Electrical wizardry - any electrical engineers out there?

[willpom]

Hi

This is an 'out of interest' inquiry which I may have a go at doing for the urban bike, perhaps the Audax if it works.

Installing Tacx Lumos bar end lights with indicators but rather than use AA batteries run it off the dynamo. https://www.tacx.com/products/extra/bike-lightning

Current setup: SP PV8 dynamo, B&M Luxos IQ2 U front & B&M Secula rear.

The Luxos IQ2 is the newer one with power in spades as well as the dedicated cable to the dynamo, so you can therefore run something (other than the USB charging) direct from the dynamo without turning the Luxos IQ2 on. Could run a cable under tape down to one bar end and in (drill a hole) to first light then another inside handlebars to second. But don't worry about that.

So my question is what electronic wizardry would I need to stabilise the dynamo supply and provide a few minutes standlight. My thoughts would be dynamo supply in, capacitor for standlight, some other gubins to stabilise (if you need to), then 2 outputs for each light, to be the size of an AA battery. If anybody could do a circuit diagram with parts required (from Maplin say) that'd be amazing!

Thanks, Will

[Brucey]

the tacx webpage says ' two AA batteries' implying that the lamps run off ~3V DC. However on the same page it says [4] 1.5 V batteries, so it isn't clear what the voltage is. Because the lights still need to work when you are using partially-discharged cells of various slightly different chemistries, these lights will probably work OK from 2.5V or 5V depending on which it actually is.

The USB output from your luxos spits out a regulated 5V, so in theory you ought to be able to run two of the tacx lights in parallel (if they are 6V lights which still work on 5V, this would be trivially easy, just wire it up); or series from the USB outlet if they are nominally 3V lights. If this works this will almost certainly be more efficient than taking a regulated 5v supply and converting it to a regulated 3V supply. However, (esp if 3V) there are problems;

1) do the lights 'remember' if they were last on or off for long enough to be able to turn them on and off even when they are in series?

2) If the tacx lights flash, they may not drop 2.5V all the time; if the current draw is zero between flashes then one of the lights will see the full 5V which (without steps to mitigate this possibility) will probably cause it to fail.

3) 6V or 3V, depending on the current draw, there is no guarantee that the hub generator will power both the usual lights and the Tacx ones at the same time.

If they are nominally 6V lights that will run OK from 5V I think this can be made to work, but if 3V... not so easy. Maybe there is an elegant solution to this but then again.... perhaps not. It kind of smacks of one of those things that might seem like a good idea until you actually have to do it; then you realise that it may be very difficult to do very well.

cheers

[old_windbag]

Looking at the data for these lights it seems to be two separate lights each with 2 AA batteries, so 4 for the set. Either way if it were 3V on each light or 6V feeding the two my feeling is perhaps a buck-boost PWM controller as a solution. If you wish to use the 5V of the luxos usb output then a PWM controller would typically allow an input voltage of say 3-40V DC, the output voltage can then be designed from chosen components to be from say 1V to 50V, the current of the LED lights is not stated but we're talking of IC's sourcing up to 3A or so( but your luxos source current will play a part too as well as Bruceys comment of not being able to supply all lights together ). I've put the link below as typical of whats available, if buying a plastic dual inline package you could knock the circuit up on some veroboard then put inside a tiny waterproof box. The IC given purely as an example costs just over a pound at RS trade counter ( better than maplin for the range of components supplied ). If you follow the links for documentation you'll find data sheets and apps notes giving example circuits and the calculations needed to set output voltage from given input etc. With an IC like this it means if it's 3v needed you can design as a buck, if its 6V you can design as a boost. The output side will have a reasonable capacitor to help the variation of current draw when bar end lights in use.

http://www.ti.com/lsds/ti/power-management/buck-boost-inverting-controller-products.page its a tl5001

There are hundreds of similar IC's but there are many online tables and apps notes to pretty well design a circuit for you, its then a case of buying the parts and building it up. You should be able to create something for £10-15 or less. I think the data sheet for the tl5001 has a 5v-3.3V circuit as an example but it should be fairly explanatory to achieve your goal. This may not be the answer you're looking for but it may give you some guidance to start off.

Edit: Having looked at the luxos usb output, it seems to indicate that under heavy load if the cache battery is discharged( by usb device ) then the usb is turned off until the cache battery is recharged. So the output is dependent on the draw from the cache battery and could turn off if discharged by the load of your lights. This is the gist of the translated german B+M info. That may or may not be a show stopper depending how power hungry the tacx lights are.

[willpom]

Hi

Each light runs off 1 x 1.5V AA battery. They are independent in this form.

