USB battery pack on the cheap! (56k - lots of pics)

[KRHAiNOS]

I saw the iPod/Firewire one on HackADay.com recently, and realized that I could do a similar one with USB. Instead of paying $20-some for a similar device, you can build one yourself for $5 or less, and some time with the soldering iron.

Supply list:
- 1 x 9-volt battery clip/holster (available cheaply at RadioShack)
- 1 x LM7805 voltage regulator (No more than $2.50, Digi-Key lists one for 90-cents)
- Some sort of container, I used the plastic shell of a ferite bubble.

I believe the USB bus has 1Amp for the whole USB chain, so if you have a device that draws 1Amp, I'd be a bit leery, and use something with more airflow than a ferite bubble. The only modification you'd need would be to add a heatsink. It features a little hole so you can screw it on to a metal plate.

Basically, the construction is pretty self-explainitory. The LM7805 is a 3-pin IC -- Pin 1 (left) is the 9-volt + in from the battery, Pin 2 (center) is a ground, and finally, Pin 3 (right) is your 5-volt output.



Alright! 5 volts! Tests OK on the multimeter.




The pictures above of the Sony CLIE handheld and Sony MiniDisc portable are proof-of-concepts. They function as intended, but since each device draws something close to 1Amp (if not over), I don't feel comfortable running the voltage regulator without a heatsink. The LM7805s typically have an overdraw circuit and a fuse so if you draw too much, it'll shut itself off. Same goes for shorting it -- if it quits "working" - you didn't cook it! Just take the load off and it should start functioning again. If you're just powering simple devices like SIIG's USB FM transmitter (which is why I built this in the first place), or those silly USB fans/LED lamps/whatever, the above should work fine.

I'll be running some more tests after I get out of class.

As I keep mentioning over and over, the heat generated by the LM7805 is my primary concern.

[Rumz]

That's awesome. You'll have to see how long your MD will run off of a 9V battery. Wish I were handy with electronics and soldering irons

[KRHAiNOS]

Alright, i'm out class now, so I can to some extensive testing with it.

Right now : It's still in it's original casing, with a brand new 9V batt on a Sony MZ-NF610, with a LP2 80minute MD filled to the brim. Volume is set at 25/30 -- loudest without distortion. I didn't want to risk my N910 in case something goes catastrophically wrong.

The setup :
I pulled out the rechargable AA battery, plugged in the unit using my USB sync cable, and hit play at 5:25PM --- let's see how long it lasts and how hot it gets!

Also, MD units only draw 3volts, not 5volts. Which makes it run a lot cooler.

I'm going to run it until the battery dies, to get a final verdict on runtime and other items of interest.

EDITS :
It's been around 30 minutes : The LM7805 is barely warm, MD still cranking out the tunes!
I feel that I can safely deem this device MD-safe (assuming the device doesn't exceed 3.x volts/1Amp)

about one-and-a-half hours later : Still going strong...Multimeter reads 8.27volts if that means anything to anyone

OK, I chatted with some of my EE buddies, and did some really rough math.

I figured that the Duracell batt I'm using is rated at 565mAh. Apparently, some batteries are rated up to 800mAh. And found tha the MZ-NF610 draws 140mA when seeking (disc spin up/down), and 30mA when playing.

so :
565mA x 1hr = 140mA x Xhr (seeking)
X = 4.03hours

565mA x 1hr = 30mA x Xhr (playing)
X = 18.3333.. hours

The only mA ratings I don't know are when it's recording or when it's charging.

After the math :
Theoretically, you could get up to 18 hours of playback, assuming my math is correct. If it's wrong, please correct me!

[manicbizomber]

NEVERMIND

It was supposed to be funny, but then he had to be all gay and stuff.

[Sabian Guy]

you are commended for this great discovery. thank you.

[Israel]

The 78xx can benefit significantly from bypassing with a .01uF ceramic cap. Not as critical for battery-powered operations but if you run a half or full-wave bridge across the input it will help tremendously to install the bypass.

Also, Radio Shack sells aluminum heatsinks for this package that will improve output/performance/service life. Just put some silicone grease on the back of the 78xx and bolt it to the heatsink.

[KRHAiNOS]

h'OK, so, I fell asleep before the battery actually drained, but I can at least give you a good idea of how long it lasted :

It was still playing at 7am -- which means it was running for 12 hours.

But it was dead when I actually woke up around at noon, which would've made it 17 hours.

[p2k]

Originally posted by Israel
The 78xx can benefit significantly from bypassing with a .01uF ceramic cap. Not as critical for battery-powered operations but if you run a half or full-wave bridge across the input it will help tremendously to install the bypass.

Also, Radio Shack sells aluminum heatsinks for this package that will improve output/performance/service life. Just put some silicone grease on the back of the 78xx and bolt it to the heatsink.

Correct me if I'm wrong, but you dont need a bridge retifier unless your inputing AC into the input of the voltage regulator.

As for the heat sink, it is completely unnecessary, I've run a To-92 package, which is smaller than that, at 0.5A without a sink continuously for weeks.

You should consider a T092 packages 5volt regulator as it is much smaller. It should be plenty to power it.

[KRHAiNOS]

Originally posted by p2k


Correct me if I'm wrong, but you dont need a bridge retifier unless your inputing AC into the input of the voltage regulator.

As for the heat sink, it is completely unnecessary, I've run a To-92 package, which is smaller than that, at 0.5A without a sink continuously for weeks.

You should consider a T092 packages 5volt regulator as it is much smaller. It should be plenty to power it.

Awesome! Thanks for the suggestions!

Yea, I was leery about running without a heatsink, but realized the MD drew waaaay below 5v/1A, but in fact 3v/30mA-140mA. I'm not sure if the N910 draws more or less, but as far as I can see, it's utilizing a fraction of the 7805. So for the moment, it would work -- but I'll definatly consider the T092 in project in the future.

the USB "Sync&Charge" cable used (which I discuessed here )

[p2k]

oh the TO92 is a package as in a size of the physical regulator not a part.

you can get 78L05 i think in a TO92 package.

Oh and if your really worried, just put a 500mA quick blow fuse inline with the output of the regulator...