BIG capacitors - good for what?

[Pete.]

I've got some large 3 phase capacitors which came out of a switch cabinet and I'm wondering what they might be good for before I decide what to do with them. The black ones are about 5" diameter and about 8" tall and 154uf. Silver one is taller and thinner and I think it's a relacement for one of the black ones since one cabinet had three black and the other has two black and a silver.

What use might they be or shall I just make bin fodder of them?

[awemawson]

Power factor correction, or making a static single to 3 phase converter

[Swarfing]

Spot welder

[vtsteam]

Or making a highly efficient generator head out of a 3 phase motor (power factor correction, again)

There's a REALLY good book about doing this, that I have somewhere -- I forget the title -- but I'll put it up tonight as soon as I find it..........

(Back a few minutes later...)

Ahhhh yes, here it is, "The Home Power Producer's Guide to Electrical Reality" by Bill Rogers.

One of those small masterpieces that tells it like it is, and provides truly USEFUL information backed by engineering theory and experiment.

[Pete.]

I have a transformer that trips the breaker in my workshop sometimes when I first power it on. This has prevented me from utilising it as an autotransformer to bump-up the supply voltage in my lathe. Is there anything these capacitors can do to reduce the 'kick' of initially powering that transformer up?

[awemawson]

In a word - No!

You need a 'soft start' Modern ones comprise a Silicon Controlled Rectifier in series with the load, and it's triggering phase angle starts at 180 and progressively advances to 0 degrees.

More old fashioned ones comprise a power resistor with a relay contact across it. A second or so after power is applied the relay triggers shorting out the relay resistor.

[John Rudd]

More old fashioned ones comprise a power resistor with a relay contact across it. A second or so after power is applied the relay triggers shorting out the relay.

I think you mean short out the resistor......?

[awemawson]

Correct - it's been a long day !!!