http://citycyclingedinburgh.info/bbpress/ CityCyclingEdinburgh Forum » Topic: Dynamo lights question en Thu, 02 Jul 2026 08:25:52 +0000 http://citycyclingedinburgh.info/bbpress/topic.php?id=9554#post-102735 Mon, 04 Mar 2013 12:49:26 +0000 DaveC 102735@http://citycyclingedinburgh.info/bbpress/ <p>Thanks chdot,</p> <p>I'll defo pop along and get some. I found a pack of heatshrinked 8 NiMH AA cells in a broken childrens toy, little used in my son's toybox. Its now sitting in a waterproof container on my bikes rear panier powering my B&amp;M lights :O) </p> http://citycyclingedinburgh.info/bbpress/topic.php?id=9554#post-102598 Sun, 03 Mar 2013 13:38:38 +0000 chdot 102598@http://citycyclingedinburgh.info/bbpress/ <p>Cheapish NiMHs (from Thursday)</p> <p><a href="http://www.lidl.co.uk/cps/rde/xchg/lidl_uk/hs.xsl/index_39656.htm" rel="nofollow">http://www.lidl.co.uk/cps/rde/xchg/lidl_uk/hs.xsl/index_39656.htm</a> </p> http://citycyclingedinburgh.info/bbpress/topic.php?id=9554#post-101731 Sat, 23 Feb 2013 21:58:20 +0000 DaveC 101731@http://citycyclingedinburgh.info/bbpress/ <p>Defo need something smaller...</p> <p><img src="http://i126.photobucket.com/albums/p86/Dave_Crampton/2013-02-22214429_zpsd9c5e2c1.jpg"></p> <p>And I messed up sonewhere on photobucket reducing the size!!! </p> http://citycyclingedinburgh.info/bbpress/topic.php?id=9554#post-101659 Sat, 23 Feb 2013 09:09:13 +0000 Dave 101659@http://citycyclingedinburgh.info/bbpress/ <p>DaveC, you could test it on your actual dynamo-equipped bike (so if it runs low, just plug in the real deal)?</p> <p>I rode through most of four nights of PBP on 10x AA batteries (Lithium primary) so you should be fairly happy once you get something sorted out. </p> http://citycyclingedinburgh.info/bbpress/topic.php?id=9554#post-101648 Sat, 23 Feb 2013 00:26:55 +0000 Uberuce 101648@http://citycyclingedinburgh.info/bbpress/ <br /> http://citycyclingedinburgh.info/bbpress/topic.php?id=9554#post-101644 Fri, 22 Feb 2013 23:43:56 +0000 DaveC 101644@http://citycyclingedinburgh.info/bbpress/ <p>Well she is plugged in and running... or crawling as at the mo, the batteries need a full charge. Front is ok ish on its own but add the rear Standlite and its way too dull at the front and and I'd not be happy on the roads at night with the rear. The battery box is <em>ample</em> and I found a larger 9V multicell battery on Maplin but can't find it now. Think I'll just get a small 9V switchable enclosure instead and see how long it lasts on the run home. </p> http://citycyclingedinburgh.info/bbpress/topic.php?id=9554#post-101598 Fri, 22 Feb 2013 16:43:33 +0000 Dave 101598@http://citycyclingedinburgh.info/bbpress/ <p>It will light up with 5x 1.5V AA, but my best long-term results were with a Li-pol cell for my normal LED bike lights (8.5V nominal IIRC).</p> <p>I didn't need to worry about waterproofing because the battery box was inside my tailbox. I used one with the type of connector that fits a 9V square battery and then the wire was continuous right through to the light.</p> <p>BTW, one polarity is brighter than the other. Use the bright one (obviously).</p> <p>I got my Cyo maybe 2 1/2 years ago and only got the dynamo 18 months ago, so it's not shown much ill-effect for being thus used for the relatively long term. </p> http://citycyclingedinburgh.info/bbpress/topic.php?id=9554#post-101596 Fri, 22 Feb 2013 16:23:30 +0000 DaveC 101596@http://citycyclingedinburgh.info/bbpress/ <p>Yes, I'm wondering if I should have bought 6 C cells or even 6AA's now!! Shucks.... Oh well I can always use it for something else....</p> <p>Dave, What gland did you use to waterproof your lighting cable out of the battery box? </p> http://citycyclingedinburgh.info/bbpress/topic.php?id=9554#post-101593 Fri, 22 Feb 2013 16:08:33 +0000 steveo 101593@http://citycyclingedinburgh.info/bbpress/ <p>6aa there must be a lot going on to drop that much voltage. </p> http://citycyclingedinburgh.info/bbpress/topic.php?id=9554#post-101591 Fri, 22 Feb 2013 16:00:56 +0000 DaveC 101591@http://citycyclingedinburgh.info/bbpress/ <p>@Dave Ah really!! I didn't know, Many thanks. I'll pop a few 0.5W 10ohm thin film resistors in series (in parallel just incase ~ 3.3ohms) and go.