Capacitor sizing on power supply

[Jackal66]

Hello,

I had just assumed that the factory Hurco Capacitor for the power supply was sufficient for my new set-up. After all, the voltage is now lowered to 77 volts DC, from 92 VDC.

According to calculation from Bob Campbell's formula ( If I worked it correctly) the capacitor should be around 40,200 uf.

The factory single cap is 8700 mfd & 150VDC.

Does this sound correct?

My servo motors are rated 90VDC, 12A cont., 20A peak.

The transformer is 1800 volt amps. Power supply is 77 vdc through the rectifier and old capacitor (8700mfd).

What do some of you experienced electronics people get?

The factory cap is the physical size of a beer/soda can, but I doubt that makes a difference.

Thanks for the help,

JAckal

[Al_The_Man]

Actually lowering the voltage requires a larger capacitor to maintain the same % ripple.
for e.g. for three motors rated at 12A continuous, to operate all three simultaneously at rated continuous and allow for a 10v p.p ripple at that current would require a 30,000µf capacitor at your DC voltage..
It is very seldom you operate all three at the rated current so some leeway is the norm.
It depends on what % ripple you aim for and also something to keep in mind that increasing the µf value more than you need actually increases the VA requirements of the supply.
Al.

[Jackal66]

Al,

Do you think I should just run with the (1) factory cap that Hurco used with it?


With their sizing , it has worked for all of those years on many machines out there.

Thanks,
JAckal

[Al_The_Man]

You can only try it, you can always parallel it later if you see any problem.
But remember you are also lowering the voltage from the original.
Al.

[Jackal66]

I have (2) of these caps. A friend sent me a spare during his retro. I might just go ahead and parallel them both.

Thanks for all of the help, AL.


JAckal