Got it then you need a proper DC bus with charge circuit if it gets
some good power, and safety discharge, you never want charged
caps in some place around, at this high Voltage.
Question do you build the rectifier, do you get it from something
existing ?
Basically yes, you need slow charge to not blow something provided
the load behind is great enough to need it, otherwise you'll get
as you do, blown fuse or damage something else, that depends
on inrush current.
I and others can perhaps provide a couple hints, depends on what
you are really going to design, ie from bulks or custom.
Regards
Jean-François
On 8/7/24 09:45, Viesturs Lācis wrote:
Hello Jean-François!
I am using Mesa 8i20 servo drives that do not have built-in power
supply, it takes DC as power input so I am trying to figure out how to
do that properly. It seems to me that only a pair of rectifier bridge
and capacitor is not enough to keep fuses happy.
I do not worry about discharging the capacitor - what I observed from
initial testing with one 8i20, it seems to me that drive does slowly
discharge it - voltage dropped to few volts within a minute or so.
Peter, is that intended or was it just some kind of happy moment and I
actually should worry about discharge circuit as well?
Viesturs
trešd., 2024. g. 7. aug., plkst. 10:19 — lietotājs Jean-François Simon
(<jfsimon1...@gmail.com>) rakstīja:
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, or implemented existed
modified circuits ?
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.
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.
It's quite wrong Caps remain charge, that should never happen,
all drives discharge the internal caps at standstill, something's
failed or missing.
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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