Re: (ET) Power of Elec-trak motors?

[Christopher Zach <cz alembic crystel com>]

David Hamilton wrote:
> I'm not an Elec-trak owner - I don't think too many made it to Australia 
> -- but I joined your forum because I am planning to convert a locally 
> manufactured ride-on mower to electric. I plan to replace the single 
> 13.5 hp IC motor with a deck motor and a drive motor.  The deck is about 
> 36" in diameter.  Any suggestions for how powerful both motors should be?

Well, let's see....

Motor power is kind of based on what you need to do. I have an E20 
tractor with snowblower, tiller, and mower deck. I use it to mow grass 
(pulls about 100a at 36 volts when going up hill), blow snow (up to 300a 
dwhen blowing up hill) and till the soil (200-300a).

So if we do a little calculating knowing about 746 watts equals 1hp then 
we can look into things:

Mowing lawn: 100a*36=3,600w/746=4.8hp
Blowing snow: 300a*36/746=14.4hp
Tilling soil: 200a*36/746=9.6hp

Which kind of matches what you see out there with gas mowers. In other 
words a good 6-8hp is needed to mow, tilling takes around 12-14hp, and 
blowing snow takes a solid 15-20hp.

Now with my Elec-trak, each accessory has it's own motor. If you're 
doing a conversion you will probably use existing belts and such to do 
the work. So you need one motor that can drive the accessories.

More important IMO is the type of motor. The Elec-trak uses a 
shunt-wound drive motor, and IMO it's the greatest idea ever (small ones 
use magnet motors, but they're littler). The biggest advantage of a 
shunt motor is the simplicity of control: You can just power the field 
and armature, then drive off. If you go up a hill the motor will try to 
maintain speed and will pull more current. If you go down a hill the 
motor will try once again to maintain speed and you will get free regen. 
On a device like a lawn tractor this is *GREAT*; the mower blades want 
to stay at the same speed, and you can keep a constant ground speed 
while going up and down hills.

Also think about how you mow with a gas tractor; you set the motor speed 
to "full", engage the blades, put it in a gear, and drive off. You don't 
fiddle with the throttle, and the belt clutch is what you use to start 
and stop anyway. So the optimal control in a tractor oddly enough is a 
simple "on/off" switch and the transmission to select a gear.

99% of my driving in the E20 is like this, as is 98% of my driving on 
the Craftsman.

So the answer to your question is this: If you just want to mow, put in 
a 5hp shunt wound motor. If you want to blow snow then you're going to 
need a good solid 15hp motor. And use a belt-driven transmission; those 
stupid hydro-drives burn up about 30-40% of your power.