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About jraef

  • Birthday 22/07/1956

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  1. Mark, Hope everything is OK with you after this latest round of temblors. You guys should start figuring out how to turn earthquakes into electricity!
  2. Soft starters on capacitor start single phase motors is a tricky business. Are you sure this was properly thought out? The reason is, when the start capacitor is in the circuit, the capacitor charging current looks like a shrt circuit to the SCRs in the soft starter, and can cause them to mis-fire. At the same time, the high harmonics created by the soft starter heats up the capacitors, causing them to swell and fail. It's usually a race to see which one happens first. Does this Chinese mfr regulary design a soft starter into their unit? If not, did you ask for it? If so, they may not have understood the risks.
  3. I know it's kind of late now, but I have been off of this forum for a while after changing jobs. What JOhmega responded with is correct if you were changing speed via a different gear ratio as you had proposed. What your designer compatriot said would be "inversely" correct if you were changing speed by changing the number of motor poles in the stator, however it goes the other way (hence "inversely correct"). If you wanted to maintain the same torque from a motor by changing pole count to slow it down, the motor would get physically SMALLER, not larger and of course your kW rating would be cut in half as well. But you cannot change the number of poles to affect such a small speed change, you can only change them in pairs. So at 3600RPM (assuming nominal), that is 2 poles. Your next option is 4 poles, which would be 1800RPM. There are no other values in between, so his point is essentially moot for this application. But you said "inverter driven", so let's explore that option as well. If you use your inverter to change the speed, you will in fact retain the SAME torque at the lower speed. that is what an inverter drive does. In that effort then, it remains the SAME motor, so there is of course no change in the physical size of the motor. But there are a few caveats: The motor mechanical (shaft) power will be lower than original, because the mechanical power is a function of torque and speed. So even though your torque remains the same, you are reducing the speed by 17%, so you will reduce the mechanical power (kW) by the same amount and you will have a 208kW motor. The motor cooling capacity will also be reduced by a similar amount. This is for the most part offset by the fact that the motor will be drawing less current (presumably), but is worthy of consideration depending on the type of motor you have and the ambient conditions. I would highly suggest that the inverter drive be of the "Vector" type for the best performance on traction systems like you have described.
  4. Found one similar today. they are buying web adds on sites geared towards electricians, although it appears they are only doing business out of Malaysia, probably to avoid the scrutiny of our FTC. http://www.e-cleanenergy.com/saver/ Seemes to be the same basic "technology" as the Keseco unit. I guess you can't beat a good scam... A little further digging reveals that what they are alluding to is actually a real technology advancement in ELECTRONIC MEMORY SYSTEMS to improve the energy consumption of memory devices, or more imprtantly, improve the density by utilizing electron spin itself as a way of storing digital data. That technology is called "spintronics" and although still under peer review, apparently shows some promise, IN THE COMPUTER MEMORY ARENA. But what these scammers have done, as has been the case so many times before with scams, is to capitalize on unfamiliarity with a new "buzz word" and make false claims about it, figuring that at least for a little while, the confusion will work to their benefit. I noticed in one of Keseco's partner websites, they had what appeared to be a "typo" on the term spintronics, by having a space between spin and tronics. But then I noticed it was consistently the same throughout the website. they must have been caught and told to stop using that term. Classic...
  5. Yes, I did hear about Somar, good ridance to bad rubbish. But there are still people selling them here and in canada, probably the poor souls who invested their life's savings into a distributorship deal.
  6. No, and I hope we never see them here! From the looks of this, it is even more ridiculous than most of them. I'm telling you though Mark, we need to shed our last vestiges of human decency to get rich by making some bogus product like this and selling it to the ignorant masses. Seems to be working for these guys! Sure, legitimate engineering types like us laugh at them and fling scorn in their direction on web forums, but they are all the while banking money and setting themselves up for retirement. I can only imagine (hope?) that maybe they don't sleep well at night. I still do.
  7. Looks like pure drivel to me.
  8. I'm stepping a bit out of my comfort zone here, but I have an application possibility for a regen VFD to be used on a small 25kW hydro generator that will be grid connected. The concept is to use the regen VFD so that the output of the generator can be maintained, albeit with reduced capacity, in low flow conditions. The question I'm not sure of is this: If we reduce flow to where it is only getting 12kW of mechanical input, will the motor/generator be operating at peak efficiency because the VFD is reducing the synchronous speed to always be just below the mechanical input power, or would we consider the efficiency of the motor be operating at the lower end of the efficiency curve because the load is lower? I would imagine it wouldn't be any different that if it were a motor, so in reality I want to know is, when we reduce speed in a motor with a VFD how do we evaluate the motor efficiency at the reduced speed? is it based on it being a lower kW motor, or does the motor efficiency load curve stay the same regardless? To my mind, if we have reduced the speed to 50%, essentially we have changed the motor to a 12.5kW motor, so the efficiency would still be somewhere in the higher range. Any thoughts?
  9. Looks to me as though their "HARSVERT" drive is a knock-off of the Toshiba TOSVERT MV VFDs, probably an older generation than what Toshiba sells now.
  10. Probably not. The issue is, over fluxing the motor will increase the current draw with relation to the load, which means the motor will run hotter under the same load than if it got the correct V/Hz. But for a few minutes I doubt you can create any permanent harm. However are you saying you are going to give the motors 380V 50Hz and they are wound for 380V 60Hz? If that's the case, would will be under-fluxing the motor. You will have less torque and slower speed, so less kW at the shaft. Still should be OK for testing though.
  11. Sounds as though the working principal is one of separating you from your money. You then go broke, can't afford to pay the power bill and turn everything off, thus saving energy!
  12. Yes you are correct. Having the PFC capacitors on line downstream of the soft starter usually creates a race to see if the SCRs in the soft starter are damaged by the di/dt of charging the capacitors, or the capacitors fail due to the high harmonics from the phase angle firing of the SCRs during ramping. Either way, you lose.
  13. Short Cycle protection for refrigeration compressors is essential, it has to do with the thermal expansion / compression cycle. Failure to use it can result in the loss of your compressor. Copeland Compressor white paper
  14. Sounds like a software glitch in the controller. Have you tried contacting Nokian?
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