Re: (ET) ET - DC Motors 101

["Konstanty, Walter (GE Energy)" <Walter Konstanty ge com>]

Chris,
   These are technically compound motors but classified as stabilized
shunt as the "compounding" is very light.  In some applications we may
design a heavy series to droop the speed a lot more with load to prevent
breaking something.  Many forklift motors are series wound for high
torque starting and higher speed as the load goes down from acceleration
but current limited to prevent overspeed but the transmission usually
holds it back.

   Typical shunt motors run faster at no load, droop to rated speed at
full load and rise in speed at overload (because of that armature
reaction effect).  Very bad if you have 2 motors running a steel mill
for example.  One can go "unloaded" and the other "overloaded" at the
same speed which is why a stabilizing shunt winding was used to always
make the speed droop with load and prevent these bad things from
happening.  We make motor-generator sets for large mining draglines and
the generators have a differential field to cause the voltage to go from
600 at no load to 40 volts (at twice rated amps) when the bucket hits a
BFR (big friggin rock) so the motors get a lot of current and low volts
to power thru the ground.  It's all in the magnetics with high tech
controls connected to the joystick.

  The E20 motor is a "stacked out" E15 motor.  The guts are slightly
longer to provide more torque in same speed and frame.  It's all
diameter squared times length.  With different control schemes, the E15
may close the step voltage solenoid a little faster or not exactly at 24
volts... I notice that on mine too.  
Now, I'm curious... 
...Walt

-----Original Message-----
From: Christopher Zach [mailto:cz alembic crystel com] 
Sent: Monday, September 17, 2012 9:39 PM
To: elec-trak cosmos phy tufts edu
Subject: Re: (ET) ET - DC Motors 101

Indeed, that is a lot of info, well thought out and presented. Would you
consider these shunt motors, compound motors, or something else
entirely?

I'm still curious as to why my E20 motor will start up without load and
without a field and the E15 motor will not (nor will the E12 motor I
have on the pressure washer). I'm driving both the E15 and the E20 these
days, and what gets me is that the E20 just feels smoother at a given
speed and does not have a problem going from stop to full field/full
armature without delay. The E15 lurches even from speed 2 to 3, it feels
significantly more "rough".

This might be due to the transmission, but it is from personal
observation on specific machines. I think I will get out there this
weekend with a stopwatch and time both tractors going up my hill
forwards and backwards to see how they do. They both have the same
battery technology, so the only difference should be the shunts in
series with the armature, pulley ratios, and the motors.

Chris





On 9/17/2012 4:55 PM, Robert Troll wrote:
> Walt -
>
> Let me be the first to say that it is always a joy when you step into 
> the conversation. Your depth of knowledge regarding these machines is 
> second to none. It is going to take me weeks to chew on your answer.
> Thanks for contributing. *slow clap*
>
>
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> Elec-trak mailing list
> Elec-trak cosmos phy tufts edu
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