More on Power Steering

[John Wayland <dat1200@europa.com>]

Hello to All,
      I've read the posts on power steering (PS) with great interest.
Like Randy Holmquist pointed out, a simple switch on the dash allows the
driver to choose power assist or not...this is how I have the PS set up
on my heavy electric Toyota, Red Beastie. The switch controls a 100 amp
12v continuous duty solenoid. This truck originally had PS when it was
gas-powered, and now as an EV with almost twice the weight to steer, it
REALLY needs PS! However, like many others have expressed, at higher
road speeds, especially while driving on the freeway, I prefer to turn
off the PS. I do this for the better road feel the truck has at speed,
not to save power...this truck's got plenty of storage capacity on
board!
     For me, running power steering from the second shaft of the
traction motor is unacceptable. The thing that is so nice about having a
separately-powered PS unit, such as the '92 Toyota MR2 12v unit I have
in the Beastie, is that you have full power assist even when you aren't
moving yet, such as when you are pulling out from a tight parallel park
situation. With a traction motor driven system, you'd have to rev the
motor in neutral to make the PS work.....how 'un-EV'!
      As to comments about tying a cutoff to 4th & 5th gear, this
certainly wouldn't work with the Beastie. I take it up to 50 mph in 2nd,
and at speeds of 30-45 mph just leave it in 2nd all the time. On the
freeway, 3rd is almost always used, while 4th and 5th are pretty much a
waste of time....OK, I do use 4th when I want to take the Beastie up to
75 or 80 mph. Tying the cutoff to 3rd gear might be acceptable, but
never in 2nd, as I use this gear all the way down to 15 mph or so, where
the PS is pretty much needed.
     For an automatic cutoff, several have mentioned using a speed
sensor that works off the speedo cable...this is a good idea. I would
like to suggest that it be a gradual reduction, rather than an abrupt
cutoff, as Randy Holmquist warned about:

>If its speed related you never know for sure when its going to cut 
>out and chances are one day you...will be accelerating
>around a curve and the power will cut out...Under normal
>conditions you could make the turn without the power because 
>your going fast enough but its the sudden change that's the 
>problem. You tend to react to the sudden loss and may over react 
>putting you where you don't want to be. :(

   Couldn't have said that better myself! The MR2 unit has extra wires
that are intended to network with the vehicle's various speed sensors
and power controllers that run the pump in the stock system it came
from. I might eventually check into the rest of the system to see if I
can adapt it over to the Beastie, but in the mean time, the simple and
effective dash switch works fine for me.
     For those considering using an MR2 unit, remember that it does take
a bit of power! Running at 14 volts, it draws 18 amps at idle, and
typically 25-40 amps for most steering assists. If you lock the steering
wheel it sucks down 50+ amps! I use twin DC-DC converters backed up by
an Optima YT battery, too. An interesting note on this......I had first
used a battery that was of questionable condition, and even with twin
converters, when I first switched on the PS, the 12v system would stall,
causing the CD player to blip out and the lights to dim briefly. On
those regularly locked steering twists with my daughter learning to
drive at the wheel, this became a more regular event. I removed the
suspect battery and sure enough with a 50 amp load it fell to its knees
to something pathetic like 9 volts or so. I installed a fresh Optima YT
and all the symptoms disappeared, showing that even with 75 amps of
DC-DC power, there is a real need to have a 12v battery backup as a deep
current reservoir when using PS in an EV that has other heavy current
12v demands from high power lights and sound systems. Most all the time,
the 12v battery is not called on, but when you jam the steering wheel to
a locked position and suck 55 amps just for the PS, with the lights,
heater fan, wipers, and a powerful sound system all turned on at the
same time....well, do the math!

See Ya.........John Wayland