</p> <p>6 AA you say? That would be 9V right? and that ok is it? Cheers. Originally I was wondering how long a 9V small square battery would last, but I imagine not very long. I'll try out this 4 D cell supply this evening then.</p> <p>Dave C </p> http://citycyclingedinburgh.info/bbpress/topic.php?id=9554#post-101590 Fri, 22 Feb 2013 15:55:22 +0000 Dave 101590@http://citycyclingedinburgh.info/bbpress/ <p>Dave, you have checked your favourite site for the skinny on this, right?</p> <p><a href="http://mccraw.co.uk/battery-powered-dynamo-lighting/" rel="nofollow">http://mccraw.co.uk/battery-powered-dynamo-lighting/</a></p> <p>Just plug some batteries into the light and it will go on. 6 AA rechargeables would be perfect.</p> <p>There's a lot more inside a dynamo headlight than an LED. B&amp;M explicitly say you can run the Cyo on DC in the manual IIRC. </p> http://citycyclingedinburgh.info/bbpress/topic.php?id=9554#post-101573 Fri, 22 Feb 2013 14:32:29 +0000 steveo 101573@http://citycyclingedinburgh.info/bbpress/ <p>Probably not, theoretically it would be fine but if they're not precisely balanced one ends up trying to drop more voltage and melts down usually causing the others to burn up too.</p> <p>In the with rectifier case the resistor is actually very efficient, its only dropping about 0.1w as heat in a 2w circuit thats pretty good, you'd struggle to beat 5% loss. </p> http://citycyclingedinburgh.info/bbpress/topic.php?id=9554#post-101570 Fri, 22 Feb 2013 14:18:23 +0000 DaveC 101570@http://citycyclingedinburgh.info/bbpress/ <p>Steveo, if I bought 5 of these <a href="http://www.maplin.co.uk/0.1a-positive-fixed-voltage-regulators-46470">100mA 5V regulators</a> and wired them in parallel would they work with such a low I/P voltage?</p> <p>Well if anywhere had more than one in stock.... I'll just see how the resistors go. Have loads of 10ohm res at work and can take a handfull if required. </p> http://citycyclingedinburgh.info/bbpress/topic.php?id=9554#post-101569 Fri, 22 Feb 2013 14:16:10 +0000 steveo 101569@http://citycyclingedinburgh.info/bbpress/ <p>Thats the thing, there are only about 5 components required. 4 diodes for a rectifier and a supercap, the capacitor will likely have regulatory circuitry but they'll sit "after" the cap and shouldn't effect this. </p> <p>I'd love to see a diagram for these good quality lights and compare them to my aluminium block. </p> http://citycyclingedinburgh.info/bbpress/topic.php?id=9554#post-101567 Fri, 22 Feb 2013 14:03:57 +0000 DaveC 101567@http://citycyclingedinburgh.info/bbpress/ <p>Good idea. I bet they are the surface mount components so no chance of doubling the output... </p> http://citycyclingedinburgh.info/bbpress/topic.php?id=9554#post-101566 Fri, 22 Feb 2013 13:57:14 +0000 steveo 101566@http://citycyclingedinburgh.info/bbpress/ <p>I'm not entirely clear why these deliver different power outputs. The only thing that springs immediately to mind is the lower one uses half wave rectification so only part of the ac cycle is used the rest lost to a blocking diode. In that case the 30 would present as not having a diode and would need a bigger resistor. </p> <p>Theoretically the lower power one should be able to run at the same power output as the larger one, odds are they run the same LED they're just wired differently inside. If that is the case then your only concern would be heat sinking, try and find out what emitter they use we can take it from there. </p> http://citycyclingedinburgh.info/bbpress/topic.php?id=9554#post-101562 Fri, 22 Feb 2013 13:19:06 +0000 DaveC 101562@http://citycyclingedinburgh.info/bbpress/ <p>Aye but now I wonder if my two different B&amp;M lights have a diode in or not?? I have these two lamps:</p> <p><a href="http://www.rosebikes.co.uk/article/b--m-lumotec-lyt-bn/aid:553802">Lymotec Lyt BN</a> 30 Lux.</p> <p>and </p> <p><a href="http://www.rosebikes.co.uk/article/b--m-lumotec-iq-cyo-t-senso-plus-60-lux/aid:457434">Lumotec IQ Cyo T Senso +</a> 60 Lux</p> <p>I'm just hoping the only difference is the power output and the cap inside providing power for ~10 mins to the wee leds at the botom of the light lense?