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Old 03-02-2015, 13:40   #1
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Testing Wheel Drive Motor

I'm currently troubleshooting a nonfunctional Raymarine ST4000 Wheel Drive Autopilot. The control unit seems to be working fine but I get zero response from the wheel drive motor.

From research it appears that this model's control unit was plagued with deficiencies. However, I want to confirm all other components of the system are working, including the wheel drive motor before I pull the control unit to get it tested.

As background:

The control unit is receiving power (12.5V according to voltmeter) and receiving accurate data from flux compass. When put in auto and a course change is inputted, it seems to attempt to try to respond for 10-15 secs before giving either a Low Batt, No Data, or Off Course warnings. (according to internet the first two are common errors on this model). With no visible or audible response from wheel drive.

I tested voltage in cable at connection to wheel drive and got variations between only 0-2V. A thread on sailnet says this is normal as the unit only "pulses" to activate drive motor (can anyone confirm or reject this theory?).

On that same thread, someone said they tested the drive motor by connecting directly to a 9V battery. My question is: is this a safe way to test the motor considering it operates with only 2V pulses? Would I be a risk of frying the drive motor by testing in this manner? If this is an okay method, would I be prudent to ground the 9V battery before connecting to motor?

Thanks!
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Old 03-02-2015, 17:46   #2
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Re: Testing Wheel Drive Motor

After work bump...


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Old 03-02-2015, 18:39   #3
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Re: Testing Wheel Drive Motor

The 2v pulses only tell the motor to move, via an electronic relay. The motor actually runs on 12v.
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Old 03-02-2015, 18:53   #4
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Re: Testing Wheel Drive Motor

DC motors are typically driven with PWM, pulse width modulation.

100% power would be a continuous 12 V supplied to the motor.
0% power would be 0 volts.
50% power is achieved by switching the 12 volts on and off rapidly such that the 12 volts is on half the time.

The pulses happen rapidly enough that a DVM would average the pulses to read somewhere between 0 and 12 volts. If you spin the compass such that the controller thinks you're way off course you would probably see about 12 volts.

Manual seems to indicate PWM

From: http://www.ganssle.com/jack/st4000.pdf

MD1 MD1 When Autopilot engaged and depending on
direction of drive, intermittent variable length
pulses, nominal 12V; otherwise 0V
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Old 03-02-2015, 19:06   #5
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Re: Testing Wheel Drive Motor

Switch the autopilot on and check it says standby on the read out. If you now press and hold down either the +10 or -10 or +1 or -1 buttons the motor in the whell drive unit should run until you release the button. If it does not there is something wrong with either the motor drive circuit in the head or computer unit or the motor.

To check the motor connect it to 12V and it should run, if not the problem is in the motor.
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Old 03-02-2015, 23:45   #6
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Re: Testing Wheel Drive Motor

Thank you everyone for your input. Sounds like the best way to test is to simply connect directly to house battery. Won't be able to go out there till Thursday but I'll keep you posted.


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Old 04-02-2015, 09:22   #7
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Re: Testing Wheel Drive Motor

If you are going to rely on it get and carry a spare motor and belt. If you are going to scrap it can I have the bits, I have a good motor with a blown gearbox!
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