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Voltage Regulator for 75HP

L

leachy

Contributing Member
Just looking for for some advice. I have a 75hp 1986 model that is only fitted with a voltage rectifier so at higher RPM the voltage gets over 1above 16V, not good for the battery or electronics. I have managed to get my hands on a Mercury voltage regulator #88825A7 and was wondering if I can use this to limit the voltage. There are two terminal one say red and the other yellow. Does anyone know if I can make the connection from the battery terminal of the rectifier to the terminal which says yellow and the other one which says red to the battery.

Thanks in advance.
 

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Thanks for the pic, how have you mounted that? under the engine cover or external. As you know space is very limited and the heat build on the components.
 
leachy said:
Just looking for for some advice. I have a 75hp 1986 model that is only fitted with a voltage rectifier so at higher RPM the voltage gets over 1above 16V, not good for the battery or electronics. I have managed to get my hands on a Mercury voltage regulator #88825A7 and was wondering if I can use this to limit the voltage. There are two terminal one say red and the other yellow. Does anyone know if I can make the connection from the battery terminal of the rectifier to the terminal which says yellow and the other one which says red to the battery.

Thanks in advance.
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Does your rectifier have two input wires (from the stator) and either one or two output wires (positive and ground)? I would think so.

When a rectifier/regulator replaces a rectifier the wiring is almost always the same. Two wires for input from the stator and two wires output for the battery. One of the two output wires (the ground) may come from a connection point on the motor and not directly from the rectifier/regulator.

If the correct rectifier/regulator is chosen it should be a plug and play replacement.
 
Thanks for the information. I guess the original was just a rectifier, but need to get the voltage down so was just looking at the regulator to add in. The S/N 9453744, Belgian made 4 cylinder. As you can see there isn't a lot of room.

Regards
Leachy
 

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Here is a link to an Ebay seller that is offering the conversion kit. You might want to see if he will send you a copy of the kit installation instructions so that you have better visibility of how it is installed. What goes where.

 
That module kit (OEM) is a clipper or you could call it a regulator as it bleeds excess voltage to ground . The CDI kit posted is a rect/reg
 
The CDI unit is a rectifier/regulator assy and the Merc OEM kit is just a regulator/clipper add on. The CDI unit works by comparing the actual output voltage with a reference voltage and using feedback to adjust the output voltage as necessary.
 
faztbullet said:
The CDI unit is a rectifier/regulator assy and the Merc OEM kit is just a regulator/clipper add on. The CDI unit works by comparing the actual output voltage with a reference voltage and using feedback to adjust the output voltage as necessary.
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If I am now understanding this correctly, the Mercury part gets added to the existing rectifier. That is, two separate parts doing the job of what one integrated rectifier/regulator does.

Which would agree with the configuration shown in post #2.
 
boscoe said:
If I am now understanding this correctly, the Mercury part gets added to the existing rectifier. That is, two separate parts doing the job of what one integrated rectifier/regulator does.

Which would agree with the configuration shown in post #2.
Click to expand...
Yes that is correct. For some reason on the Merc smaller motors (below 90hp) of that era they only fitted a rectifier.

The guys selling the OEM regulator on Ebay shared the instructions with me and the regulator is mounted between the spark plus on the head of the motor.

Regards
Leachy
 
Yes that is correct. For some reason on the Merc smaller motors (below 90hp) of that era they only fitted a rectifier. It was possibly OK as the output is relatively low in amps and the older flooded lead/acid batteries could be topped up with water from over charging and getting warm, plus they had a higher internal resistance to counteract the issues.

The modern batteries are typically sealed and dont have the higher internal resistance, plus people have a lot more electronics which require a more stable voltage and higher amperage.

Im just trying to keep the old Merc engine I have as its probably done less than 50 hours from new.

The guys selling the OEM regulator on Ebay shared the instructions with me and the regulator is mounted between the spark plus on the head of the motor.

Regards
Leachy
 
It needs to mount on a flat bare aluminum area as it does get warm and needs a good ground to bleed current to. Flat area above exhaust would work.
 
Yeah I was planning on doing that and possibly looking at an aluminum heat sink. I can imagine it gets very hot under there. This is the position in the pics from the manual. there are already the two mounting points cast into the head to suit.
 

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This is from the documentation if anyone is interested.
 

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