Adding an alternator to 6HP Tohatsu

MattFL

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Has anyone added an alternator to a 6HP Tohatsu, and was it strait forward? It seems they sell kits but I would love to hear from someone who has done it, or seen it done. This would be great to run some lights on our jon boat so the kids could fish at night.
 

km1125

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Aug 10, 2016
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Are you referring to the four strokes? I've done it on those. They don't generate a lot of power at idle, but are OK when up higher in the RPMs. It's pretty easy, you just have to pull the flywheel, so getting the flywheel nut off and using a puller on the flywheel is about the hardest part. To get to the flywheel you also have to pull off the pull-start assembly, but that's only three 10mm bolts.

You have to know which version you have. The older models (I think -A2 and before) only have one coil inside for the alternator, but I believe the newer ones have two. I don't think it changes the output though, as they are both rated for 60W (roughly 5A)

Depending on what you want to use it for, you may need a rectifier. If just used for incandescent lighting, you don't, but for LED lighting or charging the battery, you'd want/need the rectifier.

I've been playing around recently with mine and just added a full-wave rectifier to it. The stock one is just a diode, so you lose 50% of the output turning it to D.C. with just a diode. A full-wave rectifier allows the use of all the output but it does add a bit of voltage drop (about 0.7V). I've also just started to put a DC-to-DC converter so at low RPMs it would develop more voltage but I haven't tested the total output yet.
 

MattFL

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Thanks for the reply. It is a 4-stroke, I bought it new in 2012, model MFS6CDS. It would be just for lights. A full wave rectifier sounds like a great idea, there are a pile of them on Digikey, slap on a heatsink, bury in conformal coating and you're probably good for many years of fun! Where do the power wires come out from the motor?

Edit --> going by this page:

https://www.tohatsu.com/marine/int/a...pair_kits.html

It looks like I need part# 3GR-06128-0, which seems to sell over $250 at places that have it in stock, wow! And the rectifier kit is another $50, they are crazy.. Maybe I'll stick with batteries for now, unless a knock off appears.
 
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pvanv

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The Tohatsu rectifier is a rectifier/regulator, so you won't overcharge.
3GR061280MALTERNATOR KIT, F4/5/6C$257.98
3GR761600MRECTIFIER KIT, F4/5/6C$207.03
 

MattFL

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With those prices, I'm not sure if they're trying to actively discourage people from buying them, or if they think people who want/need them see money as no object!? I'm referring to the Tohatsu kits.
 

km1125

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Paul, maybe you can help me understand this. When I look at the parts manual for the A2 models, it shows a single alternator coil but when I look at the B/C model service manual, it shows a two coil alternator (see pic below). On the earlier models there is nowhere to put a second coil, as the ignition exciter coil is there, but on the later models that space is vacant and it appears you could use a dual coil. Do they actually do this or do all the models use the same single coil for an alternator?

Also, I do think the "rectifier/regulator" is just a simple rectifier, just by looking at the test data. The voltage on these alternators does not increase with RPM like a generator would and it basically "self regulates" to avoid overcharging a battery.

 

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km1125

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With those prices, I'm not sure if they're trying to actively discourage people from buying them, or if they think people who want/need them see money as no object!? I'm referring to the Tohatsu kits.

It's especially crazy because it's essentially the same as the exciter coil used for the ignition in the earlier models (but with heavier wire and less turns/in) and those they sell for ~$50.
 

MattFL

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I would bet that they use a shunt type regulator. These are super common on motorcycles, because they're simple, fairly reliable and cheap to make. When the voltage hits a pre-set limit, the regular just shunts the coil(s) to ground. When the voltage drops it un-shunts. It does this very very fast. Crude but effective.
 

pvanv

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Paul, maybe you can help me understand this. When I look at the parts manual for the A2 models, it shows a single alternator coil but when I look at the B/C model service manual, it shows a two coil alternator (see pic below). On the earlier models there is nowhere to put a second coil, as the ignition exciter coil is there, but on the later models that space is vacant and it appears you could use a dual coil. Do they actually do this or do all the models use the same single coil for an alternator?

Also, I do think the "rectifier/regulator" is just a simple rectifier, just by looking at the test data. The voltage on these alternators does not increase with RPM like a generator would and it basically "self regulates" to avoid overcharging a battery.


Both versions produce 60w max. The newer B/C version is dual coils. It's a 4-diode full-wave bridge rectifier. Even at low speeds, without a regulator, a full battery would eventually overcharge. Charging comes standard on the sailpro models.
 
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