[waltsn]

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]

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]

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]

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]

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]

dump load

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

 

[pedcab]

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]

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]

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

 

[TohatsuGuru]

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

 

[pedcab]

Well, not quite magic, but it sure can't be seen flowing arround until it starts burning something so sometimes it sneaks from where you least expect it

My boat has 40+ years and I suspect the electronics on board to have arround 20 (a 1st generation electronic autopilot Autohelm1000 and a 1st generation electronic bidata), thats where my fears come from . The GPS and VHF are handheld units and run independent from the onboard electric circuit.

Furthermore I do usually run my outboard at high RPM, slightly over three quarters of max RPM, since I experimented that to be the "economic cruise" speed, burning arround 1,8 to 2L/hour at arround 7knots. That and because I've discovered from previous experience as an Optimist dinghy coach, with many thousand outboard operating hours, that Tohatsu 2stroke outboards are like diesels: They like to be pushed hard and don't get along very well with low RPMs for long periods, they tend to choke and smoke a lot, so mine gets "punished" as often as I can and I don't worry very much about it since those Japanese guys really know the way to do it...

Thanks you for your suggestions which are always welcome coming from a professional...

 

[waltsn]

There are two different outboard / batteries in this thread. One is a smaller battery but I have a 200 amp hour battery (the two six volt golf cart batteries). What I am worried about is that the 60 watts of solar is going to keep the batteries topped off - and then I run the outboard on top of this.

For a normal sailing day where the outboard might be on for 1/2 hour max, nothing to worry about. But on this one particular trip as an example, I did 185 miles in a week. At 6 mph, this is 31 hours of motoring - at 4 amps, this could be trying to put an extra 124 amp hours into the battery. However.. Im also using about 15 to 20 amp hours per day and the solar is also on a charge controller (so should shut off when the battery is full).. so once again, maybe its only the very first day of the trip I need to worry about - but only a little. Im also sort of liking the idea of some sort of electric cooler.

Tohatsu guru, maybe you can answer this. When I got my Honda a few years ago, the rectifier was blown. Im guessing this happened by disconnecting the alternator when the motor was running - creates a big voltage spike which can back bias the rectifier diodes and dammage them.

Is this still a concern with the new Nissan 9.8 or is there some protection built in for this now? Can you disconnect the Nissan/Tohatsu 9.8 battery wires while the engine is running? On the Honda, after I fixed the rectifier, I put a big capacitor on the outboard side of the charging wires and this allowed me to disconnect from the battery while running (the cap inhibits the big voltage spike). So I may do the same thing again - a switch and a big cap. But maybe its not a problem anymore?

Or, get the cooler/fridge load and have cold beer (or at least run it when Ive got the excess charge to make the ice last longer)

 

[TohatsuGuru]

On an engine with a regulator or one with a regulator/rectifier you need to keep the battery connected at all times or the load will blow the rectifier. Virtually all smaller engines, including the Nissan/Tohatsu 9.8 and a lot of larger ones,today, have done away with regulators as part of the factory equipment so you can run them disconnected. It's a crappy idea though for two reasons. First, if the two battery leads touch you can/will blow something on the engine. Fuse, CD module, etc. Second, if the two leads touch you can blow the boat up. IE Sparks by fumes from a fuel tank, etc. Don't worry about your golf cart batteries. They are very forgiving compared to all the newer styles and types of batteries and you can't damage them from the amps being generated on a small outboard.