Cloink

Hi audioguru Thanks for all your time - you've still missed some of my points though. I already have 8AA's in use for the circuit. My hope was to reduce the AAs to AAAs (to save weight and also 'cos the AAAs would fit in the casement in which the LED array is housed whereas 8 AAs don't). Of course I can do this but I'll only get around 2hours usage instead of 8 or so as the charger won't make a significant difference. I'm fortunate enough to have a dad who sells rechargeable batts so I'm ok on that score!! The batts are indeed rated at 1.2V (some at 1.25V), but even when in use, the 8 together still registered over 10V using my multimeter (even as high as 10.5V), this was at c.350mA. I still however believe that, given a clean design sheet, one could manufacture a wind-powered dynamo-and-LED light set. As I mentioned, the crude arrangement I had was enough to power one high luminosity LED - not much I know but this was from cobbled together bits and bobs from someone who doesn't really know what they're doing. Obviously I'll have to wait 'til I'm a millionaire and I can commmission someone to make one for me! Finally, I'm sure you've picked up on this, but with a diode in place to prevent the batts draining through the dynamo, the small current that the diode allows in reverse would surely be enough to negate any output from the dynamo in the first place, especially if left connected when not in use. Anyway, I've fallen out with the whole project, 3 of the LEDs have stopped working (presumably blown) and I've lost the battery pack which had my 8 AAs........... Oh dear. Cheers, Clark.

First things first. audioguru was right to have reservations about how much power the fan/dynamo can produce. When blowing on it, taking the output directly into a bridge rectifier and not into the multiplier, I can keep a single high luminosity LED lit. On the other hand, a fully charged 2200 micro-F cap does not keep the LED lit for a significant amount of time (i.e. not long enough to sit at traffic lights) [if I remembered all the equations from school I could have worked that out!] So - regardless of whether my dynamo can create enough power to light up the LED(s), I'd need some stonkingly large caps to keep them going while I'm stopped. Back to my rechargeable batts then.** My crude calculations suggest I can get about 10-40mW from the dynamo. Let's say 1mA @ 20V. Doesn't really seem worth the hassle trickle charging the batts either, it's gonna take a long time to put any significant charge into 750mAH AA's. I do have a slightly different question though, if anyone's still reading (!). My battery charger registers, for the sake of argument, 1.4V when charging a batt that when isolated registers 1.3V. Now I've convinced myself of this, but could someone confirm? With the battery in the charger, the charger MUST have a driving potential of 2.7V mustn't it? Because the driving potential from the battery is fighting against it. Back to a possible trickle charging dynamo. To charge a 10V battery pack, I guess I need to generate a driving potential of 20V (or so). Although the v-multiplier worked with no load, as soon as I attached a load, the voltage dropped drastically (almost to zero!) Am I right in thinking the lower the capacitance of the caps in the v-mulitiplier, the less will be the voltage drop (if at the expense of a higher ripple)? Anyway, in conclusion, I think the output from a wind-powered dynamo is too small to be really worth utilising. **One could maybe attach a (well balanced) weight to the dynamo so that when stopped the angular momentum kept it going... But that's mechanics not electronics! MP, sorry, no diag, there's not really one to talk of. I simply rectified the dynamo output with an off-the-shelf bridge rectifier. The v-mulitiplier circuit is already on this site. In both instances I just connected the AC out from the dynamo to whichever circuit. Also, no, I have no oscilloscope and am not likely to have access to one so I can't investigate the exact waveform of the AC. Thanks everyone. Cheers, Cloink.

A site with a full-wave voltage multiplier of arbitrary factor if anyone else was looking for one.... http://members.tm.net/lapointe/Cockcroft_Walton.htm

Yes, thank you, that was very much more helpful and I will consider finding diodes with a lower voltage drop, or just looking for a different method - or maybe giving up altogether, after all, I've already got rechargeable batts. But for interest, before I savaged the motor, it was a 'fancy' one which lit up when switched on - via 4 LEDs inserted in its casing. When used in reverse as a dynamo, with no other load attached, these 4 LEDs lit up as I cycled down the street and the fan turned. Yes, the LEDs were lower power output than the high luminosity ones in my 'traffic light' (as you have christened it), and there were less of them, but clearly there is SOME usable power being produced. The motor/dynamo has 4 windings, and 3 terminals. 2 points are common and I'm taking the output from the non-common terminals, after finding that this gave the greatest (AC) p.d. My half-way understanding of the subject leads me to conclude that the common terminal is the 0V rail, and the non-common terminals are producing a simple AC wave. However, with no oscilloscope, these are educated guesses based on investigations with my multimeter, but either way, with no load, I can blow on the dynamo and register upwards of 8V AC across these terminals. Not for very long though - I start to go dizzy!! I'm using this particular one because it was in the bargain bin and cost me all of 98p (GBP0.98). Being a brushless motor(dynamo), however, (and uses bearings, not bushes) I feel that it will be quite efficient at its job, plus it has the added benefit of already having a rather good fan attached, and a casing with points I can use to attach it either to my bike or the 'traffic light'. I will return (maybe) when/if I can update you with my achievements or failures. Though I suppose it's more likely if I fall on the side of 'achievement' rather than 'failure'...... Many thanks again, Cheers, Clark.

