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Old 07-02-2008, 12:33   #1
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Outboard alternator question

I have a 30hp Tohatsu outboard on my catamaran. The cables for the starter motor/alternator run directly to my batteries. Is this normal? Should the alternator be running through some sort of charge controller?
I notice that the higher the RPMs on the engine, the higher my voltage reads on my battery bank. Thanks in advance.
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Old 08-02-2008, 05:49   #2
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The alternator output, you describe, sounds like an “unregulated power supply”, intended to operate running lights and gauges - not provide battery charging.
Accordingly, I’d agree with your suspicion that you would be advised to install a voltage regulator/charge controller.
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Old 08-02-2008, 14:12   #3
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There may be a regulator already installed and it could be surging with the RPM's. See the link below for your motor.

Tohatsu Outboards: Authorized North American Distributor for Tohatsu Outboards, Parts, & Accessories.
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Old 08-02-2008, 18:22   #4
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Originally Posted by Tnflakbait View Post
I have a 30hp Tohatsu outboard on my catamaran. The cables for the starter motor/alternator run directly to my batteries. Is this normal? Should the alternator be running through some sort of charge controller?
I notice that the higher the RPMs on the engine, the higher my voltage reads on my battery bank. Thanks in advance.
More details please. What makes you think the alternator is wired directly to the starter? On my inboard diesel the (internally regulated) alternator output is brought to the starter motor post in the wiring harness, so the main cable to the battery goes to the starter motor and nothing else ( or actually everything else). A 30 hp Tohatsu manual that delmarrey linked shows the alternator output goes to a rectifier/regulator module, and the output of that goes to the starter post.

How high is the voltage getting? My guess would be that the regulator is set to around 14.4 Volts. The alternators on most outboards are pretty small, so a big bank of batteries relatively discharged would be accepting all the current that the alternator would put out, at that point the voltage is determined by the state of charge of the battery and the amount of current applied. Current output of the alternator will not be max until the engine reaches a certain rpm, so voltage will also vary due to engine speed. Once the batteries are charged enough to hit the 14.4 volts, then the regulator would limit current flow to not exceed that voltage.

If the voltage is getting much higher than above, then I would suspect a broken regulator.

To really troubleshoot, add an ammeter and voltmeter (make sure you know where and how), find out from the manual the max output of the alternator, rpm needed for full output, and voltage at which the regulator kicks in. See if everyone is meeting specs.

John
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Old 08-02-2008, 18:37   #5
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First invest $20 in a digital multimeter from Walmart or Target. Check the voltage at the battery, if it never exceeds 14.4 volts then don't worry about it. Odds are that your alternator puts out so little power, that it can't get the battery high enough to damage it.

But first, the number from the multimeter will tell you what's possible.
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Old 08-02-2008, 18:44   #6
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The alternator output, you describe, sounds like an “unregulated power supply”, intended to operate running lights and gauges - not provide battery charging.
Accordingly, I’d agree with your suspicion that you would be advised to install a voltage regulator/charge controller.

If you mean that you could connect an unregulated alternator to your lights without a battery in the circuit, I disagree. Our club had 6 hp outboards with unregulated outputs. Most small outboards had (have?) unregulated outputs. Once when I went to use the boat, a few of the bulbs didn't work, they had a beautiful silver mirror coating on the inside of the bulb. An unregulated alternator is a current source. So it puts out the current it is designed for and the voltage will vary to make that happen. The voltage rose until the filaments evaporated and plated out on the cold glass bulb.

The battery in the circuit provides the sink to regulate the voltage. They don't bother putting on a regulator because the current output is (theoretically) small enough that you won't over charge your battery.

If you meant something else then "never mind!"

John
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Old 08-02-2008, 19:40   #7
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Thanks for all the replys.

"What makes you think the alternator is wired directly to the starter?"

When I run the engine the voltage gets as high as 16 volts on the battery volt meter. This seems high to me. This weekend Ill disconnect it while running and test it with the multi meter.

Update soon.
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Old 08-02-2008, 21:42   #8
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John-
The silver coating in your bulbs can, and often does, mean they are getting LOW voltage not high voltage. With high voltage the capsule heats up enough to keep the metal in vapor form and it actually rejoins the filament--at least on halogen bulbs and often on plain tungsten ones. With low voltage, the glass never gets hot enough so the metal vapor mirror plates it, and then the filament burns out. Look at an old "instrumentation" bulb and you will see this, they run cold for long life--with a very thick filament.

