christ0ph

A couple of days ago I realized after I posted a question on the Tung Lin dynamo (which is an old style unregulated type, so the voltage can go up to as much as 18-20v.) that I should find and post some regulator circuits here.

Anything over their design voltage - like 18-20 volts that I read one users saying the Tung Lin put out at times, could burn out a lot (most?) LED lights - even many of the ones with internal voltage regulation circuits because its simply too high.

This is a concern for me if I get it because I have an inoled which is a great light but I don't want to fry it with voltage outside of its design range. They sell a regulator for higher voltages.. but I can't justify spending $20 for a $5 part.)

Dynamos these days are usually 6 volts but having a 12v dynamo has a lot of things going for it, (more power) if you can tame the beast to give you a reasonable voltage even when you are flying downhill .. (note, when engaged, if there is a bigger power load, it will have more drag)

So...I was just reading another board and I came across these very basic tutorials on making a basic power supply.. which is a transformer.. AC-DC rectifier and voltage regulator.

This is exactly what's required.

The power coming out of a dynamo is going to be AC, just like the AC coming from the secondary of a transformer.

Basically the latter 2 of these tutorials apply. (I'm including links to all 3 for completeness, because they go together)

To go from AC (dynamo) to unregulated DC (LEDs, etc) all you need is four diodes (configured as a bridge rectifier, which you should also be able to buy as a single part with four leads- its more convenient that way) For lighting purposes, no filtration is really necessary unless you are going to also power cell phone/GPS/MP3 player.. but you still want regulation to prevent overvoltage...

The three links below represent a good overview of power supply basics, in 3 parts - in video format.

Basically its useful to know to save a couple of bucks..

I saw the original links here

Hey guys

I just got done with a trilogy of videos that will show you how to make simple regulated power supplies. The first video is about how to safely get from mains voltages down to a lower, safer AC voltage. The second shows you how to build a simple unregulated power supply. Then if you want voltage regulation, the third one covers simple linear voltage regulators. Hope this is useful!

Electrical Transformer Tutorial

Diode Tutorial and How to build an AC to DC power supply ***

Voltage regulator tutorial and USB gadget charger circuit ***.

If you want to build a much more fancy DC-DC converter, Google "Buck converter" or "Buck-Boost converter" But that's serious overkill for most simple lighting and charging applications.

CaptainCool

I'm not well read on dynamos, but I'm guessing you'll need a DC-DC converter if you choose a 12v dynamo over 6v in order to get more power.

christ0ph

Its not necessary for most people here's applications. There are reasons you might want one, though.. (the highlighted ones below)

"4. The system should meet all of the design stipulations stated below:
I. Circuit should receive large variable DC voltage on the input
II. Circuit should output a constant DC voltage
III. Circuit should begin output without needing to meet an initial threshold voltage
IV. Circuit should output a maximum load current
"

Basically, if you just want lighting, with no charging, or if you dont mind only charging when you are riding at a respectable speed, (which I am guessing is pretty low on the 12v dynamo) save your energy and just build the simple regulator but oversize the components.

the need for a buck-boost converter depends on if you are wanting a constant output voltage at all speeds.. (that is a very demanding, perhaps even semi unusual design requirement..)

Read this paper..

Also, some batteries want to be charged at less or the same as their output voltage, others want more. Pick the appropriate voltage for your application.

A well designed simple voltage regulator is going to limit the voltage quite adequately...The LED light will work on a battery or on a direct connection. The regulator is only going to heat up when you are flying down that hill at 35 MPH.. (But better it heat up than your expensive LED light.)

You can mount the voltage regulator to the inside of an aluminum box whose outer surface will radiate that heat away nicely..

CaptainCool

Actually, I hadn't considered that, but it is a good point. And now that I think about it, a wide-input flashlight module like, say, this one would handle almost everything past the rectifier and first big cap, on either dynamo voltage.

I'm assuming a 12v dynamo puts out twice the voltage and half the current of a 6v dynamo at the same speed, and the rated voltage is provided at some nominal cruising speed. With a (low dropout) regulator, there's a tradeoff:

6v:
- Only lights up/charges closer to cruising speed
- Provides twice as much power
- Generates little heat

12v:
- Lights up/charges at a lower speed
- Half as much power going to the light
- Other half of the power turned into heat

christ0ph

The Tung Lin dynamo is 6 watts, but you're right, a fair amount of energy can end up wasted as heat in a lot of different situations.

I read somewhere that the Tung Lin can under some circumstances put out 18v or even a bit more.. like the older dynamo hubs.. so I'm concerned..if I get tha one, to limit or utilize that extra voltage.

A flashlight or LED driver is very flexible, especially compared to nothing at all..
Those LED drivers are pretty sophisticated devices, they contain a switching power supply, basically.

The economics of scale make them very affordable! But I don't expect a unit - whatever's in there, thats designed for as low as 6volts - to handle >18 volts gracefully.

christ0ph

Just stumbled across this - very nice..

Anybody who wants to build a homebrew bike LED lamp and drive it from a dynamo should check these two web pages out. This guy really did some amazingly thorough work on documenting dynamos and then building a versatile dynamo/LED solution.

He tests a bunch of different dyanamos as well as explains the rationale for using various kinds of rectifiers and LED power circuits - all the way up to a pretty sophisticated hybrid voltage doubler/regulator driver

All the commercial bike lights use some kind of driver. My post above was about using a commercial light wih an integrated driver..

If you are building your own lamp from raw LEDs you need something like this, either a commercial one (they are very cheap now, so that makes sense) or build your own.. which can be nicer..

This shows why its so useful.

https://www.pilom.com/BicycleElectron...moCircuits.htm

https://www.pilom.com/BicycleElectronics/Dynamo.htm

Looigi

I didn't check out your links but I'll mention that most three legged regulators and similar dissipate power equal to the excess voltage times the current draw. The need heat sinks and get hot due to this. What is much better is a "switch mode" regulator which is much more efficient.

unterhausen

the unloaded voltage of many hub dynos is reported to go up to 100v. So it's generally a bad idea to switch on electronics while riding. But if you are driving a power led, most of them can take 1A which exceeds the current driving capacity of all of the hubs I'm familiar with. So it is unlikely to matter what the voltage gets to when driving an LED because the LED will drag down the voltage to the Vf of the LED. If powering something else, like a power supply, there may be an issue.

christ0ph

The light I'm using (inoled extreme) is very bright. It also must have an internal LED driver - a nice one, as..

this is what its back looks like.:



Both the headlight and my makeshift taillight (a oldish red Lumileds luxeon star LED) continue working (although not anywhere near as bright) for a while - several minutes at least- after the supply voltage (currently just a battery pack) stops.


This is what I'm slightly worried about... just with a 12volt dynamo..

https://www.peterwhitecycles.com/inoled.asp > "inoguard"

Or here: https://www.inoled.de/en/accessories/inoguard

BTW, this light combo is very nice.. - my old light was a dynamo light but it used an incandescent, and that was nothing like this in terms of brightness, and when i stopped at traffic lights, it went out completely.

If I'm not adding additional electronics, there really is no reason to get a 12v dynamo.. maybe I'll just get a 6v one..