Looking for somone to build a small electronic circuit

Fifer

espresso wrote: »

You obviously don't understand the difference between alternating current and direct current. The OP needs a stabilised DC voltage, so "it goes without saying that" your suggestion won't work.

But dynamos produce DC, don't they? It's just the amplitude is a little variable and needs to be stabilised. I suspect a LM7805 would do the job, provided the dynamo output doesn't fall below about 5.5V too often.

espresso

KillerWatt wrote: »

Look up the definition of the word "Dynamo", then look up an LM7805 and see what that does.

If of course the OP's "dynamo" turns out to not be a dynamo, then a simple IN4001 will provide the DC required.

A bicycle dynamo produces approx 6V AC.

One rectifier diode will not give a smooth enough line input for a LM7805 - read the product spec. for yourself. Half wave rectification is also very inefficient.

espresso

Fifer wrote: »

But dynamos produce DC, don't they? It's just the amplitude is a little variable and needs to be stabilised. I suspect a LM7805 would do the job, provided the dynamo output doesn't fall below about 5.5V too often.

kabayiri

espresso wrote: »

You obviously don't understand the difference between alternating current and direct current. The OP needs a stabilised DC voltage, so "it goes without saying that" your suggestion won't work.



Let KillerWatt make a fool of himself, the Dragons like a good laugh now and again!

:rotfl:

It was just nice to see a blast from my past, mention of things like LM7805s is like 741 op amps....it reminds me of that classic Spitting Image song "RS232 Interface Lead" :rotfl:

I think the OP is either going to buy something, or buy a spare battery, anyway (my guess).

KillerWatt

espresso wrote: »

A bicycle dynamo produces approx 6V AC.

If it produces AC then it is not a dynamo.

espresso wrote: »

One rectifier diode will not give a smooth enough line input for a LM7805 - read the spec for yourself. Half wave rectification is also very inefficient.

Half wave rectification does indeed have a degree of inefficiency, but not enough to be of concern to the OP. I have built a fair few regulators in my time, so I know what they will put up with.

I'd be interested to know what you'd recommend for rectification though.

espresso

KillerWatt wrote: »

If it produces AC then it is not a dynamo.


Half wave rectification does indeed have a degree of inefficiency, but not enough to be of concern to the OP. I have built a fair few regulators in my time, so I know what they will put up with.

I'd be interested to know what you'd recommend for rectification though.

The OP is looking for a solution, not the definition of a dynamo.

I'd recommend that the OP does not waste any time and money following your suggestion. The absolute maximum line input regulation required by the LM7805 is 100mV if that means anything to you! Simply not possible using a diode.

KillerWatt

espresso wrote: »

The OP is looking for a solution, not the definition of a dynamo.

I know what the OP wants, it was you that called in to question what a dynamo was when you said I didn't know the difference between AC and DC.

espresso wrote: »

I'd recommend that the OP does not waste any time and money following your suggestion. The absolute maximum line input regulation required by the LM7805 is 100mV if that means anything to you! Simply not possible using a diode.

I know exactly what input regulation is, but I never suggested a diode regulates anything and I seriously doubt for one minute that the OP's "dynamo" is ever going to make in excess of 25V.

Am still interested in your thoughts on how the AC should be rectified before it's fed to the 7805 though.

Fifer

Sorry, but I'm with Killer Watt on this. A dynamo is a DC device and fluctuating is not the same as alternating. A rotary generator which produces AC is an alternator. If a bicycle 'dynamo' produces ac (I'm not a cyclist, so wouldn't know), then it isn't really a dynamo. But as an electronics engineer, I believe Killer Watt understands the difference between AC and DC perfectly. (By the way, where did the transformer in espresso's diagram come into the discussion?)

uk-tyler

This is the reason I started this thread. I don't know enough about electronics to build a circuit. I presume the 6V 3W output from the wheel is AC. Whether this is a dynamo or a generator I don't know.
Shimano market them as dynamo hubs though.
The spare battery option is a non starter, I'll be touring for a few weeks and don't want to carry that many batteries.
I'm hoping the device from Ebay will be good enough to charge my phone during use, and keep my AAA batteries topped up. It is not an ideal solution, but cheaper than me buying all the bits and building something from scratch. After all I presume a good soldering iron would cost me the £25 that box costs.
The schematic I found on the internet was this one:
Scrub that, I can't post pictures or links, I'll try again after I get more posts under my belt.

Fifer

There is this from Nokia which might be worth considering. (Out of stock at Play.com unfortunately - you might find it elsewhere).