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Siemens micromaster 420

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appletree:
Hi All
I don’t know if anyone can help/comment, i have just got a new old stock Siemens micromaster 420 single to three phase VFD, it did not come with the CD manual, however the manual is on the Web.
I  do not know how old the drive is, its modern but might be 7 or 8 years old.
Whilst looking through the manual i came across this section in 2.1of the link below. (unable to copy from PDF).

http://docs-europe.electrocomponents.com/webdocs/0391/0900766b80391560.pdf

Basically it talks about supplying the unit with a reduced supply voltage (Variac) and progressively increasing over a day.

I have a lot of experience of mitsubishi VFD’s and this idea is a bit new to me. I have a variac so could do it, just wonder what some of the clever electronics would make of low voltage e.g. 25% and rising.

Comments please Phil 

philf:
Hi Phil,

I think this is fairly normal practice for electronics with big electrolytic capacitors to avoid a big bang and horrible fumes when you power up after years of sitting idle.

I was advised to do this with a big ABB inverter which I converted from 415v to 230v single phase operation. It had stood idle for probably more than 10 years. When the input approached the operating voltage of the inverter the display came on - maybe displaying under-voltage to start with.

The fact that they advise you carry out the procedure would give me confidence that no harm can come to the electronics.

Cheers.

Phil.

John Rudd:
Phil,
Hopefully my comments will help.....

Basically what they are saying is that because your unit has been sat on some shelf for a prolonged period, the dc bus capacitors will need reforming.....the process involves applying a low-ish voltage to the unit for a period to aid the reforming of the electrolyte in the caps....it seems its a staged process they recommend..

A capacitor stored for a long period will lose capacity, by reforming, the capacity can be recovered...generally...hopefully the capacitors havent dried out and are recoverable, otherwise the only other course of action is to replace them with new ones....

John Rudd:

--- Quote from: philf on March 22, 2017, 07:30:57 AM ---Hi Phil,

I think this is fairly normal practice for electronics with big electrolytic capacitors to avoid a big bang and horrible fumes when you power up after years of sitting idle.


Phil.

--- End quote ---

An uncharged capacitor of largish capacity presents a short circuit when a voltage is applied to it....depending on the voltage, the current can be quite high sufficient to blow the bridge rectifier and/or up stream fuses....if the capacitor isnt reformed, then it wont charge up....hence the big bang and release of magic smoke ( and potentially other smelly substances.... :lol: )

awemawson:
I understand that the mechanism is that the thin insulating anodised layer that is formed during manufacture, can dissolve back into the electrolyte unless there is a voltage potential applied occasionally in the right direction to reform it.

Anyone remember the 'wet electrolytics' that you could actually hear the electrolyte sloshing about inside? The can was the cathode, and the anode was an extrusion with loads of fins to increase surface area. Now they DID make a mess when they popped - AMHIK  :lol:

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