Re: Charging output?
The 7.5 horse, if equipped with the "lighting coil" (charge stator) only put out 600 watts (5 amps) at wide open - at idle it doesn't put out enough power to light a single 10 watt navigation bulb.
Until somewhat recently most charge stators on outboards below about 150 horses only provided enough power to keep a fully charged battery "topped up" and power the nav lights.
They were never designed to provide power for all the "must have" electrically powered toys which are now on boats.
A 9 amp Merc stator puts out zero amps at idle, about 6 amps at 2000 rpms and 9 amps from 3000 rpms on.
The 16 amp will put out 5 amps at idle, and puts out the full 16 amps by 2000 rpms.
Now add a very (low end) 27 pound thrust Minn Kota trolling motor that you run for 2 hours doing some trolling - it sucks up about 70 amps.
Even with a 16 amp stator you would have to run at a minimum of 2000 rpms for over 4 hours solid just to replace the power the trolling motor "sucked out".
When considering power, recharge capacity etc on "older motors" - (the current 90 horse 4 stroke Merc has a 50 amp alternator) you should plan on using the motor(s) to supply enough power to keep the "starting battery" topped up and maybe run the lights and gps, but install a second (deep cycle) "house battery" to run the "toys" and invest in an on-board charger so you can plug the boat in back at the dock (or on the trailer).
In most cases, your motor will never be able to supply enough power to keep the house battery charged, and in some cases, couldn't even put a dent into replacing the amout of power being sucked out of it....
