3 to 9W VPG … variable power generator

[Brucey]

You can draw ~6W out of your standard '3W generator' at ~15 to 20mph simply by using the right load. Such generators make ~3W at ~10-12kph and are capable of more at higher speeds with the right load.

cheers

[ConRAD]

You can draw ~6W out of your standard '3W generator' at ~15 to 20mph simply by using the right load...

~6W at ~15mph (~24km/h) ?? could you please tell me HOW with a practical example ??? … believe me, at 15mph I can’t get more than 3.1W !!!
BTW my load is NOT "any-type-load" but is the precise load of the schematics here below.

I'll appreciate any type of clarification, thank you.



All the details HERE

[Brucey]

well you are probably throwing away about 2 to 3V in your converter, and probably drawing no current from the generator whenever the rectified output voltage is less than 5.6V. Both these things will mean that your power output will be reduced. As a load, it isn't well matched to the characteristics of the generator, not if you want to get maximum power from the generator. So even the power going into the 'converter' is likely to be less than it could be.

The ideal load for any generator is well understood and varies with the impedance of the generator.

However a typical shimano generator will produce about 600mA at full chat and will make 6V AC at about 12-15kph. A typical LED headlight will draw ~500mA @ 5V (2.5W) and you can drive two in series at 25kph, getting almost full brightness.

If your load draws less current at similar voltages and/or you throw volts away then of course you won't get the same mount of power out. Designing really efficient circuits isn't at all easy.

If you follow the links posted earlier in this thread you will see exactly how to build a circuit that draws more power from a typical generator.

cheers

[ConRAD]

... well you are probably throwing away about 2 to 3V in your converter ...

.. what ?? ... throwing away 2 to 3V ???
I'm just using the most common configuration in the world I guess, but what I'm frankly afraid of is that even people who designed it are perhaps not much aware of how to improve it !!

Thanks anyhow, cheers.

[edocaster]

You can draw ~6W out of your standard '3W generator' at ~15 to 20mph simply by using the right load...

~6W at ~15mph (~24km/h) ?? could you please tell me HOW with a practical example ??? … believe me, at 15mph I can’t get more than 3.1W !!!
BTW my load is NOT "any-type-load" but is the precise load of the schematics here below.

I'll appreciate any type of clarification, thank you.



All the details HERE

The problem here isn't the dynamo. It's the e-werk.

Look at: http://www.forumslader.de/typo3temp/pics/590d4cd9bb.png

...at 20km/h, yes, you are getting 3W output. It doesn't really matter what resistor you are putting if the e-werk is giving that result. As Brucey mentioned, measuring all this through the e-werk isn't optimal, as the e-werk is trying to regulate a voltage and not showing you the real voltage the dynamo can reach. To measure this more cleanly, just replace the e-werk with a bridge rectifier, and let the voltage rise across your resistor. You will almost certainly get higher voltages at lower speeds. P=V(squared)/R, so you can get much more power if you allow the voltage to rise.

How you usefully transform that higher voltage to usable power at the voltage you need is down to whatever circuit you put downstream.

Beyond that, you can squeeze a little more current at lower speeds if you use a boost capacitor in the bridge rectifier. This combination of allowing a higher voltage and using a boost capacitor seems to be how the German Forumslader system works:
http://www.forumslader.de/12V-Version-m ... 209.0.html
http://www.forumslader.de/fileadmin/use ... -Diode.jpg
and from the link at the top of my post you can see it produces far more power than the e-werk at the speeds you mention.

[ConRAD]

... look at: http://www.forumslader.de/typo3temp/pics/590d4cd9bb.png ... at 20km/h, yes, you are getting 3W output...

... and since I'm interested in e-werk only, in a very few words you are confirming that at 20km/h ... you can't get more than 3W, or more precisely 2.75W, that is exactly the power that I've been able to measure!!!

[Brucey]

yes of course. We said (weeks ago) that you need to change the load. The e-werk determines the nature of the load, so yes you need to change it. All the links and suggestions for increased power output have not kept the e-werk in the system.

cheers

[ConRAD]

... so yes you need to change it ...

... that's sound good ... but change it with what ?? any suggestion?

Thanks a lot.

[Brucey]

other than that you have so far wanted to run with an e-werk, and want more power, we don't know what you want to do. The e-werk is just a means to an end, not an end it itself.

There is nearly always more than one way to skin a cat, but doing so efficiently is difficult, and the correct circuit designs -although easier than building a new generator- are not easy per se. If you want to power gadgets whilst on the road that is one thing; if you want to charge a cache battery that is quite another.

cheers

[edocaster]

... so yes you need to change it ...

... that's sound good ... but change it with what ?? any suggestion?

Thanks a lot.

I wonder if anyone sells the Forumslader charger ready-built? It would seem to be the highest power solution.

Can an engineer look over the circuit at: http://www.forumslader.de/fileadmin/use ... -Diode.jpg ?

- It looks like a rechargeable battery ('akku') is supposed to be connected on the right. Will the system work without the battery if you only want 5V (USB)?
- I presume D8 raises the 12V regulator to about 12.8V. Why? Is it specific to the 'akku' battery charging output?
- What's D9 for? To prevent the battery flowing back towards the 12V regulator?

[ConRAD]

... it is zer chermans' fault; they 'decided' ...

... very interesting indeed but ... who is zer chermans ?

[Brucey]

'the Germans' ; many years ago they plucked a (nice round) number out of the air for bike light power and wrote it up into a DIN standard or somesuch. Amazingly they not only mandated a minimum power for a dynamo at a certain speed (quite sensible) but they also mandated that you should only be able to use such a generator in Germany (i.e. no battery lights were allowed) and furthermore that the generator should only produce a maximum power into a test load of 3W; higher powers were forbidden.

The ideas that;

a) bulbs might become more efficient and/or
b) that some cyclists might need more light than a 3W generator might afford

were not allowed for within their standard.

cheers

[ConRAD]

... they plucked a (nice round) number out of the air ...

... ohh, that's fantastic !!! ... how many other things are like that in the world !!!

[andrew_s]

The 3W limit is so that you don't blow the bulb the first time you ride down a hill

At the time the standard was written, LEDs weren't even a twinkle in anyone's eye, so the standard was for filament bulbs.
If you want something that gives a small enough drag that people won't rebel and use batteries (& therefore be unlit much of the time), that gives a light that's OK at slow speed, and which doesn't result in a blown bulb the first time you go down a hill using a dynamo from manufacturer A and a light from manufacturer B, what they came up with is perfectly reasonable.

It might be nice if standards and laws got updated as soon as technology improved, but what do you do about the mass of people still using the old stuff - command them all to upgrade? Besides which, I expect governments consider they have more important things to do than changing laws so that cyclists can use better lights than those which have been perfectly OK for the last 30 years.

[[XAP]Bob]

to be fair to ze chermans the rest of their lighting regs have improved, but that maximum is arguably not needed any more. Most LED based lights have their own protection built in, so we could use the extra power for other things quite easily.

They only need to derestrict the dynamos and insist that they are marked as such (similar to the Son "delux" which is just a Son20 rated only for use with LED lamps)