Alternator + Inverter vs Generator

[Brent Swain]

Bolt an engine and an alternator form the auto wreckers to a piece of plywood and put a belt between them and you have something that will charge your batteries, run your power tools and weld. If the alternator quits you can get another from the auto wreckers for $35.

[ctsbillc]

I think is a boat comes with a generator, all is well and good, but I've got to agree installing one is an expensive proposition, and a heavy one.

The down side of the alternator aproach is efficiency, the Lundel alternator is a pretty basic thing and only gets 65% efficiency, and the batteries only give about 65% efficiency too, so you will burn more diesel, and eat up engine hours.

Running the engine like this you will NEVER get to the price of installing a diesel generator though, no mater how much you run it, so it is a good approach.

Solar is getting cheaper, and supplementing your big alternator with solar panels is a nice approach.

Bill

[staylucky]

Originally Posted by s/v Jedi

85 hours per month is an avg. of what, 2.5 to 3 hours per day. So, that costs $3 plus a gallon of diesel is $5 per day, giving me 15 kWh plus hot water (water heater is plumbed into the heat exchanger circuit). My batteries are topped up, I can make more than 100 gallons of water daily if I would need to, have a cool boat at night (no need to run A/C during the night, just take the heat of the day out before bed time), rinse my boat with fresh water saving me lots of stainless polishing, run laundry at will etc. I rather spend daily $5 on this luxury than on an extra Cuba Libre in the watering hole. Most cruisers I meet complaining about genset costs spend a lot more in the bar every day!

nick,

it sounds like you have had many happy years and hours running the coolant loop of your northern lights 6kw genset to your water heater. i am wanting to do the same thing, but northern lights has recommended that i don't because such a small generator will have trouble getting to and maintaining operating temperature.

do you have problems getting up to temp, or any other problems, with this setup? any complications or extra maintenance issues, or tips on setting it up?

sorry to dredge up an old thread. thanks,

chris

[smac999]

Originally Posted by ViribusUnitis

Yet I never see this. Why is that?

pretty much every boat I work on gets an inverter installed. generators suck. they are noisy at anchor. but we don't need A/C up here. we open the windows. if you need A/C you're pretty much stuck with a gen.


though having both is best. so you can run gen for an hour a day if needed to recharge if your boat is not moving for a a while.


edit: just noticed how old this thread was...

[s/v Jedi]

Originally Posted by staylucky

nick,

it sounds like you have had many happy years and hours running the coolant loop of your northern lights 6kw genset to your water heater. i am wanting to do the same thing, but northern lights has recommended that i don't because such a small generator will have trouble getting to and maintaining operating temperature.

do you have problems getting up to temp, or any other problems, with this setup? any complications or extra maintenance issues, or tips on setting it up?

sorry to dredge up an old thread. thanks,

chris

Northern Lights doesn't know what they are talking about. I am using a 40 liter Isotherm and don't even notice it for temperature. The thermostat controls temperature and heat goes to the water heater instead of overboard the raw water. The return from the waterheater is still pretty hot.

[valhalla360]

Originally Posted by s/v Jedi

I have noticed that it is standard practice in the USA to heat water with the AC powered electric element. In the EU, every boat uses the heat exchanger in the water heater instead, plumbing it into the genset or engine coolant loop.

It's quite common to plumb into the engine cooling system in the USA. Of course dock power in the USA is typically cheap or free, so using electric water heating is more popular.

The problem with using the main engine as a generator and using the cooling system to heat water is the engine may never heat up enough when just idling to charge the batteries.

[valhalla360]

Back to the OP:

What are you trying to run and for how long?
What size boat do you have?
What is the make and model of the main propulsion engine?

If you are running the air/con 24/7, a generator starts making a lot of sense.
If you don't even have air/con and most of your loads are fairly small, you probalby don't need 5000watts of power. A solar power system may be sufficent with a smaller inverter.
Does the engine have enough excess power to pull several HP for electic generation?

[Lepke]

My boat came with 2 generators. The previous owner ran one all the time, often with a light load. Both had glazed cylinder walls from running at speed under light load. The same would happen to a main running at high idle or faster on a light load. I had to rebuild both the generator engines.
Now I have a 120/240 inverter. When running the mains, one charges the starting batteries and the other does the inverter banks. All ac goes thru the inverter. If I have shore power or a generator is running the inverter charges the batteries. When ac is cut off, the inverter switches over to the batteries. When the batteries get low it starts one of the generators. I almost never use the generators unless I'm anchored for a couple days.

[wayne.b]

Originally Posted by neelie

I am equipped the traditional way, i.e. diesel genset and smallish engine alternators but am reconsidering the other paths to electrical heaven.

One idea I am mulling over is switchable 300A Alternators driven by the main engines and a portable petrol generator (e.g. Honda EU3000i or maybe even the 2000? ) for the odd days that you need airconditioning and as a backup charging device.

This seems like a cost, space and weight efficient solution.

So far, the main drawback I see is the need to store 30 gallons of petrol.

Anyone else see other drawbacks?

===

Don't underestimate the power required to drive a 300 amp alternator. I have one mounted on my port side engine, a 280 hp diesel. It is driven by 3 belts and required a custom made alternator mount and adjustment arm. When the alternator kicks in to recharge a 1,000 amp-hour battery bank, there is a noticeable "grunt" from the engine and a small drop in RPMs. I installed the large alternator to eliminate the need for running a generator while underway and that goal has been met. We can run any single high powered load such as the microwave, toaster oven, hair drier or stove top. Of course it also does a good job of recharging the inverter bank while underway and that has done a lot to minimize generator time.