Re: Power supply questions

Thanks for the info, Dave.

The 75V caps are less than $10 (surplus), and are the only ones
available from C & H Sales that are within range. They won't break
the bank.

-Tom Murray

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "turbulatordude
<davemucha@j...>" <davemucha@j...> wrote:

> 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