</p> <p>My problem wil be if the two lights require different resistances I'll have to add more resistors to switch in and out.... pita... and potential (no pun untended) to blow the lamp requiring more inline resistance. </p> http://citycyclingedinburgh.info/bbpress/topic.php?id=9554#post-101558 Fri, 22 Feb 2013 12:44:07 +0000 steveo 101558@http://citycyclingedinburgh.info/bbpress/ <p>That is much easier than my block of maths above... </p> http://citycyclingedinburgh.info/bbpress/topic.php?id=9554#post-101556 Fri, 22 Feb 2013 12:43:07 +0000 DaveC 101556@http://citycyclingedinburgh.info/bbpress/ <p>Actually thinking about this I can buy 4 2.2ohn resistors to produce:</p> <p>1.1 (2 in parallel - 2.2||2.2)<br /> 2.2<br /> 3.3 (2|| + 2.2)<br /> 4.4 (2.2 + 2.2)<br /> 5.5 (1.1 + 4.4)<br /> 6.6 (2.2 + 2.2 + 2.2)<br /> 8.8 (2.2 + ....)</p> <p>I may only need three but will buy 4 - 2.2ohm 3W resistors £2.56!! Simples. I can use connector blocks to hook them together until I find what I want and solder from there. </p> http://citycyclingedinburgh.info/bbpress/topic.php?id=9554#post-101554 Fri, 22 Feb 2013 12:41:31 +0000 steveo 101554@http://citycyclingedinburgh.info/bbpress/ <p>2w is probably over kill, but has a good safety margin built in. It really depends if the light has a rectifier built in, it almost certainly does but it is possible to make an led light with out one. </p> <p>This is going to look a bit like maths, sorry to any classics students reading.</p> <p>Your resistor is governed by Ohm's law, VIR.<br /> I is current in amps, you want between 0.4a and 0.6a depending on required battery life and how well heat sunk the body is. I'd guess not very well as a first pass.<br /> V (voltage in Volts) in this case is the voltage drop you need across the resistor. This is the difference between the nominal voltage of the LED + the voltage dropped by any other components and the - the input voltage (batteries)<br /> R (resitance in Ohms) = V/I.</p> <p>To make this easy assume I = 500ma = 0.5a<br /> the LED nominal voltage is 3.5v and any other diodes drop 1v.<br /> If you have a recitifier V = (3.5+1)-4.8 = 0.3<br /> R = V/I = 0.3/.05 = 0.6 ohms (round up) = 0.68R </p> <p>Sans rectifier v= 3.5-4.8 = 1.3v<br /> R = V/I = 1.3/.5 = 2.6 ohms (round up) = 2.7R.</p> <p>To work out how big the resistor needs to be you need P=IV, P is power in watts, I is current again in amps, and V is voltage.</p> <p>with rectifier P=IV = 0.5a x 0.3v = 0.015w round up 1/4w will be fine.</p> <p>with out P=IV = 0.5 * 1.3 = 0.65 round up to 1w.</p> <p>Worth noting these are nominal values the LED could drop more or less voltage as could the rectifier. Your battery voltage will come off the charger at more like 1.55v and drop to 1.2v after a little while but if you build in enough margin the high initial voltage will be fine. The current and thus the light output will not be linear but will ebb with the voltage of the batteries since the voltage drop across the resistor is setting the current. </p> http://citycyclingedinburgh.info/bbpress/topic.php?id=9554#post-101541 Fri, 22 Feb 2013 12:08:48 +0000 DaveC 101541@http://citycyclingedinburgh.info/bbpress/ <p>Great news Steveo, many thanks again. I work for a semiconductor design company and am fortunate that we have a lab with test equipment here.</p> <p>Not sure we'll have many 2W 4.7ohm resistors though. I wish I had asked before I bought the parts now as Maplin is the other side of town from me.</p> <p>I have a multimeter at home which is capable of measuring current and I might just swing by Maplins on the way home and buy a bunch of resistors. Had you a range in mind? </p> <p>All 2W I assume, but what? 3.3, 4.7, 6.8, 8.2?? Then add them one at a time in series, measuring the current consumption with the meter? I've just looked at maplin and they have 3W wire wound which go as low as 3.3ohms</p> <p>Cheers again, Dave C </p> http://citycyclingedinburgh.info/bbpress/topic.php?id=9554#post-101536 Fri, 22 Feb 2013 11:51:54 +0000 steveo 101536@http://citycyclingedinburgh.info/bbpress/ <p>Probably not, I think that'll just be shunt to stop the voltage going over the vMax for a incandescent bulb. --Ninja'd</p> <p>For testing you'll need a resistor to limit the current to a level the led can handle. Something like a 2w 4.7ohm from maplin will keep the current right down.</p> <p>The only other concern is the diode in the rectifier, that converts ac from the hub to dc for the light, it might drop the voltage to the led by as much as 1v. You should be fine though. 