Please please read the postings properly. I'm sorry, I know I'm really a guest on this site, and I do appreciate all your help, but I'm quite exasperated that you haven't read my points. I want to trickle charge the batts from the dynamo, I DO NOT expect to get 4W of power from the dynamo. Depending on how much power I CAN generate, and I'll keep you posted when I've got it working, then maybe, just maybe, I can generate enough power to trim my batts down from AAs to AAAs without having to recharge them after every 2 hours' use. If I'm REALLY lucky - and if I can find a full wave voltage multiplier circuit that more than doubles the p.d. - then I may just drag enough power out of the dynamo to power a lesser LED array in which case I'll have a rethink. Yes the PC fan motor started life as a 12V DC motor, but I've taken the PCB off it and I'm just taking the 'raw' AC output it generates in its new 'skeleton' mode. I am also quite well aware that I need to regulate my eventual DC output -- the dynamo will of course provide a different p.d. depending on how fast I'm going, so I have to multiply it up maybe 4 or 5 times so that when it is - and I am - going slowly I still have the 10V I need. When I'm going faster, this multiplied voltage will be way too high, so yes, I need to step it down. I have found circuits elsewhere that show me how to tap off a constant voltage. Is there any other unsolicited advice you'd like to give me? I only asked a few simple questions. Regards, Cloink.

Thank you, very much appreciated! It's a brushless motor (from a pc-fan) - I will triple-check when I get a chance but my multimeter gave very spurious results when I connected it in DC-mode, but very consistent results when connected in AC-mode (of course, this was when I was blowing on the fan blades to turn it). I have already attached the fan/motor/dynamo to my bike and seen the blades turn - it's about 4" dia (same size as a pc-fan obviously!) Yes, there'll be more resistance when I connect a load on it, but I still think it will turn, if more slowly. But no, there will be negligble extra wind-resistance from the fan/dynamo. I need 10V+ because I have a vast array of LEDs, 3 in series x14 sets in //. They are 3.2V/30mA rated: that's 9.6V plus a bit for the drop across the resistors. This already works with a 10.5V supply (8 rechargeable NiMH AA batts). The whole setup draws c.350mA when connected. Honestly, I do, mostly, know what I'm doing, I just can't get my head round the voltage multiplier circuit. Many thanks again, Clark.

Thanks for all your responses but PLEASE could you answer the questions Q1 - Q3 directly? (I've got Q4 now.) Of course I can't increase the power output by multiplying the voltage, but if the multiplier is only a half-wave multiplier then I can only presume it will have a poor efficiency. Yes I'm sure it's AC, it's a motor in reverse. (Not that that necessarily means it's AC output, but it I've tested it, it is definitely AC.) The 6V/0.5W dynamos are hugely restrictive (you must have noticed how much more effort it takes to cycle with it engaged), in this age of high-output LEDs, I'm convinced I can make something wind-powered that can at least trickle charge my rechargeable batts or hopefully if I'm lucky just power an LED-light directly, keeping a reserve in a large capacitor for when you're stopped at traffic lights, etc. I'm hoping for something like 10V 50mA, so that would be 1/2W. Thanks in anticipation, Clark.

Ooo-kaaay.... Sorry, that's not really helped. Q1 Can I use the electrolytic caps I've already got, or do I need to go get ceramic ones? The other site I mention is http://www.tpub.com/neets/book7/27m.htm Towards the bottom of that page it's got "Figure 4-49. - Full-wave voltage doubler" - after having talked about half wave doublers & triplers. Q2 Is the multiplier circuit given on this site a half-wave or full-wave? I want to get as much power as possible as I'm generating AC from a wind-powered dynamo on my bike and the output isn't going to be too great to start off with. Q3 If it's a half-wave multiplier, can you tell me how to do a full-wave tripler/ quadrupler/ etc? The above site only shows a doubler, but I need to multiply by more than 2. Q4 You're saying to minimise ripple I can just use a whopping great cap as the final one rather than including a cap in // with the load? Elsewhere in this thread, someone says you must use all the same size caps else it may become unstable. Many thanks, Clark Pearson.

Just looking for a bit of help, I'm not an electronics whizz, remember some from school & uni, so assume I'm an idiot please! I'm trying to make the voltage multiplier circuit, but nowhere does it say whether ceramic caps must be used or whether electrolytic ones are ok. (Just to be absolutely sure I'm not using terms that mean the wrong thing, ceramic caps charge whichever way you connect them - yes? - whereas electrolytic ones only charge 'the right way round' - yes?) Also, another site I found has a voltage doubler circuit but it's connected differently (as far as I can tell) and outputs (rippled-)DC not AC and seems to only charge the caps in the same direction whichever half of the AC cycle you're on. I'd rather assumed that the multiplier on this page is AC output. Which has put me in rather more confusion than before, not less! Help very much appreciated.