Two front dynamo headlights plus rear light?
 

I have multiple bikes with dynamo head lights.

I was wondering if modern dynamos can provide enough output to power two headlights and a rear light.

Specifically, this is the setup I was thinking of:
1. SP PV-8 dynamo
2. Two B&M IQ-X headlights
3. One B&M rear light

Any thoughts?

Cheers, Duppie

Presumably the illumination will no pick up as quickly when you increase speed with 2 headlights as compared to one. At full speed the combined light output of 2 lamps may be higher or not than output of 1. However you will have more control on the shape of the illuminated area.

As in PBP..
 

I'd suggest a Battery headlight for the 2nd one, to turn on at the crest of a hill (In Chicago?), with an anticipated fast down hill,
so you have enough light for that rate of speed..


doubling the load means the dynamo power is split... so perhaps less output per light, .. not double the brightness..


I used to have a Schmidt E6 halogen bulb head light pair secondary was switched On or bypass through,
Primary was switched On/Off..

For When you went faster and needed that extra light



..

When I first bought a dynohub (back in 2013) I picked up a couple discontinued D Lumotec Oval lights on a clearance price. I ran the two headlights wired in series, I needed to go faster to get the lights to initially light up (instead of a rapid walk pace, I needed a jogging pace for the lights to light up) but I had twice the light at normal riding speed.

Thus, I think it should work fine for you as long as you do not have to pedal slowly up a steep hill that is tall enough to take more time than your standlight will last, as your standlight might be your only light at slow hill climbing speeds.

Taillight, I did not use a dyno powered one but since taillights take very little power compared to headlight, I would assume it would work but like the headlight it might not work well at lower speeds.

I think you need to wire in series, but wiring it in series means that both lights have to be turned on, as each electron will go through both lights, turning one light off would turn both off. I have no clue if it would work in parallel, I only tried it in series.

Since then I have bought better lights and went back to a single headlight. No longer using dual lights.

https://cimg4.ibsrv.net/gimg/bikefor...ea8019cbe7.jpg

I think the power draw might be getting significant with two, probably over 10W. While you can get that much power out of a dyno ( Dynamo LED Light Systems for Bicycles (electronic circuits) ) it all comes from your legs.
With my IQ-X I don't really need a brighter light (maybe in the rain) but a flood beam on fast downhills. For this my Zebralight helmet light works perfectly well.

Someone here on BF did this with his daughter's bike. [MENTION=63590]jyl[/MENTION], would you care to weigh in and say how well it worked?

Running two headlights in series was a fairly well known technique back in the era of incandescent headlights. Compared to modern LED lights, they were truly weak, so any advantage or improvement was worthwhile. One virtue of incandescent bulbs was that they were designed to be electrically identical. When operating, they were nominally 12 ohms in resistance, resulting in about 6VAC out of the dynamo.

Modern LED headlights don't seem to be designed to look like a 12 ohm resistance, so it's harder to know how it will work with two wired in series. In addition, some dynamos are intended to be used with lower power headlights, so this just makes it harder to know if they could power two lights in series.
My guess is that if you wire two identical LED headlights in series, there's a good chance that it will work. Presumably one headlight will have the taillight attached. The other headlight will have to be isolated from the frame... many are designed to have one terminal connected to the frame via the mounting hardware. If both lights were to have their ground terminals connected together through the frame, I think that one of them wouldn't get any power.

Be aware that operating two headlights in series will result in less light when riding at low speeds. Most schemes like this include a switch to short out one of the headlights at low speeds.
I've made a LED headlight that was equivalent to wiring two headlights in series. It included a circuit that monitored the dynamo speed and shorted out one half of the LEDs when below 14mph. The increased light when operating above 14mph was noticeable, but wasn't as much as I hoped for. The next headlight that I built was the equivalent of one headlight.... the extra weight and size of the extra LEDs, optics, etc.,, just wasn't worth the small additional light.

Steve in Peoria

Good point on grounding.

He said he is using an SP hub. I also used a SP hub in my light setup in the photo above in post number 4. SP hub is not grounded to the frame.

I ran one wire from the hub to one light, grounded both lights to the shared steel bracket (the bracket was part of my circuit), the other wire back to the hub was from the other light. Thus, I grounded the mid point in my circuit. Not sure what the OPs plan is however, he or she should be careful how they ground it.

And the taillight might complicate grounding, some are and some are not grounded.

I suppose if you are used to dealing with lights that use the frame ground, perhaps it's okay. Personally, I get asked to help fix people's lights now and then, and get annoyed trying to figure out how things can go wrong. I've seen cases where the taillight and headlight have a grounded terminal, and the ungrounded taillight wire gets plugged into the headlight connection that is grounded. Seems like the manufacturer could at least have some form of polarized connectors when this is possible.

On the plus side, it is sometimes possible to open up the light and cut/break the connection to the grounded mounting point.

