CI-700 motors misbehaving

On my Celestron CI-700 mount, when I have it hooked up to the 110v to 12v Celestron
power supply, the motors work fine at all speeds including 20x.

When I hook the mount up to my truck's cigarette lighter socket (and
I also tried it with my wife's car), the tracking speed seems to
work OK and also 16x speed.

However, when I try 20x (by holding one button and then the opposite
button on the hand controller) both RA and DEC motors (independently)
slow down to a crawl.

When I put my ear to each motor, 1x sidereal and 16x sound good but
at 20x the motors seem to make a "growling" sound with the car
battery -- which is not the case with the 110 power supply.

Any Ideas?

Thanks!

--Mike

My CI-700 mount displays precisely the same behavior. The dedicated Celestron power supply produces over 15 volts and runs the motors without stalling at 20x. A 13.8 volt regulated power supply also provides enough juice to run the motors at 20x. However, my deep-cycle Marine battery (rated at 31 amps and fully charged to approximately 12.8 volts) is insufficient to prevent stalling at 20x. I even went to the length to replace one of the motors (at $105.00 from Celestron) and the stalling continued at 20x with less than approximately 13.5 volts. I believe that the motors lack the torque to run at 20x without these elevated levels of voltage. At least in my situation, adjusting the worms in an attempt to minimize friction only resulted in unacceptable lags when changing slewing directions. While I regard the CI-700 as a very good mount for the money, and with relatively low periodic error, it has some rough edges, one of which you've touched upon. BTW, if you leave your car engine running, and therefore utilize the 13.7 volts produced by your alternator, I imagine you'll be able to use 20x through your cigarette lighter without stalling issues. Chuck