Michael Hoskinson wrote: > I've > connected it through a pulley reduction setup with a > separately mounted shaft in between the motor and pump > that has a large pulley run from the motor and a small > pulley running the pump.
Sounds like you nominally need at least a 12:1 reduction (6000RPM motor<=>500RPM pump). And, it sounds from your description that you are achieving this with a double reduction using a jackshaft between the motor and pump (small pulley on motor drives large pulley on jackshaft, small pulley on jackshaft drives large pulley on pump). Sounds like the right way to go about it. I would suggest starting with the largest pulley that will fit on the pump and sizing the others to achieve the desired overall ratio, since you don't want either of the small pulleys to be too small. > I replaced that motor with one that looks a little stronger. > I don't have specs for it but it has a thicker shaft and ball > bearings rather than bronze bushings and it is rated 6000 rpm. > It does seem to work better but the commutator end of the > housing gets sizzling hot after 5 minutes or so, and I pulled > the plug on it when smoke started to rise. It was drawing up > to 8 amps for short periods, about 4-6 amps when the pump was > bypassed. The initial experiments were done with just a > bridge rectifier plugged into 120 V house current, but these > numbers were with my 96 volt test pack (103 VDC measured). 4-6A @ 103VDC = ~400-600W (0.5-0.8HP). Seems like quite a bit for bypass mode! 8A @ 103VDC = ~1.1HP, so the work done by the pump itself seems to only consume the 0.3-0.6HP difference. (Of course, these numbers are for the power into the motor, not out of it; I would guess the mechanical output is probably about 75% of this.) Have you tried measuring the power consumption of the motor with no load, then with just the belt to the jackshaft in place (i.e. determine the loading of just the jackshaft bearings/windage and the primary reduction belt)? This info might help you to decide if it would be worthwhile replacing the V-belt setup with a more efficient toothed belt arrangement once you get the ratios sorted out using the cheaper (and more readily available) V-belt prototype. At these power levels, you could also consider using readily available bicycle chain and sprockets as an efficient replacement for the belt setup. It will be noisier, though perhaps not to the point of being objectionable... you'll have to make that call... and it would need periodic lubrication which the belts avoid. Can you determine the speed that the pump or motor is actually running? Increasing the reduction ratio to allow the motor to spin faster, until either the motor rated speed is exceeded or the suspension rises too slowly, should get you the least possible heating. If the motor is totally enclosed, then adding some ventilation might help. If the motor has ventilation, then a fan might help. However, if you can reduce the load/heating by altering the reduction ratio and/or improving the mechanical efficiencies of the reduction system, these are the places to look first. You could try varying the belt tension and see what effect it has on the current drawn by the motor; leave the tension set where the load is minimised without excessive belt slippage (a bit when the motor first kicks in may be unavoidable). Hope this helps, Roger.
