The clue is in the commutator. That is a mechanical switch which does approx. the same as the diodes in an alternator. If the dynamo intrinsically produced DC it would merely need slip rings as in an alternator.
On 7/27/2009 11:26 PM Dave Plowman (News) spake thus:
What in the world are you talking about? "Mechanical switch"?
The commutator is a set of rotary contacts. My VW (old 6-volt one) had a generator with a commutator. Produced DC without any diodes.
WTF do you think the purpose of the commutator is? It mechanically switches the output from each armature winding. If you replaced that with slip rings so a single armature winding was not switched you'd get AC. Basic electromagnetic theory.
If you don't believe me have a look at this:-
Then it ran on AC - like many small two strokes etc. They have a rectifier if they need to also charge a battery.
You are mistaken in your understanding of a DC generator with a commutator. Dave is quite correct in that the basic machine generates a bipolar output, which is made unipolar by the synchronous switching action of the commutator.
Arfa
Alternators contain a pair of slip rings, one brush contacting each ring to transfer the generated AC voltage to the output terminals. A generator has a commutator that is made up of many copper segments separated by insulating strips. One or more pairs of brushes ride on the commutator. Armature coils are connected between comm bar pairs. As the generator rotates, the coils sweep through a stationary magnetic field and electromagnetic induction creates an AC voltage across the comm bars which are cleverly arranged so that the positive and negative brushes cross over the right bars at the right time to convert AC to DC without diodes.
Old cars used generators 'cuz power diodes were in short supply a hundred years ago. Automotive alternators became practical around
1960, thanks to silicon power diodes. Alternators are less costly to manufacture and are more rugged.Bryce
The limiting factor on how high you could rev a dynamo (and therefore the max output) was set by the commutator. On an alternator the slip rings carry little current so they can be revved much higher - thus giving a better output at low engine revs too. Of course many older cars had a much more restricted rev range than modern ones so the dynamo served pretty well - especially since loads were lower.
Note for old car nuts - you can now buy alternators which are externally identical to a dynamo. Well, a Lucas one at least. ;-)
Thanksfor the links and as always a great story.
Yeah I have a 4000 watt standby AC generator that rely's on residual magnetism. There are two types a brushed type (through which you would flash the field with a 6 volt lantern battery) and a non-brushed type that I forget at the moment how you get it going when the residual is gone. But I can almost 99.9% guaranty you that if I remove the field connection on my Harley that the alternator would produce zero volktage.
The output voltage at the comm is DC not a 'switched by windings and com bar AC'.
Yes, so i now noticed, there are some solutions but alas a bit bulky. I did some research already and have experimented with car alternators, i got so far i can make one that charges at 400rpm but the wind is too unpredictable and the field coil needs to be energized all the time which drains your battery in dead moments, rather a pm alternator as suggested as i don't feel much for having to build a dynamo from start, but hey, if i have to... But i did buy some motors on ebay as suggested, they are treadmill motors. Someone else suggested the use of a motor off an electrical bicycle, benefit is that it's weatherproof. I just thought someone here could sell me some instead of on eekbay. What i would like is an easy off the shelf solution, but i can see that there isn't really one. Thanks everybody for the input on this.
Bart
Wind turbine kits which include everything except the tower and the wind are available ... but at a price.
PM alternators avoid the need for field excitation, but now you need some other way to efficiently regulate output voltage as turbine speed changes.
No need to keep the field energized when the turbine isn't turning. A bit of control electronics solves that.
A local college just announced an associate degree program in wind power. I wonder whether the diploma comes with a pair of wooden shoes!
Bryce
As well thanks from me, i know about otherpower but i think i come right anyway.
Bart Bervoets
I fooled with a funny little generator my brother gave me. It had little power. To get it started it had a separate brushed section to get DC. Push a little button to get it going.
I'm thinking I want to build a wind generator.
Too bad around here, we have miles of rivers, but ZERO water driven energy. They have new turbins out that you put in rivers and get some energy. Yeasr ago they did not even think of that. They still don't.
greg
Now I'm feeling awfull about all the nice big DC motors I,ve thrown away.
greg
We had lots of municipal hydro electric generation until sometime in the 1980s when most were dismantled, ostensibly under pressure from environmental interests, the state DNR, and utility consolidation.
Michael
On 7/28/2009 6:27 AM Meat Plow spake thus:
So you agree that a generator (motor used in reverse, i.e., driven instead of driving, with a commutator instead of slip rings) produces DC without rectification, not AC, correct? That was my point.
I'm not disputing that the current direction in a generator reverses with each set of commutator bars contacted by the brushes, so I guess in that sense one could consider the commutator a "mechanical switch". I just regard it as the way the thing is wired to produce DC.
The problem with rivers is that without a falls, there's no vertical head to run a high speed turbine or Pelton wheel:
This is usually solved by building a dam, which has profound aesthetic, ecological, and environmental issues. It is possible to use a fully immersed low speed turbine, but to get enough energy from the usual slow flow rate and high volume river, the number of turbines and/or their size tend to be large. For example:
Also:
Another problem is that the power output of the water turbine is directly proportional to the head and to the flow rate. Unlike the wind turbine, where the output is proportional to the cube of the air speed, water power generators tend to become very large at higher power outputs. Where the flow rate is minimal, the usual solution is a higher dam.
There are problems with everything. Here is what is being done tomorrow.
greg
I thinks it allready been planned. These things can be installed near existing river lock dams which will not affect river traffic.
greg
snipped-for-privacy@zekfrivolous.com (GregS) wrote in news:h4nj56$iik$ snipped-for-privacy@usenet01.srv.cis.pitt.edu:
better to use nuclear powerplants.
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