Mercury 200hp Voltage Issue

jwilkes

Cadet
Joined
Jul 10, 2007
Messages
14
I have a pair of Mercury 200hp carb engines on my recently purchased 1994 Robalo 2520. Both engines run smooth up to 5,000+rpm's.

I had an issue recently where I couldn't get my tachs to work; traced it back to one of the voltage regulators, which was fried. Replaced one regulator with a used one, and now both tachs work.

At rest with the battery switches off, my batteries read 12.8v each. My port battery is a starting battery, and my starboard battery is a combo starting/deep cycle (house battery). At a 600-800rpm idle, both of them read 13.6-14.4v. When I increase the rpm's to 1,000+, voltage will spike to 15.5-16v and not fall back down until I back the throttles down to idle. This is on both engines, read with both a multimeter at the battery and also on the dash gauges.

It's my understanding that voltage shouldn't rise over 14.4+/- at all, am I correct?

Should I pony up the cash and replace all 4 regulators with brand new ones? It's the regulators that control the voltage output, correct? I understand that if a stator is bad, it will fry the voltage regulators.

Anything else I should be looking at or considering before I spend more money??

Thanks!!
 

Jlawsen

Master Chief Petty Officer
Joined
Apr 22, 2012
Messages
810
Re: Mercury 200hp Voltage Issue

I have a pair of Mercury 200hp carb engines on my recently purchased 1994 Robalo 2520. Both engines run smooth up to 5,000+rpm's.

I had an issue recently where I couldn't get my tachs to work; traced it back to one of the voltage regulators, which was fried. Replaced one regulator with a used one, and now both tachs work.

At rest with the battery switches off, my batteries read 12.8v each. My port battery is a starting battery, and my starboard battery is a combo starting/deep cycle (house battery). At a 600-800rpm idle, both of them read 13.6-14.4v. When I increase the rpm's to 1,000+, voltage will spike to 15.5-16v and not fall back down until I back the throttles down to idle. This is on both engines, read with both a multimeter at the battery and also on the dash gauges.

It's my understanding that voltage shouldn't rise over 14.4+/- at all, am I correct?

Should I pony up the cash and replace all 4 regulators with brand new ones? It's the regulators that control the voltage output, correct? I understand that if a stator is bad, it will fry the voltage regulators.

Anything else I should be looking at or considering before I spend more money??

Thanks!!

The motors after about 1992 use a combined regulator/rectifier with two red wires. The larger red wire is the charging output and the smaller one senses the output voltage and feeds that back to the regulator. Both reds are connected to the battery positive terminal at the starter Solenoid. Your motor has two reglator rectifers and all 4 reds go to the same post. If you leave the small red off like I found a lot of them over the years then your regulator won't know what to do and it will just pump out whatever voltage the stators is producing. That still works because in a battery circuit the battery will act as a regulator. That's how it was done for years before electronics demanded better control.

I should mention that you may not have a second red wire because some of them didn't have it and some of them did. The CDI aftermarket version usually has it. If you replace yours with CDI's then get the 5 wire units not the 4 wire. That will give you the feed back lead and in my opinion much better regulation.
 

jwilkes

Cadet
Joined
Jul 10, 2007
Messages
14
Re: Mercury 200hp Voltage Issue

The motors after about 1992 use a combined regulator/rectifier with two red wires. The larger red wire is the charging output and the smaller one senses the output voltage and feeds that back to the regulator. Both reds are connected to the battery positive terminal at the starter Solenoid. Your motor has two reglator rectifers and all 4 reds go to the same post. If you leave the small red off like I found a lot of them over the years then your regulator won't know what to do and it will just pump out whatever voltage the stators is producing. That still works because in a battery circuit the battery will act as a regulator. That's how it was done for years before electronics demanded better control.

I should mention that you may not have a second red wire because some of them didn't have it and some of them did. The CDI aftermarket version usually has it. If you replace yours with CDI's then get the 5 wire units not the 4 wire. That will give you the feed back lead and in my opinion much better regulation.

Thanks for your reply- good info! My current regulators are a 5 wire; 2 reds (1 male & female), 2 yellows, and the gray sender.
 
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