Reforming hi voltage caps

kiwi_abroad · 25th November 2001, 08:09 PM

Hi All,

I have back home in storage 2 Switchmode power supplies designed to power Telephone Exchanges (and therefore have very low electrical noise). They are 2.9kW each, voltage selectable between 40 and 70volts.
Anyway, inside them there are 3 450V capacitors, around 350uF each (I can't remember exact details). As these have not been switched on for over 2 years, will it be a good idea to reform these caps before I turn them on. If so, how? I'm comfortable opening the PS modules up, but I don't want to have to desolder the caps to remove them. Does anyone know how to reform hi voltage capacitors

Thanks, Adrian

walker · 25th November 2001, 08:59 PM

Reforming capacitors is done by limiting the inrush current and holding the rated voltage for about an hour. Connect a resistor 1k ohm, (larger for higher voltages but it isn't critical) in series with the cap. Apply full rated voltage and leave it supplied for an hour.

More information on farradnet and on manufacturers sites.

Regards WALKER

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25th November 2001, 08:09 PM	#1
kiwi_abroad diyAudio Member Join Date: Sep 2001 Location: Wellington, New Zealand	Hi All, I have back home in storage 2 Switchmode power supplies designed to power Telephone Exchanges (and therefore have very low electrical noise). They are 2.9kW each, voltage selectable between 40 and 70volts. Anyway, inside them there are 3 450V capacitors, around 350uF each (I can't remember exact details). As these have not been switched on for over 2 years, will it be a good idea to reform these caps before I turn them on. If so, how? I'm comfortable opening the PS modules up, but I don't want to have to desolder the caps to remove them. Does anyone know how to reform hi voltage capacitors Thanks, Adrian

25th November 2001, 08:59 PM	#2
walker diyAudio Member Join Date: Nov 2001 Location: Perth West Australia	Reforming capacitors is done by limiting the inrush current and holding the rated voltage for about an hour. Connect a resistor 1k ohm, (larger for higher voltages but it isn't critical) in series with the cap. Apply full rated voltage and leave it supplied for an hour. More information on farradnet and on manufacturers sites. Regards WALKER