How about put the propeller in a liquid, like water. The propeller could be a paint stirrer. Or if the load requires more torque, the mixers for drywall cement, mortar, or tile grouts. They are readily available, can use a drill chuck that threads on the end of shaft to fasten it the power source. The water can be thickened by adding sand to make a slurry. Tamas Rudnai wrote: >> I would like to test with a load, but haven't figured out >> a way to do that yet. (The cart is not ready yet.) >> Anybody know how to put load on a 500W motor sitting on a desk? >> > > Have you tried to put a propeller to the shaft? The only thing is that the > load depends on the rotation speed, otherwise that's how I usually test > airplane model motors and engines. The one I use is around 180W and need a > fairly small propeller (9x7) -- your motor (as you said 500W) would need > around 13x8, 14x8 or 15x10. Be aware of safety when you do that! You bearly > can see the propeller (ideally the outer part is moving near sound speed), > so be very careful where you put your finger when it is running. Also that > in very rare occasion it can brake, so do not stand or look from the side or > the front of it. Oh, and it has a huge pulling force, do not underestimate > it :-) > > Tamas > > > > On Wed, Aug 5, 2009 at 12:17 PM, Chris Loper wrote: > > >> Reposted, this time with the schematic. Schematic also here: >> www.chrisloper.com/low_side.png >> >> A few weeks back, I asked for advice on building an >> H-bridge for an electric go-cart (24V 500W motor). >> Heeding the sage advice I received, I have instead built this >> PWM'ed lowside driver using a 16F88 and an IRF540. >> low_side.png >> Running on my desk, with no load on the motor (drawing ~1A), it runs great! >> >> I'm sure that there are all kinds of problems with it; >> I've never done anything like this before and >> I would appreciate any suggestions. >> >> I would like to test with a load, but haven't figured out >> a way to do that yet. (The cart is not ready yet.) >> Anybody know how to put load on a 500W motor sitting on a desk? >> >> I know that driving the gate at only 5V is not good, >> and I plan to replace the IR540 with a logic level FET. >> I did a search on Digikey and found this one: >> DIGIKEY IPP0165N03L G 30V 50A Rdson=.0065 $1.03 >> >> http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=IPP065N03LGIN-ND >> Datasheet: >> >> http://www.infineon.com/dgdl/IPP065N03L_rev1.02.pdf?folderId=db3a30431441fb5d01148c401f250e27&fileId=db3a30431441fb5d011492371ebc0fe2 >> One US dollar! It seems almost too good to be true. >> Are there other parameters that I need to check? >> >> For the freewheeling diode, I'm using this one that I found attached >> to a IRFZ34 scrounged from some unknown device a long time ago. >> It just says C8255 and I was unable to find a datasheet for it. >> I don't know if it is sufficient. >> I ordered a MBR2545CT (dual schottky rectifier, 25A 45V). >> Is that the right kind of diode for this application? >> >> What else should I do to protect my PIC from this high power stuff? >> Especially when I replace the 9V battery with a connection to +24V? >> >> Thank you, >> Chris >> >> -- >> http://www.piclist.com PIC/SX FAQ & list archive >> View/change your membership options at >> http://mailman.mit.edu/mailman/listinfo/piclist >> >> >> > > > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist