Another question on LED bike lighting systems

[eHomer]

Can I tap the forum's knowledge of Bike dynamo lighting with LED's ?


I know it sounds superfluous on a Pedelec forum where there's already a nice big battery onboard, but I'm thinking about my human powered bikes.

Have the advances in LED lighting and the much lower consumption made dynamos less attractive ? I know they'd advanced to the point where they could keep the rear light temporarily on while stopped at traffic lights, but I believe the front light went out.

Are there any good ( and fairly cheap ! ) central battery LED light systems for bikes that use a 12v rechargeable battery with a good (many hours) capacity between recharging ?

 

[neptune]

I would say that it depends on what you are trying to achieve. In the original dynamo systems, all lights went out when you stopped pedalling. I believe some Raleigh roadsters with hub dynamo had the facility to keep at least the rear light on when parked. A battery tube was fitted onto the seat tube for this purpose, but I am not sure if it used throw-away batteries, or rechargables. Most likely disposables. Rim dynamos are only suitable for short trips, as they cause noticeable drag. Hub dynamos are much better, but expensive, unless you can find a second hand one.
Unless you do a lot of dark miles, use cheap battery LED lamps. Rechargable batteries are warranted if you do a lot of night travelling. If you want to use a traditional dynamo, fit an extra battery powered rear light.

 

[oigoi]

In my experience of messing about with dynamos they actually put out an ac current whereas an led usually needs a dc current. I did have one that powered my walkman when I was a teenager but I put the output of the dynamo through a bridge rectifier to make the ac into dc

 

[neptune]

@oigoi. What you say is true. Hoewever, remember that LEDs are diodes, Light Emitting Diodes. So if we connect two in parallel across the output of the dynamo, and connect them with opposite polarities, they will both light. One will use the positive half cycle and the other the negative half cycle of the AC waveform.

 

[eHomer]

Thanks for the replies, all info and ideas are appreciated.

Some of the "stay on" dynamo systems used a capacitor instead of a battery, but I don't know if that was for LED as well.

Looking on Ebay, there are some very expensive front lights for dynamos, with "daylight run dimming" and "run on" and all sorts of fancy jdeas, but I'm not sure how useful that would be.

I'm seriously considering building a complete lighting systems from parts, with LED bulbs, a small central rechargeable battery (maybe a pack of AA Nimh), and a dynamo to keep it charged.

The voltages and ac/dc conversions will complicate things a bit, but I'm very surprised that something doesn't already exist off the peg.

My initial simplistic thoughts lead me to believe that it would just be a case of buying propriety front and rear LED bike lights and connecting them together with one central AA NIMH battery pack and then adapting a dynamo to trickle charge it,

I'm ready to be shot to bits on this idea though, age doesn't necessarily bring wisdom !

 

[rog_london]

Some of the "stay on" dynamo systems used a capacitor instead of a battery, but I don't know if that was for LED as well.

Looking on Ebay, there are some very expensive front lights for dynamos, with "daylight run dimming" and all sorts of fancy jdeas, but I'm not sure how useful that would be.

The voltages and ac/dc conversions will complicate things a bit, but I'm very surprised that something doesn't already exist off the peg.

My initial simplistic thoughts lead me to believe that it would just be a case of buying proprietry front and rear LED lamps and connecting them together with one central AA NIMH battery pack and then adapting a dynamo to trickle charge it,

Of course they do exist 'off the peg' but they're not so common in this country as they are on the continent....

Germany has a requirement that bicycles have dynamo-driven lighting. This is because they consider it a problem that people use just batteries (rechargeable or otherwise) and they are liable to go flat at inconvenient times - so a dynamo has to be the primary source of supply.

They have some decent systems but they're not cheap, as you suggested. They are all LED types these days. With LEDs you can incorporate capacitors which will keep the lamps running while you are stationary. I understand something like two minutes riding gives a full charge to these and then the lights will maintain full brightness for up to four minutes while stationary. The ones I've seen (Busch and Muller) have 'running lights' and a main high power LED on the front - the main LED goes out when you stop but the running lights keep going, as does the tail light.

This is all driven off a Shimano hub dynamo in the front wheel - and there's negligible drag when it's working.

I doubt that the capacitor system would be much use with standard filament bulbs - they waste too much current as heat.

Rog.

 

[eHomer]

Thanks Rog.

I've just found this too: Dynamo LED Light Systems for Bicycles (electronic circuits)

 

[neptune]

Rog offers sound advice here. IMO it is a lot more fun to make something yourself, and you get exactly what you want at a fraction of the cost. Designing the circuit is fairly simple and you can get all the help you need here. First you need a dynamo, a hub dynamo is best. There are still plenty of the old Sturmey Archer types about in junk and scrapyards. You could start with a rim dynamo, and upgrade later. If you wish to charge batteries, then as Oigoi says, you need a bridge rectifier to change the dynamo`s AC to DC. Either buy a small bridge rectifier or make your own using four diodes[ not Light Emitting Diodes].

