Nissan/Tohatsu 9.8 charging system

waltsn · #1 (**permalink**) 12-09-2009

Ive got on order a new Nissan 9.8 four stroke.

This outboard looks like it has the same sort of magneto - rectifier setup my current 1990 Honda BF8 outboard does. In larger outboards and inboards, the charging system has a regulator which has feedback to the alternator to control how much charge is being put out depending on the battery voltage. This also makes the charging less dependent of RPM. The magneto - rectifier on these smaller outboard has no voltage feedback.

So first question is to confirm the charging system in this Nissan 4sk 9.8 hp outboard has no regulator (looks like it to me from the schematic in the manual).

Second, assuming a magneto - rectifier setup, I have seen an RPM dependent charge output from my old Honda BF8 (I have a linklite charge monitor). Im assuming the new Nissan 9.8 will do the same.

However, I "think" I may have also observed somewhat of a battery voltage dependence on the charging. Ie, as the battery voltage rises, the charge output went down. But Im just not sure and I also have seen my old Honda put out over 20 volts when operated into just a resistive load - ie, this was about the "open circuit" output of the charger.

Im worried about all this because there is one trip I do where I motor a lot (Lake Powell) and Im already generating all the charge I need with 60 watts of solar. Im wondering if I have some chance of over charging the batteries because the outboard has no regulator. On the old Honda without electric start, no problem, just dont connect the charging system for this trip. But the new outboard has electric start which needs the battery to be connected to be started and its dangerous to the rectifier to disconnect the battery after the outboard is running.. Id rather avoid the aftermarket regulators which just put a load on the sytem if the battery voltage gets too high.

I may do more of a controlled experiment on the outboard where I vary the battery voltage at a constant RPM measuring current and also vary the RPM at a constant voltage and measure current- but its a bit of a pain to set this all up so no sure Ill actually get around to doing this...

tommays · #2 (**permalink**) 12-09-2009

They dont put out that much and if you were topped off you should be just be sure it wont dammage it to unplug the charge circut

waltsn · #3 (**permalink**) 12-09-2009

Probably right about the charge not being enough to worry about.. The last trip we did 185 miles over a week mostly motoring in a sailboat so the outboard is running for a LOT of hours. Otherwise, I wouldnt be concerned at all.

(edit - the "battery" being charged is also two 6 volt golf cart batteries - maybe another reason not to worry much about this)

pedcab · #4 (**permalink**) 12-09-2009

My Tohatsu 5hp, which I also use to charge my 35Ah battery (space limitations suck

, puts out (after the rectifier) anything from 7V (idle) to 18V(full rpm while in forward gear), this meaning it isn't very much of a reliable generator when it comes to keeping batteries safe and sound...

To prevent damage to the batteries (and to sensitive electronic equipment) I fitted my electrical instalation with simple DIY dumpload that "burns" excess voltage (through a high power lamp) whenever the battery reaches its fully loaded state, which I can preset in my dumpload circuit, of 13.8V.

This way my engine is always connected to the battery (altough it only outputs enough voltage to charge a battery if operated at more than half of its max RPM) and I don't have to worry about overcharging issues...

Just to finish, I'd like to point out that many instalations charged with an outboard don't get overcharged purely because of the sheer size of their battery banks that will take forever to charge with ans outboard. In Fulô, as said before, I use a 35Ah automotive battery (due to space limitations and weight saving issues) which WILL get overloaded and overheated IF the charging voltage coming from the outboard isn't somehow regulated...

Check our previous discussion over this subject of my regulator over HERE

Regards!

TohatsuGuru · #5 (**permalink**) 12-09-2009

No regulator and variable output depending on RPM. Don't worry about overcharging the battery as you don't have enough amps to matter.

RXBOT · #6 (**permalink**) 12-09-2009

Instead of a light 4 a dump load why not a coldplate in the icebox?

pedcab · #7 (**permalink**) 12-09-2009

Quote:

Originally Posted by TohatsuGuru

No regulator and variable output depending on RPM. Don't worry about overcharging the battery as you don't have enough amps to matter.

Are you absolutely certain on that? Sorry for the disbelief but, supposing that Tohatsu isn´t fouling us and that the output of the alternator is really 55W as stated, then a current of about 4A is expected and this, I belive, is enough to fry a small capacity battery such as mine.

I would love to ear a reasoned justification for not having to have a dump load/regulator fitted in this application so, if that's the case, please share your arguments with us all. I'm sure there are a lot of worried minds out there waiting to simplify their electrical instalations, including me who would be more than happy to dump the dump load

pedcab · #8 (**permalink**) 12-09-2009

Quote:

Originally Posted by RXBOT

Instead of a light 4 a dump load why not a coldplate in the icebox?

Or something else that has a consumption similar to the generator output...

PS: The circuit is also suitable for wind generators, high power solar panels, etc...

tommays · #9 (**permalink**) 12-09-2009

Its 55 watts at 6000 RPM or what ever the max rpm is , i sure try to not run mine at full

TohatsuGuru · #10 (**permalink**) 12-09-2009

Having re-read your first post I should probably withdraw the "don't worry about overcharging the battery as you don't have enough amps to matter."
It didn't register that you were only using a 35 amp battery. You need to consult the battery manufacturer and find out what the limit is for that individual battery. Having said that, you should still be fine. Your best or worse case scenario is a combined input to the battery of 12 amps. A standard 70 amp marine battery can handle that without question....And any 35 amp motorcycle or lawn tractor battery should be be able to handle that as well...Most can handle 20 to 25 amps, so I think your safe, but you need to double check. As to the necessity of having to regulate the voltage...Not really needed unless you have a very sensitive electronic suite on board. Thirty years ago electronics were a little less forgiving then they are today, but even then the damage was limited to the theoretical rather than the experienced. In general the practical effect of amperage to the battery is much less than the perceived possible effect. For a engineering explanation you would need to consult someone other than me. I'm a "rock doubles as a hammer" guy who thinks that electricity is magic