From: jlittler on
On Feb 9, 2:51 pm, atec <"atec77 "> wrote:
> jlitt...(a) wrote:
> > On Feb 9, 12:58 am, atec <"atec77 "> wrote:
> >> Andrew McKenna wrote:
> >>> sharkey wrote:
> >>>> Andrew McKenna <NOcmorSPAM3...(a)> wrote:
> >>>>> I think your critics are thinking of their bicycles with dynamo
> >>>>> powered headlights :-) More electrical load might make you discover
> >>>>> that you need to push harder to achieve the same results but there's
> >>>>> no way the dynamo itself gets harder to spin.
> >>>> What? You need to push harder to spin it but it doesn't get harder to
> >>>> spin?
> >>>> -----sharks
> >>> No, you need to push harder to get the result if you add electrical
> >>> load. It cannot possibly get harder to spin.
> >> Now thats wrong in so many ways .
> > Actually he's dead right if you read it carefully - typical engineer's
> > wording though. They never speak english.
> > The MECHANICAL load is unchanged IE the effort to physically spin the
> > metallicy bits around will be unchanged regardless of electrical load.
> The way I understand it that statement is wrong , mechanical input
> required to generate electrical energy bears relationships to each
> other, more electrical energy required means more drive is required to
> overcome the resistance to turning .A change in turning momentum is
> proportional to energy required.

And your statement is indeed correct - there's a difference between
the mechanical input and the mechanical load. Pure semantics of
course. mechanical load (as torque) plus electrical load(as torque)
equals mechanical input required(as torque). The mechanical load is a
constant (ceteris paribus), the electrical load changes with, well,
the electrical load <grin> (1). To be more accurate the torque/turning
force that you have to provide to generate a current equal to the
current being drawn is increased as the current required increases(2)

(1) there obviously being more than one meaning of the word load in
this context - one being current drawn, the other being turning force
(2) still not sure I'm explaining that particularly well
> > HOWEVER if you then add the bit you guys are busy arguing about -
> > which strictly speaking isn't mechanical load as such within the
> > alternator/dynamo/generator (although it will be EXTERNAL to the
> > system) you are adding additional torque requirements to overcome the
> > additional physical resistance to turning created by the electrical
> > field.
> > JL
> > (not a 100% sure I've turned that into English successfully, it's
> > tough being a translator ;-)- Hide quoted text -
> - Show quoted text -- Hide quoted text -
> - Show quoted text -

From: Theo Bekkers on
Knobdoodle wrote:
> "Andrew McKenna" wrote:

>> No, you need to push harder to get the result if you add electrical
>> load. It cannot possibly get harder to spin.

> I bet if you said this 100 times it would still be just as hilariously
> stupid!
> What on earth are you actually trying to say?

I think he's saying that if you turn an alternator with no load and with
full load, no extra power input is required. That must be why our back-up
gen-set gets louder when we put the air-con load on it. 3.9 litre John Deere
with a 3 phase 44kw alternator.

Anybody want to tell me it doesn't use more fuel when we load it up to 40

Try holding one of these permanent magnet alternators in your hand and spin
the rotor with your other hand. Easy isn't it? Now twist the output wires
together and give it another spin. That would be max load. What do you mean
it stops dead? It surely doesn't require more turning force?

Simple brakes for an induction motor is to short the terminals together.
This is wired into a lot of machinery. Stops very quickly. An induction
motor is the same design as your perm magnet alternator.


From: Theo Bekkers on
jlittler(a) wrote:

> (ceteris paribus),

What kind of a bus is that?

> (2) still not sure I'm explaining that particularly well

Those of us that agreed with you understood it.


From: Theo Bekkers on
Hammo wrote:

> Actually, I'm gonna use solar power!

Isn't petrol just very old solar power?


From: Theo Bekkers on
sharkey wrote:
> Theo Bekkers <tbekkers(a)> wrote:
>> I must say I'm a little surprised that modern bikes use total waste
>> regulators. I haven't looked into it and most schematics would show
>> a little box marked regulator with no indication of what it
>> contains or how it works. I thought that kind of 'engineering' went
>> out with the Triumph Zener diode. Surely you only need to
>> encapsulate a couple of components to make a switch mode regulator.
>> Otherwise you've got a 400-500 watt heater. In that size the
>> regulator would need to be glowing. People heat their bedrooms with
>> that much power.
> See the oscilloscope part of this thread. Modern ones do, indeed, use
> switchmode regulators, and it's a good reason to integrate rec and reg
> because the SCRs which switch in and out get to be three of the
> diodes.
> Oh I give up on ASCII art:
> All the controller needs to do is to only turn the SCRs _on_ when
> Vsense is too _low_.

Well, as they do work as switch mode power supplies, it is not a total loss
system and when you turn on the headlights you will use more, albeit only a
tiny bit more, power from the engine, requiring more fuel.


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