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October 28, 2008
News - Your November Caption Con…
Guy in the wizard’s hat: “My god, these people are crazy!”
News - Your October Caption Cont…
about a year ago
He’s dead, Jim.
about 3 years ago
Right. Keep in mind that these protection circuits aren’t perfect though. I have a friend who was powering a project off of USB and accidentally energized the circuit with reverse power from another source. The result was -5V applied to the USB bus. Luckily his Mac was still under warranty and he was able to bring it in, act all unknowing-like and say “it doesn’t work anymore.” I’ve had similar problems when a project was drawing pulsed power and may have been injecting some RF.
Bottom line: Be smart. Your computer is convenient for many things, but it’s a whole lot more expensive than an LM8705 to replace.
about 3 years ago
Final update: Shorting the data pins of the USB connector results in it operating like a 1.1 spec compliant USB Dedicated Charger. I think. Anyways, it charges my Galaxy Nexus at full speed.
Charge speed for the unit is still about 350mA. The circuit was already heating up pretty good as it was, so I don’t think it’s rated to be tweaked for much more. Also, I couldn’t figure out what values needed to be changed to increase the current limit. Maybe someone else can figure that one out, but for now, according to my measurements, this thing will take 10 hours to charge on USB.
I’d love to hear if someone can reproduce my results here.
Update: I’ve put an ammeter in between the cell and the charging circuitry. The cell voltage is about 3.9v open circuit.
So in constant current mode charge (USB Power from PC) it seems to be putting about 350mA into the cell.
Putting it in 2A/5V mode and asking it to charge my Galaxy Nexus shows the phone as charging but the load on the cell is about 600mA. Stepping up from 3.9v to 5v, even if 100% efficient is going to mean this is only charging the phone at about 500mA. This probably means that it’s not displaying itself as a spec USB “Charger” device. I’m going to dig into this some more tonight if I can find the time.
Edit: More info. The solar panel charging circuitry is comprised of a single schottky diode (Vf ~= 0.25v) between the solar cell and the battery. This is to prevent reverse leakage through the solar panel. Note that this isn’t a lipoly charging circuit, it’s a trickle charger. If you intend to buy this product and attach a larger solar cell, you will probably destroy your lipoly if it ever reaches full capacity.
USB: A voltage divider of 49.9kΩ(low) & 43.2 kΩ(high) on both data pins. This is similar to the Minty Boost’s iPod compatible charging design, but it definitely isn’t USB Charging Spec 1.1 compatible and will only charge my phone for one at 500mA. I’ll try shorting the data pins and seeing what happens.
Conclusion: So far, this is turning out to be a bit of a disappointment. I’m hoping that I can hack this thing to charge quicker over USB and to act as a proper dedicated charging device for my phone. If I succeed, I’ll share the results here.
I just got mine and did some tests with it. I never trust these often poorly designed circuits until I’ve vetted them. First, things seem to operate nominally at unboxing. It detects sunlight and will charge my cell phone and power my projects. That’s great! The strange thing is that I plugged it into several USB power sources (PC, dedicated cell phone USB chargers) and saw virtually no charge current on the lipoly. After some experimentation, it appears that it is trickle charging this 3800mAh cell at around 100mA.
I’m not counting out tester error here, but I see a 100mV spike on the cell voltage (3.87 to 3.88) when I plug it into USB and can see my hobby peak charger (Accucell 6) drop its charge current by approximately .1A whenever USB is connected as well. (This is when I’m charging the cell directly with the unit opened up.) This would suggest that the total expected charge time on this thing would be around 38 hours…? I haven’t been able to confirm the constant voltage portion of the charge profile.
Can somebody please confirm / deny this? I really hope I’m wrong. This seems like a really slick product for little projects and other hacks!
about 5 years ago
Can somebody at SFE confirm this? I would really like to use this system at 915 MHz. If it is tuned for 433 MHz output, then what is the output power at the other bands?
No public wish lists :(
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