Also, don't assume an "alternator" is an alternator. The word is bandied about by many companies to mean all kinds of alternators, generators, and any kind of hybrid you can think of. An unregulated automobile alternator is not just a current source, it can easily put out 17VDC and higher voltages, while the actual current that it can put it is very much limited by the physical design of the coils and the speed it is running at. Case in point, a 110-amp auto alternator may only put out 20A at idle speeds and not put out 100A until it reaches 6-8000rpm shaft speeds.

Back to flakbait's problem: If he's seeing 16V on a real meter (not some $10 speed shop gauge<G>) then that's too much for a battery. Many outboards use a MAGNETO (which is a generator) and no regulation with that. If that's what he has, he'd probably need a dump regulator for the battery.

Sometimes these systems are designed cheap and dirty but for reasons. Magnetos are lightweight, cheap and reliable with comparably high outputs, and if the boat has thin cheap wiring to the nav lights...the 16V may drop to 14.4 volts before it reaches the bulbs anyway. Making everyone but the battery happy.<G> There might be method in the madness.
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Old 10-02-2008, 19:16   #9
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John-
The silver coating in your bulbs can, and often does, mean they are getting LOW voltage not high voltage. With high voltage the capsule heats up enough to keep the metal in vapor form and it actually rejoins the filament--at least on halogen bulbs and often on plain tungsten ones. With low voltage, the glass never gets hot enough so the metal vapor mirror plates it, and then the filament burns out. Look at an old "instrumentation" bulb and you will see this, they run cold for long life--with a very thick filament.
Yes I've seen those bulbs, they look like they had dirt on the inside of the glass. That was not what I was talking about, the entire surface of what I saw was coated. If you start out with a cold bulb, apply enough power to vaporize the filament almost instantly, then the glass hasn't had enough time to heat up. This had happened more than a decade ago and I didn't verify things that I was told at the time, so I decided to try an experiment. Our club now has Hondas. I measured the voltage output with the engine revved up, one engine reached 25 volts, the other 30 volts, unloaded, into a digital voltmeter. I attached a 3 watt, 12 volt bulb to the output, no battery was in the system. I measured 3 amps flowing through the bulb with the engine revved up, a 3 watt bulb should draw 1/4 amp at 12 volts. The bulb was very bright, but it did not die. I should have measured the voltage with the bulb in the circuit but I forgot. Our club no longer has the Evinrudes we used to have. I have been told by more than one person that they can put out close to 90 volts, unloaded. If I find someone with an Evinrude or Johnson I'll try to get a measurement. I couldn't find an outboard reference, but I did find a motorcycle reference. Motorcycles have similar permanent magnet alternators. From: TUNING YOUR PERMANENT MAGNET ALTERNATOR CHARGING SYSTEM
"In the case of the 3-wire alternator, you want to see the same voltage from all 3 possible combinations of output wires. It could be quite high - my SR500 amazed me with open voltages of over 90 VAC! "

If we assume that the voltage is possible, I then decided to use a source close to that value, I plugged it in the 120 volt outlet at home. The result was a bulb plated as I remembered in the past. See the pictures below. Another experiment I might try is a higher wattage bulb, so lower resistance, more power dissapated. Watts=I^2*R. Might be able to get the Honda to do the job.


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Originally Posted by hellosailor View Post
Also, don't assume an "alternator" is an alternator. The word is bandied about by many companies to mean all kinds of alternators, generators, and any kind of hybrid you can think of. An unregulated automobile alternator is not just a current source, it can easily put out 17VDC and higher voltages, while the actual current that it can put it is very much limited by the physical design of the coils and the speed it is running at. Case in point, a 110-amp auto alternator may only put out 20A at idle speeds and not put out 100A until it reaches 6-8000rpm shaft speeds.
Ok, I was being sloppy. If the alternator rpm is high enough such that the output current curve is essentially flat.
Alternator output curve:
Output Curve -- 150A Welding Power Generator

Once again there are physical limitations, but an unloaded unregulated car alternator, I believe is going to put out a lot more than 17 volts.

Here's a permanent magnet car style alternator. It puts out 100 volts unloaded.

