easy way to generate an ac signal

[Onetap]

Dunno, I was hoping someone could tell me in short words. It did though, honest Guv.

I've had a car jump started by the AA some years ago and they have some gizmo they connect and they checked something with a meter before disconnecting their leads.

I didn't disconnect the alternator, I disconnected the jump leads and the engine stopped.

The 'flat' battery was not simply flat, it was dead. Zero volts, zero amps. No idea why that would happen but a new battery wasn't charging and the alternator, previously good, was kaput.

[Onetap]

=20

If you say so, I don't know about such stuff. According to the web page I read, that would wreck the diodes in a convent= ional (internal regulator) alternator and clever modifications were needed to make a car alternator suitable.

[Alan Braggins]

The signal then needs to be processed, that bit I can handle.

might give you some useful ideas.

try your local tip/recycling centre for bikes with old Sturmey-Archer Dynohubs.

(A car alternator will need either external power for the field coils, or modification to use permanent magnets:

)

[RobertL]

elling a wind turbine. We will probably drive the input using a drill. I'm = going to need about 10 models. I am only wanting to show the very basics. T= he signal then needs to be processed, that bit I can handle. Can someone gi= ve me a link to a suitable component to produce the ac voltage on ebay? tha= nks

Bicycle hub dynamo?

Robert

[Alan Braggins]

Or the display has that wrong and is cheating, which I suspect is Tim's point.

[Dave Plowman (News)]

Then it wasn't the jump start that killed the alternator but the battery being effectively open circuit.

[Terry Casey]

Dunno about here but used to be commonly available in French/Belgian hypermarkets for five euros (or ¤7 in les Halfrauds!)

You don't see them so much though, as LEDs gave caught on there as well but I saw one a couple of years ago in Hema in the Netherlands knocked down to ¤3!

On close inspection, the legends embossed on the casing were interesting.

Apart from the obvious CE mark and the rating (6V 3W), others included BS6102/3 and, surprisingly, MADE IN FRANCE! (Not even Fabrique en France!)

[Tim Watts]

So spinning an unpowered fan at 5000 RPM whilst cleaning it with air-in-a- can is risky? Not had a problem doing that - yet!

[John Williamson]

Could be you've had good luck, but all the makers instructions I've seen recommend that you hold the blades still while doing that particular job.

And as you say, "yet". Are you listening, Murphy? ;-)

[Jules Richardson]

My truck has black for the positive and red running to the chassis, despite being negative earth.

cheers

Jules

[harry]

So called DC machines are in fact AC. The comutator and brushes is a mechanical inverter. The electronic inverter just replaces the commutator

And if you turn the shaft, it will generate AC.

[harry]

de the alternator,

in his shed that you can modify to get the AC out.

r and power one to spin the other. Or it to the back of a PC and run it fro= m the fan in that.

Well now we all know what an ignorant halfwit you are. Tell us all how you can make a motor run on DC.

[harry]

Seems like you do.

[harry]

Yes really.

[John Williamson]

It will indeed generate AC *at the windings*, which is fed into the output of the "inverter" formed by the switching transistors. As these are semiconductors having rectifying properties, the voltage will get no further. To tap into the AC, you need to remove or bypass the drive circuitry.

In a similar vein, to use a car alternator as a motor, you need to swap the diode pack for a drive control pack, which will switch the poles of the stator in sync with the magnetic field generated by the rotor. Basically, the control pack is a multi-phase, variable frequency inverter.

To use a car dynamo as a motor, you just need to connect the field winding (stator) and the brushes to a power source. In this case, the "inverter" is reversible in function, and works just as well as a rectifier.

[Clive George]

Not only can you still get them, with the arrival of decent hub dynamos and more recently of LEDs there has been a resurgence in popularity.

A dynamo hub front wheel with LED lights will give you the most reliable lighting possible - it'll go years without needing any maintenance providing the wiring is done sensibly.

And re batteries lasting nearly forever - a dynamo generates 3-4W if connected up appropriately (can be more if you're clever about it and prepared to work a bit harder - 6W was a standard bright light setup for people riding over 15mph or so). Batteries can't deliver that kind of power for "nearly forever", and LEDs aren't magic - you need that sort of power for a decent amount of light.

The brightest lights are battery LED, but they use rather more power than a dynamo can chuck out and consequently have battery life/size compromises to deal with.

[polygonum]

Ball-bearing motor?

[Clive George]

Didn't Hornby demonstrate that adequately for many years?

[tony sayer]

In article , harry scribeth thus

You really ought be a bit more careful in quite what's stated on these matters....

[tony sayer]

Thats sounds rather unlikely and if it did thats very poor design for an aircraft electrical system.....