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One thing you can do is use twisted pairs for your wires. Each twist of the wires will radiate the outbound energy 180 degrees out of phase and tend to cancel the radiation at long distances.
Back in the old days of land lines, the nations phone system was largely unshielded, depending on the effect of twisting the wires to keep EMI out and crosstalk in. Much less expensive also.
I still suggest my transistor radio sniffer. Find where your problem is and fix the actual source, it has often occurred in my experience to be something very different than what my first guess was.
As to the filters being different, that is not surprising at all. What is needed is a low pass filter that will let 60hz through but block the kilohertz and up noise. The exact cutoff frequency hardly matters, and almost all of the filters you can buy are a single stage Pi (CLC) filter. Effectively they are all the same, the amount of attenuation you get at RF frequencies will be almost identical. Buy a unit based on their current carrying ability, and price.
D
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Hey, Dana - I'm familiar with twisted pairs. This girl I used to date had a twin sister and... OK, never mind that. I've never heard of twisting to eliminate outward radiation of electromagnetic noise. But, I don't know why it shouldn't work in that direction. The only problem would be to twist that half inch 220v power cable. Yikes! I'm not sure the insulation would survive it.
More significantly, I think we have to distinguish between the electrical noise introduced by the spindle and carried on the power line and the electromagnetic fields which radiate outward from the cable. I have a hunch that the more significant problem is the noise carried on the power line to the circuit box and, from there, distributed to the rest of the house. While shielding and twisting may be helpful, it only addresses the symptom.
To address the line noise, I'm getting passionate advise in two different directions. The Yaskawa engineer insists on improved grounding. We already know that grounding the ShopBot didn't help. And I'm not sure how I can significantly improve grounding for the VFD. In the other direction, I'm told that a filter is the way to go.
The Yaskawa manual talks about two different input side filters which apparently serve a different purpose. So far, the Yaskawa engineer has been steering me away from the filters and has avoided explaining the difference. There's some pretty sparce documentation for one of the Yaskawa filters which explains the wye/delta capacitor configuration used (http://www.yaskawa.com/site/dmdrive..../2Y25-0349.pdf) to achieve better RF attentuation than a wye configuration. The eecontrols filter sold by ShopBot is a double stage filter. The spec (http://www.eecontrols.com/documents/...inefilters.pdf) unfortunately only goes into detail on the line of single stage filters. And if you know what any of this means with respect to the problem at hand, I would love to get your input.
At the moment I'm still frustrated by even the so-called experts' apparent inability to give me useful information. If I find out more I'll post here.
Andy
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Andy- the power cable I used on my bot is Carol 12/4 (a General Cable product), my vague recollection is this is internally twisted as a group. There are multiple 12/4 products from GC, I can get you a specific part number if you like.
That rubber sheathed cable goes from the SB to the junction box, after that the power lines are enclosed in metal conduit.
One other thought about your emi problem. Be sure all of your connections are tight. (Power off before checking!) Nothing emits broadband RF like arcing, and its a huge fire starting opportunity I'm sure you are aware. One thing to do is just put your hand on the power cable near junctions and plugs to see if it is heating at all. Heating is a sign of trouble. The cables should be very near room temperature.
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Oh.. feel free to tell more about those twins. Its of no interest to the general community I am sure, but I would be happy to study the situation carefully for its technical merits ;)
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Footnote- just looked at the info from Yaskawa, that is a "C only" network, which I would not recommend. The ones from EEC are "CLC" Pi filters like I spoke of before, they would be much more effective.
THe EEC products are marked as single phase, if your spindle has single phase power its just a matter of getting TWO of the D-MSC 30 (for the current requirements [assuming 30A is enough for the spindle]). If you have a three phase power requirement, then look around for a three phase filter equivalent to the D-MSC 30.
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I have the 30Amp single phase spindle. Scott Worden installed the D-MDC 30 which, annoyingly, is not described in detail in the PDF (only superficially on the first page.) This is what's sold by ShopBot and seemed to work for him. It's the double stage version of the MSC filter.
I think you just convinced me to go with the eec filter though.
Thanks so much for your input! I really appreciate everyone taking an interest.
Andy
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By the way, I just found my old transistor radio (for you youngsters - that's an iPod that streams music wirelessly for free) and tried running the spindle. The results were pretty spectacular: as soon as the spindle started running (at .5 or .6 on the display), there was significant noise on the AM band. I didn't bother with FM since AM is closer to the DSL frequency range than FM. As long as I was near the Shopbot, there was a lot of noise. It definitely got worse near the spindle and the cables. And it didn't seem to matter at all where along the power cables I checked. So, there was significant noise from the spindle all the way back to the wall outlet.
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Now you have found the source of the emissions. Using the suggestion of a pre-ipod music streaming device (I love that description). You know what specific problem you are trying to solve.
That technique has worked for me before. I learned about it from an RF engineer I used to work with. He taught me all kinds of practical things in working with RF I have never seen elsewhere. Glad I could pass it along.
The EMI filter should help, and twisting should help again. Between the two it should make a significant difference. Even then the interference will still be there, but it should be much less. Metal rigid conduit or flex conduit should provide a solution also (as it is a faraday cage).
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Could not having your shopbot grounded well enough lead to crashes? lately i've been running just fine and then i get communication error. I'm gonna ground it better and see if that fixes the problem.
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Tim -
It sounds like a lot of people have fixed their communication problems by properly grounding the bot. See the excellent ShopBot Wiki page on grounding: http://shopbotwiki.com/index.php?tit...g_your_ShopBot
Also, make sure the thin control wires are as far as possible from the power cable to the spindle. As discussed in this thread, the spindle feeds a ton of electrical noise back into the powerline. The noise in the line translates into electromagnetic fields which are much stronger closest to the power line. If your control wires are placed too close to the power line, the electromagnetic fields will induce fairly strong electrical currents (noise) in them. And, of course, you don't want electrical noise competing with the commands you send along the control wires.
All -
I was able to find the EE Controls' (www.eecontrols.com) D-MDC-30 Power Line Filter at their NC distributor, www.controlsource.com, for $95. With a little luck, in a week or so I'll be surfing ShopBot forums and DVR'ing my wife's TV shows while my bot makes sawdust.
Andy
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Success!!
I received my EE Controls D-MDC 30 Powerline Filter ($105 including shipping from Control Source in NC) yesterday and installed it (in a separate box outside the VFD.) So far so good! I currently have the spindle running at 18,000 and have no degradation in DSL.
Thanks for all your help, ShopBotters!
Andy
