Re: cap didn't pop

Dave,

The stuff is corrosive and electrially conductive. Here's the hi-tech
way of cleaning it up.

Remove the board from the mounting plate and wipe off the heatsink
compound from the MOSFETs (it's messy). Clean the plate thoroughly
using a solvent like MEK or acetone.

Get a hairdryer, a cardboard box(6" by 8" by 6"), an old toothbrush
and liquid soap (dishwashing soap). Turn the faucet to hot water,
pour a little soap on the board and start scrubbing it under the
faucet like there's no tommorow. Rinse very thorougly and repeat if
necessary.

After you are done, shake the board dry (or use compressed air). Put
the board in the box and close it, insert the hairdryer nozzle
between the box flaps and turn it on at a low setting. Go away for 10
minutes and think about how bad it is to reverse polarity on a cap.

When you return, turn off the hairdryer and remove the board. Re-
grease the MOSFETs and mount it back on the plate. Cross your fingers
and turn on the power. If the drive has not been damaged, it should
take off OK.

Mariss

--- In CAD_CAM_EDM_DRO@y..., "turbulatordude" <davemucha@j...> wrote:
> Hi Marriss,
>
> I have to disagree with your statement that caps blows up with the
> sound of a firecracker. It was not too loud, and not too much
> smoke. What scared me the most were the sparks from the 201.
>
> I just put together a huge power supply, 68,000 uF cap and a 10 amp
> transformer, connected a 201 to a NEMA23, 6V, 0.85a stepper Vexta
> stepper, and used a 6.19K ohm set resistor. ( talk about overkill )
>
> I connected the PC's 5 volt to the #10 pin and used an aluminum
> 470uF cap with about 18 inches of leads from the power supply to
the
> 201. I cut the 470's leads to about 1/2 inch. I had a 6 amp fuse
> (one of my many mistakes) in the +V line. I wish that blew first,
or
> at all.
>
> I started testing the table with running 5 inch jogs on a 400 step
> motor, with a 1/2-13 all thread rod.
>
> At 10,000 maximum steps, the motor started missing, although I was
> not sure if it was during acceleration or where it started.
> Acceleration was 200 steps in TurboCNC.
>
> I reduced to 5,000 maximum steps/sec and it worked fine. I
increased
> to 8,000 and increased the acceleration to 2,000 and during the
ramp
> period, it started missing steps. I stopped the step command when I
> heard the missing, and shortly thereafter heard the first pop.
>
> I turned off the 110 to the transformer, but have no fast dump for
> the cap. Since I do not have any drain on the 68kuF cap, it keeps
on
> going... and going... and going...
>
> I looked at the 201 and within a second I could see the sparks as
it
> was releasing all kinds of magic smoke.
>
> At that time I was pulling the wall plug.
>
> With some quick overview, the major destruction was the
catastrophic
> freeing of electrons in such a way that all components that used to
> occupy the space between the pot and the angled resistor have been
> liberated and have joined Elvis in the hereafter.
>
> The pictures are not too good, but you might get the overall idea
of
> the location.
>
> Oddly enough, there was also some heat transfer grease liberated
from
> under the opposite corner, just under the #12 connection.
>
> I connected the stepper to the 201 with about 30 feet of #18ga
wire,
> that was coiled on the floor. That means there was 4 feet to the
> stepper and 4 ft straight to the 201 and a sizeable coil on the
floor.
>
> No e-stop.
>
> All that said, my questions now come towards not repeating the
> performance and clean-up.
>
> #1) immediate handling, how aggressive is the fluid from the
cap ?
> do I need to scrub everything or just wipe down the stuff that is
> easy to get to ?
>
> Now, the simple stuff, what else did I do wrong ?
>
> I put a photo in the photo's section under the Daves Unit folder.
> (I web read, not e-mail, so I don't know how to attach a photo)
>
>
> Dave
> (again stepless in NJ)