Well, keep in mind that the lift motor does not have permanent
magnets. It's actually a series wound motor with two field windings.
The power path goes from the battery, to the switch, to one or the
other field, to the armature, and then back to the battery.
The result is the motor **is** a series motor, so as the load
increases the draw on the field and armature increases as well.
Likewise if you double the voltage you double the field strength and
the armature strength so power output doubles.
I think the key danger is heat; more power means more heat in the
motor and too much heat will short out the windings as the insulation
melts. However if it can get the blower lifted in 3 seconds instead of
10-15 (what it takes when it's struggling at 18
volts) then that could mean the motor suffers **less** damage at 30
volts than 18. Maybe.
Chris
*From:*Rob Brockway [mailto:getractor yahoo com]
*Sent:* Sunday, December 23, 2012 6:31 PM
*To:* Christopher Zach; Elec-Trak
*Subject:* Re: (ET) Testing lift motor at higher voltages
I don't know how accurate this is, but I have heard that a lot of DC
motors are designed so they have a 50% voltage safety factor so you
don't demagnetize the permanent magnets. So a 12 volt motor design
will likely demag at 18 volts or higher (at locked armature amps).
Interestingly if you demagnetize the motor speed will tend to increase
under light load.
Rob
*From:*Christopher Zach <cz alembic crystel com
<mailto:cz alembic crystel com>>
*To:* Elec-Trak <elec-trak cosmos phy tufts edu
<mailto:elec-trak cosmos phy tufts edu>>
*Sent:* Sunday, December 23, 2012 4:16 PM
*Subject:* (ET) Testing lift motor at higher voltages
So this afternoon I had to switch the E20 over from mowing to
snowblower. Note that it is **much** easier to do when you put the
snowblower on two moving dollies. They're a good height, and it's a
snap to roll the thing around the shed.
At the same time I figured I would try to boost the voltage draw for
my lift motor. Normally it's tapped to 18 or so volts on the BB600
pack, right about the middle. The next closest battery terminal would
be 30 volts, so I gave that a shot.
**wow**. Motor zips up and down fast, lifts deck as if it was not
there. So I removed the deck and put on the snowblower. Greased the
lift pulley and gave it a shot.
**wow**. Motor zips up and down fast, lifts snowblower as if it was
not there. This is good, as normally the motor struggles to lift the
blower and sometimes stalls. Now it runs it right up in a few seconds.
In fact I worry that I will rip something out if it hits the highest
lift point. So I reduced the lift fuse from 30a to 20a.
Now, this is a "new" lift motor from Bill Gunn, top of the line. Not
sure how long it's going to last with this, but I did note that it's
duty cycle is now a lot less since it's not farting around struggling
to lift. Zip it's up in 3-4 seconds. Then off.
So now I am thinking: One of the big problems with the lift is that
the motor will stall out sometimes and then trip it's breaker.
Stalling a DC motor puts a lot of strain on the commutator bars and
the brushes. Is it better to have the motor still spinning (and pretty
quickly I might add) at 2.5 times it's rating? Seems like it would be
drawing less current, which is good. So what's the downside?
I wonder what the switch in the lift is rated at. If I'm opening and
closing way above its rating, that might blow up.
Chris
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