Re: (ET) Solid state controls

["Christopher Zach" <czach computer org>]

Yeah, the E15 does things differently than the E20. On the E20, they 
reverse
the armature current using a pair of push-pull solenoids. On the E15, they
reverse the field current using a DPDT relay.

The problem is when you go from fwd to reverse in the E15, the back-emf 
from
the armature surges the contacts and burns the daylights out of them. When
you go from fwd to reverse on the E20, the arc is absorbed by the (much
larger) solenoid breakers. Plus the field current is relatively weak 
anyway.

But the E15 design is a lot less expensive; I guess that's why they 
migrated
to it.

Chris

----- Original Message -----
From: "Pieter Litchfield" <plitch attglobal net>
To: <elec-trak cosmos phy tufts edu>
Sent: Tuesday, July 23, 2002 4:06 PM
Subject: RE: (ET) Solid state controls


> As the owner of the E-15 with bucket loader that loves to eat relays, my
> suggestion would be that whatever controller is designed, be sure it can
> withstand the abuse hard use will heap on it.  For example, my tendency 
> to
> rapidly shift from reverse to forward while using the bucket has had dire
> consequences for my relays.  A better design could improve on this
behavior,
> or at least prevent the idiot behind the wheel from making the quick 
> shift
> ( a timer or charge-up delay circuit?)
>
> As a gross observation, my E-12 while not as elegant a control design
seems
> far more robust than the E-15.  At least I haven't cooked relays there
yet.
> But this does suggest that a prime characteristic of a power control
system
> for an E-15 ought to be "robust-ness" and "fault tolerance."
>
>  -----Original Message-----
> From: owner-elec-trak cosmos phy tufts edu
> [mailto:owner-elec-trak cosmos phy tufts edu]On Behalf Of Bob Murcek
> Sent: Tuesday, July 23, 2002 2:11 PM
> To: elec-trak cosmos phy tufts edu; ssawtelle fcc net
> Subject: Re: (ET) Solid state controls
>
>
>   Steve,
>   No, reducing speed with a soild-state controller does not cause loss of
> torque.  On an E12 at least the 1st and 2nd "speeds" are created by 
> adding
> resistors in series with the armature circuit.  When the armature current
> tries to increase, say to go up a hill, the voltage drop across the
> resistors increases, causing the motor to slow down.  Since the power 
> lost
> in the resistors is wasted, resistor-based speeds should only be used to
get
> going smoothly.
>
>   Solid-state controllers turn the power in the armature circuit on and
off
> rapidly (not sure of the rate, but it's apparently supersonic in mine),
> varying the ratio of the on time to the off time to control the average
> voltage seen by the motor.  There's very little waste since the
solid-state
> switch is either on or off.  When you go uphill with a solid-state
> controller and the armature current tries to increase, it's free to do so
> during the times when the controller is in the on state, so a slowdown
> doesn't occur.
>
>   Possibly the biggest advantage of a solid-state control in an ET is the
> extremely fine and smooth control at very low speeds, like when taking up
a
> load or parking in a tight spot...Bob
>
>
>   >>> "SteveS" <ssawtelle fcc net> 7/23/2002 1:39:55 PM >>>
>   Ah, good explanation. I see now how it makes sense on an ICD mower. 
> With
> my
>   E12S, with 'only' 3 speeds forward X 4 gears, I still have pretty much
all
>   the control I need. I do find, however, that any speed less than full
>   throttle has poor power. I can climb a hill in full throttle that 
> stalls
> out
>   on lower settings (same gear). That seemed illogical at first, but I
> assume
>   it's because the motor has less than full armature current. Does the 
> E20
>   have the same characteristic?
>
>   I presume a solid state control would have the same effect (lower
settings
>   for slower speed sacrifice power as well)?
>
>   SteveS
>   E12S
>
>
>   ----- Original Message -----
>   From: "Christopher Zach" <czach computer org>
>   To: "SteveS" <ssawtelle fcc net>; "Elec-trak" <>
>   Sent: Tuesday, July 23, 2002 12:49 PM
>   Subject: Re: (ET) Solid state controls
>
>
>   > Hydrostatics are nice on an ICE based mower because you usually have
to
>   run
>   > the engine at full speed in order to keep the blades spinning.
>
>
>   -- snip snip snip
>
>
>
>