Hoppy wrote: > > Hello, > > Consider 2 permanent magnet motors - one rated 40 volts dc and the other > rated 75 volts dc - being used as generators for small micro hydro system. > > Both turn at 500 rpm. > > Which motor would output more amps? > > Thanks, > > Chris
This can be a trick question, however I don't think it is intended this way. As others have already noted more information is required. Let's look at what else is required and the consequences. I will assume that because you say "output more amps" you are intending to use the motor as a generator. 1. Voltage rating is meaningful only if the RPM at which it is rated is also given. For example a motor rated at 40VDC at 1600 rpm and one rated at 75VDC at 3000 rpm are probably the same motor. 2. Assuming that both are rated at the same RPM, then the relative charging currents can depend on other factors. Consider for example (a) direct battery charging. Each generator will have a no load voltage which must be at least that of the battery or no charging will take place. At 500rpm (or any rpm for that matter), the no load voltage of the 75V rated unit is nearly twice that of the 40V rated unit. Now if the battery voltage is between these two values, the 75V generator will be delivering charge to the battery, whilst the 40V unit won't deliver any charge at all. Indeed the 40V unit may actually be drawing power from the battery, unless there is some protection against this, e.g. a diode. (b) resistive load: If the generators are driving straight into a resistor that has a very low value compared to the winding resistance of the generators, then the generator with the lowest resistance will deliver the larger current. That is, it's not the voltage rating that matters - it's the winding resistance. However, for motors of comparable size and quality the lower the voltage rating, the lower the winding resistance. So in this case the 40V motor would probably deliver more current. Regards, Max Enfield Planetary Power ------------------------ Yahoo! Groups Sponsor --------------------~--> Has someone you know been affected by illness or disease? Network for Good is THE place to support health awareness efforts! http://us.click.yahoo.com/RzSHvD/UOnJAA/79vVAA/FGYolB/TM --------------------------------------------------------------------~-> Does your company feature in the microhydro business directory at http://microhydropower.net/directory ? If not, please register free of charge and be exposed to the microhydro community world wide! NOTE: The advertisements in this email are added by Yahoogroups who provides us with free email group services. The microhydro-group does not endorse products or support the advertisements in any way. More information on micro hydropower at http://microhydropower.net To unsubscribe: send empty message to [EMAIL PROTECTED] Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/microhydro/ <*> To unsubscribe from this group, send an email to: [EMAIL PROTECTED] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
