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Author Topic:   Engine charging system and/or Battery problem
lhg posted 05-02-2001 08:56 PM ET (US)   Profile for lhg  
Let me first set up the situation.

One of my Merc 200 EFI's, with factory 40amp alternator, was showing voltage on the voltmeter, while at planing speeds, of over 16 volts. Previously, these engines have always shown exactly 14 volts under similar conditions, and never higher.

So I took it in for Mercury service, and under the warranty they replaced a rectifier and stator, I think. At no cost to me. I did not replace the combination starting/deep cycle flooded battery.

Now, here is my problem. The voltmeter still reads as high as 15 volts when planing, but everything seems to be fine. But after running the engines for about 2 hours, I coincidentally happened to cleaning under the full transom deck (where there is a battery on each side) and this battery was noticeably very warm! Not boiling hot, but very warm, emitting a lot of heat.

Question, before I arrange for service again (with a different Dealer): Had I previously damaged the battery with the 19 volt charging (that's what it was doing prior to repair)?
Would the battery be the problem and causing the alternator to charge it at the rate of 15 volts? Should I replace it, and then see what the charging voltage is?

Or, is the engine still not repaired properly, and the battery is not the problem?

Or could both the engine charging system and the battery be the problem?

If anybody more familiar with marine electrical charging systems could help, I'd me most grateful.

triblet posted 05-02-2001 09:01 PM ET (US)     Profile for triblet  Send Email to triblet     
There's a battery for each motor? Swap
the batteries.


B Bear posted 05-02-2001 09:44 PM ET (US)     Profile for B Bear  Send Email to B Bear     
I agree with Chuck swap the batteries and check the electrolyte levels. And most importantly you should check the battery charge with a hydrometer.

According to my "Preventive maintenance of electrical equipment" by Charles Hubert, the source of power for charging a lead-acid battery should be 2.5 volts per cell, the temperature of the electrolyte should not be allowed to exceed 125 dgrees F.. Each cell should produce about 2.05 volts, that means for a 12 volt battery there will be 6 cells,
so the charging voltage would be around 15 volts.
As the battery is reaching a full charge the charging rate should tapper off to prevent excessive gassing and temperatures from damaging the plates.

So that leaves these possiblities;
If the battery cannot reach full charge, keeping a high charge rate and heating the battery, there can be a damaged plate.

If the battery is at full charge and the charging current does not tapper off the problem is in the charging circut (which can damage the barrery plates if enough of the electrolyte level is lowered in the cells).
Hope this helps,

daverdla posted 05-02-2001 09:57 PM ET (US)     Profile for daverdla  Send Email to daverdla     
I wouldn't swap the batteries yet. You may end up with two bad batteries. The stator is the stationary part of a motor or alternator winding - basically the winding attached to the inside of the case. I've never heard of someone replacing a stator and not the whole alternator but it is possilbe. The rectifier is the part of the circuit (diodes) that converts the AC output of the alternator to DC.

I don't know how different the charging system on an outboard is from an automobile but there needs to be a voltage regulator. The regulator typically limits the voltage to 14VDC, your previous reading. Just in case, you may want to get it serviced again. Don't rely on the accuracy of panel mounted gauges. Overvoltage can damage the batteries and possibly other electronic components on your boat.

lhg posted 05-02-2001 10:45 PM ET (US)     Profile for lhg    
Thanks for the comments - So there is a good possibility that the previous 19 volt charging rate from the previously bad regulator may have damaged the battery?

Evidently the Mercury voltage regulators use 14 volts as the charging maximum. Never before have I seen the volt meters read higher than that, until this problem occurred. Incidentally, the 19 volts seemed to have destroyed the Teleflex voltmeter and I had to replace it.

bigz posted 05-03-2001 09:39 AM ET (US)     Profile for bigz    
Larry, check the cells as stated with a hydrometer that will tell you if you blew the battery --

You own a multimeter? If not buy one and learn how to use it this will tell you straight away what component is shot or not functioning properly in all your electrical systems ---

In this case it might be the charging system output again and the regulator is the culprit --

If you have a multimeter it can be used if not use your dashboard voltmeter.

Start with everything turned off, take a direct reading at the battery this will establish your reference voltage if you have a multimeter. If not using the dash meter just turn on the key either way copy the number. Start the engine get it up to about 2000rpm. The voltage should increase 1v to about 3v+ but no more than 3.5v over the reference voltage -- if it does your regulator is shot. If no increase in voltage is present with the engine running at 2000 rpm the charging system isn't working.

