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</o:shapelayout></xml><![endif]--></head><body bgcolor=white lang=EN-CA link=blue vlink=purple><div class=WordSection1><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Dear Frank<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><div><div style='border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0mm 0mm 0mm'><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>The motor will not slow down under no load if you drop the voltage because it is a synchronous motor. You would have to change the frequency of the AC to change the speed.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>That said, if it was lowered enough the motor couldn’t ‘keep up’ to the 60 cycle synchronous rotation and would slip, slowing down as a result, however that slippage is strongly dependent on the load which would be really inconvenient. Being a square box the speed would actually change 4 times per rotation as the load alternately came and went. <o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>I suspect that the motor is rated at 1725 RPM <i>under full load</i> not actually ‘all the time’. Under no load it might be very close to 1800 (60 cycles per second * 60 seconds per minute / 2 sets of windings gives 1800).<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>As it is geared down so much I suspect the motor will not be working hard at all. Given that you want about a 30:1 reduction and there is a general rule that you should not step down more than 7:1 at a time, I suggest you get 2 sets of 1-1/2” and 8” pulleys in series which will give you 28.4:1.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>If your speed is 1725, the shaft will turn at 60.64 under load. That is pretty close. It might go a tiny bit faster but the pulleys are not all <i>that</i> accurate anyway so you would have to measure it to know. It is slow enough you can count while watching.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>With such an installation you should use Goodyear belts (the ones that are fan belts but look like they have big teeth). If you drop the voltage it will only have to slip a little (magnetically speaking) in order to drop one or two RPM but it will fluctuate a little during the turn because the box is square.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>I have a book here for calculating how much power can be transmitted through the belt contact angle on the small pulley based on their centre distances, if it matters. I don’t think it will. Pick a centre distance that matches a common belt.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Regards<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Crispin<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:10.0pt;font-family:"Tahoma","sans-serif"'><o:p> </o:p></span></p></div></div><p class=MsoNormal><o:p> </o:p></p><div><p class=MsoNormal><span lang=EN-US style='font-family:"Arial","sans-serif"'>Dear Frank</span><span lang=EN-US><o:p></o:p></span></p></div><div><p class=MsoNormal><span lang=EN-US> <o:p></o:p></span></p></div><div><p class=MsoNormal><span lang=EN-US style='font-family:"Arial","sans-serif"'>1: Box shape and diameter are VERY important. At "critical speed", for a given combination of rotational speed and container diameter, centrifugal force will hold the pellets stationary against the container wall, and there will be zero tumbling and pellet wear. A machine running at say 95% critical speed will create very little abrasion, but a machine running at say 60% of critical Speed will create a great deal of abrasion effect, because of the cascading action.</span><span lang=EN-US><o:p></o:p></span></p></div><div><p class=MsoNormal><span lang=EN-US> <o:p></o:p></span></p></div><div><p class=MsoNormal><span lang=EN-US style='font-family:"Arial","sans-serif"'>2: Do you want to turn the drum/container/box for a fixed time, OR a fixed number of revolutions?</span><span lang=EN-US><o:p></o:p></span></p></div><div><p class=MsoNormal><span lang=EN-US> <o:p></o:p></span></p></div><div><p class=MsoNormal><span lang=EN-US style='font-family:"Arial","sans-serif"'>3: One could calculate the required HP, but the simplest and least costly thing is to try the 1/3 HP motor, and if it does not overheat after say 4 consecutive tests, it is good for the job. If it does overheat, then you have proven that you need a bigger motor.