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Alternator Ouput n KW?

coozer - 29/9/08 at 12:31 PM

If I was to run an alternator at constant speed, say 2K 24 hours a day and use a 240v convertor how much power in KW would I get out of the setup?

I'm wondering if this would give me enough to power the house on stand by, ie the fridge etc when theres no in and make any sort of saving to my electric bill.

Is 2K fast enough to get the best out an alternator and how easy would it be to wire into the ring main of the house? Thinking about how a wind turbine wires into the house and gives it back to the grid.

Anything readily available to use that would be better than an alternator??

Any thoughts on power generation anyone??

Steve

paulf - 29/9/08 at 12:42 PM

I have thought about doing a similiar set up but also extracting the waste heat to heat water etc.
From what I could see the set up would not be very efficent unless you can collect all the waste heat and would need to run on heating oil if a diesel or natural gas to be cheap enough to run, petrol is no good as the tax is to high.
Looking at generator outputs and fuel consumption it seems the cheaper generators are very ineficent and i think a car alternator and inverter would be even less so, but if you controlled it to only run when there is a demand for both heat and power it may be worthwhile.
What is your 2000rpm power source?
Paul.

quote:
Originally posted by coozer
If I was to run an alternator at constant speed, say 2K 24 hours a day and use a 240v convertor how much power in KW would I get out of the setup?

I'm wondering if this would give me enough to power the house on stand by, ie the fridge etc when theres no in and make any sort of saving to my electric bill.

Is 2K fast enough to get the best out an alternator and how easy would it be to wire into the ring main of the house? Thinking about how a wind turbine wires into the house and gives it back to the grid.

Anything readily available to use that would be better than an alternator??

Any thoughts on power generation anyone??

Steve

Delinquent - 29/9/08 at 12:45 PM

quote:
Originally posted by coozer
Any thoughts on power generation anyone??

Generally still inefficient and not cost effective, unless you have a fast flowing river running through your back garden.

Alternators aren't that great as generators, due to various inefficiencies and rpm needed to work. Depends on what alternator but you could expect between 1kw and 1.5kw depending on efficiency (I'd guess no more than 80%)

[Edited on 29/9/08 by Delinquent]

Macbeast - 29/9/08 at 12:46 PM

What are you using to drive the alternator ? Petrol ? Think of the tax - it's got to be cheaper to take power from the mains.

If an alternator is reckoned to give out charging current of 50 amps, that would be 600 Watts. But I doubt if any car alternator could do that 24/7. And then you have to consider converter efficiency - say 80% ?

Got to be cheaper to buy a 1KW petrol generator to cover outages when mains fails. Connect it to back feed a 13 Amp socket HAVING REMEMBERED TO THROW THE MAIN BREAKER TO ISOLATE FROM INCOMING SUPPLY.

[Edited on 29/9/08 by Macbeast]

tegwin - 29/9/08 at 12:48 PM

Im guessing a small turbine or waterwheel could turn an alternator.....you need a big one off a diesel truck/4x4...

In theory the circuitry required to allow the alternator to suppliment the house supply when the demand is low would not be too difficult...but you are playing with a lot of power...which could cause fire/pain...

I think I would be inclined to use some form of battery between the inverter and turbine to help smooth out any iregularities...

And, if you removed the rectifier from the alternator you would already have AC....so just use a step up transformer....

coozer - 29/9/08 at 12:55 PM

My power source is free but a bit contentious

Not sure if it'll work but I'm going to give it a go just as an experiment. Was just wondering how much an alternator would give and if it was a viable enegry source.

The unit could be cooled in theory by the source

[Edited on 29/9/08 by coozer]

Macbeast - 29/9/08 at 12:56 PM

quote:

And, if you removed the rectifier from the alternator you would already have AC....so just use a step up transformer....

I wonder what the frequency would be though?

Are alternators 8-pole? Which would give you 267 Hz. Might make your clocks run a bit fast

quote:

My power source is free but a bit contentious

It's a hamster, isn't it ?

[Edited on 29/9/08 by Macbeast]

Delinquent - 29/9/08 at 12:57 PM

quote:
Originally posted by coozer
My power source is free but a bit contentious

Not sure if it'll work but I'm going to give it a go just as an experiment. Was just wondering how much an alternator would give and if it was a viable enegry source.

The unit could be cooled in theory by the source

How are the water company going to feel about you using this "free" energy that they pay for to create the pressure?

