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Originally Posted by independent View Post
Hello everyone.

I've been charging my N900 from solar for the past year or two using various methods. I am currently doing final testing of my proto USB solar charger Maximum Power Point direct regulator which charges to a maximum of 800mA from a 5w solar panel (ie %80 efficient into the battery). Before I tried this I direct charged my batteries in an adapted external charger. A home-built external charger can be easily modified to run off a bicycle dynamo (as opposed to off a solar charger) with the addition of a low-dropout full-bridge rectifier and some decent capacitance.
Thanks, very useful. If you post the chip numbers and describe or post the schematics it would be great!
Posts: 836 | Thanked: 1,061 times | Joined on Jan 2011 @ Touring
BTW I think I will be hacking the Yobao Long March battery pod with an independent 1000ma charging circuit so that I can charge and discharge at the same time when running the dynamo.
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Originally Posted by biketool View Post
Just curious how much time are you getting off of a double scud now?
Since the thumb boost i get something like 4 days, but i really don't use my N900's very heavily, for just GPS?, don't know, all i have used it jspeed to measure speeds from time to time.

So it is not that i need to make a bike charger, thou it is very simple when you have battery power, i can just put a DC-DC circuit in and set it to 4.2V and plug it in my DIY charge port that you can see in my battery thread.
Posts: 836 | Thanked: 1,061 times | Joined on Jan 2011 @ Touring
Originally Posted by dr_frost_dk View Post
Since the thumb boost i get something like 4 days
Thumb boost?

Also big thanks to dr_frost_dk for pointing to the e-cigarette USB chargers a great super inexpensive source for ~500ma 3.6v(actually 4.2v) li-ion charging circuits and the exhaustive battery testing!

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Posts: 1,459 | Thanked: 2,507 times | Joined on Oct 2010 @ Denmark, not far from redkarma

And yes those chargers are DIRT cheap and work very good, i use them on flashlights and such, don't take up much space and have and indication light and the best part you can now charge from pretty much anywhere, something that is not in short supply now a days is USB ports
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Originally Posted by biketool View Post
Thanks, very useful. If you post the chip numbers and describe or post the schematics it would be great!
There are essentially two approaches I've used with LM2596 regulators so far. The first approach is 6v solar panels into an external regulator. This is the system adaptable to a standard 6v hub or bottle dynamo setup. The second approach is my current approach and uses Maximum Power Point (without the tracking) regulation and 12v solar panels (18-20v open circuit, 16v maximum output).


A few of us have been making ultra-low cost MPP regulators based on LM2596-adj regulators and documenting it on Here is the thread:,146685.0.html
The actual Power Point regulation is done by regulating the solar panel before it gets into the regulator. I've used an LM723 regulator, OperaHouse uses zenar diodes. Both do the same thing, turn the LM2596 on when the maximum power point is reached. The LM2596 switches at 150k. Large capacitors store the energy while the solar panel voltage (and power rises). This happens all very quickly. The LM723 regulator has the advantage that the power point is adjustable, it's an old but efficient and robust regulator.

The LM2596-adj boards you buy on ebay have a number of pitfalls. OperaHouse gives some good advice on the thread above on how to find the best of the bunch. These boards most likely have counterfeit LM2596 chips as in bulk (1k) the chips themselves are more expensive than the boards cost including shipping anywhere in the world. These chips also are soldered (some may be welded) to the board so heatsinking can be difficult.

EDIT: The chips on the LM2596 boards are almost guaranteed to be FAkE. The genuine LM2596 pins are staggered. The ones on ebay are inline.


The photos show a plain LM2596 regulator with current limiting (current limiting ie 3 pot LM2596 regulators are less efficient than single pot regulators) as you buy them on ebay. They are installed in a gutted external charger as you buy them from dealextreme at low cost. There is low-ESR capacitance (the most expensive part of this regulator). I used a 6v solar panel and made my own connectors out of Deans style connectors (really like them). This regulator is not a Maximum Power Point one as there is not enough headroom on the solar panel. This system (ie not a MPP regulator) would work well adapted to work off a 6v dynamo with the full-wave bridge rectifier as suggested above.

You could make an external charger or a USB dynamo charger this way. Keep in mind however if you make a Nokia USB charger you will need a decent amount of current on the port when you connect otherwise it will be current limited to 95mA. You could do this by spinning the wheel in the air before you connect the n900 (and then hop on straight away and cycle). This or install a switch on your handlebars or something like that to cut in while you ride. There are also problems with voltage rising on the input capacitors with dynamos, it could be worked out by monitoring the voltage levels. It doesn't appear to be a problem with the MPP regulator and 12v solar from what I've found.
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Last edited by independent; 2012-08-30 at 19:29. Reason: spelling

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I've been using an Oyama OY340-2L solar panel with a built in liPo battery. works very well but needs exposure to quite a bit of light. I plug in a bigger panel or charge via usb when i need to top it up. It has a 4Ah cell for storage and can give 5v at 2.1A. Very interested in the bike dynamo type though.
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My take on this thread, would be to get a few pcb protected lipo's, a dc powered lipo charger, and a sepic (single ended primary inductive converter) to get a constant voltage (with variable wattage/amps) to always squeeze every watt of power out of the dynamo when its kicking out lower voltages. albeit at an a effeciency loss to get the current produced at lower dynamo voltages, but the energy would be wasted anyway so its a net gain as far as dc/dc sepic conversion effeciency.

Thats how i charge my vlra's using a 20w solar panel, since my sg-4 morningstar won't use the wattage produced below ~14v to charge the batterys. The sepic takes a voltage as low as ~3v depending on the IC/board, and boosts it up to whats needed, or bucks it down if the voltage is too high, though the charger can handle well above the panel max voltage (21v), that may not be the case with a dc powered lipo charger expecting 12-15v like the tenergy one i have.

Use that to charge ~25wh of lipos with a dc powered charger and a sepic to get enough volts (at the expense of reduced amperage/watts, but its better than wasting the power produced), stuffed into a waterproof SS waterbottle with the charger and sepic.

Then just use either a 5v regulator, or another sepic to charge your n900 from a female (water resistant) lead coming out of the bottle.

SEPIC dc/dc converters are pretty neat for getting every last watt out of low voltage sources, by boosting them up to whatever voltage is necessary to charge. Great for dynamo's and solar panels when they can't kick out enough volts to power the charger, though you lose a few % in effeciency lossses, i'd wager theres a net gain from the otherwise wasted low voltage power boosted to whats needed. And you get overvoltage protection, since any voltage above what the sepics set at, is buck'd down at a higher amperage.

Joule thief circuits might be worth looking into as well, to get enough volts when your source voltage is too low to power the charger in question. You'd want to implement some kind of voltage regulation though, sepic boards capable of 10w are cheap on ebay though, i'd just buy one of them. If you know what your doing though, designing your own voltage regulator/buck/boost/current limiting board, is fun too.

Just don't use a non-regulated joule thief as your usb output supply. Theres nothing to stop overvoltage damage to your usb devices, assuming your dynamo can pump out high voltages. But using a zener diode, a resistor, a transistor, possibly a few caps, and a inductor, its a cheap way to diy a boost dc converter.

And then just hook up one of those 5v 3a regulators/another sepic to a female usb jack with the center two pins shorted, and connect that to your phone.

I built a 6 cell usb nimh charger with a sepic, and it works great for a simple battery pack for my n900. My current project is using lipo's instead of nimh's in a similar application.

Another thing to take into account, is you may want a simple rf low pass filter, since i would assume power coming from a dynamo/dc motor/altenator is fairly dirty frequency wise, and possibly even ac depending on your dynamo/generator. But most voltage converter boards already have the circuitry to accomplish that, and its easy/cheap/a better option to just spend a few bucks on a sepic regulator.

Last edited by eleseur; 2013-01-03 at 03:36.

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Originally Posted by quipper8 View Post
Is anybody using the bike2power case with the n900?

If yes, does sometimes the power button get pressed
while the phone is in the case?

It seems to be of good quality and especially waterproof.
Looks a lot better than the cheap stuff on ebay.

Posts: 98 | Thanked: 320 times | Joined on Jul 2010
Originally Posted by thomasjfox View Post
If yes, does sometimes the power button get pressed
while the phone is in the case?
The bike2power sales team replied to my inquiry:

"I measured the inside space of the case. The case will fit a phone up to 75mm x 140 mm x 35 mm, which means Nokia N900 will fit perfectly. There are 3 foam pads provided to adjust for various phone thickness, and flexible strips to hold the phone in place."

I'm just not sure if I'll spend $35 for shipping from the US to Germany

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