Over reving a mercury electrical system without a regulator Question

If an engine is designed for 5500 RPM maximum, would over reving the engine (say 6000 RPM) be it ventilating or just under proping it to gain in rpm,s unprotected by a regulator cause the rectifier to overcharge the system causing damage to the rectifier powerpack battery etc? Or does the timing or votage output reach a top out of current at a certain point. This is to help in posts recently by others and for my own interests

Re: Over reving a mercury electrical system without a regulator Question

Regulated puts our about 14.5v. Unregulated puts out about 16 volts. You have to have more voltage than is on the battery to cause it to charge. The big factor is the current capacity of your charging circuit and the power usage from your battery.

I think I am correct in stating that the unregulated outputs are from low amperage regulators so even though it has the capacity to put out 16v basically unloaded, it doesn't do all that much to overcharge your battery. If you are concerned about it just feel your battery and if unsealed look at the top near the caps. If overcharging, it will be warm to hot to the touch and you will see fluid residue around the edges of the caps.

From my OEM Merc manual, for a manual start outboard in the 75 to 125 hp category (my manual covers these engines), late '90's production, a 9 ampere alternator, with optional rectifier is rated at 0 amperes at idle up to 10.5 amperes at 5000 rpm. It says that the basic engine voltage output, unrectified, is to operate running lights only. Soooo if you ran at WOT for extended periods of time and started the engine rarely, had a full battery to start with, and had no electronics or lights to consume energy stored in the battery, looks like you might be able to over charge it. I'd assume that on a smaller engine, like a little 9.9 hp fishing motor it would be significantly less. If for no other reason, the space under the flywheel would be much smaller and thus no room for the alternator to be very large.

Oh, it's the amperage that charges the battery. The voltage just pushes the amperage and the battery charge level vs the applied voltage and current capacity with the load on the circuit at the time set the charge rate.

HTH,
Mark

Re: Over reving a mercury electrical system without a regulator Question

The battery will act somewhat like a regulator in those older systems that had only a rectifyer and not allow the voltage to go much higher. However the higher voltage will make the battery "boil" (charge faster) and lose water. This is the reason that matenance free batteries are not reccomended for those older motors. You can not replace the water that is lost like you can on a regular battery. So, in answer to your question; with a proper battery and good connections no damage is likely to result to your electrical systems and the voltage will not just keep going higher and higher at above WOT rpms.

Re: Over reving a mercury electrical system without a regulator Question

16 is in fact what I thought a safe output would be at WOT and thats what my 40 HP was putting out maybe 16.5 Posters are saying there reaching 17 volts which I read was not to be exceeded or switchbox failure would be eminant. The other concern is the AC red blue wires to the upper portion of the switchbox and the internal rectifier inside getting to much current blowing the switchbox

Re: Over reving a mercury electrical system without a regulator Question

Thank you sir so the stator can only produce up to a certain output then, but the maintanence free battery is what causes the system failure due to lack of water.

Re: Over reving a mercury electrical system without a regulator Question

If you were to look at the service manual or even on the motor somewhere it will say "DO NOT RUN WITH BATTERY DISCONNECTED" or something like that. If the battery is disconnected with the engine running be prepared to replace some parts. The battery provides the necessary buffer to the high voltage the stator can generate without the battery to buffer it.

Re: Over reving a mercury electrical system without a regulator Question

Voltage regulators are under $50. It really doesnt make sense not to use one.

Re: Over reving a mercury electrical system without a regulator Question

Thanks for the input getns. I may just get the regulator as I,ve spent tons on the rebuild. I,m not having issues with my system but wanted to know some good info on these systems that run just a rectifier, for me, and for some good information for other readers to know and it looks like theres plenty.

Re: Over reving a mercury electrical system without a regulator Question

FWIW, I think it's important to know as well that not only should one not run the motor without a battery but that one should also avoid running the motor with a battery on a low charge as this creates greater current flow from the stator and can lead to premature failure.