My simple guess you fried the one battery, and need a new regulator. Was the warranty repair done recently?

triblet posted 05-03-2001 10:02 AM ET (US)     Profile for triblet  Send Email to triblet     
Also check the connections to the voltage
regulator. I had a loose connection there
that was causing high voltages.


hauptjm posted 05-03-2001 11:39 AM ET (US)     Profile for hauptjm    
Twice, I have had his problem, but with automobiles. Both times, the ultimate result was a ruined battery. Again, both instances were caused by a faulty alternator. What exactly, was wrong with the alternator, I'm not sure. The voltage regulators were in effect rendered useless, and allowed for the overcharging of the batteries. Oddly enough, the VR in both cases was not damaged.
jimh posted 05-12-2001 09:24 AM ET (US)     Profile for jimh  Send Email to jimh     
I believe there are two styles of battery charging in outboat engines:

--flywheel "stators"

Flywheel Stators Charging Circuits:

In smaller outboards the charging system is composed of a number of coils ("stator" "charging coil" "lighting coil") that are located under the flywheel, usually on the top of the powerhead. The flywheel contains a number of permanent magnets which are aligned to rotate over the coil. The magnetic field of the magnet cuts the windings of the coil, inducing electrical current flow in the coil.

The current from the coil is a pulsating alternating current, which is applied to a rectifier. The output from the regulator is a pulsing direct current.

Before being sent to the rectifier, the output of the charging coil is also often used to excite the tachometer. The number of pulses per revolution is determined by the number of magnets and the design of the coil. The tachomoter integrates the pulses into a current that deflects a meter (pointer type tachometers) or counts them with a digital counter (digital tachometer).

Typically there is no regulating mechanism. The number of windings in the coil determines the voltage, which is set so that at running speeds the charging circuit can furnish a limited amount of current to the load. The current available is usually 2-4 Amps. The connection of the battery across the output of the charging circuit is really the regulating mechanism.

The output voltage of the charging circuit will rise until it hits the terminal voltage of the battery. Any increase in output voltage above that has to drag the battery along with it. If the battery is in good condition, it will have a very low internal resistance, and it will take considerable current flow to drag the terminal voltage higher than about 13.2 volts.

If the battery is discharged to a lower voltage, it will drag the charing circuit output down to that voltage, and the battery terminal voltage will rise slowly with charging.

If the battery is in poor condition it will have a higher internal resistance, allowing the charging circuit applied voltage to more easily pull the battery terminal voltage up to higher voltages. If you have a strong charging current and high voltage, you probably can force the battery voltage to higher level, like 14-16 volts.

Alternator Charging Circuits

An alternator acts as a current amplifier, using the mechanical power of the shaft rotation to apply the energy to the electrical circuit. A small current flows from the battery through the field winding of the alternator, which creates a magnetic field. The rotating coil (rotor) in the alternator has a current induced in it as it revolves in this field. The coil often consists of three windings, whose outputs are applied to six rectifiers, creating a direct current output which is accumulated and appears as the output of the alternator.

A regulating mechanism is contained in the alternator which adjusts the amount of current flowing in the field winding. This in turn adjusts the amount of current flowing in the rotor. The regulator modulates the field current so as to produce a constant output voltage, approximately 13.2 volts, suitable for charging batteries.

If a failure occurs in the regulator, it may fail in such a way that it applies full exciting voltage to the field winding at all times, leading to the generation of a high output voltage at all times. In such a failure mode the alternator will continuously produce maximum output voltage and supply as much current as it can to any load connected to it.

If the alternator has high current capabilities, it could force even a good battery to quite a high terminal voltage. Excessive charging of the battery causes "boiling" of the electrolyte, excessive heating of the solution, and potential damage to the battery plates, case, etc.

Another failure mode for an alternator (or any charging system) is a fault in the main rectifiers. The action of the retifiers is important! Connection of the coil--a piece of wire in terms of the battery point of view--will cause current to flow from the battery through the wire, unless something intercedes. The action of the rectifier blocks flow of current from the battery into the charging coil. If a rectifier fails, it may allow the battery to discharge into the coil when the engine is not running, burning up the coil and discharging the battery.

Only one of the six rectifiers needs to fail to allow this, and the failure may only be partial. None the less, current will flow from the battery, backwards through the failed rectifier, eventually discharging the battery and possibly damaging the coil.


triblet posted 05-12-2001 08:57 PM ET (US)     Profile for triblet  Send Email to triblet     
My '97ish Evinrude 90 has a stator coil AND
a regulator.


jimh posted 05-14-2001 09:35 AM ET (US)     Profile for jimh  Send Email to jimh     
The nice part about the regulator design in an alternator system is that the regulator applies its action to the low-current winding of the field. This in turn regulates the output of the high current rotor winding.

