[pct-l] USB device charging

Wed Mar 17 14:08:11 CDT 2010

I didn't write the following for PCT hiking, but it might prove useful:

I started with a short cable because it seemed silly to carry a long  
cable with me all the time.  Because of the case I use, "cableless"  
options (built-in connector) are not an option.  Also, many of those  
are rigid or have a case for the phone.  I like my case and making my  
phone 2-3 inches longer makes the connector in the phone the break  
point if it flexes!

ProCable Shortz  in 7cm (2.5") or 20cm (7.5"), a few different places  
carry them, this is an example:
http://www.radtech.us/Products/CablesiPod.aspx#ProCableShortz

I have the 7cm, and a retractable USB extension (that I bought at  
Fry's).  I bought the short cable from Radtech, but other places carry  
them.  They are a good company with great support.

For batteries, that's more complicated.  Many battery suppliers don't  
publish the capacity of their battery packs and some that do (Lenmar)  
overstate them drastically.  Many wish to say crap like "recharge your  
device 3-4 times" - WHICH device?  My old iPod, my BlackBerry, my  
iPhone 3Gs?  Others are even worse with "adds 27 hours of talk time!"   
WTF does that mean?  "My iPod Touch has 0 hours so far, so now it has  
27?"

So I deal in "mAh".  That says, if you're not into battery juice,  
"this battery will put out the stated voltage (in this case, USB spec,  
which is 5-5.5V) at so many milliamps for one hour or 1 milliamp for  
so many hours and anywhere in between. So, an iPhone 3Gs battery is  
3.7V and 1220mhA.  Simplistically, we'll call that 4514VmAh as the  
capacity of the battery.  In a perfect world, you'd need a charger  
battery that put out that much energy to fill it back up, but you will  
actually need more.  There is loss and power used to drive the  
circuitry to charge the battery and change the voltage inside the  
battery pack from what ever it is to 5V for USB output.  Since USB  
output is 5V, a battery pack of 903mAh is one charge of the iPhone  
3Gs.  Let's round to 1000mAh of USB power for a full charge.

The other item to be on the lookout for is the rated output power in  
milliamps (mA) or amps (A).  USB port output for running attached  
devices is about 500mA at 5V (so 2500VmAh).  If a device like the  
iPhone 3Gs needs 4514VmAh to fully charge, then at 5V and 500mA, it  
will need about 1.8 hours to charge - about 2 hours with loss, etc.   
Some chargers are offering 1000mA (also called 1A, or high output)  
charging ports for devices that can use the extra juice.  I believe  
that older iPods (and maybe the original iPhones) are limited to  
drawing 500-ish mA from the port.  The iPhone 3Gs will do a "fast  
charge" if it detects a "high output" port.

I have a Lenmar battery pack that claims to be 750mAh, it makes about  
30% charge of the iPhone.
http://www.radioshack.com/product/index.jsp?productId=3184995  nowhere  
NEAR 750mAh, but I got a couple at Fry's on sale for less than $10.   
Very small and can carry in my pocket with my short cable for an  
emergency.  (No high output port, I can use the iPhone faster than it  
can charge it; in some situations.)

I bought this one for Helen as a bigger battery.
http://www.radioshack.com/product/index.jsp?productId=3912660   It  
claims 2100mAh and should be able to charge the iPhone 3Gs twice!  Not  
so, once and some change.  I bought it at Fry's and didn't get such a  
good deal.  Both of the Lenmars came with Apple cables, don't use  
them, they won't work with the iPhone or some later model iPods.   
Apple changed the spec of their cables...  (Again, no high output port.)

My current favorite battery is making me frustrated.  It's the  
Duracell "Instant USB Charger".
http://www.duracell.com/en-US/product/instant-usb-charger.jspx  I  
bought it at WalMart for $20, on a whim, and it's turned out to be my  
"pocket favorite".  It's very flat, so it's good for the pocket.  At  
$20, it was a bargain!  It advertises 1120mAh and DOES do a "flat to  
full" charge of my iPhone 3Gs.  Ever since, when I see them - they are  
$30 - not as much of a bargain.  Some of the things I DO like about  
it, it comes with a very short (portable) power/recharge USB cable AND  
is has an actual ON/OFF switch.  Most of these types of devices do  
NOT, and as such are always powering the power conversion circuit and  
slowly draining.  Very slowly, but draining just the same.  Also, it  
seems that it does put out more than the minimum for a faster charge.   
This one is so small and flat that I might consider hiking with more  
than one and call it "done", but then I start getting cheap...

Then there's BIG juice.  This would be for something like the bus ride  
to camp and back.  Usually, I'd be in a car with a 12V->USB adapter.   
I wasn't on the charter to Joshua Tree so I don't know if there was  
any power on the bus for devices, so do have that. But I go looking  
and I did order something.  I can't vouch for it's performance yet.

I considered looking for the larger Duracell.  The Powerhouse Charger:
http://www.duracell.com/en-US/product/powerhouse-usb-charger.jspx  but  
at 2000mAh, it would be two charges at best and was not that  
compelling, unless I could find it deeply discounted.  I could not.

I considered something VERY expensive, but with other uses for after  
Snow Camp, and of very high quality:
http://www.hypershop.com/HyperMac-External-MacBook-Battery-100Wh-p/mbp-100.htm 
  but just couldn't bring myself to cough up the bucks (still, it  
would charge the iPhone over 50 times! ;-) Definitely a 1A, high  
output, power port.  I could power my laptop on some car/plane trips  
and power my iPhone as well.

The same company has a device meant more for iPhone/iPod use, and I  
considered it as well:
http://www.hypershop.com/product-p/hm36-black.htm still pricey for  
3600mAh (about 3.5 full charges) but very good quality and probaby IS  
3600mAh!  Definitely has a 1A, high output power port. (May still get  
something from these guys, if I get a bonus at work or something!)

What I ended up ordering was:
http://www.imaxpower.com/IMP500-3G-3Gs-iPhone-iTouch-external-battery-p/imp500.htm
I liked that it came with a "wall wart" charger that I use for it or  
for my iPhone or iPod Touch.  I doubt that the cable will work for  
either.  I purchased it through Amazon, last night, and it shipped  
this morning.  I'll let you know how it does when I get it.  The  
online reviews have said 4+ full recharges of iPhones and a charge  
rate that implies a high output port and a 3rd party doc "confirms"  
it.  I verified with the vendor that the capacity is 5000mAh at 5V, so 4  
full charges should be expected with some power left over.  At 130g,  
this might be "trailable" at about 1oz per iPhone charge.
Reviews:  http://forums.macrumors.com/showthread.php?t=565215 and

I was going to get http://www.imaxpower.com/product-p/imp880.htm to  
share (with GF), but then what happens to is after the trip is over?   
This device probably has a high output port, but now I'm not so sure...

BillB

On Mar 17, 2010, at 11:17 AM, Jim Keener ( J J ) wrote:

> Greetings,
>
> I received this charger yesterday and tested it today on a fully  
> discharged iPhone 3GS. It charged up to 82% of the iPhone's battery  
> capacity and ran out of juice. Bad charger.
>
> Walk well,
> Jim Keener ( J J )
> _________________
>
> jj at ridgetrailhiker.com
>
> http://postholer.com/jj
> http://ridgetrailhiker.com
> http://olderhealthier.com
>
>
>
>
>
>
> _______________________________________________
> Pct-l mailing list
> Pct-l at backcountry.net
> To unsubcribe, or change options visit:
> http://mailman.backcountry.net/mailman/listinfo/pct-l
>
> List Archives:
> http://mailman.backcountry.net/pipermail/pct-l/