Re: Power supply questions

Hi Tom,

The calculation for Cap's is

C= ((80,000 * I) / V)
C is the value in microfarads.
I is the current.
V is the voltage

You can wire caps in parallel so that is not a problem.
No need to get them rated for 75 V if you will run at 30 volt.
50volt would be fine and less costly.

Personally, I find caps to be cheap enough to use enough for the
calculation plus rounding up to the next range.

some on here said less will work fine, but I would not considder my
unit completed until I had the full rating. just my personal
opinion. I would not test unless I had at least half the full value
so considder what you would max out with and what you want to use.

If you blew one controller board, what is the cost vs. the cost of
the full compliment of caps ?

Question to the group, what would happen with less than 15% of the
full rating uF wise? would you blow caps, over heat, loose power or
is there some other problem ?



I use fuses rated at full load, then round up to the next common size.
chances are that if you need the fuse it will be catastrophic failure
and not just tipping over the limits.

There is no reason that you cannot use a seperate 5volt transformer,
but you already have 5 volt in the PC. it's on a pin in the joystick
port so you can get a 15 pin cable and an empty socket and wire them
from PC to power supply.

I put in a simple power supply connector from the PC, you know, the
barrel end connectors. it's hard to beat free.

Dave





--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Tom Murray
<thomasm923@a...>" <thomasm923@a...> wrote:

> I hate repost my recent questions, but I really need some help in
> building a power supply.
>
> Questions below:
>
> My Taig mill is ordered, and one of the things that I have to do
> while I wait the 6 to 8 weeks for delivery is make a power supply.
>
> There's a few things that I'd like to ask the group to get me
> started...
>
> First, I am wondering if my choice of caps is correct. I will be
> using a 30 volt transformer to supply power to three 24 volt servos
> rated at 6 amps peak. I doubt that it will ever need to supply more
> than 12 amps at once, if that much, but let's assume that the

maximum

> current is 15 amps. I am looking at some surplus capacitors rated

at

> 17,000 MFD, 75 VDC. Would a pair of these in parallel be sufficient?
>
> Second, I wonder if it is ok to attach a smaller transformer to the
> same AC input that is hooked up to the main transformer to supply 5
> volts to the Geckos?
>
> Third, how does one calculate the rating of the fuse that is

needed?

> I assume that it should be a slow-blow type, but what would the
> correct amperage rating be? A little over the maximum current, a
> little under, or dead on?
>
> Thanks,
> Tom Murray