouldHaveWorked (Customer) asked a question.
I have a servo amplifier that sat a bit to long on the shelf. The OEM procedure to reform the caps is by reducing the line voltage and then dwell and step up over a period of hours.
In theory I should be able to use a frequency drive to do it. Set max output voltage to % then run it a 60HZ.
Has anyone used a drive this way?
Does the manual have this procedure documented?
Eaton has their procedure in this manual:
From B&R Acopos 1016 amplifier manual.
"If modules are not supplied with nominal voltage for a longer period of time, the DC bus capacitors must be formed
as follows.
The nominal voltage is the voltage permitted at the mains connections on the respective module.
Power is only supplied to the module; the output stage or controller is NOT permitted to be switched on during this!
Storage time up to 1 year: → No action required
Storage time 1 to 2 years: → Supply the module with nominal voltage 1 hour before commissioning.
Storage time 2 to 3 years: Supply the module with an adjustable power supply and increase the voltage in steps.
Observe the following sequence:
1. Supply with 25% of the nominal voltage for 30 minutes.
2. Supply with 50% of the nominal voltage for 30 minutes.
3. Supply with 75% of the nominal voltage for 30 minutes.
4. Supply with 100% of the nominal voltage for 30 minutes.
Total forming time: >2 hours
The module is now ready for operation."
My thinking is a freq drive will work as an adjustable power supply in this specific application particularly since the drive wouldn't actually be running anything. Plus I have drives here but don't have power rheostats
My OPINION is do not use a VFD for this..
A VFD does not actually reduce Voltage to the 'Motor' it Just reduces time 'On' and lets the Pulse Charge the Magnetic Strength of the Coil in the Motor, simulating a low voltage run condition..
You are charging a Capacitor, and when you hit it with a Peek of ( Say ) 600 VDC, no matter how long, it might complain..
I like the Variac Method..
Cap
This is the best reply. I’ve thought of this before but in a different way. I tried to take a VFD into a three phase transformer and be able to get different voltages out. It didn’t work well at all. I thought the inductance of the transformer winding would homogenize the spikes enough but it didn’t work. I know three phase variacs are not cheap. Maybe you can find a VFD repair shop to do it for you cheaper than buying a variac.
The Supply Power does not have to be Three Phase.. The Line Voltage comes in through a Three Phase Rectifier, and charges the DC Buss line.. Drives Generally can be powered up by Putting Single Phase Power on the any two of the Three Input Terminals. I've used that to Program a few Replacement 100 HP Drives in my Office, before Installing in the Field..
The 110 VAC Variac feeding backwards into a 110 By 240 or a 110 by 480 Transformer sounds like the 'Lab' way to do it.. I'd recommend that technique.
A procedure I learned back in the Last part of the Last Century, was to just Power up the Drive for a Day, and DO NOT RUN IT. The then 24 hours later run it.That has worked for me in the past.
Last week I needed to power up a P7 Yaskawa Drive that has been sitting Outside in a 'Not very well Sealed Fiberglass Enclosure' for 7 Years in the Boneyard. I used the Power up Only ( 480), then the Next day I started the motor using the Drive.. The Motor was fine, however the Gear Box it was hooked to was full of water and locked up.
Depending on your Level of Bravery, you could hook the Drive to the 110 Line for a Few Hours, then the 220 Volt Line, then 480 ( If so Rated ) and see how it goes..
Middle part of Last Century, there was a Technique of Using Varying Wattage of Light Bulbs in Series powering OLD Antique Radios to slowly bring them to Life so the Caps would not Blow..
You will not know what worked 'Best' until it Didn't.. and that would be a Fatality to the Drive.
Good Luck, Please keep us posted..
Cap
The Supply Power does not have to be Three Phase.. The Line Voltage comes in through a Three Phase Rectifier, and charges the DC Buss line..
See my post about the instructions in the ABB manual. The applied power may not need to be AC -- the rectifier will convert the AC to DC anyway. DC will pass thru the rectifier to re-form the capacitor. This would require a controllable DC power supply with a significant voltage output -- which could be a limiting factor for some.
I agree a variac is the proper tool.
I ordered an open box variac. Saving one servo amplifiers justifies it.
I'll just have to get setup to reform on the DC bus side for the ones that prescribe that method.
Inrush is to high to power it at line voltage, either the breaker or caps blow.
I'll have to build a cabinet to store drives and power them up once a month next year.
I do not mean to muddy the waters around capacitor reforming.
The B&R manual does not provide details about how to power the drive, how to provide the lowered voltages...
The variac method has traction here and in other forums.
ABB has a document about how they suggest reforming capacitors in their ACS50, ACS55,ACS150, ACS310, ACS350, ACS355, ACS550, ACH550 product lines.
Page 4 shows a circuit diagram for applying a DC voltage to THEIR drives through a 100Ω/500W resistor directly to the U1/V1 (or functionally equivalent) terminals.
I am not going to promote or defend one method over another. Just trying to add to the body of knowledge.
Not muddied at all
I think they work under the philosophy that if you don't know how to managed the voltage yourself then you aren't qualified to do it to begin with.
It seems split pretty even between supplying the AC bus and DC bus to reform
My OPINION is do not use a VFD for this..
A VFD does not actually reduce Voltage to the 'Motor' it Just reduces time 'On' and lets the Pulse Charge the Magnetic Strength of the Coil in the Motor, simulating a low voltage run condition..
You are charging a Capacitor, and when you hit it with a Peek of ( Say ) 600 VDC, no matter how long, it might complain..
I like the Variac Method..
Cap