Homebrew PCBs

"What's the inductor L1 for?"

- Absolutely no idea, I was hoping you'd clear that up, hence the schematic
request.  I saw that somewhere, can't remember.


"U2/3/4/5 are a mystery to me."

- Sorry, I wanted to explain the acronyms and forgot.
- PolySwitch, a resettable device to protect against excessive current,
voltage and temperature (more in DigiKey catalog).
- ICL, incurrent rush limitted.
- ZOV, zinc oxide varistor.


"What is the EMI coil, what is the input? mains?"

Input is the secondary coils via a terminal block, 24V, 24V 48VCT.  An
electro-magnetic interference coil, supposed to remove common waveforms
across all signals.  I read somewhere it is a good idea to place these when
cables enter a PCB, to remove interference they pick up.


"A very small electrolytic parallel with a big one is just not changing
anything, esp. if you have a ceramic cap too."

- I didn't know much about the filter caps, even less when more than 1A is
involved.  I thought electrolytic caps acted like ceramic caps, the large
ones filling in larger gaps in the waveform, the smaller ones filling in
some more of the remaining gap.


"I dunno about your fuses, you certainly have a great many. I wouldn't want
to predict which one will trip first. Also, i wouldn't see the need."

- I only have one fuse on each stepper.  I don't want to have one general
fuse and then have to figure which circuit is the problem.
- The ZNRs and MOVs are there to act as crowbars in case of a short further
down the line.  They don't have the same speeds, so I put one of each model.
- If I place the fuse on the 115V line, the crowbar devices are kinda far
removed.
- I do note that the ZOV has a clamp rating, I assume that makes it a
crowbar-type device.  I have that device in series instead of parallel, not
gonna do much that way.  Technically, I should also have a fuse at that
point also.
- Determining which fuse will be blown is not a problem.  The fuses will be
mounted on the front panel along with an indicator lamp.
- Since the ZOV has clamping capability, I am considering placing one on the
primary side of the transformer along with 2 more ICL and a fuse.  That
would give me an immediate indication of where the problem is; primary,
secondary or post-voltreg DC signal.


"What i would have done if i had to use a transformer supply and not a
SMPS:"
hot->fuse->(NTC)->primary1->primary2->neutral.
(ntc in case of toroid transformer)

- I have no idea what NTC is.  I don't understand the coil configuration
either, I've only dealt with single 115V primaries so far.


I could increase cap size as you recommend.  As I said, I don't have any
sample to work with, nor do I know how to calculate required caps.

Robert
:)



-----Message d'origine-----
De : Homebrew_PCBs@yahoogroups.com [mailto:Homebrew_PCBs@yahoogroups.com] De
la part de Stefan Trethan
Envoyé : juillet 10 2005 16:21
À : Homebrew_PCBs@yahoogroups.com
Objet : Re: [Homebrew_PCBs] Drilling station 40V 3A power supply


You certainly have a few surplus parts in there ;-)

ST



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