I'm talking about the un-regulated pass thru on the dynamo supply side of the Luxos. Not the USB as that can be used for other things. So in effect straight off the dynamo. Don't know if that makes any difference? I thought it was the amps that account for the draw and volts was a rating at which things work? Physics was never my strong point.......

What is an IC?

[[XAP]Bob]

Integrated Circuit (microchip)

The Dynamo output is a nominally constant current varying frequency AC.... You'd need a bridge rectifier and a smoothing capacitor and you'd normally end up with about 6V - too much for the lights on their own.

[al_yrpal]

http://www.pilom.com/BicycleElectronics ... rcuits.htm
Or
http://makezine.com/2009/06/07/how-to-p ... e-charger/

The parts you need from Maplin :-
AQ96E W02 diode bridge rectifier
UJ54J L78S05CV voltage regulator
VH52G PC Elect 1000uF 63V capacitor

Plus circuit board, pins etc..

Connect to a Teknet type battery pack and power your lights and what have you from it

Al

[Brucey]

....Each light runs off 1 x 1.5V AA battery. They are independent in this form....

ah! In which case there must be a voltage doubler in each lamp; you can't run LEDs from 1.5V without.

I suspect that by the time you have regulated 6V to 1.5V and then doubled up again the whole arrangement will lack efficiency, but if the current draw is small enough, maybe that won't matter.

BTW the appeal of using the 5V USB output is (if I understand it correctly) that there should be a small backup battery in the Luxos U so that the USB output will keep working for a while when you stop. If instead the tacx lights go out every time you stop, and then need to be turned on again when you start moving, that would be annoying, so Al's suggestion of a rechargeable battery pack for the Tacx lights is a good one too.

cheers

[old_windbag]

So you wish to use the dynamo AC output. Well rectify and smooth as per above posts ( diode bridge, smoothing capacitor etc ) then use a buck regulator as suggested in my previous post. I've dug out a fully built module now we know you need buck only that is based around switching regulator hence more efficient than the linear regulator. An example is the link below:-

http://www.gearbest.com/development-boards/pp_139336.html?currency=GBP&gclid=CLLvh_uUs8kCFUjmwgod260PGQ

Not very expensive when added to the input components and a waterproof box, connectors and so on. This is just one of many modules available but it has the input and outut voltage range you desire and good output current ( 3A max ). Fully adjustable output voltage to match what you think is correct for the Tacx.

This should be easy to experiment with. Try ebay, farnell, CPC, RS components, Digikey, maplin as alternative suppliers I'm sure one of them will supply it.

[willpom]

Well, I've emailed Tacx for the specs, will see if they are forth coming. Otherwise I suppose the best thing to do is buy a pair and investigate.

An example is the link below:-
http://www.gearbest.com/development-boards/pp_139336.html?currency=GBP&gclid=CLLvh_uUs8kCFUjmwgod260PGQ

Would this be the whole gubbins or would I also need the diode bridge etc?

BTW the appeal of using the 5V USB output is (if I understand it correctly) that there should be a small backup battery in the Luxos U so that the USB output will keep working for a while when you stop.

I understand this would make it simple but I'd want to keep the USB free (especially if I use on the Audax bike) to power other things. The B&M Secula runs happily straight off the dynamo and has a built in standlight so I guess there is a capacitor in it somewhere to store charge for a few minutes.

Was hoping for an elegant solution small enough to fit in place of one of the AA batteies. I'm probably being very naive about this being easily attainable.......

[old_windbag]

You would still need the rectifier and cap if running from the dynamo output. If from the usb then this should do what you need. This is not huge around 45mm l by 20mm w by 14mm h. Considering the circuit thats not too bad and all you need is a pot twiddler or jewellers screwdriver to adjust the output to whatever value you need, youll need a multimeter for that. You could get away with this and the two extra components soldered in mid air and tacked to the back of the module then heatshrink the whole assembly with inline wiring. But to do that well its best to have a hot air gun. It wouldn't be hard to find something small to fit it in though, its a big hobby market out there. This module is also short circuit protected for any mishaps along the way.

Edit: one thing to note is that to get full 3a out may need the heatsink added but somehow i can'see you drawing that.. . 4.5w from the dyno hehe. So in reality i wouldn't be expecting to drive this very hard but it may be worth paying a couple of pounds more and get this from a reputable manufacturer as it seems as with so much today that there are inferior quality chinese copies. That shouldn't be hard though going to rs, farnell, maplin etc.

[edocaster]

Connecting a device made for batteries to a bike dynamo while parallel to existing made-for-dynamo lights is not 100% trivial. The voltage required for your design may either be too high to light, or low enough that it robs the main light (unless you limit the current).

Does the Luxos keep closely to the 6V spec?