Autohelm Type 1 Linear Drive

[OneBoatman]

I am trying to marry a mid 80's UK built Autohelm linear drive (Type 1) to a Simrad NAC-3 computer with AP-48 control head which. The linear drive has a 7 pin connector and 2 motor power wires. Can anyone help me identify which of the 7 pin wires are for the clutch? Inspecting one end of the 7-pin connector I found that the red wire was not used, so which of the remaining six engage the clutch? The Black wire was found to (-) 12V when it was connected to my old Autohelm 5000 control head and the Brown wire (+).

[dougcn]

I just did so with my older Autohelm to work with a NAC-3 autopilot computer - also on a Pearson 386. (Hull 9). Pretty easy task. You can’t use the existing pins and connector, as they’re connected to a circuit card in the drive that is a part of the Autohelm computer. You need to open the case, remove the circuit card and then connect directly to the two wires on the drive motor and the two wires on the clutch. Once inside the case, be careful with the slip rings on the clutch, as they are fragile. I added short lengths of wire that I brought out of the case to a terminal block to allow for easier connection and removal. It works well with the NAC3.

[stormalong]

Your mid '80s type one drive is hopefully the newer model. The drive design was changed in the mid '80s. Could you post a picture?

The older version is not serviceable - the parts are not available. The newer version is the same unit sold today although one plastic gear is now metal. The newer ones use a recirculating ball drive that is far superior to the older version.

There are only four wires in use on the drive. Two for the drive motor and two for the clutch. Not sure what the seven pin connector you are referring to is. The motor drive wires are thick and the two clutch wires are thin. If you have extra wires going into the drive I have no idea what they are for. You should be able to identify the clutch wires with an ohm meter or by taking the cover off the drive and looking at the clutch coil. The course computer black box is useless when adapting to a different brand of autopilot.

I have a similar Autohelm autopilot and a stockpile of spare parts. Mine is set up with a newer Raymarine autopilot and an Autohelm 6000 that can be switched in if the newer one fails.

[OneBoatman]

Thank you dougcn this is helpful. It seems you had the same generation Autohelm linear drive. I haven't opened the case on the drive so I hope it will be obvious to me in identifying the two wires serving the clutch. Also could I leave the circuit card in place in the drive since the 7 pin connector, the master if you will no longer be used. Couldn't I just trim the card exit wire off and extend the two clutch wires back out the pre-existing hole that the 7-pin wire used. Thank you also to stormalong for your reply, however my drive was built before they went to the more universally compatible 4 wire version.

[dougcn]

The 7 pin connector comes out easily and makes a good place to run the new wires. Removing the old card is easy, it’s held in place with a few screws and there are terminal blocks on the card for the motor and clutch wires. Leaving it connected would likely interfere with the NAC. To open the case, you just remove the two pin screw plug near the 7-pin plug connector.