Steve in Peoria

Wouldn't work well.
Each IQ-X can consume up to 7W. The dynamo hub only delivers 3W above 20kmph.
So you would need 5 hubs to power two headlights at 20kmph.
https://www.bikeforums.net/electroni...l#post20716028

https://www.bikeforums.net/electroni...l#post20718471

I use double wire all the way. Peter White sells very skinny wire that I am able to get to the weeping hole in my fork. I don't ground it to the frame anywhere

Thank you all for responding.

I am not *that* powerful or fast of a rider, so it seems like I may not be able to consistently get full brightness out of both lights, which would sorta negate having two lights to begin with.
For now I'll stick with one IQ-X. I have that light on another bike and I am quite happy with it on that bike

I'd look at the watts carefully.

Hub dynamos are available in 1.5W, 2.4W, and 3W.
The old Bottle dynamos are up to 6W (unregulated?)

Headlights are also made for different watts.

So, for example, the B&M One-Five is designed for 1.5W. So, you should be able to wire two of them in parallel (or serial) to get 3W (see below).

However, that B&M One-Five is rated at 30 Lux.

The B&M IQ-X is rated at 100 Lux.

To hack stuff together, you'll really need detail specs of Volts, Amps, Watts

Watts = Volts * Amps

I think it is:
Parallel wiring: Volts constant, Amps half
Serial wiring: Amps constant, Volts half.

A battery sink will help with evening out the power input/output.

The notes indicate that the B&M One-Five could be damaged by a 3W dynamo. I'm a bit surprised by that, but to some extent it will depend on the volts.

So, for example, a 12V, 1.5W (0.125A) light should be perfectly happy being connected to a 1000A, 12V car battery, but it could be damaged by a 24V input, even at low amps.

If it was being hooked up to a power source with a constant voltage, that sounds correct.

Dynamos, on the other hand, are relatively complex. They can be modeled as a voltage source that is proportional to the dynamo's rotational speed. This voltage source is in series with a large inductance (which provides an impedance that is also proportional to the speed) and a fixed resistance.

Combine this with the possible use of a switching power supply in the light, which in the case of a buck converter, effectively has a negative resistance (i.e. when the voltage goes down, the converter will try to draw more current).

Figuring out how these all interact requires some circuit analysis. Calculations were much simpler back in the days of incandescent bulbs... but they were so incredibly dim by comparison!

Steve in Peoria

Yea, and there are options to convert the IQ-X into DC.
But for this, the IQ-X E would be cheaper - just the on/off-switch isn't available then.
IQ-X für Forumslader: Forumslader
http://www.forumslader.de/fileadmin/.../Manual_EN.pdf
http://www.forumslader.de/fileadmin/...st_english.pdf

I don't think so. The dynamo makes A/C, and the lights expect that. A battery provides DC and expect it on input, too.

LEDs require DC input.

It is easy to convert from AC to DC with a bridge rectifier, and perhaps some capacitors.

Going from DC to AC can be done in a number of ways. I believe high frequency is also used to regulate power.

Many of the more advanced headlights should already have some provision for stopping, and low voltage, thus using either batteries or capacitors.

Dynohubs are AC. The hubs are alternators with permanent magnets, nothing more, no rectifiers, no voltage regulators, etc.

The rectifier is built into the light if an LED. And the light usually has some ability to protect itself from too much power, such as when going down a hill.

The old incandescent sidewall lights usually lacked over voltage protection, but those now are mostly in the scrap heap although I have a few in in a box somewhere. (I added zener diodes to mine to trim off the peaks on downhills.)

Exception - some taillights lack the rectifier, but since you are supposed to wire your taillight to the headlight, the manufacturer(s?) that makes taillights without rectifiers provides rectified current to the taillight.

I am pretty sure the output of a dyno is DC, in the sense that the output voltage doesn't cross ground. Dynos are DC generators. The fact that the output looks a lot like a sine wave and you can treat it like AC notwithstanding.

Boy, can we add more misinformation? Let's try harder.

are you addressing that to me?

Not sure what a ground has to do with it. There are two wires out of a dynohub. On Shimano hubs, one wire is grounded to the fork and on SP hubs neither wire is grounded to the fork, I have not used an SON so I do not know about that one and I have never seen a Sanyo. All three hubs operate the same way, AC current to the two wires.

If you tried to charge a battery directly from hub output, it is not going to work unless you use a rectifier. If you include a rectifier to convert AC to DC, you could actually charge a battery with the hub output.

I actually built up a four cell NiMH AA battery charger that works from hub output, but I only built it for emergency use if my other charging gizmos failed, it had no auto shut off and all four batteries of the same brand and model would have to start at a nearly identical state of discharge to charge properly. Thus it was not an ideal way to charge batteries but I thought for emergency backup since it weighed almost nothing, it would work. I included a small volt meter on it so I could see charging progress.

I can't think of anything ...

I've got two SON hub dynamos and two bottle dynamos. They all generate AC power.


Steve in Peoria

You're sure wrong. All bicycle dynamo hubs do deliver only AC.

Use an Oscilloscope, hook it up, spin it, and watch the screen..

and you will know..





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