Electric generation, probably simple question!

[Ricco1]

I have a wind turbine along with solar panels. Also a generator and, obviously, the boat's engine, all can produce electricity.

 

My alternator is a smallish one, 40 Amps. If I watch this in action I see the v belt going round fairly fast, but certainly not at breakneck speed.

 

My wind turbine on the other hand, in a good wind, goes round at a fair old rate, certainly faster than the alternator assembly. The 'works' of the wind turbine are a serious bit of kit, weighing 20 kilos. On the other hand I can pick up any alternator very easily with one hand.

 

So my alternator, in a good wind, gives me 2 or 3 amp whilst the alternator chugs along giving 40 amps. Can anyone explain this difference?

[Phil Ambrose]

Your alternator is unlikely to give you anything like 40amps, to do so it would need to be running at a far faster rate than even a fast cruising speed. The potential output can only be achieved at a very high speed, the charging output rises in a steep curve plus the high output you hope for will also be governed by the SOC of your battery bank, as the SOC increases so the output of the alternator drops off.

Phil

[Ricco1]

Your alternator is unlikely to give you anything like 40amps, to do so it would need to be running at a far faster rate than even a fast cruising speed. The potential output can only be achieved at a very high speed, the charging output rises in a steep curve plus the high output you hope for will also be governed by the SOC of your battery bank, as the SOC increases so the output of the alternator drops off.

Phil

 

OK cheers for that but if we say the alternator produces 20amp that's 10 times as much as the wind turbine, which appears to spin much faster. That's my question really: the 'works' are substantial on both but the alternator produces much more. Is there another factor, more resistance or drag or something with the alternator?

[Phil Ambrose]

I am not knowledgeable enough with wind turbines to offer any useful info but I'm sure someone will be along shortly to help out.

Phil

[springy]

AIUI Its partly to do with getting the energy needed into the alternator to generate the power - an engine & belt driven alternator

will be able to deliver a fairly high torque into the generator electro-magnetics and hence higher current at a given voltage/rotation speed,

I suspect that the torque levels available from a modest (say less than 6 foot diameter) wind turbine blade would not be that high

in average conditions and hence if you tried to run high power electro-magnetics it would stall/run slowly

 

springy

[Loafer]

AIUI Its partly to do with getting the energy needed into the alternator to generate the power - an engine & belt driven alternator

will be able to deliver a fairly high torque into the generator electro-magnetics and hence higher current at a given voltage/rotation speed,

I suspect that the torque levels available from a modest (say less than 6 foot diameter) wind turbine blade would not be that high

in average conditions and hence if you tried to run high power electro-magnetics it would stall/run slowly

 

springy

 

He's right. There is far more motive force on your alternator, driven by a 40-odd HP engine, than any normal, boaty, wind gennies can ever hope to produce.

[Arthur Brown]

It's easy to transfer power from an engine to a generator and get lots of electricity out, it's a LOT less easy to couple a generator to the wind unless you have a massive fan (it's something to do with the swept area of the fan).

[nicknorman]

I doubt the wind turbine is spinning as fast as it looks and surely slower than the alternator. The difference in weight may be due to the wind genny having permanent magnets whereas the alternator has electromagnets.

[Ricco1]

Cheers for the answers, they explained it well.

[emlclcy]

the output from either requires the same input, 748watts = 1 horsepower I believe, from your engine or the wind

[Paul's Nulife4-2]

Hi Gang,

 

If memory serves, and as a very rough guide,I seam to remember my wind gen giving out something like

 

1 amp in 6 Knots of wind

2 amp in 10 knots of wind

Frequently

 

5 amp in 16 Knots of wind

Occasionally

 

7 or 8 amp in 20 knots of wind

Rare, But always welcomed

 

On a Average 24hr period I get anything up to around the 25 / 30 Amp Hrs from my Wind Generator, Tends to be more in the Winter months.

I get again on Average anything up to around the 20 / 30 Amp Hrs from my Solar over the same time, But Tends to be Less over the Winter months.

So say 40 / 60 Amp Hrs put back into my Battery over a 24 He period From my small 120w Solar, and Wind Generator combined.

But again, these figures can vary hugely depending on Battery SOC, and power requirements at the time, just as much as the Weather conditions !, all I can say is,,,My system is what I consider balanced for me, works for my style of cruising and livaboard life.

I got thease figures using my Wind speed instrument before it broke some time ago, that was mounted on my wheel house roof, so now I just let it do it's thing and have got a Grn led when it's putting amps out, a Yellow led when the Regular is beginning to cut in and a red led when it's off,,

What RPM that is ,ain't got a clue sorry, but maybe with a spot of paint on the Blade, and the use of a Car Timing Strobe Gun you could get some RPM results !.

Edited June 4, 2015 by Paul's Nulife4-2

[Arthur Brown]

One of my non boat friends has an off grid house entirely supplied by a three blade windmill.

[Chewbacka]

Your 40A alternator is about 500w at full output, which with losses will take about 1 horse power from the engine.

Your wind turbine is probably not that big so will in a good wind be rated at about 50W. If you want more power out you need more power in which is a much big set of blades and an alternator to match.

[Peter-Bullfinch]

I have had 200w of solar plus an mppt controller on my boat now for quite a while. It all works rather well. I keep a careful note of fuel consumption and it used to be a small fraction over one litre per hour. Now it seems to have dropped to a fraction under a litre per hour.

Four leisure batteries and a 70amp alternator.

Is it perhaps as I get older I'm unconsciously going slower or could the solar set up be reducing fuel consumption?

[Paul's Nulife4-2]

I have had 200w of solar plus an mppt controller on my boat now for quite a while. It all works rather well. I keep a careful note of fuel consumption and it used to be a small fraction over one litre per hour. Now it seems to have dropped to a fraction under a litre per hour.

Four leisure batteries and a 70amp alternator.

Is it perhaps as I get older I'm unconsciously going slower or could the solar set up be reducing fuel consumption?

Maybe a combination of the two lol.

 

To be fair, if your solar stops you fireing up the iron horse even just once a week for the sole purpose to charge your batteries, then it's a winner !. But with a Good, well fitted solar / Wind system balanced to your needs is invested in, then you should be almost self sufficient in as far as your power need go. I am !.

Edited June 4, 2015 by Paul's Nulife4-2

[Phil Ambrose]

Paul is correct, balanced to your needs is the pertinent phrase. So often I hear people moan about their solar set up and when I ask them a few questions it becomes apparent that what they have installed is totally inadequate, in short they expect miracles and are not prepared to lay out on a system that works for them.

Phil

[larkshall]

Don't forget your alternators may have different windings. Some are wound to produce optimum power at 3k rpm, others at 1.5k. Wind turbines (bigger ones) incorporate gearing. The bigger the fan swept area the lower the rpm, but the more shaft horsepower output. This output speed is then geared up to drive an alternator at the specified operating speed