Defective voltage regulator or something else?

[hkeiner]

I have a 1996 Mercury 150 V6 Carbed Ser. No. OG397853​

The voltage readings measured at the battery posts show approx 12.5v when the engine is off. The voltage jumps up to approximately 13.5v right after the engine is started and stays there until the engine warms up. I understand that this is normal behavior and shows that the system is charging the battery.​

My problem starts when the engine warms up. The voltage reading then intermittently jumps between approx. 13.5v and approx. 18v. That is, it may read 13.5v for 5-15 seconds, then jump up to 18v for 5-15 seconds, and then back down to 13.5v for 5-15 seconds. This continues indefinitely. The engine does not seem to run differently at either idle or WOT when the voltage reading is higher or lower. The engine does not seem to be running hot. Also, the battery is not boiling out water or anything like that.​

I tried doing the standard bench tests, as shown below, on the two voltage regulators and they checked out OK. My guess is that either the voltage regulators fail only when they are warmed up or the standard ohmmeter bench tests don't detect the type of failure that I am experiencing.​

Before I go out and buy two new voltage regulators, I was wondering if there are any other possible causes for fluctuating voltage spikes other than the voltage regulators (such as bad ground, bad stator, bad power pack, bad battery, etc.). I don't think so but I thought it prudent to check with those more experienced than I am.​

Any thoughts on this will be appreciated​

-------------------------------------------------
Voltage reg test using an ohm meter. ​

Zero the meter. ​

Connect negative lead to either yellow lead
Connect positive to the thick red lead
Scale Rx10
Reading 100-400 ​

Reverse the above test.
Scale Rx1
Reading 40k to infiinity. ​

SCR checks.
Connect Negative to Yellow lead
Connect Positive to Case ground.
Scale Rx1k
Reading 10k to infinity ​

Tach circuit.
Connect negative to ground case lead or case.
Connect positive to gray lead.
Scale Rx1k
Reading 10k to 30k.
-------------------------------------------------------​

 

[Laddies]

Re: Defective voltage regulator or something else?

It sounds like the regulator going bad but before replaceing them ck all electical connections for corrosion and tightness

 

[JUSTINTIME]

Re: Defective voltage regulator or something else?

want an easier way

get your meter, switch it to a/c volts
start the motor
connect the leads to your battery
if u read more than .8 volts, u have a bad reg/rec

 

[hkeiner]

Re: Defective voltage regulator or something else?

Thanks for the tip on checking the AC voltage at the battery with the motor running. I assume that this test would indicate whether the rectifier function of the voltage regulator works OK or not. Would this test also confirm that the DC voltage spikes I am experiencing are being caused by the voltage regulators?

 

[Texasmark]

Re: Defective voltage regulator or something else?

Your engine should have 2 ea 20 amp regulators located center aft of the engine under the plate containing the trim relays. You can disconnect one at a time to see which is intermittent....and 18V says it quit regulating and may be as simple as dirty grounds...see later. Your tach is a grey wire and will be plugged into one or the other. If you disconnect the one with the tach you will have to switch it to the other if you want the tach to work while troubleshooting.

There are two yellow wires coming from the stator (under the flywheel) that feed each regulator (4 total). I'd assume that merely unplugging the stator wires (and insuring that they don't touch ground), will suffice in disconnecting the regulator you wish to disconnect.

As stated, your problem may be due to bad grounding. Don't have the engine in front of me but black is usually ground, or the case of the module grounds to the engine block when you mount it.

Cleaning of the leads (removal and reinstallation when finished) should solve that if that is the problem.

Being a solid state module it should be pretty husky as compared to the old reed type mechanical regulators.

Mark

 

[hkeiner]

Re: Defective voltage regulator or something else?

Thanks for the additional information on a grounding problem being the possible culprit.

On my motor, the two 20 amp regulators are grounded to the engine block with four bolts (two on each regulator) that sandwhich the regulators between the block and a large metal plate holding the coils. There are no ground wires on the regulators. Only two red (12v output), two yellow (input from stator), and a grey (output to tach). To detemine if a bad ground on the voltage regulators is causing my problem, I removed and cleaned the surfaces of the voltage regulators, the metal plate, and the bolts as best I could to ensure a good ground. The voltage spikes continued. Unless a bad ground elsewhere in the electical system can cause voltage spikes, I guess I can conclude that one (or both) of the voltage regulators is bad. My next step is to disconnect one at a time and see what happens.

As a side note, I talked to the parts guy at my local Mercury Authorized boat shop about buying replacement regulators. He asked me if the voltage regulators on my motor were the "old type" (with clear potting showing the circuits inside the regulator) or the "new type" (with black potting that does not show the circuits). I told him that mine have the clear potting. He said that I should replace both regulators as the "old type" were very problematic and can cause multiple problems. I am always a bit dubious about buying stuff based upon the recommendation of the person selling the stuff so I thought I would ask others if the poor reputation of "old type" regulators is common knowledge.

 

[Laddies]

Re: Defective voltage regulator or something else?

The clear potted reg were troublesome, I've seen many with the wires burned off. Do yourself a favor and buy CDI regulators not Mercury

 

[hkeiner]

Re: Defective voltage regulator or something else?

The clear potted reg were troublesome, I've seen many with the wires burned off. Do yourself a favor and buy CDI regulators not Mercury

Thanks for the advice. I ordered two new CDI voltage regulators today.

Regards,

Hal​

 

[hkeiner]

Re: Defective voltage regulator or something else?

I installed two new CDI voltage regualtors and the charging system is working OK now. Thanks for all the advice.​

 

[Texasmark]

Re: Defective voltage regulator or something else?

Glad you got her fixed and thanks from all interested for your feedback....helps the next time someone has a problem.

Mark