Hub Dynamo-DIY Voltage regulator questions

[NATURAL ANKLING]

Hi,
Would of thought by now there would be a an add on to hitch up to any AC generator to a pack including battery/s.
Which would make these cycle dynamos very attractive for most commuters / enthusiasts
Saves all those home projects we make over the years.

[andrew_s]

The Schmidt/SON website says that you've got to be doing 25kph before you get extra light overall from a second lamp, and I would expect that you would need to be going quite a bit faster before it actually looked any brighter (at least without doing on-the-move comparisons by switching the second lamp on and off).

Whether there's a speed threshold will depend on how much the AC waveform is smoothed by the lamp electronics.
Back in the early days of LED lighting, I had a DIY light that was just a bridge rectifier and 2 Cree LEDs in series. That would flash when you turned the hub axle one notch by hand (pressing on the SON spade terminals so the snap forwards wasn't restricted by my grip).

[[XAP]Bob]

It is interesting that this works for you. In the 1970s, when dynamo sets were sold without regulators, the inevitable result of the headlamp bulb blowing was that the output voltage would rise, due to the much lower current drain of the rear lamp, and the rear lamp would blow shortly afterwards. Are you using a high power rear lamp, or one with overvoltage protection?

If you are always charging then the open circuit need never arise - the lack of OV protection on my Biologic ReeCharge led me to fit a couple of switches - one to disconnect power from the ReeCharge (so I get all the power to lights) and one to the headlight (so I can turn that off in daytime).

The tail light wasis/ my "nominal load" to ensure that the voltage didn't go crazy at high speed.

Modern LED lights have protection built in.

I'm guessing it's never really been tested heavily, since I don't think I ever got to a zero load on the rectifier situation....

[robc02]

It's worth mentioning that a silicon diode bridge, while a simple option, loses approx. 1.4V across the two conducting diodes, resulting in approx. 0.7Watts loss at 0.5A. This might not sound much but is a good proportion of the rated 3Watts. A worthwhile improvement can be gained by using Schottky diodes instead of silicon (approx. 1V drop per pair instead of 1.4V), but the best circuit is an active rectifier using MOSFETs.

The drawback is that for any circuit where the output voltage might, even momentarily, exceed the input - such as when charging a battery or capacitor - the conducting MOSFETs will be a near short circuit to that battery / capacitor. To overcome this more complex triggering arrangements are needed - but these are available on chips such as the one described here. For a simple circuit directly driving an LED the four MOSFET circuit should do fine.

I haven't tried these circuits myself, as I've always bought commercially available lamps for their optics - and, of course, they come with ready sorted rectifier and standlight circuits.

[edocaster]

The Schmidt/SON website says that you've got to be doing 25kph before you get extra light overall from a second lamp, and I would expect that you would need to be going quite a bit faster before it actually looked any brighter (at least without doing on-the-move comparisons by switching the second lamp on and off).

Not quite the same, but when I tested getting extra light from 5 LEDs in series vs using a voltage doubler (effectively behaving as 2.5 LEDs) the crossover point was as low as 15km/h: http://www.candlepowerforums.com/vb/showthread.php?385350-5x-Cree-XM-L-dynamo-light-(in-progress)&p=4438000&viewfull=1#post4438000

Of course, shorn of using two completely separate lights, you are spared having to go through two sets of bridge rectifiers, etc.

[Brucey]

...Whether there's a speed threshold will depend on how much the AC waveform is smoothed by the lamp electronics.
Back in the early days of LED lighting, I had a DIY light that was just a bridge rectifier and 2 Cree LEDs in series. That would flash when you turned the hub axle one notch by hand (pressing on the SON spade terminals so the snap forwards wasn't restricted by my grip).

I agree re the smoothing. Re the low speed performance; I've noticed the same kind of thing with Schmidt generators too. I'm not sure that all hub generators have such good (non-lossy) flux linkage though.

Also if there is another path for the (lower) current to go at a lower voltage, it'll go there instead; my rear light starts to conduct at about 2V and when I'm wheeling the bike slowly, only the rear light flashes.

cheers

[bikes4two]

I’m the OP of this thread – thank you all for your comments and since my original post I’ve been active in finding a dynohub/USB charging solution to meet my needs.

THE VOLTAGE REGULTOR
• I looked into the various posting in the thread for a DIY option, but after careful consideration I bought the Kemo M172N for £27 delivered, from Amazon UK (the ‘N’ version offers up to 800mA at 5v on the USB connector whereas the non ‘N’ versions only give 300mA max, so you’re not making the best of the dynohub’s output power).
• The Kemo is not as pretty as the E-werks but it sits neatly on my seat stays and I can see the green LED charging ‘on’ indictor whilst pedalling and of course is reasonably priced for a known working solution.

