Originally Posted by valhalla360
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Agree about the alternators. They are Ok for topping up the batteries occasionally when the solar isn't keeping up but for dedicated heavy duty use, a purpose built generator makes more sense.
If I didn't answer this before -- it is important to note that there are alternators, and then there are alternators
Car-type alternators which are standard fit on marine
diesels are not made for bulk power production. They cannot put out their rated output for long, and are not made for high temperature operation. You will burn them up if you try to get maximum output out of them on a continuous basis. That's because a car's alternator has an easy life -- replaces a very small amount of charge lost
during starting, and runs on-board loads. There are no deep-discharge battery
banks on cars. So they are designed and built accordingly, and not for the way we use them.
bus type alternators are totally different. These massive beasts are designed and intended to produce bulk power, and are rated to do it in high ambient temperatures, 100C and more. These weigh up to 30 or 40 pounds and are massively built. They will produce their full rated output 24/7/365 even in 200 degrees F conditions.
These devices are especially good for cruising because they are simple, relatively cheap
, and easy to repair using cheap
and highly standardized parts
. You can carry an entire complete spare one without too much trouble, or don't even bother because any third world auto electric shop can fix it, or carry the few spares involved and fix it yourself.
As someone above noted, you have to be careful not to exceed the specs for front power takeoff, if you're driving one of these from the front pulley of a main engine. For my engine, that's about 5 horsepower, so a bit of margin of error over the 2.5kW output of my secondary alternator. I reckon if you were designing such an installation
from scratch, you could mount two of them -- one on either side of the main engine -- in order to even out the loads and eliminate the side loading issue.
A couple of people in this thread were arguing for normal, heavy duty AC generators -- that's also a pretty good solution IMHO. If it breaks, it's a lot harder to repair than a school
bus alternator, but in my experience, these are very reliable.
It helps if you're using 230v AC power, because the 230v 50hz versions of these generators are de-rated by about 20%, so both the engine and the generator head
are producing only 80% of the power they were designed for. One great help for reliability
is also using a charger/inverter with power boost, which allows you to strictly limit the amount of power you take from the generator, preventing it from ever being overloaded. I leave mine set on 25 amps, so de-rated AGAIN. I am hoping that the generator head
will last more or less forever, used like that.
A few people have come on here advocating solar, although that was not the question. Solar is the IDEAL power source, but only IF you can afford the windage and find space to mount enough solar to meet your power budget
, AND if you're using lead acid batteries. Neither of these will be true on my next boat. My next boat will be very low windage for good upwind performance, with dinghy
kept below deck
etc. I also expect I will be using LiFePo batteries, which work really well with large generator capacity. So I will concentrate on mechanical generation as the main power source.
With LiFePo batteries, you might not even need to run the generator much, because you can get a full charge incidental to even short motoring, if you have big enough alternators on the main engine. In fact, the generator becomes less and less important, because charging
with the main engine becomes much more efficient. If you're taking 5kW off your main engine from large dual alternators, this is already a decent load on the engine, and you won't need to run it for long -- a far cry from running the main engine for hours with a small alternator trying to charge up lead acid batteries.
By the very same principle, charging with a heavy duty AC generator also becomes much more efficient, with LiFePo batteries, due to the shorter generator runs.