I'm in the planning-phase of a bicycle mounted Arduino project, and my idea for powering it is using a good old-fashioned 6V bicycle dynamo. I'm a little cautious though, as these things (as far as I understand) produce a very "dirty" 0-6V of AC power, and I need to rectify and regulate this to a fairly clean, stable 5V DC.
Newb that I am as far as electronic hardware is concerned, I'm looking for some hints and tips (maybe if you've done something similar) as to what sort of circuitry this would involve. I know I will need a rectifier, a voltage regulator, some means of smoothing it all out (caps?), and probably some sort of buffer for under-current/power conditions (capacitor(s), a NiMH battery?).
EDIT: Looks like typically about 500 milliamps. www.instructables.com/id/Dynamo-powered-LED-bike-lights/ The Instructable also has a circuit for rectifying and smoothing the power that comes from the dynamo. They use a red LED for the taillight as one of the diodes in the rectifier. Clever.
Futt:
I'm in the planning-phase of a bicycle mounted Arduino project, and my idea for powering it is using a good old-fashioned 6V bicycle dynamo. I'm a little cautious though, as these things (as far as I understand) produce a very "dirty" 0-6V of AC power, and I need to rectify and regulate this to a fairly clean, stable 5V DC.
What will happen when you stop for a red light? How about uphill slogs? Downhill coasting? Bicycle dynamos are more like energy harvesting devices than they are like voltage sources.
You'd need a really big capacitor to even the load across very short periods (walking the bike across a street?) Rather, I'd want to use a rechargeable battery of some sort as the "evener" of source. As a bonus, if you don't get enough energy from the dynamo, you can recharge the battery from the wall, too
There are specific solar energy havesting solutions that act as battery chargers and voltage converters. I'd look at one of those, perhaps, plus a bridge of Schottky rectifiers to minimize loss from rectification. You can run the Arduino Pro on the 3.2V-4.2V you get out of a LiPo battery, in 3.3V mode. If that's not good enough, you can use a switching boost converter to step it up to 5V, at the cost of some efficiency loss. I do this in a device I've made, works fine!
It sounds like what you want to power using the dynamo is the Arduino. Is that right? Or something else?
One problem, as jwatte says, is that your power from the dynamo will be intermittent. Also, as robtillaart says, the dynamo will sometimes produce more than 6 Volts. Apparently, dynamos can occasionally produce as much as 14 Volts.
Can you tell us what you plan to power with the dynamo? You have listed the elements of the circuit you will need. Particularly a battery seems essential. If you are looking for help sketching out a specific circuit, you should tell us what you want to power.
Wow, thanks guys! Lots of great resources here - surprised I didn't turn up more of those googling around myself!
How much current are you thinking about?
These dynamos are 6V/3W as far as I've been able to figure out. That should give me 500mA as you said, except:
Apparently, dynamos can occasionally produce as much as 14 Volts.
This might be a problem.
What will happen when you stop for a red light? How about uphill slogs? Downhill coasting?
I was thinking a bank of NiMH batteries here. LiPO would probably be better but being the newb that I am and the poor reliability of the power source that could end badly
It sounds like what you want to power using the dynamo is the Arduino. Is that right? Or something else?
Yes, I'll be building the prototype with an Arduino but I'm probably going to move it to an Atmega328 on a PCB/perfboard when done. That means stepping down the current quite a bit I guess. Attached to the Arduino/Atmega will be an array of sensors (hall effect, temp, considering compass/accelerometer) most of which are 5v I believe. In addition to that, I would also like to power the 2 LED bike lights off the same power source. Now those would probably require more current than I'm supplying the arduino with, so they'll be switched with a relay or transistor right?
So I guess what I'm really building here is a battery trickle-charger with a very unreliable power source, roughly like the attached image.
The dynamo-powered LED lights project has some very interesting info, will look more into that.
What will happen when you stop for a red light? How about uphill slogs? Downhill coasting?
I was thinking a bank of NiMH batteries here. LiPO would probably be better but being the newb that I am and the poor reliability of the power source that could end badly
With a proper controller, such as the one I linked at, you'll be fine. For cells, I like the 18650 form factor. LiPo cells are typically between 2200 and 2600 mAh in that size, and you can find board-mount holders pretty cheaply.
With Google I found more than 3 different products that provide USB power from bicycle dynamos. Why not buy one directly from the shelf?
Now where's the fun in that But seriously, there are some that look like they'd do the trick, I might go for that if I can find one that's not too pricey. Found a fairly cheap one that does both USB charging and powers the lights, but unfortunately not both at the same time =/ http://www.kemo-electronic.de/en/House/Home/M172-Bicycle-charge-controller-USB-Mini-B-.php
I'll keep looking.
I like the 18650 form factor. LiPo cells are typically between 2200 and 2600 mAh in that size, and you can find board-mount holders pretty cheaply.
They do look nice - but can I safely boost their 3.7V to 5V for the sensors and stuff? Adding 2 of them, as far as I understand, complicates the charging circuitry a lot no?
Or use a 3.3V Arduino like Lilypad or Pro Mini 3.3V...
You can also get rechargeable LiFePO4 batteries in CR123 size on ebay (about 1Ah) - the PCB-mounting battery holders are hard to find though. LiFePO4 batts are the newer sort of Lithium ion batteries that are much safer (and 2000 recharge cycles).
I like the 18650 form factor. LiPo cells are typically between 2200 and 2600 mAh in that size, and you can find board-mount holders pretty cheaply.
They do look nice - but can I safely boost their 3.7V to 5V for the sensors and stuff? Adding 2 of them, as far as I understand, complicates the charging circuitry a lot no?
First, the 3.3V Arduinos can run at 8 MHz on the battery just fine in the 3.2 -> 4.2 range. There are also 3.3V sensors that can work at that voltage.
Second, you can use a boost converter switching controller to step up to an even 5V (or 5.6V if you want to compensate for some protection diodes for alternate power or whatnot.)
But seriously, there are some that look like they'd do the trick, I might go for that if I can find one that's not too pricey. Found a fairly cheap one that does both USB charging and powers the lights, but unfortunately not both at the same time =/