Wind Blue Motor Hydro Permanent Magnet Alternator

Quote:
Originally Posted by hellosailor View Post
Back to flakbait's problem: If he's seeing 16V on a real meter (not some $10 speed shop gauge<G>) then that's too much for a battery. Many outboards use a MAGNETO (which is a generator) and no regulation with that. If that's what he has, he'd probably need a dump regulator for the battery.
Depends on where you come from and what your colloquialisms are.

generator - definition of generator by the Free Online Dictionary, Thesaurus and Encyclopedia.
Generator: machine that turns mechanical energy into electrical.

Where I come from with reference to a car, a generator is a device with a commutator that puts out DC. And a Magneto refers specifically to a device with a permanent magnet to make the spark for your engine.
Probably since I've only worked on small outboards, I've never seen anything but a permanent magnet alternator in one.

Since flakbait didn't give a model number, we'll have to guess, but the owner's manuals that delmarrey linked showed that the 25 and 30 hp models have a regulator so something is broken on his system.

Quote:
Originally Posted by hellosailor View Post
Sometimes these systems are designed cheap and dirty but for reasons. Magnetos are lightweight, cheap and reliable with comparably high outputs, and if the boat has thin cheap wiring to the nav lights...the 16V may drop to 14.4 volts before it reaches the bulbs anyway. Making everyone but the battery happy.<G> There might be method in the madness.
The three photos are: bulb new, bulb with some filament speckles deposited on the top after running at 3 amps, and plated out bulb from being plugged into 120 volts.

John
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Old 10-02-2008, 20:36   #10
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"one engine reached 25 volts, the other 30 volts, unloaded, into a digital voltmeter. "
Now THAT's a mistake, using an unloaded meter as a test. When I was testing solar panels I could get an easy 12-14 volts from a panel into an unloaded high impedance meter. Connect a real load, like a battery, and that 14 volts plummeted to 2-3 volts.

It is always interesting to see the other points of view--but testing into a high impedance test instrument, without a load, is just going to mislead you.

I find the cleverness and versatility in charging systems to be at times ingenius. And at other times, I'm convinced certain engineers and manufacturers from two certain former Axis powers are still real pissed about losing WW2, and they're just doing things to screw us over.

I say two, because I'm convinced the Italian engineers really just couldn't DO any better than Fiat.<G>
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Old 10-02-2008, 22:15   #11
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Originally Posted by hellosailor View Post
"one engine reached 25 volts, the other 30 volts, unloaded, into a digital voltmeter. "
Now THAT's a mistake, using an unloaded meter as a test. When I was testing solar panels I could get an easy 12-14 volts from a panel into an unloaded high impedance meter. Connect a real load, like a battery, and that 14 volts plummeted to 2-3 volts.

It is always interesting to see the other points of view--but testing into a high impedance test instrument, without a load, is just going to mislead you.

I find the cleverness and versatility in charging systems to be at times ingenius. And at other times, I'm convinced certain engineers and manufacturers from two certain former Axis powers are still real pissed about losing WW2, and they're just doing things to screw us over.

I say two, because I'm convinced the Italian engineers really just couldn't DO any better than Fiat.<G>
Not a mistake, kind of a major point. Gord said that an unregulated alternator was for running lights and gages, not charging batteries. I took that to mean, not have a battery in the system. If I took that wrong, and he meant to have a battery, just not provide much useful charge to it, then my warning wasn't needed. If you plug that 10 hp Honda into the boats electrical system with no battery hooked up, then none of your lights are going to last very long, that 3 watt bulb had 3 amps going through it and was very bright, and this was outside in the daytime. On an old Evinrude they will just immediately burn out, as I tried to illustrate with the mirrored bulb that puzzled me all those years ago.


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Old 11-02-2008, 03:40   #12
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Not a mistake, kind of a major point. Gord said that an unregulated alternator was for running lights and gages, not charging batteries. I took that to mean, not have a battery in the system. If I took that wrong, and he meant to have a battery, just not provide much useful charge to it, then my warning wasn't needed. If you plug that 10 hp Honda into the boats electrical system with no battery hooked up, then none of your lights are going to last very long ...John
John’s valid point is very important, as I failed* to fully explain the manufacturers’ intent.
* [I can neither explain, nor defend., the commercial and/or engineering decisions of many manufacturers]

It might be reasonable to assume the presence of a battery, when the outboard is equipped with an electric start. In this case the battery acts as a buffer, effectively regulating the voltage applied to the lighting.

However, unregulated power supplies are most often found on smaller, pull start outboards, which may or (more often) may not have a battery connected. In these common examples, the lamps will have significantly reduced life, due to overvoltage resulting from running the engine at WOT.
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