</span><span lang=EN-US><o:p></o:p></span></p></div><div><p class=MsoNormal><span lang=EN-US> <o:p></o:p></span></p></div><div><p class=MsoNormal><span lang=EN-US style='font-family:"Arial","sans-serif"'>Best wishes,</span><span lang=EN-US><o:p></o:p></span></p></div><div><p class=MsoNormal><span lang=EN-US> <o:p></o:p></span></p></div><div><p class=MsoNormal><span lang=EN-US style='font-family:"Arial","sans-serif"'>Kevin</span><span lang=EN-US><o:p></o:p></span></p></div><blockquote style='border:none;border-left:solid black 1.5pt;padding:0mm 0mm 0mm 4.0pt;margin-left:3.75pt;margin-top:5.0pt;margin-right:0mm;margin-bottom:5.0pt'><div><p class=MsoNormal><span lang=EN-US style='font-size:10.0pt;font-family:"Arial","sans-serif"'>----- Original Message ----- <o:p></o:p></span></p></div><div><p class=MsoNormal style='background:#E4E4E4'><b><span lang=EN-US style='font-size:10.0pt;font-family:"Arial","sans-serif"'>From:</span></b><span lang=EN-US style='font-size:10.0pt;font-family:"Arial","sans-serif"'> <a href="mailto:frank@compostlab.com" title="frank@compostlab.com">Frank Shields</a> <o:p></o:p></span></p></div><div><p class=MsoNormal><b><span lang=EN-US style='font-size:10.0pt;font-family:"Arial","sans-serif"'>To:</span></b><span lang=EN-US style='font-size:10.0pt;font-family:"Arial","sans-serif"'> <a href="mailto:stoves@lists.bioenergylists.org" title="stoves@lists.bioenergylists.org">'Discussion of biomass cooking stoves'</a> <o:p></o:p></span></p></div><div><p class=MsoNormal><b><span lang=EN-US style='font-size:10.0pt;font-family:"Arial","sans-serif"'>Sent:</span></b><span lang=EN-US style='font-size:10.0pt;font-family:"Arial","sans-serif"'> Tuesday, February 12, 2013 2:30 PM<o:p></o:p></span></p></div><div><p class=MsoNormal><b><span lang=EN-US style='font-size:10.0pt;font-family:"Arial","sans-serif"'>Subject:</span></b><span lang=EN-US style='font-size:10.0pt;font-family:"Arial","sans-serif"'> [Stoves] Calculating the RPM<o:p></o:p></span></p></div><div><p class=MsoNormal><span lang=EN-US><o:p> </o:p></span></p></div><p class=MsoNormal><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Greetings Stovers,<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Building equipment for determining the hardness of pellets and biochar I need something to turn a 9 kg box at a speed of 60 RPM +/- 1.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>I have a 1/3<sup>rd</sup> HP motor that is rated at 1725 RPM<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Fitted with a 2” pulley attached to the motor and going to an 8” pulley gives me a shaft turning 431 RPM<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Then another 2” pulley going to an 8” pulley on another shaft gives me 108 RPM<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>I plan to adjust the 108 down to 60 using a voltage regulator. <o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Is this a good plan? <o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>And is there another factor I need to include for the weight of the box I am turning?<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Thanks<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Frank<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Frank Shields<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Control Laboratories, Inc.<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>42 Hangar Way<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>Watsonville, CA 95076<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>(831) 724-5422 tel<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'>(831) 724-3188 fax<o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><a href="http://www.controllabs.com">www.controllabs.com</a><o:p></o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><p class=MsoNormal><span lang=EN-US style='font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1F497D'><o:p> </o:p></span></p><div class=MsoNormal align=center style='text-align:center'><span lang=EN-US><hr size=2 width="100%" align=center></span></div><p class=MsoNormal style='margin-bottom:12.0pt'><span lang=EN-US>_______________________________________________<br>Stoves mailing list<br><br>to Send a Message to the list, use the email address<br><a href="mailto:stoves@lists.bioenergylists.org">stoves@lists.bioenergylists.org</a><br><br>to UNSUBSCRIBE or Change your List Settings use the web page<br><a href="http://lists.bioenergylists.org/mailman/listinfo/stoves_lists.bioenergylists.org">http://lists.bioenergylists.org/mailman/listinfo/stoves_lists.bioenergylists.org</a><br><br>for more Biomass Cooking Stoves, News and Information see our web site:<br><a href="http://www.bioenergylists.org/">http://www.bioenergylists.org/</a><o:p></o:p></span></p></blockquote></div></body></html>