In a stator coil/magnet charging circuit, I don't see any way that regulation can be added to the generation of the charging coil output. It seems to me that the charging coil will produce an output that is predetermined by:
--the number of magnets in the stator
--the strength of those magnets
--the number of windings in the coil
--the resistance of the winding
--the speed of rotation

The regulator in the circuit is probably downstream of the rectifier, and it regulates by inserting itself between the charging circuit and the load.


It is also possible for a problem in a battery to affect the charging circuit. If one cell in a battery shorts, the terminal voltage of the battery will fall about 2 volts. This will cause the battery to appear to the charging circuit to always require charging, even though the state of charge in the remaining cells is actually at the fully charged level.

Because the battery is now demanding continuous charge from the charging circuit, the charging circuit is forced to work at maximum output capability all the time. This may cause it to overheat or otherwise eventually damage itself.

Because the battery is being continuously charged, the electrolyte in the remaining active cells will begin to boil, the battery can overheat, and more plates can buckle and short, further aggrevating the problem.

lhg posted 05-14-2001 12:50 PM ET (US)     Profile for lhg    
Jim - Chuck's description is correct on most of the more modern outboards. Your engines probably do not have regulators, at least I know your Merc 50 doesn't. Don't know about the Yamaha's, but I do know that the major shortcoming of the 70 Yamaha (even current models) is the tiny 6 amp alternator output at W.O.T. Merc 75's have 18 amps, as do all engines down to 30HP. For your cruising activities you will need the combo starting/deep cycle batteries
for lighting, electronics, etc to compensate for the low charging rates.

My 1985 Merc 115's (stator/coil charging) came without voltage regulators, but Mercury offered an accessory add-on, and I installed these, which control the maximum charging voltage to 14.2 volts. They were simple to install, and about the size of a square of baking chocolate. But the maximum output of the charging system is only 9 amps, a bit low for today's requirements.

I understand that an unregulated engine will ruin a closed cell battery.

My 200's have a 40 amp stator/coil charging, which I understand is 2 20amp systems combined, also with a 14.2 volt regulator.

I understand that the Merc Optimax's have an automotive style 60 amp alternator.

lhg posted 05-24-2001 01:01 AM ET (US)     Profile for lhg    
For those who contributed their suggestions and help on this question, I have discovered my problem was a bad battery, probably from being badly overcharged at 19 volts by a previously bad voltage regulator. A new battery solved the problem, and the engine is once again charging the battery at a continuous 14.2 volts.
Arch Autenreith posted 05-13-2002 08:02 PM ET (US)     Profile for Arch Autenreith  Send Email to Arch Autenreith     

I continued to have overcharging problems. No one (even Twin Cities Marine) seems to know of or about the voltage regulators you talked about.

("My 1985 Merc 115's (stator/coil charging) came without voltage regulators, but Mercury offered an accessory add-on, and I installed these, which control the maximum charging voltage to 14.2 volts. They were simple to install, and about the size of a square of baking chocolate.") Original post 5/2/01.

Do you happen to have a part number? Or where you got them?

Thanks. Arch.

Jerry Townsend posted 05-13-2002 08:28 PM ET (US)     Profile for Jerry Townsend  Send Email to Jerry Townsend     
Larry - you beat me to the punch - namely the bad battery. The key was the hot battery which simply indicated resistance and load. This load was probably from an internal short and not caused by the higher charging voltage. The higher voltage was the result of additional load - not the other way around. Glad you got it figured out. ---- Jerry/Idaho
David Ratusnik posted 05-13-2002 08:35 PM ET (US)     Profile for David Ratusnik  Send Email to David Ratusnik     
lhg- Many fine suggestions above. You mention in your post going to a "different dealer." I believe that is a mistake. Identify the finest Merc mechanic in your area and stick with him. Let the expert get to know your engines. Going to "different dealer" strikes me as a crap shoot. They all reinvent the wheel. Find 3 guys running Mercs who are at your level of boating and go to the mechanic they have been using. Pay the guy a fair price to get it right/keep it right, and go boating. .03 David
Arch Autenreith posted 05-13-2002 10:06 PM ET (US)     Profile for Arch Autenreith  Send Email to Arch Autenreith     
I don't know why but I resurected this thread (originally from a year ago) but it's still posting them as '01 vs. '02.

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