On 8/7/24 09:33, Jean-François Simon wrote:
Hi Gene,
Not my project, i was answering to someone else.
I confirm it has to be properly designed and certified,
best to use certified apparatus in an electrical box.
Generally i would stick to 48Vdc as far as practical.
That's a good voltage for stepper/servo 3 phase drivers, and slower
subtractive machining. Moves it faster than a 1 hp spindle can cut.
That "limit" is generally safe as long as you are dry. Modern high
performance 3d printers are at 72 volts for motor power now, and will
likely soon exceed 110 DC in the next few months when the psu people
catch up. I have 2 such under construction now, that both are
operational, will require their own 15 amp 127 volt circuits. Heating
big beds to polycarb happy temps make them very hungry.
Above that, a properly constructed box with E-off
with certified parts shouldn't cost a lot and is required.
If unfamiliar, the original author should seek specialized
support to build it safely & properly, for sure.
Regards
Jean-François
On 8/7/24 13:53, gene heskett wrote:
On 8/7/24 03:17, Jean-François Simon wrote:
Hi good morning,
I never eared of a power rectifier directly connected to the line,
usually there will be like slow charge circuit through resistors,
often also a filter at input stage, like LCL with inductors.
Based on the explanations, i can't figure the details, is it so you
design and built a custom circuit,
Yes, so can you. Easier for me as I am a Certified Electronics Tech.
This stuff is potentially lethal to the unwary.
or implemented existed
modified circuits ?
actually probably invented long before me.
Essentially, yes it depends on the power rating, and passed a
point, drives have both charge and discharge circuits, as you
can't feed up instantly, it would exceed some ratings.
The parts damaged at fast charge i guess would be also the
diode bridge, some wire and connections, for capacitors i'm
not sure they would be at issue, though they can overheat
from the internal resistance.
Any cap that heats when used within its ratings is junk, replace it
with good ones.
If i got it right, you are trying assemble modules (like a
rectifier bridge with other things, DC bus and inverters),
then we need to look at the module datasheet and ratings
to fogure out these things.
Basically yes, but bear in mind this is dangerous stuff that only
needs one wrong move to make your wife a widow. Logic level voltages
cannot usually be felt, line level voltages are a different critter
that can kill. If you aren't comfy with it, get and pay someone
knowledgeable who is.
It's quite wrong Caps remain charge, that should never happen,
all drives discharge the internal caps at standstill, something's
failed or missing.
All quality drives generally will, but do not trust them. A good
capacitor, charged when disconnected can knock you against a wall a
year later. 20 microamps directly thru the heart can cause it to loose
timing, fibrillate and kill. You may not even feel it. 20 milliamps
you will feel but it will also freeze it, and if someone manages to
disconnect you fast enough, the heart will often start back up and you
will survive, but such a shock will often trigger a 6 month bout with
shingles.
In my experience as a broadcast engineer, BTDT, not the least bit
pleasant, but I'm still here as I look at my 90th. If I come off as
brutal, I'm trying to save you. Take care and stay alive.
Regards
Jean-François
On 8/6/24 22:44, Viesturs Lācis wrote:
Hello!
Recently I have posted some questions about the retrofit that I am
working on and now I have encountered an issue that I cannot figure
out.
The thing is that I am swapping original Yaskawa servo drives with
Mesa 8i20. One of the things for that was 3phase rectifier bridge (it
takes 230 VAC input and provides 340V output) and 4700 uF capacitor
for smoothing the ripple.
It took me some time and some patience from PCW to fix the config and
in the end I got one 8i20 to move one joint in the machine. So my next
step was adding 2 more 8i20 drives for remaining 2 joints. It ended up
with a blast in one 8i20. So I replaced it as well as I had to replace
rectifier bridge. But now my issue is that protection fuse is tripped
as soon as I enable machine power.
1) only rectifier bridge connected - all good
2) rectifier bridge + capacitor - fuse tripped immediately
Note that I have not yet connected DC bus to 8i20 drives.
I checked capacitor with multimeter, it was showing 180V DC (and it
did not decrease in that time that I was holding multemeters pins
there). I am not sure if that is some residual charge from previous
(which I doubt) or if that was some charge that was acquired before
fuse was tripped, but this seems to me like a good capacitor. Is that
correct?
I do not understand why was everything fine in initial testing - I did
turn machine on and off lots of times and capacitor was discharged
(and recharged!!!) numerous times. I have swapped that fuse for
identical unit from a machine that has yet to go through the retrofit
process. And it is the same.
So my question to electronics gurus - could capacitor be damaged or
was it just a beginners luck that everything worked and do I need to
introduce some inductor between rectifier bridge and capacitor to
limit the startup current that charges capacitor?
Viesturs
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Cheers, Gene Heskett, CET.
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Cheers, Gene Heskett, CET.
--
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soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author, 1940)
If we desire respect for the law, we must first make the law respectable.
- Louis D. Brandeis
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