Re: Over reving a mercury electrical system without a regulator Question

Maxz695 said:

If an engine is designed for 5500 RPM maximum, would over reving the engine (say 6000 RPM) be it ventilating or just under proping it to gain in rpm,s unprotected by a regulator cause the rectifier to overcharge the system causing damage to the rectifier powerpack battery etc?

Click to expand...

Should not damage anything unless the battery is dead. In that case it could cause the stator and rectifier to overheat.

Re: Over reving a mercury electrical system without a regulator Question

Max, Most Outboards have stator coils and either rectifiers or voltage regulators. Usually the ign system is not directly conected to the charging system, so the behavior of the charging system will not affect the ign system. Maintenance free batteries are sometimes sealed. An unregulated charging system can overcharge a bit using up the water. If the battery can be refilled, it is suitable for use. I am not an EE, but I would think that the charging system would produce only slightly more amperage at overreving conditions. I would be surprized if it was linear.

Re: Over reving a mercury electrical system without a regulator Question

Chris1956 said:

Max, Most Outboards have stator coils and either rectifiers or voltage regulators. Usually the ign system is not directly conected to the charging system, so the behavior of the charging system will not affect the ign system. Maintenance free batteries are sometimes sealed. An unregulated charging system can overcharge a bit using up the water. If the battery can be refilled, it is suitable for use. I am not an EE, but I would think that the charging system would produce only slightly more amperage at overreving conditions. I would be surprized if it was linear.

Click to expand...

Chris,

The charging current is the difference between the battery voltage and the voltage output of the generator/alternator with the capacity of the charging circuit to be considered. The charging circuit has resistance as does the battery. The voltage differential pushes current through these two resistances in series as a function of Ohms Law: I (current) = Voltage divided by Resistance. As the voltage differential decreases, via a drop in rpm or a battery charging up, the current and energy entering the battery decrease as does the heat generated by the internal resistance of the battery.

Water boils out because another application of Ohm's law which is Power (watts i.e. heat generated by the process...energy dissipated like you burning natural gas in a stove to heat your house, or an electrical space heater) is proportional to current squared x resistance.

For small alternators, the internal resistance (due to design) limits the available charging current and regardless of the charge level of the battery, or it's size, it just can't put out enough current to do much damage, i.e. generate enough heat to dissipate the water in the electrolyte mix; hence boil over.

So even though the unregulated supply goes to 16 or 16.5 volts, it only gets there when the battery is fully charged and doesn't have the capacity to really harm it on small engines with low wattage charging circuits. On larger engines, like the numbers I got for engines of my group, then it could "possibly" be a problem.

The connection of the ignition system is via the voltage supplied to it from the battery. The triggers come from a different set of coils under the flywheel and the actual energy supplied to the plugs, in a CDI is 1/2 C(V squared) where V is the voltage to which the CDI storage capacitor is charged to as a result of the battery voltage at the time of charging.

Want more, ask.

Mark

Re: Over reving a mercury electrical system without a regulator Question

Thanks so much for all the info so far guys. So It wouldn,t make much of a difference if I use the deep cycle battery 650 cranking amps thats in my van as apossed to the little reg car batt with 450 or 500 cranking amps that i can add water too. I bought as I don,t use it for anything but to start the engine on the boat? Being said the battery acts as a regulator on these older system wouldn,t the deep cycle be a better regulator than the small one?

Re: Over reving a mercury electrical system without a regulator Question

Maxz695 said:

Thanks so much for all the info so far guys. So It wouldn,t make much of a difference if I use the deep cycle battery 650 cranking amps thats in my van as apossed to the little reg car batt with 450 or 500 cranking amps that i can add water too. I bought as I don,t use it for anything but to start the engine on the boat? Being said the battery acts as a regulator on these older system wouldn,t the deep cycle be a better regulator than the small one?

Click to expand...

Yes!