4x1.2 = 4.8v, at ~500ma the LED will drop about 3.5v + ~1v for the rectifier = 4.5v so you've got a whole 0.3v to play with.... </p> <p>Actually while you are at Maplin you might want to get a selection of resistors and a multi-meter which can measure current and work out what resistor best keeps you around 500ma.</p> <p>Edit: If you want, I can hook it up to my multi meter with a load of resistors and try and find an optimal one, it won't take me half an hour and it'll save you buying stuff you'll not use again. </p> http://citycyclingedinburgh.info/bbpress/topic.php?id=9554#post-101528 Fri, 22 Feb 2013 11:38:16 +0000 kaputnik 101528@http://citycyclingedinburgh.info/bbpress/ <p>Without being an expert, I think the OV protection is to stop halogen lamps blowing up when you do an extended 30mph freewheel and as Steveo says it's current not voltage you need to protect the LED from. </p> http://citycyclingedinburgh.info/bbpress/topic.php?id=9554#post-101525 Fri, 22 Feb 2013 11:32:06 +0000 DaveC 101525@http://citycyclingedinburgh.info/bbpress/ <p>Hi Steveo,</p> <p>Many thanks for the helpfull advice. I have this <a href="http://www.rosebikes.co.uk/article/shimano-overvoltage-protection-sm-dh10/aid:196629">Shimano Overvoltage Protection</a> which I had thought about adding between the battery pack and the output of it to the lights. Its Overvoltage protection but would this help?</p> <p>Cheers</p> <p>Dave C </p> http://citycyclingedinburgh.info/bbpress/topic.php?id=9554#post-101517 Fri, 22 Feb 2013 11:18:53 +0000 chdot 101517@http://citycyclingedinburgh.info/bbpress/ <p>Of course Steveo is probably right. </p> <p>I was just thinking about 1.2 being ok instead of 1.5. </p> http://citycyclingedinburgh.info/bbpress/topic.php?id=9554#post-101515 Fri, 22 Feb 2013 11:13:53 +0000 steveo 101515@http://citycyclingedinburgh.info/bbpress/ <p>I'd be very wary connecting the batteries directly to the terminals of the light! Odds are dynamo lights have no current regulation and rely on the dynamo to never deliver more than 600ma. </p> <p>LED's are current driven devices, the voltage is (almost*) irrelevant so long as the current never exceeds their max rating. The problem with batteries, especially big cells like D, is they have virtually no internal resistance, leds also have a minuscule resistance. When you connect the battery to the LED you have a virtual dead short with currents exceeding the LEDs rating leaving you with a DED (dark emitting diode).</p> <p>Assuming the body has nothing but a rectifier inside; you'll need at least a resistor to limit the current to about 500ma ideally you'd want an LED driver but that's not entirely necessary.</p> <p>* LEDs have a minimum voltage before they start conducting, which for white is around 3v. </p> http://citycyclingedinburgh.info/bbpress/topic.php?id=9554#post-101513 Fri, 22 Feb 2013 11:09:53 +0000 chdot 101513@http://citycyclingedinburgh.info/bbpress/ <p>Should be fine. </p> <p>Rechargeables are all(?) 1.2. </p> <p>Always worked with my cameras (etc.) that take any AAs. </p> <p>Obviously Ds will last longer than AAs, but these are useful -</p> <p><a href="http://mobile.maplin.co.uk/module.aspx?moduleno=37379" rel="nofollow">http://mobile.maplin.co.uk/module.aspx?moduleno=37379</a> </p> http://citycyclingedinburgh.info/bbpress/topic.php?id=9554#post-101511 Fri, 22 Feb 2013 10:59:14 +0000 DaveC 101511@http://citycyclingedinburgh.info/bbpress/ <p>I have bought [:facepalm] a waterproof case, four D cells (and other stuff) to power my <em>other</em> bike's dynamo lights on the bike that has no dynamo wheel, as its currently clad in a studded tyre. I have two sets of dynamo B&amp;M lights on my commuters. Now, while in Maplin I bought their own brand rechargable D cells (half the branded price) which I now see are 1.2 volts and not 1.5 volts.</p> <p>Question, will this be enough to power my B&amp;M light? <em>I'll try it at lunchtime with a bench powersupply but I fear I have wasted a tenner (£4.49 for 2 D cells) on batteries.</em> Maybe I could take it all back and get a 5 cell battery holder? But my battery charger at home only has room for four so I thought it might be ideal.</p> <p>Cheers. Dave C </p>