On 1/25/2015 4:30 PM, David Roden wrote:
If the motor smells funny, and it's not a hot oil smell, you're probably cooking the varnish on the windings.
I think it was oil. I totally rebuilt these motors, then put them on the shelf. Handy. :-)
I think you're right that for a given power output, double the voltage SHOULD mean half the current. But that doesn't mean that you should just double the voltage, because the power oiutput WON'T stay constant.
Sure, the power output goes way up, which is nice. The RPMs really don't go up much under no load, as the series field plus the series armature cancel each other out. The trick is you need to derate the fuses on the unit as well, with 36 volts a 10 amp fuse is what you should have in the harness. Regardless, the motor is now so strong it will probably rip out the deck if it gets stuck, so be careful lifting.
The thing I like most about the higher voltage is the motor does not "cog" and stall while lifting the blower. While it's nice to sit there and lift super slow, it means the motor is building up that heat over a long period of time, and the commutator bars carry a lot of current for a long time per rotation. This is why I think I have 3 motors over the years fail with blown commutator bars. Running higher voltage puts less time on the motor, and by spinning faster the load on the bars is spread out a bit more.
When you increase the voltage, you increase the available power output at all speeds. I think this is not just because of Ohm's law, but also because it bucks more of the current-limiting back EMF. Again, my understanding from EV work (subject to revision by true engineers) is that the main danger is at high load, low speed, and therefore high current. However, at high speed you can also fireball the brushes with too much voltage. So getting carried away with the overvoltage thing is a hazard all round.
Right. The motor is not going to overspeed as a lift and derating the fuse will help limit the overall current. The real problem is too much torque ripping things off the deck (or maybe the blower) if you hit the stops.
On the buick window motors there is a circuit breaker in the motor. That basically fuses at 18 volts and will be useless to clear a 36 volt load. So the moral is to use a real fuse and do not expect the breaker in the motor to do anything worth-while.
Be a bummer to have your lift let its smoke out in the middle of moving 18" of snow, eh?
Since I switched to 36 volts I have had no problems for 2-3 years now. It's why I had two motors sitting there ready to go (and several parts motors). The only reason I had to swap out the Bill gunn motor was because a wire to it broke off, I'll fix that later but I'll also remember to check out how the brushes look.
And I've moved 48 inches of snow with the Elec-trak blower; it goes through anything :-)
C