[C320-list] Linear autohelm

[Greg Arnold]

   On 8/21/2022 9:25 AM, Stephen Cox wrote:

   On 8/20/2022 11:33 PM, Stephen Cox wrote:

>From the relevant Mechanical Linear Drive manual the Type 1 Linear

Drive is rat

ed at 18-36 W and the Type 2 Linear Drive is rated at 48-72w.
 Note the minimum of the Type 2 is greater than the maximum
of the Type 1.  What makes you think t he ACU-200 will
happily drive this without letting the magic smoke out that
powe rs all electronics?  Even assuming it manages for a
while what happens when you get into strong sea and wind
conditions?  The power consumption will go up and a gain, the
magic smoke will escape the ACU-200 and it will stop working.

   Comment:  Would be a problem if you were on a Cat 470.
But on a 320
   you shouldn't be drawing much juice -- about the same as
if you had an
   ACU-200 and Type 1.


The load might be relatively light but the build of the Type 2 motor indicated b
y it's ratings is such that it appears to draw more
current with a light load than the Type 1.  A rating of 48-72w indicates to me t
hat it will draw a minimum of 48w when operating.
That is 12w more than the Type 1 maximum or 33.3% more than the maximum rating.
 Does the ACU-200 have that much safety margin?
What about when the Type 2 encounters conditions that make it draw it's full 72w
 or 100% more than the Type 1 can draw.  Does the
ACU-200 have the ability to handle double the expected maximum load?  Could be a
n expensive exercise if the ACU-200 burns out.


   -
   According to Jefa here:
   -
   [1]https://www.jefa.com/steering/products/drives/qanda.htm
   -
   "More modern autopilots are able to control the speed of the autopilot
   drive unit from 0 to 100% without any steps via so called pulse width
   modulation. To be able to vary the power sent to the drive unit, they
   don't sent a continuous signal, but pulses, and by adjusting the width
   (duration) of the pulse from zero to hundred percent they can
   accurately control the speed of the drive unit."
   -
   I believe the Raymarine uses pulse width modulation.
   -
   Pulse width modulation sends many short pulses of electricity each
   second.  A bigger motor (such as the Type 2) will draw more
   electricity, but will draw shorter pulses.  Thus, the ACU will be
   working harder when it is sending electricity, but will be resting more
   often.  Every second, the ACU should be sending about the same amount
   of electricity whether it is powering a Type 1 or a Type 2.  The
   question is whether the ACU-200 can handle the bigger but shorter
   pulses.

References

   1. https://www.jefa.com/steering/products/drives/qanda.htm