Is a little Generator worth it?

[akin_alan]

I have a Tohatsu 9.8 outboard on my 30' 1974 Grampian sloop that I bought a few months ago. Very much enjoying the boat. My understanding is that the outboard charges the battery with 7 amps DC power.
I read the specs on Yamaha and Honda Generators. They put out a whopping 1000 Watts AC power! Well AC is something that I don't use much on my boat. DC is what I need. They only generate 7-8 amps DC power. 8amps x 12 volts = 96 watts DC.... I think that ain't much. I got three 90 (+-) amp batteries. Does that mean I got to run this generator for nearly 30 hours just to charge the batteries?

[Mechsmith]

I have only a 6 amp alternator on the outboard, but I also carry a 12V-35 amp gasoline powered portable just in case. You could also run a battery charger off one of the little 120 V chargers. Not efficient but it beats rowing.

The six amps has so far been enough if I start with fully charged batteries.

I use a battery isolator switch wired so that if I kill the one house battery. (Fall asleep while reading for instance) the other battery will still start the motor. Also I minimize my electricity use with a solar powered masthead anchor light.

LED running lights are on my wish list.

[whroeder]

Originally Posted by akin_alan

Does that mean I got to run this generator for nearly 30 hours just to charge the batteries?

Charging rate drops off as they charge. That, plus you won't get that peak charging rate, means it will take more than twice that long.

[k1vsk]

Not enough info to make an intelligent conclusion. You need to tell us how much power you have onboard (what is the cap of your battery bank?), how much power to typically draw from that bank, how long do you typically go without a full recharge, etc.
Buying a good (i.e., Honda) generator can be a great addition but it's impossible to advise without the above info to know if you need it.

[sailingdog]

I'd point out that the Tohatsu is only going to give you 7 amps when it is running full out... usually it will give less than 2-3 amps.

The small gasoline generators aren't really good for charging the batteries on a boat, since they have relatively low output. Using the AC side would make more sense, since you can run a fairly beefy AC battery charger with 1000 watts... one that puts out over 40 amps @ 14.4 VDC pretty easily.

If you have AGM batteries, then this might make sense, since you could get them back up to 80-85% of charge level relatively quickly. But, with wet cells, with their more limited current acceptance rates, charging them to the 80-85% level will take more time...

IMHO, you'd be better off, if you only use the boat on weekends or occasionally, rather than living aboard, to get a medium size solar panel to recharge the batteries. I've written a basic primer for solar power on boats which you can read here.

Originally Posted by akin_alan

I have a Tohatsu 9.8 outboard on my 30' 1974 Grampian sloop that I bought a few months ago. Very much enjoying the boat. My understanding is that the outboard charges the battery with 7 amps DC power.
I read the specs on Yamaha and Honda Generators. They put out a whopping 1000 Watts AC power! Well AC is something that I don't use much on my boat. DC is what I need. They only generate 7-8 amps DC power. 8amps x 12 volts = 96 watts DC.... I think that ain't much. I got three 90 (+-) amp batteries. Does that mean I got to run this generator for nearly 30 hours just to charge the batteries?

[mitiempo]

As stated above you could use the generator to power an ac charger. Best to keep the charger to about 35% of the generators output for the most efficient charging though. Some chargers don't get along that well with the waveform produced by many generators and will produce a lower amperage when the generator is producing near its max output.

But why go sailing to listen to a generator if you don't have to. With LED lighting and careful management, especially if you don't have any refrigeration or electronics like radar using power, a solar panel or two as mentioned above can supply all you need.

[Architeuthis]

Originally Posted by mitiempo

But why go sailing to listen to a generator if you don't have to. With LED lighting and careful management, especially if you don't have any refrigeration or electronics like radar using power, a solar panel or two as mentioned above can supply all you need.

Dad? LOL just kidding but I know the argument well.

Seriously you do not need the LED lighting. My Dad did the loop from Thunder Bay to Cuba with only a couple of very old cheap wet cell batteries. It can be done.

If you get rid of all the stuff that uses electricity, even oil lamps can be used for navigation, not only will it be cheaper but it is much more like "real" sailing.

Of course to be a real sailor you have to get rid of that engine and be towed into harbours, with a row boat I assume, just like the old days.

So for some, no generator, no engine, for others they wouldn't be on the water without one.

[jaschrumpf]

Originally Posted by akin_alan

I have a Tohatsu 9.8 outboard on my 30' 1974 Grampian sloop that I bought a few months ago. Very much enjoying the boat. My understanding is that the outboard charges the battery with 7 amps DC power.
I read the specs on Yamaha and Honda Generators. They put out a whopping 1000 Watts AC power! Well AC is something that I don't use much on my boat. DC is what I need. They only generate 7-8 amps DC power. 8amps x 12 volts = 96 watts DC.... I think that ain't much. I got three 90 (+-) amp batteries. Does that mean I got to run this generator for nearly 30 hours just to charge the batteries?

I'm a bit confused with the power conversion. A Honda 1000W generator puts out 1000W at 120V AC. 1W = 1A X 1V, so in this case:

1000W = ~8A X 120V

If you replace that 120V with 12V and keep the wattage the same, don't you get:

1000W = ~80A X 12V

The power output is the wattage, and it should remain constant, shouldn't it? If you lower the voltage, doesn't the amperage increase? Or is this one of those AC/DC things?

[Architeuthis]

You are correct 1000w is 8amp at 120v and 80 at 12v.

With AC it is better to use KVA to avoid the confusion. To get Watts in an AC circuit you need to know the Power Factor (PF) but lots of us just us Watts which means we are using a PF of 1 which doesn't really happen in real life but close enough.

In other words I understood the OP was referring to the DC winding that comes with many generators which is limited to about 8 amps at 12volts, and as pointed out rarely gives you even that.

[mitiempo]

A lot of generators like the Honda have separate DC outputs and this not a very high amp output. These DC outputs cannot be used simultaneously with the AC outputs.