The Craftmans Shop > New from Old
Rebirth of a Denford MIRAC CNC Lathe
awemawson:
Not so sure there Tom, it seems to be one step forward - two back today :scratch:
I'd removed the auto oiler / lubrication pump before panel spraying, and also cut a hole to replace the fixed power cord clamp with a 15 amp IEC socket. So today I wanted to refit the oiler and connect up the socket - nice and simple.
First I wanted to investigate why the oil reservoir was swathed in blue insulation tape - as I'd guessed it was cracked - no big issue, I gave it a good wash out in very hot soapy water (can't use a solvent as I don't know the plastic) to de-oil the crack, then glued it with a speciality plastic glue. Bolted it back on the machine and re-made the five drive wires (this oiler runs when the spindle is turning).
Then I made up a little cableform from the termination block that the the fixed power lead went to, to the IEC input socket. Powered up and it tripped my RCD in my main fuse board. :bang:
Lots of faffing about looking at wiring and scratching my head - it all looked fine - but I dis-connected the oiler anyway, tried again and it was still tripping. Hard to make an error in the Live Neutral and Earth cableform - and no there wasn't !
Lots of experimenting trying to isolate the leakage, but as yet not found it - if I disconnect the earth tag on the mains input it powers up ok and the chassis floats at about 100 volts above earth :bugeye:
awemawson:
Now I couldn't for the life of me understand how I could have introduced an earth leakage fault doing what I've done.
So as Sherlock Holmes used to say, when every other possibility has been eliminated what remains must be the truth - look at the old mains lead - sure enough the earth was disconnected - this is NOT a new fault, I've tripped over someone else's unfinished problem :clap:
b4dyc:
That will give you something to do then. You was looking like you were near finishing otherwise :Doh:
awemawson:
So a bit of diagnostic progress:
Removing the earth from the input IEC connector and putting an AVO8 Mk7 on AC volts between the IEC Earth tag and the removed machine Earth, and the machine powered up I was reading 88v AC - roughly what I'd read before and enough to give you a tingle on a grazed knuckle - (ask me how I know!).
Now the internal resistance of the AVO is high enough to limit the earth fault current sufficiently to not trip my 30mA RCD in the fuse box, but is low enough to swamp stray capacitive effects that you would get using a modern electronic meter like a Fluke.
So by a process of elimination working though all the mains using devices in the machine I found that the main spindle drive inverter to be the culprit. Now as inverters switch at high frequencies they do tend to cause quite a bit of earth leakage, but in this case I'm sure it is excessive. I strongly suspect the input filter components in the enlarged view, but getting at them to replace wouldn't be easy.
As I have a 13 amp socket for lighting on my three phase Bridgeport, that is derived from phase 1 and neutral, and the three phase distribution has a 100mA RCD I moved the extension lead from a 30mA protected socket to this 100mA protected socket and sure enough it didn't trip (I'd left the AVO in circuit but rotated the knobs to measure AC 10 amp so effectively a short circuit restoring earth continuity.
Out of interest I turned the knobs back to AC volts and I was measuring very low volts - nothing like before where I had 88 volts AC. All very odd - so I put the machine back onto the 30mA protected circuit with a solid earth by removing the AVO and pushing the faston connection back together, and darn me the bally thing works and doesn't trip the 30mA RCD any more :clap:
The only conclusion that I can draw at the moment is that whatever was causing the leakage has been blasted away by the (presumably) less than 100 mA current that initially flowed, and is now in oblivion :scratch:
So although I don't like disappearing faults, at least it's working and no longer dangerous as it was.
To prove all was working I tried to make another M6 brass bolt, but the darn program wouldn't run - couldn't fathom it, until I noticed the little bit of text saying 'Low Lubrication Oil Level' - of course I hadn't filled the reservoir when I glued the crack to give it time to set. Filled her up, off the program went . . . .BUT the crack still leaks :bang:
...ah well . . . :med:
nrml:
Why don't you fold and solder a sheet metal box that can sit within the cracked plastic oil reservoir? It would be a simple solution for the problem. My personal experience with gluing plastic containers of any sort has always been bad.
Do you think that the tripping might have been caused by a bit of swarf in the electronics which fell off when you were dismantling the boards?
Edit:
The reason I ask is that there appears to be some swarf / dust on the black sheet metal panel and on top of the lowermost mosfet in your last two pictures.
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version