As you say, your battery can be four AA NIMH cells. It might pay to fit a 5 volt regulator between the battery and the lamps to protect against overvoltage, but that is unlikely to be strictly necessary. If you need more info just ask.

 

[eHomer]

Thanks Neptune.

I'm suitably enthused now.

quote:"and you get exactly what you want at a fraction of the cost."

My kind of talk !


I think this ebay item would be a good start for the rear light body: http://www.ebay.co.uk/itm/221133264929?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

My tinkering with boats has already made me aware of the need to use red leds rather than put white leds behind red covers. The spectrum produced from white leds changes the colour behind red glass compared with incandescent bulbs. I notice this one on ebay has the leds behind clear plastic.

Though, on second thoughts, I am a little confused again, because cheap led rear lights do use coloured plastic ?

 

[Deleted member 4366]

Red light can pass through a red translucent cover. White light is made up of all colours plus infra red and ultra violet. Only the red light can pass through a red cover. That's why you see it as red. The rest of the light is filtered, so presumably gets converted to heat, which seems a bit of a waste.

Making your own lights is a great idea if you're bored and want something to do over Christmas; however, the Modern LED lights that you can get from Ebay (or wherever) are so good and simple to use that they're almost certain to be a better solution if you need proper lighting for night-time riding. You can buy Cree t6 torches for about £12 with battery and charger, which you simply clip to your handlebars (no wiring) and rear lights that run off AAA batteries that run for days. When riding in daylight, you can unclip them, so no weight penalty and no complicated wiring. You can't beat simplicity. You can't buy the parts as cheap as you can buy the ready-made lights, so it makes no sense to make your own other than as an academic exercise.

 

[eHomer]

Red light can pass through a red translucent cover. White light is made up of all colours plus infra red and ultra violet. Only the red light can pass through a red cover. That's why you see it as red. The rest of the light is filtered, so presumably gets converted to heat, which seems a bit of a waste.

What I meant by "spectrum" was that white light from LED bulbs doesn't contain the same full spectrum of white light as a normal incandescent bulb. The problem is worse with green starboard lights, which appear blue when a white LED is placed behind the green lens filter.

Not such a problem with red, but it does change hue a bit, as well as getting much dimmer.

Anyone converting old boat nav lamps that were originally supplied with the coloured lenses for white incandescent bulbs needs to use coloured LEDs. (red or green) to avoid the colour shift that they get from white LEDs.

"LED’s work on a set colour wave length, so if a white bulb is placed in
a green lens it will usually result in a blue-ish light. A white bulb behind
a red lens will result in a very dull ‘claret’ coloured light which is often
not bright enough to meet the collision regulations. Therefore it is
important that you choose a direct colour replacement LED light bulb,
ie. green for green, red for red, and white for white. This applies equally
to ‘warm white’ bulbs."



from Navigation Lights Menu


Thanks for the info on the Cree T6 torches, they look like a good solution for the front.

 

[103Alex1]

I'm actually quite keen on front hub dynamos. The B&M system mentioned above is actually very good but I don't know how much they cost as they came with the bike (presumably because it is German). There is no noticeable drag and the upside is you never have to think about whether you've got charge for them so shouldn't ever be without lights unless a bulb goes / they can be on as additional lighting at no extra cost if you want to fit brighter battery-powered primaries.

My rear light from the dynamo kit is brighter than any of the pricey battery-powered ones I've tried, gets a lot brighter when I apply the brake and stays on for ages after I stop and turn off the main switch. The front one stays on when I stop at traffic lights etc. too (must be a built-in capacitor or something). There's also an auto-sensor setting option so lights come on automatically as light levels drop (great if you're riding towards dusk). The main benefit is pretty much worry-free lighting.

Other downsides - you can't easily fit front panniers with a front hub dynamo installed (apparently !) .. and you have to remember to disconnect the dynamo if you take the front wheel off.

 

[Deleted member 4366]

I'm actually quite keen on front hub dynamos. The B&M system mentioned above is actually very good but I don't know how much they cost as they came with the bike (presumably because it is German). There is no noticeable drag and the upside is you never have to think about whether you've got charge for them so shouldn't ever be without lights unless a bulb goes / they can be on as additional lighting at no extra cost if you want to fit brighter battery-powered primaries.

My rear light from the dynamo kit is brighter than any of the pricey battery-powered ones I've tried, gets a lot brighter when I apply the brake and stays on for ages after I stop and turn off the main switch. The front one stays on when I stop at traffic lights etc. too (must be a built-in capacitor or something). There's also an auto-sensor setting option so lights come on automatically as light levels drop (great if you're riding towards dusk). The main benefit is pretty much worry-free lighting.

Other downsides - you can't easily fit front panniers with a front hub dynamo installed (apparently !) .. and you have to remember to disconnect the dynamo if you take the front wheel off.

There's no drag when you have the lights off, but as soon as you switch them on, there'll be drag slightly more than the power you take out, so that if you have 5w bulbs front and rear, you'll get at least 10 watts of drag, which I reckon you should notice. You can't get something for nothing.