TEST RESULTS
• My electrical load will be a Lithium Ion battery pack (12,000mAh used for testing purposes) or my newly acquired smartphone which I will be using solely as a handlebar mounted GPS device (Doogee DG700).
• For testing purposed I cut a USB lead so I could measure DC voltage and current drawn from the converter into the load (in this case my Doogee DG700, switched on with the battery requiring charging and the screen on with a bright white background).
• I mounted the dynohub fitted wheel in my truing stand, attached a cyclometer for speed indication and connected up the Kemo.
• With the wheel spinning (care of my 2-speed power drill – chuck pushed against the tyre tread) I got the following 5 volt output from the Kemo:
- 5.5MPH delivered 0.15Amps (150mA)
- 13.5MPH, ) 0.47Amps (470mA)
• By comparison my standard mains USB wall charger pushed out 0.45A (450mA)
• Connecting the battery pack in lieu of the phone gave very similar results

ROAD TESTING
• Unfortunately my cheaply acquired HB-NX30 dynohub (bought used as ‘not known as working’) is intermittent in operation, so I am awaiting the delivery of a new dynohub and spokes to build up a new wheel hopefully this week-end.
• Once I have a stable setup, I will carry out some road tests to see how long it takes to charge the battery pack and the reliability of the whole shebang over time (I guess I’ll have to go cycling in the rain – heck!).

[nickpaton]

Interesting and what appears to be a well developed circuit. Believe it can easily be replicated on Veroboard or similar. Google Translate converts to English http://www.gregorkarnas.com/radio/projekt/usb/index.htm

[DoctorRad]

The simplest way is to use four NI-MH batteries to passively regulate the voltage.

I've seen it opined that this works up to a point, but once the Ni-MH batteries are fully charged, if there's no discharge, then you are effectively over-charging the Ni-MH cells, which will quickly destroy them. Larger cells will help, but do you really want to be lugging around 4x C or D cells? That said, 4x high-capacity D cells would be a pretty good reserve of power.

Once the batteries are fully charged, however, they will quickly heat up if charged any more, so one way to prevent excessive overcharging would be to use a thermal switch to disconnect the dynamo if the batteries' temperature rose too high. Ideally, you'd probably want to do this at around 50C or less. What I was never able to find was a small, self-resetting thermal switch with which to try this out. Now I look again, though, these might work if they'd fit in the middle of four NiMH cells:

http://www.ebay.co.uk/itm/291558407397

[DoctorRad]

Interesting and what appears to be a well developed circuit. Believe it can easily be replicated on Veroboard or similar. Google Translate converts to English http://www.gregorkarnas.com/radio/projekt/usb/index.htm

Looks fairly standard, but I wonder if the LED and resistor permanently across the output would be enough to prevent the regulator from frying itself if there was no device on the USB port? It probably wouldn't take much of a load but I don't know if a few tens of mA from a standard LED would be enough.

[DoctorRad]

Hi,
Would of thought by now there would be a an add on to hitch up to any AC generator to a pack including battery/s.
Which would make these cycle dynamos very attractive for most commuters / enthusiasts
Saves all those home projects we make over the years.

This is the most economical solution I've come across which claims to have over-voltage (no load) protection: http://cycle2charge.de/index.php/en/

[jacksonz]

I've used the 4x Ni-MH battery technique for many years now. It's a hack, but at least for me it works very well.

Certainly the batteries should be disconnected from the dynamo when no devices are being run or charged, otherwise there is a definite risk of battery overheating/damage. I run an Etrex and charge my phone from the battery pack during the day's ride. I've never had a problem with overcharging. After a recent 4 month cycling holiday I tested the batteries in a smart charger and could not detect a performance problem.

It probably works because I ride slowly and stop quite a bit, so that some kind of balance is achieved between input and output.

I added 2x 7.5 volt Zeners across the dynamo to protect against overvolting. No doubt if the battery pack accidentally disconnects then a high voltage will be applied to the dependent devices (if there is no zener protection).

In practice the system works well, but I think it would only suit those that like experimenting....

[NATURAL ANKLING]

Hi,
USB out put is 5vdc, li-ion batts should not see over 4.2 volts to be safe.

Any usb plug in charger should limit that peak to battery

[DoctorRad]

Hi,
USB out put is 5vdc, li-ion batts should not see over 4.2 volts to be safe.
Any usb plug in charger should limit that peak to battery

True, but we're not talking about hitching a Li-ion battery up directly to a dynamo or a USB device. Two possible solutions involving batteries are:

1) Use 4x NiMH (not Li-ion) series cells in series across the output of a rectifier attached to a dynamo. These will limit the voltage across the output to a nominal 4.8V (more when fully charged) which is still within the USB voltage spec. You could also use 5x or 6x cells (6.0V or 7.2V nominal) and regulate their output down to 5.0V for USB. Be careful in either case not to over-charge or over-discharge the cells.

2) Use a USB cache battery (external battery pack) after a dynamo-USB regulator to store energy when not needed (devices fully charged etc) to use later. These packs are usually based on Li-ion batteries, but include both charge regulation and post-battery voltage regulation to 5.0V for USB. One of the better brands I've come across for this is Zendure. Their packs are very rugged and don't have a switch to start any attached device charging - very useful when the battery pack is buried inside a handlebar or frame bag. They also support pass-through charging, i.e. they will provide power at the same time as accepting it from their input.

[ConRAD]

Aiming to increase the buffering capacity of too tiny batteries such as the ones incorporated is some ac/dc usb devices (e.g. Luxos U, e-werk usb, etc.) I’m testing the below arrangement.
With a standard e-werk set at 4.9V I repeatedly varied the speed from 10 km/h to 20 km/h alternating in-the-between frequent and prolonged stops (0 km / h) ..
With the GPS switched-on and set at 50% backlight everything seems to work perfectly.