Episode 86 - Three Portable USB Battery Packs You Can Build [Discussion]

[haku]

David Calkins & Patrick Norton re-cover building your own portable battery powered USB charger, only this time they show you how to build three different types of charger and discuss the benefits/drawbacks of each method.

Watch or download here

[haku]

Excellent show! Enjoyed the discussions about different battery types & voltages and would like to suggest in a future episode invloving voltage/batteries etc. that watts & watt-hours are explained/discussed, because it can put battery capacity & power usage more in perspective, ie a AA 1.5v 2.5AH battery holds about as much energy as a PP3 9v 400mAH battery.
With watts & watt-hour figures you can start to quantify how much a particular battery pack will last on a particular device, after using a multimeter to test how much amps the device draws.

I recently picked up an Energizer Energi To Go Phone Charger for £1.99, under testing I managed to pull 450mA+ from it and the output voltage dropped to 4.5v (nominally 5v) but it powered my flat battery Archos AV500 for 50 mins from 2x freshly charged AAs. Just need to modify it so it has a USB socket on instead of it's useless plug. What voltage does Ladyada's Minty Boost drop down to if you put a 500mA or higher load on it?

On the subject of rechargable AA batteries, I have a charger that can give you a mAH capacity rating for AAs through a charge/discharge cycle, really handy to find out which of your batteries have lost siginificant amount of capacity from what's printed on them, ie some of my NiMH 2500mAH rated batteries are now below 1000mAH through old age & not leaving charge in them when not in use.

[fishtoprecords]

Good show, but I went to http://www.ladyada.net/
and can't find the schematic, discussion, etc. for the version there unit.

What's the URL for inside the site to go directly to the right place?

[haku]

http://www.ladyada.net/make/mintyboost/

I loved the show too. Even though some of the information was basic, I learned a thing or two about batteries. The show was info packed and no bs. I looked for the schematic also. There was some kind of schematic with chip link. I wonder if two plus the four batteries would have charged the iphone. Anyway it would also be neat to see what you could hook to the usb cable as a universal power source to power a light, small fan, or etc. I wonder if one of those wind up flashlights could be adapted to work as a power source to charge a usb device.

[haku]

The buck/boost chip used in Ladyada's charger can take up to 8v so I'm guessing you could wire 4x AA's instead of 2 to increase the longevity of the output.

I picked up a bundle of cheap windup flashlights from a store that recently closed here in the UK (Woolworths), interestingly the battery inside was a LIR2032 - a Lithium Ion Rechargable 3.7v 35mAH CR2032 sized coin battery.
I did some tests with my multimeter to find out just how much power you could generate from winding it, 'comfortable' winding seemed to average around 1.3 watts, you could get 2.4 watts at maximum arm achage.
I guess with the MintyBoost circuit hooked up to the battery you could get enough power whilst winding to give a mobile an emergency charge but the coincell in the torch doesn't hold enough to charge a mobile phone, just enough for the 3 bright LEDs.

Some windup torches already come with a USB socket for charging a mobile, the best human-powered torch with USB socket I saw didn't have a winder but a cord hanging out the back which you pull like a starter motor on a lawnmower, a lot less arm achage than continually winding for up to several minutes!

Someone gave me an old dryer, I want to take the motor out of it and install a crank. I wonder what output I could get from that. I may go to Goodwll (thrift shop) and see if they have a used stationary bike cheap. Now to figure out a way to hook up the motor to it. I would be afraid i might blow a garden variety 7805 though. I know nothing about these things. I just like to to hook up things together.

[gowest]

A quick note on the charging problem with the 4 cell LM7805 and the iPhone: The 7805 usually needs more than one volt voltage difference between input and output for higher currents. If the iPhone needs a couple of 100mA, you probably will measure that the output of the LM7805 is significant less than 5V. So a six cell setup should do the trick. And gives you a lot more power than a 9V battery. And it should also do the trick with six rechargeable batteries, that work at nominal 1.2V.

BTW: The 9V testing of the 7805 is missing in my podcast.

[smeerkaas]

It still says Roger Chang as host in the End Credits.

[fishtoprecords]

Originally Posted by haku

LIR2032 - a Lithium Ion Rechargable 3.7v 35mAH CR2032 sized coin battery.

A really big problem with coin sized batteries is that they have large internal impedances. So while you can get the rated amp-hours out of them, you can only do it very slowly. Draw too much, and the voltage drops. The shape of the battery makes it hard for it to supply much current.

Most coin cell only provide 100 millwatts continuous. A few can provide 200 mw, but they are big and expensive.

The target engineering for them all is to drive a watch for a year, so the tiny draw is fine. Just don't try to power a radio with them.