Powering up capacitors

[Simonta]

A little of topic but relevant to the skills on this forum. Please excuse me Saab or move to JB as you see fit.

Many moons ago, I learned through experience that one had to be careful powering up capacitors that hadn't been used for some time. Is this still true of modern(ish) kit - say late 90s early 00s. Reason for asking is that I have some stuff that has been in storage for about 4 years including some power amps and so on that I imagine have fairly large capacitors in the power supplies.

Do I need to be careful powering them on? If so, what can be done? How about powering them up on a variable supply, e.g. starting at 100v and slowly winding up to 240v?

Any thoughts?

Cheers

Simon

[glad rag]

Are you powering up the caps separately? OR the whole unit??

If the latter then you may put more demands on it as a whole with the lower voltage. I don't THINK 4 years storage should have had any detrimental effects (but it's a dielectric device) but if they want to go BANG they will.

Be very careful with any tinkering you do, they are supposed to be designed to discharge slowly back through the circuitry, but if you power up/down then decide to tinker you could be exposing yourself to some quite high voltages, although probably not in the same magnitudes as those found, say, inside your humble micro-wave. Now they are dangerous.

GR.

[mixture]

Simonta,

As glad rag says.....

Are you powering up the caps separately? OR the whole unit??

If the former.... then as the old saying goes .... "If you have to ask how to do something potentially risky, it's not something you should be considering doing" (or a saying along those lines anyway !).

If the whole unit, e.g. a whole computer.... then who cares.... power it on and see what happens (all chassis casing etc. safely in place obviously !) You'll waste more time trying to figure out how to test capacitors safely.

All my own opinion... caveat emptor... follow any suggestions at your peril !

[green granite]

The original question invites the response of "What sort of capacitors are we talking about"?

[FullOppositeRudder]

I would endorse the cautionary remarks by others so far. Electricity is a force which demands respect, and can cause injury or worse if it's not treated with caution tempered with a full understanding of the situation.

However on the basis of what you have told us, and if I understand the situation correctly, namely that it's a complete piece of commercial equipment with covers intact, I would simply plug the device in and turn it on - unless you have a good reason to suspect that something is amiss.

The inrush current to large capacitors which are fully discharged can be very high in those first microseconds after switch-on, but in the case of more recent equipment, and provided that the caps are in the equipment as OEM components any potential problems in this area should have catered for in the design.

My amateur radio linear amplifier can cause a momentary flicker in the household lighting when it is first turned on - mind you it supplies 2,400 volts to the plate of the valves and the storage capacitors are 'significant'. But it's 1980's equipment and so far there have been no causes for stress or immediate evacuation :eek:.

Of course this is simply my non professional opinion - I'm not an electronic design engineer, simply someone who messes about with such things on an experimental basis. I've also seen newly completed projects produce a variety of audio, visual and other sensory displays :uhoh:, but that is surely outside of the charter for this forum.

Give it a try, but keep your hand on the switch, and know where the door is .... :E

regards,
FOR :ok:

[cats_five]

Where has this kit been stored? In the house? If not, let it come to room temperature for a few hours before turning on. If it's cold there will be consensation on it which might cause problems.

[P.Pilcher]

If you have any problems of a technical nature with this then you can try the vintage electronics restoration guys who lurk on: www.vintage-radio.net/forum/index.php (http://www.vintage-radio.net/forum/index.php) They are all experts on the various ages of electronics there.

P.P.

[Loose rivets]

Beat me to it. Super forum. They power up kit that's been standing for years by way of a variac. A substantial transformer than can be altered in ratio by a mechanical wheel.


It's a subject close to my heart. I took out a very weighty Panasonic from 7 years of storage this summer. I should have rigged a major reduction in voltage for the first try. But staying in very restricted flat - so I didn't. Stood back and kept my fingers crossed.

After a week or so of running, I knew two things. The electrolytic capacitors were probably through their crisis period, and that I LOVED that 25 year old amp even if I can't carry it far now.

[P.Pilcher]

It's a subject very close to mine as well! I cut my teeth on their form of electronics when I was a teenager and then went on to read the subject to get an honours degree in it in the mid 60's from what was then THE university electronics department in the country (and I only was required to get 3 "C's" at A level to get in as well - says something for todays standards don't you think).
All commercial pilots are required to have a basic knowledge of electricity and ohm's law to pass their exams. In certain cases it isn't too good and I used to get much pleasure in improving this by discussions with some of my FO's in the cruise at FL 300!

P.P.

[Loose rivets]

I have a pilot pal that used to think that red electricity came out of red wires, and black out of black...as long as one didn't mix them, one was okay. He taught me met, and I tried to give him a feel for all things electrical.

I don't suppose he had all that much confidence in me, we'd grown up together and he'd witnessed my putting an electrolytic across an industrial charger. When it started bulging, we ran, instead of turning the thing off. Loud as a firework- a 1950s one - and took ages to clear up the debris.

He went on to fly the Britannia, so something must have gone in.

[Simonta]

Thanks for all of the responses. I actually started working life as an electronics engineer and have, through "hands on experience" of various voltages/currents, learned a healthy respect for electrickery. So don't worry fellow PPRuners, not about to fry myself!

I was thinking about using a variac but from the posts on here, it seems light the blue touchpaper and retire is the way to go ;-)

To answer specific questions, I have no idea of the specifics of the caps, having never opened the boxes but the total RMS of the power amp is around 800w so they might be as big as .05F, maybe 0.1F so a healthy belt if they do let go. Probably standard dielectrics, doubt there's any oil in there.

The boxes have been in professional storage, low humidity and fairly constant temperature so I'm not concerned about condensation or corrosion.

I'll let you know if the results are "interesting" :}