(I suggested something similar recently)

coozer - 29/9/08 at 01:02 PM

quote:

How are the water company going to feel about you using this "free" energy that they pay for to create the pressure?

How did you come to that conclusion??

richardlee237 - 29/9/08 at 01:02 PM
Alternative power sources are quite interesting but rarely practicable.

Using a car alternator you could get 500 watts or so but if you wanted this continuously it would substantially shorten the life.
Bung it through an inverter and you might get 400 watts of ac. Just about enough for half a kettle.
On top of that the local electricity company will not like you connecting to the mains as invertors are a source of harmonics in the distribution.

To power a house you need about 10 kw and to get that out of the wind is some propeller.
Even if you live by a river, to extract this sort of power you need a strong flow in a duct, just like a mill race.

If you are seriously looking at saving energy then home made solar heating panels from old radiators or fridge bits are the way to go.

People forget what an exceptionally well packged energy source oil is and it only becomes apparent when you look for other sources

Stott - 29/9/08 at 01:04 PM
Can't comment on the whole project, just the alternator bit:

In modern compact alternators efficiency at 1800 rpm is circa 30% as the torque required to generate a given current is great, they are more efficient at 6Krpm and above, only at these speeds would it be viable to use in the application you want

Taking the torque values for a given current output at differing speeds between 1800rpm and 10K has shown, in my experience no more than 73% efficiency, and that's a really good one, designed to be efficient rather than power productive. Most are low 60s. If you took a similar alternator from around the year 2000 say, and tested it, you could probably expect less than 50% efficiency.

Cut in speed is generally accepted to be around 1800-2000 rpm too, depending on manufacturer. Any lower than this and it wouldn't excite.

Edit: Forgot to say that if you could drive it and cool it (23 deg C) at 6Krpm you could get 3KW DC at about 50-55% efficiency out of a modern large alternator (off a big Dailm Chry vehicle or the like)
HTH

[Edited on 29/9/08 by Stott]

Mr Whippy - 29/9/08 at 01:10 PM
quote:
Originally posted by coozer
My power source is free but a bit contentious

5000 hamsters in a giant wheel is cruel!

tegwin - 29/9/08 at 01:11 PM
With a big enough photovoltaic array you could power a ground/airsource heatpump to provide heat for the house

Mr Whippy - 29/9/08 at 01:21 PM
quote:
Originally posted by tegwin
With a big enough photovoltaic array you could power a ground/airsource heatpump to provide heat for the house

why not just replace them with solar panel water heaters and use the hot water to heat the house? You can store the heated water in an insulated tank in the garden that is then pumped from during the night. What I was wanting to do for the next house.

smart51 - 29/9/08 at 01:23 PM
quote:
Originally posted by richardlee237
Using a car alternator you could get 500 watts or so but if you wanted this continuously it would substantially shorten the life.
Bung it through an inverter and you might get 400 watts of ac. Just about enough for half a kettle.

A 35A car alternator generating a fairly typical 14V or so delivers about 490W. If you get 400W out of an inverter, you're doing fairly well. An average kettle is between 2 and 3kW so your inverter delivers between 13% and 20% of a kettle's worth of power.

Your hour may use around 400W of quiescent power, that is when everything is switched off that you switch off. That leaves your central heating timer, your alarm clock, the clock on your microwave, the video on standby, all that stuff.

The telly might use 100W or more. The stereo perhaps 10W plus twice the power that goes out of the speakers. Other gizmos are about the same. Things that get hot use more power. An electric oven, a kettle, an iron, an electric fire, they're all between 1kW and 3kW. 3kW is about as much as you'll get out of a mains appliance.

If you have an alternative power generator connected to your houses mains, like a solar panel for instance, you can expect to save much of the quiescent current that your house consumes, which is a big part of your electricity bill. Don't expect the national grid to like it though.

What is the source of this free power?

tegwin - 29/9/08 at 01:37 PM
quote:
Originally posted by Mr Whippy

quote:
Originally posted by tegwin
With a big enough photovoltaic array you could power a ground/airsource heatpump to provide heat for the house

why not just replace them with solar panel water heaters and use the hot water to heat the house? You can store the heated water in an insulated tank in the garden that is then pumped from during the night. What I was wanting to do for the next house.

My understanding is that hotwater solar cells are not particularly efficient in the UK...Whereas ground/air heatpumps are more so...

