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BUILT-IN CHARGER
The Otis S-71 originally came with a built- in battery charger. In 2005 most of these are
not functioning and an external charger must be used. In my S-71 the transformer
apparently has an internal short. The transformer and rectifiers are under the front “hood”
behind the dash. The 20-ampere ammeter, timer, and AC power cord connector are on the
operator control panel between the seats. Behind this panel, located on the Fwd-Rev
Switch Assembly, is a 20-ampere fuse between the charger output and the batteries.
The built- in charger uses a transformer and two diodes (my S-71 has two silicon diodes)
in a standard full- wave rectifier circuit. The timer operates off the AC input and allows
charging for the desired number of hours to prevent overcharging. The ammeter confirms
that charging is taking place. The transformer and diodes may be accessed by removing
the glove box in the dash. The glove box mounts with two bolts and tapped L-brackets
that grip behind the dash. To remove, unscrew the two bolts about 8-turns each. It should
then be possible to wiggle the glove box free of the dash. The transformer and diodes are
just inside and to the left.
The recessed male AC power connector on the S-71 is a type no longer made in 2005. I
made a mating female connector from an L5-15R female connector by sawing the plastic
connector body to lengthen the arc of the opening for the ground terminal.
120
115
110
Red, Positive, to LB
Brown, Negative, to 20A Fuse and Ammeter
Red
Red
Black
White
Timer
Transformer
Mounted on Control Panel
Mounted Behind Dash
Ground to Chassis
