O-200 alternator polarity change

nicholm · Post by **nicholm** » Mon Apr 12, 2010 3:37 pm

The O-200 installation on our Condor is set up with a Motorcraft alternator for positive earth. The alternator is currently not charging but I've a few fundamental checks to do before panicking about it. The main question is 'how to change to negative earth'? Also, will the TCM 654046 lightweight starter wiring need to be changed with the polarity change. If so, how? There is currently no fixed tranceiver or transponder installation in the AC and the drive to change to -ve earth is to be able to install Microair equipment safely.

Thanks for your help!

ROB THOMASSON · Post by **ROB THOMASSON** » Tue Apr 13, 2010 6:41 pm

Is it an alternator or a dynamo? If the former there is no way of chaning it over other than fit a replacement

nicholm · Post by **nicholm** » Tue Apr 13, 2010 9:15 pm

Many thanks for your response.
I'm pretty certain it's an alternator. Four connection posts in use labelled STA, FLD, GND and possibly SAT (not really decipherable but seems to be the main output!). Solid state, separate, firewall mounted voltage regulator (anonymous as far as I can see) connected to GND, FLD and SAT. It's evidently an old unit and I was contemplating replacing it with the Airworld sourced lightweight unit - but would like to change polarity when doing that. Any ideas on the starter?

nicholm · Post by **nicholm** » Sat May 08, 2010 12:54 pm

Polarity changed successfully after removing starter motor and bench checking that it rotates in the same direction regardless of polarity (field wound not permanent magnet!). Alternator had been tinkered with to install a home made diode bridge (possibly incorrectly resulting in +ve earth output?).
Alternator now identified as Ford 1G 40 - 65 amp as fitted to F-100 to F-350 pick up trucks - so rebuild spares in transit from US.