I know I would rather have a ground source heatpump over a solar/gas/water type system...

smart51 - 29/9/08 at 01:39 PM
quote:
Originally posted by Mr Whippy
why not just replace them with solar panel water heaters and use the hot water to heat the house? You can store the heated water in an insulated tank in the garden that is then pumped from during the night. What I was wanting to do for the next house.

I had a couple of quotes for this work and the prices were astounding. Especially as you can buy a DIY kit of the same thing for about �10,000 less than the quoted prices. The actual cost saving was minimal too.

nstrug - 29/9/08 at 01:47 PM
You will need a rectifier/regulator, batteries and an inverter. If you can get the alternator speed up high enough for it to operate at an efficient level, it should all work.

Be careful to match the output of the rectifier/regulator, the rating of the batteries and the output of the inverter correctly otherwise bad things will happen.

You need to use a so-called "grid connect" inverter that will synchronise its output with the mains frequency.

Nick

Mr Whippy - 29/9/08 at 01:48 PM
I was actually going to make my own setup that will be in the garden. I looked into ground pumps and the only produced 1/3 above what was actually put into them. Solar heating a heavily insulated house (half buried foam insulated concrete dome) is very efficient.

http://static.monolithic.com/gallery/homes/index.html

smart51 - 29/9/08 at 01:58 PM
quote:
Originally posted by tegwin
My understanding is that hotwater solar cells are not particularly efficient in the UK...Whereas ground/air heatpumps are more so...

I know I would rather have a ground source heatpump over a solar/gas/water type system...

Solar hot water panelscan reach 80 or 90% efficiency whereas PV panels are lucky to get 15%. Heat pumps typically draw heat of between 3 and 10 times the power input, but are usually at the lower end. In terms of solar to heat, you're better off going direct.

Solar heat panels work off light, not heat so as long as it is light, they're working, even on a cloudy day, even if the ambient tempreature is a little below freezing. The thing with a cloudy day is that daylight isn't as bright. On a sunny spring or autumn day at noon, or in the summer over much of the afternoon, you're getting about 1kW of light per square metre pointing directly at the sun. Your panel's mounting angle will reduce the effective square metres. A cloudy December day will give so little light to the panel that it will have a neglegable effect on your water temperature.

Even so, a good system warms the water in the top of you hot water tank. The more sunshine you get, the more of the tank is heated up. When your timer switches on in the evening, the boiler heats the rest of the tank. In the summer, the boiler may never switch on. On other days, it will be on for less time.

Super insulated hot water tanks lose only a couple of degrees per hour, so any water you don't use in the evening will still be warm enough for a shower the following morning.

Stott - 29/9/08 at 04:31 PM
If you're serious about using an alternator though you should look at the higher power ones which will give around 220 - 250 amps @ 6Krpm, & 23 deg C which is around 3KW, they are probably as efficient if not more so than older, very low power items

t16turbotone - 29/9/08 at 05:11 PM
if you are serious, go to machine mart and buy part number 010643005 this is a generator pod rated at 2.2kva just supply a turning force of 3000rpm to it!!
all for 170 quid no invertor losses, and continuous rated

Litemoth - 29/9/08 at 05:39 PM
My humble opinion...

Using alternators to cut the fuel bills is a well trodden path but only if you've got lots of power to drive them with and can drive them quickly!.

Power out = power in minus losses so if you want 5kW out there's got to be lots more than that going in.
If you want to use an automotive alternator (the outputs and efficiencies of which have been explained by Mr Stott who more than knows his stuff in this area) then the thinking seems to be to use a 12v system (no inverter so reduced losses) to heat your central heating water passively. 12V emersion heaters seem to be the way to go.
When you come to fire up your central heating system, the water is already heated to a greater or lesser degree so less is taken from the metered energy sources. The option to charge battery banks is an option too.

If you're serious, self-build low speed 'Axial Flux' alternators are the way to go. You can build them DIY and there are lots of people who've got websites showing you how its done.

[Edited on 29/9/08 by Litemoth]

[Edited on 29/9/08 by Litemoth]

tks - 11/10/08 at 03:51 PM
i have ready that any 3phase motor can generate power if you go 5% over its slip rpm...

so if you take an 5KW motor it will generate 5KW @ 50Hz if you turn it @ about 1560rpm.....

goole for it... DYI wind mills use them to.
You need to calculate a capacitor to connect to the engine...

[Edited on 11/10/08 by tks]