Reforming capacitors (technical description, not politics)

Tothwolf tothwolf at
Thu Jul 30 08:42:10 CDT 2015

On Wed, 29 Jul 2015, Charles Dickman wrote:
> On Wed, Jul 29, 2015 at 3:34 AM, Eric Smith <spacewar at> wrote:
>> Some people seem to think that "reforming" an aluminum electrolytic 
>> capacitor is some kind of cheat, akin to zapping NiCd cells or 
>> rejuvenating CRTs. Actually reforming is the same electrochemical
>> ....
> Reforming is standard practice with industrial motor drives. 
> Manufactures (ABB, Allen-Bradley, Siemens) will require that a drive 
> that is not powered for a year or more have the DC bus capacitors 
> reformed or any warrantees could be voided. The procedures they 
> recommend are very similar to those that have been discussed here. ABB 
> suggests a 3phase rectifier and current limitting power resistor or a 
> current limiting DC (1000V) power supply.

VFD manufacturers are also very specific about the lifetime ratings of the 
large capacitors used in these units, and often specify that they are to 
be replaced after X number of power on hours. VFD's also aren't /just/ 
used for process machinery...they are also used for air handling 
equipment, and with a large facility, you /really/ do not want that sort 
of critical equipment to spontaneously fail.

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