Re: (ET) Solid state controls

["SteveS" <ssawtelle fcc net>]

I'm enjoying this thread, learning lots.

Why would the E15 system be cheaper? On the E15 you are reversing heavy
current loads, wouldn't the solenoids for that be much more expensive than
the relatively lightweight (though more complex)E12 relay?

SteveS



----- Original Message -----
From: "Christopher Zach" <czach computer org>
To: "Pieter Litchfield" <plitch attglobal net>; <>
Sent: Tuesday, July 23, 2002 4:38 PM
Subject: Re: (ET) Solid state controls


> 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
> >
> >
> >
> >
>
>