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capacitors reforming

Created by: SAQIB ALI at: 2/9/2010 8:38 PM (8 Replies)

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2/9/2010 8:38 PM	Rate (0)
SAQIB ALI Member Joined: 12/10/2009 Last visit: 2/24/2010 Posts: 16 Rating: (0)	please anyone clear me why reforming of capacitors is done? and why we use precharging resistors in inverters? regards

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2/10/2010 3:18 AM	Rate (1)
Graeme Gold Expert Joined: 6/4/2008 Last visit: 3/19/2018 Posts: 1181 Rating: (271)	Hi, Capacitors, if left for more than 1 year without power tend to degrade (recoverable) to a point that they may possibly explode (it does happen) if a full DC voltage is suddenly applied. The capacitor reforming circuit gently re-introduces the capacitors to voltage, you leave the forming unit attached 1 hour for every year without power. Please see the attached document (section 6) for more info and if you wish to make one. The pre-charging resistors in the drive basically perform a similar function, each time the drive is switched on from status 008 to 009 the capacitors are "pre"-charged via the resistors, after which the rectifier takes over and full DC power is then available(You may briefly see the status 010, this is when the pre-charging is active). You cannot run the drive until the pre-charge cycle is complete (See the status word) Regards, Graeme Attachment Forming.pdf (954 Downloads)
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2/12/2010 2:58 PM	Rate (0)
SAQIB ALI Member Joined: 12/10/2009 Last visit: 2/24/2010 Posts: 16 Rating: (0)	hi please clear if precharging does the same function of reforming before every start of the inverter then why we do reforming separately regards

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2/21/2010 2:58 PM	Rate (0)
SAQIB ALI Member Joined: 12/10/2009 Last visit: 2/24/2010 Posts: 16 Rating: (0)	awaiting your prompt response please

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2/21/2010 10:15 PM	Rate (0)
Graeme Gold Expert Joined: 6/4/2008 Last visit: 3/19/2018 Posts: 1181 Rating: (271)	That is a good logical question!! You are correct, the pre-charge is essentially the same as re-forming, the big difference is as follows: When the pre-charge applies voltage at the power on stage, the voltage builds exponentially (current is minimal), when the voltage has reached 87% (I think), then the main rectifier switches in and applies full power (full current is available). The main difference is thatwhen re-forming, there is no main rectifier that will switch in and possibly destroy the capacitors, instead, you supply the caps with a limited supply, 1 hour for every year without power. If the drive has had power less than 1 year ago, re-forming is not necessary. Hope this clears things up. Graeme
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5/4/2015 6:43 PM	Rate (0)
GBMC Regular Member Joined: 11/26/2007 Last visit: 2/14/2018 Posts: 5 Rating: (0)	Hi Everybody, Another thing for capacitor reforming for Sinamics drive. Do I need capacitors reforming if drive (Sinamics) does not operate more than year? Please guide me. Thanks a lot GBMC

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5/14/2015 12:09 AM	Rate (1)
Graeme Gold Expert Joined: 6/4/2008 Last visit: 3/19/2018 Posts: 1181 Rating: (271)	Hi, in short, yes. Any Siemens Drive/Any Drive Manufacturer that uses Electrolytic Capacitors require reforming after a 1 Year period with no power. Electrolytic Capacitors are generally the weak link in any electronic circuit as they exhibit this property, and they also dry out over time. I remember the days when most computer motherboards could be revived by replacing the Trolly Caps
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6/10/2015 1:13 PM	Rate (0)
Min_Moderator Moderator Joined: 9/3/2014 Last visit: 2/16/2018 Posts: 5722 Rating: (119)	New question published by Silvio_Morais is split to a separate thread with the subject Forming DC link capacitor differences. Best regards Min_Moderator

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3/18/2017 4:25 PM	Rate (0)
jayjb007 Member Joined: 3/16/2017 Last visit: 3/20/2017 Posts: 1 Rating: (0)	what is precharging. and why prechargigng require ??????

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