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1996 20hp Mercury charge

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dee004

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Hi all. Dee here I'm new to the forum from Ontario. I have a very good low hours 1988 20HP Mercury 2 stroke [POST TITLE LISTS WRONG YEAR IT'S 1988 NOT 1996] pull start outboard. I would like to add a charge circuit to charge my battery and am wondering what I need to accomplish this. Do I need just the charge coils and rectifier or a flywheel as well? Also how would I go about getting the part numbers for the required parts. I tried the only Marina around me but they didn't seem too interested like it was some sort of imposition to them lol. Thanks in advance. Cheers Dee.
 
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You only need the charge stator and rectifier - the flywheel, ignition stator, trigger etc all remain the same.

The charge stator is no longer available from Merc but with some looking you can probably find some "old stock".

The part number changed over the years but has been listed as: 86704A2, 86704T2 and finally 86704A10.

Any of the 3 post OEM or aftermarket Merc rectifiers could be paired with the charge stator.

If you do hook this up you must ALWAYS have it connected to a battery - the power produced needs to go somewhere or it can "cook" the stator/rectifier. There is a Isolation Block (basically just a couple of posts, grounded to the block) that can be added (or may be present on the engine - some models had them from factory) that you can connect the charge stator wires to if not being used (just remove the wires from the rectifier and connect to the block), that can be used if you want to run without a battery connected.

You should be aware that (this) charge system only puts out a maximum of 4 amps (at full throttle). It puts out barely 1 amp at about 2000 rpms. So while it is "enough" to keep a fully charged battery "topped up" (electric start application), it is impractical to charge a deep cycle battery that is somewhat discharged.

My electric trolling motor might draw 20 amps running it at trolling speed for a couple of hours. To "recharge" it you would have to run 5 solid hours at full throttle to replace that 20 amps depleted - not practical. So depending on your application this may not be worth the effort.
 
galamb said:
You only need the charge stator and rectifier - the flywheel, ignition stator, trigger etc all remain the same.

The charge stator is no longer available from Merc but with some looking you can probably find some "old stock".

The part number changed over the years but has been listed as: 86704A2, 86704T2 and finally 86704A10.

Any of the 3 post OEM or aftermarket Merc rectifiers could be paired with the charge stator.

If you do hook this up you must ALWAYS have it connected to a battery - the power produced needs to go somewhere or it can "cook" the stator/rectifier. There is a Isolation Block (basically just a couple of posts, grounded to the block) that can be added (or may be present on the engine - some models had them from factory) that you can connect the charge stator wires to if not being used (just remove the wires from the rectifier and connect to the block), that can be used if you want to run without a battery connected.

You should be aware that (this) charge system only puts out a maximum of 4 amps (at full throttle). It puts out barely 1 amp at about 2000 rpms. So while it is "enough" to keep a fully charged battery "topped up" (electric start application), it is impractical to charge a deep cycle battery that is somewhat discharged.

My electric trolling motor might draw 20 amps running it at trolling speed for a couple of hours. To "recharge" it you would have to run 5 solid hours at full throttle to replace that 20 amps depleted - not practical. So depending on your application this may not be worth the effort.
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Thank you very much for the in depth reply. You answered my question and I see that adding a charge coil and rctifier to my engine will not be practical as it's requirement is to charge my trolling motor battery. My Honda suitcase generator puts out 8 amps so it looks like it may be my only option unless I trade out my Merc for another more practical engine. Cheers, Dee
 
I have a 24 volt troller and charge it with the 115 Merc. I also have a decent size solar charger that supplements everything. They have become pretty affordable. You might consider solar too. 100 watts can be had for about 100 bucks. They work pretty well.
 
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timguy said:
I have a 24 volt troller and charge it with the 115 Merc. I also have a decent size solar charger that supplements everything. They have become pretty affordable. You might consider solar too. 100 watts can be had for about 100 bucks. They work pretty well.
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Thanks timguy, you have touched on a very good point. I actually do recharge with solar on land as I have two solar setups. One at home an 1100W 48V system and on my RV a 360W 12V system. The problem is the real-estate on the 14ft aluminum boat is quite limited and not really anywhere to install a panel or two. Cheers.
 
Right, Dee, no room for the wife and dog then. On the 17 footer it can sit right on the left dash, behind the windscreen.
 
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