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San Juan 21 MKII
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Discussion Starter · #1 ·
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.
 

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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
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San Juan 21 MKII
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Discussion Starter · #3 ·
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.
 

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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.
 

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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
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San Juan 21 MKII
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Discussion Starter · #6 · (Edited)
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.
 

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San Juan 21 MKII
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Discussion Starter · #7 ·
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?
 

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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, .
 

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Misanthrope
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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?
 

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San Juan 21 MKII
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Discussion Starter · #10 · (Edited)
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?
 

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Any alternaror that is un regulated will have variable voltage which will increase as the RPM increase. When you hook up a battery it will act a resistance which will limit the voltage to 13 or 14 volts. you will need a amp meeter to test the amperage going to the battery which can only be done when the battery is connected to it.
 

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San Juan 21 MKII
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Discussion Starter · #12 ·
Any alternaror that is un regulated will have variable voltage which will increase as the RPM increase. When you hook up a battery it will act a resistance which will limit the voltage to 13 or 14 volts. you will need a amp meeter to test the amperage going to the battery which can only be done when the battery is connected to it.
Cool, thank you, knowing that it is a simple resistance calculation could help a lot. I must still be missing something, though. Google tells me that a small AGM like mine will tend to have an internal resistance of between 10 and 60 milliohms at its highest point, when fully charged. Tohatsu tells me that the max output of the system is 60 watts, and so ohms law tells me (dividing 60 by .05 and then taking the square root of the product) that the peak voltage this system can ever put into this battery will be less than 2v!

That's got to be wrong, but I can't find where my mistake is. Can you help me further?
 

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That is 2V on top of the battery voltage. So, if the battery is charged to 12.5V and you are putting enough current into it to drop 2V over the internal resistance ... then 14.5V is what you are going to have to apply to the terminals of the battery. That 2V is because there is current flowing into the battery. You will measure 14.5V outside the battery but the battery itself (internally) is still only charged to 12.5V. When you stop charging into the battery, you will once again measure 12.5V on the terminals of the battery (since the 2V went to 0V as current went to 0A).

Just remember, internal resistance is _not_ what produces the voltage that a battery is useful for. The battery itself (plates and electrolytes) produces that voltage. Internal resistance is what causes you to have to apply a increasingly higher voltage to the battery to charge it ... internal resistance is also what causes you to get an increasingly lower voltage from the battery as you draw higher currents from it.
 

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Something I wanted to point out. This motor doesn't have an alternator. An alternator, by definition, has voltage regulation. That is because the magnetic field on the rotor is produced by an electromagnet which has to be produced and controlled by the regulator circuitry. An un-regulated alternator wouldn't produce any voltage at all because there would be no electromagnetic field on the rotor. Granted, some forms of voltage regulation are fancier than others ... but alternators necessarily have some form of voltage regulation.

A magneto generator, which is what you have, doesn't have an electromagnet on the rotor. It has permanent (think refrigerator) magnets. There is no way to vary the strength of these magnets operationally. Therefore, voltage regulation within the magneto generator itself is not possible. The output voltage of a generator depends on 1. the strength of the magnetic field and 2. the speed of the rotor. Since you can't control #1 then output voltage is going to vary with #2 (as you've seen).

You can, technically, build some circuit (of various levels of complexity) to regulate the output of a magneto generator. However, it would be external to the generator and it would be, to simplify, inefficient.

The first answer you received, the tech was giving you a standard answer assuming he was talking about an alternator. Some people don't know enough to know there is a difference. He either fits in that category or didn't put enough thought in to realize you don't have an alternator.

The second answer was getting closer to the truth but "sufficient" charging current and voltage at anything above idle is a very loaded claim. What exactly is sufficient ... if you are measuring 10V without a battery connected then you certainly aren't going to be able to charge at that engine RPM when a battery is connected.
 

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San Juan 21 MKII
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Discussion Starter · #16 · (Edited)
That is 2V on top of the battery voltage. So, if the battery is charged to 12.5V and you are putting enough current into it to drop 2V over the internal resistance ... then 14.5V is what you are going to have to apply to the terminals of the battery. That 2V is because there is current flowing into the battery. You will measure 14.5V outside the battery but the battery itself (internally) is still only charged to 12.5V. When you stop charging into the battery, you will once again measure 12.5V on the terminals of the battery (since the 2V went to 0V as current went to 0A).
Okay, that's terrific. This and all your other comments really helps clear the fog away for me, thank you.

I guess the question now is how to determine whether it is safe to use this as a power source for the controller or, if it is not, whether I can make it so by adding additional smoothing or peak voltage limiting.

If I can't, then I am left with having to manually monitor the state of charge of the battery and connect or disconnect the engine from the circuit manually. Not the end of the world, but kind of a pain.
 

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San Juan 21 MKII
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Discussion Starter · #17 · (Edited)
The last answer from Tohatsu was the most correct and virtually everyone who has commented here has been correct as well. Your engine is behaving normally, the battery is acting as a inhibitor/regulator/governor/damper and mitigates the voltage flux on the outgoing current. The link below should make you feel at ease:

http://www.sailnet.com/forums/gear-maintenance/60424-nissan-tohatsu-9-8-charging-system.html
Thank you, that thread and the one it in turn links to are really helpful. They seem to confirm the need for concern, though, rather than make me feel at ease.

EDIT: Just found this thread as well; more concern but no real solution.

Outboard Charge Regulator - Yachting and Boating World Forums
 

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Man......It's just a battery.....You are wasting time that you could be spending on your boat.....If it overcharges....who cares...Replace the battery when it dies, as it is a consumable/disposible item..
GO SAILING

Kary
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San Juan 21 MKII
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Discussion Starter · #19 · (Edited)
I guess the question now is how to determine whether it is safe to use this as a power source for the controller
Well, I think I have answered this question as well, and that answer is no. The reason is that this is a shunt-type regulator that winds up carrying the full open-circuit high voltage output by the coil after the battery is charged. This is no doubt what fried it.

If I had a series-type regulator/controller, like this one, I would be in good shape.

I'll have to think about what I want to do next, switch controllers or add a separate component to tame the output from the engine.

75R20, there are so many things wrong with that post, I can't even begin to respond. ;-)
 

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Bombay Explorer 44
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An alternator, by definition, has voltage regulation. That is because the magnetic field on the rotor is produced by an electromagnet which has to be produced and controlled by the regulator circuitry. An un-regulated alternator wouldn't produce any voltage at all because there would be no electromagnetic field on the rotor. Granted, some forms of voltage regulation are fancier than others ... but alternators necessarily have some form of voltage regulation.
Being pedantic [ I was a lecturer/teacher ] and alternator does not HAVE to have a regulator. It is perfectly possible to set up any car/boat type alternator to produce an output that is not voltage regulated. In fact it is a type of shade tree test. At max rpm an output approaching 100 volts is possible [open circuit ] .
 
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