Small outboard charging systems. (Tohatsu/Nissan in specific.)

[lydanynom]

So, I keep getting different answers from various sources regarding what sort of output I should expect from the charging system on my 6HP "Sail Pro" Tohatsu.

I know that this little magneto can not be expected to produce a lot of energy, and I know that the output is rectified but not regulated so I will see a the voltage swing with RPM.

What I do not know at this point is whether the fact that I am seeing less than a volt at idle is nominal, or the fact that I see over 20 volts at full throttle. With the sort of performance I am getting right now, I would not even be able to charge a 12 volt system until above 2/3 throttle. There is a very narrow RPM band of reasonable voltage but as throttle increases voltage quickly climbs to the point where I am going to damage batteries.

None of this is good. I am measuring using a meter connected directly to the leads coming off the motor. I had originally connected the system through a switch to a charge controller, but the charge controller has malfunctioned. I suspect damage due to the poor quality and unlikely voltages coming from the motor but I can not confirm that at this time.

Does anyone have direct experience with these motors who can give me some information about what output I should expect, and how I can make safe and productive use of it, that is not based on conjecture?

I would sure appreciate it.

[75R20]

I would guess that you are testing without a battery hooked up to the output.... And if you are that sounds like "normal" readings to me. With a battery hooked up, you will not see the 20 volt peaks that you now see as the battery will act as a damper to the output. In my use on other outboards in the same class, you will get nothing at idle and will need RPM to see any output. The manual should tell you what RPM you need to get charging current out of the motor.
Best of luck
Kary
S/V Mariah
#49080

[lydanynom]

Thanks for the reply.

It is not covered at all in the manual for the motor and there does not seem to be any supplementary information available. Tohatsu USA is one of the sources that has given me three different answers in three different calls.

I'm not certain what you mean by "the battery will act as a damper". Can you explain that in more detail? I need to be able to understand what is happening (or should be happening) electrically in order to figure out whether I should be able to run this through the charge controller or not, and if not to try and figure out what I am going to need to do to avoid overcharging the battery.

In the meantime, I'll try to get a chance in the next couple of days to get a battery charged up fully and then take some measurements with it in the circuit.

[Ulladh]

I have a Tohatsu 6hp with the charger-alternator, installed by shop I trust. They tested output at 3 to 6 amp at 1/4 to full throttle.

This is just a trickle charger, enough from about 1hr run time at 1/4 to 1/2 throttle for the depth sounder all day. Try to run more than that, like nav lights, on just an hours charge a day over a few days and the lights will dim.

If I have the nav lights on, it may only be for an hour or so at dusk as I return to the marina, and I may have the motor on for the last half hour, the lights get brighter when the motor is on.

It would take a lot of run time to over charge the battery.

[75R20]

don't use anything else in line with the charge circuit, as it is not intended/designed to use it. It won't help you. The battery acts as a damper because when recieving a "charge voltage" from the motors output, the voltage will raise as the battery voltage as the battery gets charged, but you will not see the peaks that you are seeing, as the battery won't see that immediate voltage, but the voltage will charge the battery. The current output is probably less than 6 amps, and that won't push the battery voltage up very fast.
best of luck
Kary
S/V Mariah
#49080

[lydanynom]

Originally Posted by Ulladh

I have a Tohatsu 6hp with the charger-alternator, installed by shop I trust. They tested output at 3 to 6 amp at 1/4 to full throttle.

That doesn't really mean anything without either a voltage or a wattage to go with it.

6 amps at 14 volts (a reasonable charge voltage) is 84 Watts, but Tohatsu specs this alternator at only 60 watts. 6 amps at 60 watts is 10 volts, but that is obviously not going to charge a 12 volt battery. Do you see the trouble? That is part of what I need to get sorted before any of this will begin to make sense.

It would take a lot of run time to over charge the battery.

Not if the battery is fully charged when you start the motor it wouldn't. Also, I am running single 33AH AGM's, not an array of big marine house batteries.

[lydanynom]

Originally Posted by 75R20

don't use anything else in line with the charge circuit, as it is not intended/designed to use it. It won't help you.

That isn't quite clear to me. The engine wouldn't be using the charge controller, the controller would be using the power output by the engine, which we have already established is unregulated on its own.

If there is any interaction beyond that going on then that is the explanation I am looking for. What in specific is happening there, electrically, that would cause a different result depending on what type of load I have in the circuit, the battery or the controller (or open, for that matter, when I just closed the circuit with the meter)?

The battery acts as a damper because when recieving a "charge voltage" from the motors output, the voltage will raise as the battery voltage as the battery gets charged,

Again, I'm sorry to be dense, but I'm not following this. That sounds to me like the way a regulated charging system works, like a real alternator, where there is feedback to the regulator based on the state of charge of the battery and the voltage is altered accordingly. But there is no mechanism for that in this system, is there?

[Ulladh]

I can't answer your more detailed question, don't know for sure what the volt and watt output was, and for my purposes don't need to know.

Charge the battery before I install at the start of the season, have enough juice throughout the season. Take the battery out for the winter, check fluid level, trickle charge overnight then again the night before I install in the spring.

Battery is a 5 year old Westmarine Seavolt 650, .

[TohatsuGuru]

I just have to ask...Why would you call Tohatsu three times and ask the same question? Why did you not believe the guy the first time? What were the three different answers?

[lydanynom]

Originally Posted by TohatsuGuru

I just have to ask...Why would you call Tohatsu three times and ask the same question? Why did you not believe the guy the first time? What were the three different answers?

First guy at Tohatsu, when I called prior to purchase, told me that it would be outputting about 14.5 volts at dead idle and the amperage would ramp up as speed increased. Second guy at Tohatsu, when I called back after purchase (from your company*, btw, who have been really fantastic but early on referred me to Tohatsu to get more detail on this topic) but before taking delivery because I wanted to clarify the maximum current spec, told me that the previous answer was incorrect and I would not see a constant voltage, but that I would always have "sufficient" charging voltage and current at anything above a dead idle. Third guy at Tohatsu, when I called again after taking the measurements I mentioned above to try to figure out why my charge controller seemed to have flaked out, told me that what I am seeing is exactly what I should expect and the "alternator" in these outboards is not really very useful.


At this point I don't know what to think and there are way too many variables in the mix. I would just like to get a solid understanding of what the engine should be doing and exactly how it is doing it, then from there hopefully figure out what I need to do to wire it into my system. I'd rather have it run through the charge controller so that I continue to get the benefits that offers, and if that will not work as-is I'd really like to understand why before I give up on it, because maybe a simple shunt to dump overvoltage or additional rectification to get to from a lumpy half-wave to something more closely resembling DC or some other simple add-on circuit is all that is needed.

*EDIT: Just noticed your sig. I guess not your company. ;-) Didn't you used to work for internetoutboards.com?