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9 amp voltage regulator for Mercury

S

schnidly

Member
Dear Forum,

Can someone tell me if there is a voltage regulator I can install made for a 1988 Mercury 90hp 3cyl. 2 cycle outboard? The serial number is 0B302485. I installed a radio shack rectifier that is better rated than the mercury rectifier. I know CDI makes one designed to replace this rectifier, but I am not sure if Mercury made one in lieu of just the rectifier?
 
From factory there was no regulator available for the 9 amp systems in your model year.

There was an optional 16 or 24 amp system available (maybe starting in 89 or 90) that added a regulator into the circuit - it was fed by the rectifier on some models and others without the rectifier.

While these regulators are still available and could possibly be jury rigged into your system (don't know if or how well they would work) they generally list in the 180 to 200 buck range - so not a cheap experiment.

In general, with the lower amp rectified systems it is the "battery" that provides the "power regulation" (which is why a Marine battery is always the better choice for rectified systems).

Just curious, why would you want/need "regulated power"?
 
those 9 amp rectifier only charging systems work just fine so long as you do not use a maintenance free battery with them..use the type battery where you have to add water...use then to maintain your ignition battery only..i would not go getting fancy with a switch etc and try to charge a trolling motor battery for example...make sure the ignition battery is fully charged when you put the boat in the water also...the system is designed to maintain a charge..to charge a dead or low battery puts too much stress on it...
 
On the rectifier systems Merc doesn't even publish a "voltage" output rating.

They do for "regulated" systems, generally indicating that above 14.5 volts is a problem.

For rectified systems they only give "amperage" outputs.

I have seen rectified systems put out upwards of 16.5 volts. Again, a Marine or Tractor battery can take a fairly wide range of "unregulated" voltage unlike other batteries which NEED regulated power.

The system has worked well for many years. Unless it's cooking your battery, I don't see an issue.
 
Did some checking on my charging system today. I had 14.1 volts on my battery with the key off and the motor not running. At around 2000rpms I had 16.72 volts at the battery posts on my unregulated system. The amps read around 4amps on the battery cable near the battery with a clamp-on amp meter. This was at around 2000rpm also. Does this sound normal? I am using the Radio Shack rectifier that was recommended on the boating blogs instead of the oem Mercury rectifier. Took the battery covers off to check water levels and they were good and there is no sign of the battery boiling over. My battery is a 625 MCA(marine cranking amps). Is this too small? Its the one recommended for my boat. However it is an EverStart from Walmart. Thanks
 
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The OEM system would normally produce (with the 9 amp stator/rectifier):

Idle - 1 amp
1000 - 4 amps
2000 - 8 amps
3000+ - 9 amps (max power)

The service manual does suggest a test where you place the battery under load (reading 13.5 volts or less) then start the motor and bring it up to 3000 rpms.

If the reading is between 7 and 9 amps the charging system is functioning properly given that the battery is being discharged by the accessory (or whatever you are using as a power draw).

If the reading is 7 amps or less @ 3000 with "no load" on the battery, it is suggested that you test the stator.

(and I use the Wally World EverStart group 24 for all my electric start motors upto/including my 140 Evinrude - more than enough battery)
 
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''If the reading is 7 amps or less @ 3000 with "no load" on the battery, it is suggested that you test the stator.''

i question that statement if the battery is fully charged....it may take a few amps right after it uses some power to start the engine but once it recovers i would expect it to be 2 amps or less..

i think the tech that did the test for the manual either had a not fully charged battery or still had a load on it..
 
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