 

[103Alex1]

There's no drag when you have the lights off, but as soon as you switch them on, there'll be drag slightly more than the power you take out, so that if you have 5w bulbs front and rear, you'll get at least 10 watts of drag, which I reckon you should notice. You can't get something for nothing.

Never noticed any difference in effort/performance riding at night as compared to the daytime with the lights off but logically based on what you say I probably should ! Guess when you add human wattage to a half-decent motor any drag is not such a big deal.. there are so many other variable factors...

My own energy, daytime traffic, weight load on bike etc. all change considerably, so much it's really hard to detect subtle differences. I've hit some of my highest (non-downhill racing ) speeds at night and often my energy levels are actually higher at night so the bike sometimes feels easier to ride. Perhaps the carrying the weight of the day and all it inevitably brings seems like more than a few lost watts in the freedom of the night

 

[rog_london]

Never noticed any difference in effort/performance riding at night as compared to the daytime with the lights off but logically based on what you say I probably should !

With an LED system and a hub dynamo your total load including any inefficiencies in the dynamo probably come to less than 4 watts. You almost certainly wouldn't notice that.

Bear in mind that filament bulbs are not much more than 10% efficient whereas LEDs can be as high as 60% efficient. If the electronics controlling the LEDs is reasonably sophisticated (i.e. switch-mode converters of some kind) there would be very little waste. That's why those Busch and Muller lighting sets are not especially cheap.

Mechanical losses - because the dynamo is always turning if you're moving - would never be apparent.

Rog.

 

[eHomer]

With an LED system and a hub dynamo your total load including any inefficiencies in the dynamo probably come to less than 4 watts. You almost certainly wouldn't notice that.

Bear in mind that filament bulbs are not much more than 10% efficient whereas LEDs can be as high as 60% efficient. If the electronics controlling the LEDs is reasonably sophisticated (i.e. switch-mode converters of some kind) there would be very little waste. That's why those Busch and Muller lighting sets are not especially cheap.

Mechanical losses - because the dynamo is always turning if you're moving - would never be apparent.

Rog.

I was thinking along those lines when I asked the original question (honest )

I thought a really good dynamo hub, originally designed for incandescent bulbs would be a really efficient set up with LEDs, requiring about a tenth of the power generation.

I can appreciate that the up market systems designed for the German regs would be quite sophisticated in that respect, but was surprised that the bulk producers hadn't by now produced the same systems at much lower prices.

 

[Geebee]

Have you looked at Battery free bike lights | no mechanical drag, and I suspect you could diy something similar if you don't want an off the shelf solution.

 

[mtb1956]

I bought one of these. It doesn't fit my TRIKE 20. You are welcome to it for the cost of postage. It would make a useful source of cheap LEDs.

 

[Jeremy]

Have you looked at Battery free bike lights | no mechanical drag, and I suspect you could diy something similar if you don't want an off the shelf solution.

There will be a similar drag from these for a given power as there will be for any alternator/dynamo delivering the same power. They work by turning the bike wheel into the rotor of a fairly poor alternator, and generate power in same way as a hub alternator does, albeit with poorer efficiency because of the large magnet/coil gap (the hub units aren't, strictly speaking, dynamos, they are usually brushless alternators).

A well-designed alternator should be at least 85% efficient, losing only around 15% of the input power at worst. Even the old Sturmey Archer hub alternators were around 80% efficient, and they used some fairly poor ceramic magnets. The main downside with the old Sturmey Archer units (if you're looking at using LEDs) is that they used the AC from the alternator directly to drive the bike lights. For an LED set up you would need to add a rectifier and perhaps some smoothing to damp out the low speed pulsing a bit more.

TBH, I can't see the point in using a hub alternator or other form of wheel driven generator to power lights on an ebike. It's always going to be fairly wasteful overall, as the power ultimately comes from the ebike battery, anyway. For example, if you had an ebike that was 80% efficient in terms of converting battery power to motive power, and a hub alternator for the lights that was 85% efficient, then you would, in effect, be using the bike battery to drive the lights with an overall efficiency of around 68%. You can get a small DC DC converter with about 85% efficiency (or more) that will drive the lights directly from the bike battery, for less than the cost of a decent hub alternator.

 

[Deleted member 4366]

I was thinking along those lines when I asked the original question (honest )

I thought a really good dynamo hub, originally designed for incandescent bulbs would be a really efficient set up with LEDs, requiring about a tenth of the power generation.

I can appreciate that the up market systems designed for the German regs would be quite sophisticated in that respect, but was surprised that the bulk producers hadn't by now produced the same systems at much lower prices.

It all comes back to the same thing. You can't get something for nothing. Lights that help you be seen aren't very bright, don't consume much power, so you won't notice much difference, but if you want lights that light up the road, you need power that has to come from somewhere - either you or a battery. You'd probsbly be better off wiring your lights to the main battery and using your dynamo/alternator to charge the main battery. You could, of course put a dynamo on each wheel and use them to charge the battery while you pedal so that your battery will never run out.