[pct-l] nPower PEG -- some unfortunate numbers

Sat Mar 26 09:14:56 CDT 2011

I guess that's the question.   Does the PEG generate 1.5W or does it
generate less than a tenth of a watt?   I hope it's the former and hope your
testing will bear that out.

I do wish the PEG people would just come out with a direct statement of
average walking power output.  Their indirect power
specification<http://www.npowerpeg.com/specifications>doesn't look
good since it says you have to walk 26 minutes to supply the
equivalent of one minute of 3G talk.     For me, that translates like this:

I take Apple's stated iPhone 4 talk time of 7ish hours and divide that into
the 1420mah battery capacity approximate that the phone averages a bit more
than 200ma at the 3.7V to drive a 3G phone call ( 1420mah / 7h =~ 203ma ).
Since the PEG "spec" says that it can only generate power at a 26th of this
rate, that implies its generates a bit less than 8ma ( 203ma / 26 ) which,
if true, spins up into ~0.03W instead of 1.5W -- a 50X difference.

At the gut level neither number feels good to me.  On the one hand, I know
from a lot of time on a bike with a power meter what 1.5W feels like.  I
would be amazed to see that come from bobbing that small mass at walking
rates.   On the other hand, 0.03W sounds low and so that doesn't sit well
either.

I'll definitely be looking forward to your report!

Thanks,
      David

On Sat, Mar 26, 2011 at 4:44 AM, Kevin Cook <hikelite at gmail.com> wrote:

> Thanks David
>
> Your numbers don't match mine. First, I'm not planning to be talking on the
> phone! That said, here is my math...
>
> I've done some field testing of battery life in the type of use I want from
> the phone. First, I want to run the GPS all day. I'd like to occasionally
> take photos or video with the phone (this use may go away completely if
> needed). I want to type a journal using the phone as well. Some iPod use,
> but also willing to give this up.
>
> My biggest test was on a two day mountain bike ride from Flagstaff to the
> Grand Canyon following part of the old Moqui Stage route. Anyway... I ran
> the GPS all day, took some pictures and video, listened to music a fair
> amount of the time actually, and sent some email and a FB post when I had
> signal along the way. This level us use consumed 55-60% of the battery. I'll
> assume I need at least a 75% charge everyday. It would be nice to have a
> 100% charge each day.
>
> The iPhone 4's battery is rated at 3.7V 1420mAh. The PEG is rated at 5V DC,
> 500mA or 2.5W with a 1000mAh battery. I'm not exactly sure how to convert
> nPowers specs about xx minutes is xx talk time. I'm assuming that I am only
> getting 1.5W from the device while hiking. The PEG will full it's battery
> completely in less than 4 hours. This means I should get 2 charges a day,
> perhaps 3 on longer days. Let's make a pessimistic estimate of 75%
> efficiency in the battery transfers.
>
> The PEG's battery has 3.7Wh at the iPhone's voltage (1.0Ah x 3.7V). The
> iPhone's battery contains 5.3Wh (1420 x 3.7). Accounting for the
> inefficiency of the transfer, the PEG can provide 2.78 Wh(3.7 x .75) of
> power to the iPhone's battery. It seems to me that the PEG should be able to
> provide about a half charge for each charge of it's internal battery. If the
> PEG charges twice a day, then it should provide what I'm hoping for.
>
> Obviously I've made a LOT of estimates and assumptions. Only time will
> tell. I'm not willing to use all the batteries needed to recharge the phone
> everyday with one of those AA chargers. If I can't get the PEG to work, I
> will just alter my use of the phone.
>
>
> On Fri, Mar 25, 2011 at 8:16 PM, David Lippke <lippke.list at gmail.com>wrote:
>
>> Kevin, as much as I love alternative energy, I'm afraid the numbers just
>> don't work on any level for the nPower PEG.
>>
>> I've compared the power requirements per talk minute, battery capacities,
>> conversion efficiencies, etc, of the various iPhones and have mapped those
>> into nPower's stated specifications.   Those tell me that the PEG generates
>> less than 0.1 mwh per minute of walking.   I'd be happy to lay all the
>> calculations out but, at the end of the day, it only takes nPower's own
>> numbers to convict it --
>>
>> nPower states that it takes 26 minutes of walking to obtain 1 minute of
>> talking on a 3G call using an iPhone 3G.  Since a new iPhone 3G will do
>> about 340 minutes of 3G talking, give or take, that means that you would
>> have to walk for 147 hours to charge the phone (26 * 340) / 60.   So that
>> means that you would have hiked for 15(?) days carrying 11-12oz when you
>> could have gotten the same charge for less than 3 oz (iGo powerXtender + 2
>> lithium AAs).
>>
>> Looking at it economically, if a PEG costs $160 and an iGo costs < $20 and
>> two lithium AAs cost $5, this means that you could charge the iPhone 28
>> times (140 / 5) at the same price of of AA charging.    And to charge the
>> iPhone 28 times with the PEG means that you'd have to walk for 4125 hours(!)
>> or 412(?) days -- and of course the recharging efficiency will be dropping
>> all the time and so even this extreme number would fall short.
>>
>> I didn't look at the personal energy cost of carting the extra 8oz all
>> that ways but of course a "Ray-sian" calculation would do its own frowning
>> on the solution as well.
>>
>> The net for me is that the nPower PEG is a very neat idea but it just is
>> not efficient or powerful enough to warrant carriage on the basis of cost
>> effectiveness (or convenience).
>>
>> On the other hand, maybe (maybe) using it cuts landfill and pollution
>> loads and that or other reasons might make it worth it for some.  My wife
>> thinks it looks like it might be the perfect instrument -- when applied to
>> my head -- for adjusting my behavior!   :-}
>>
>> /David
>>
>> On Fri, Mar 25, 2011 at 9:05 PM, Kevin Cook <hikelite at gmail.com> wrote:
>>
>>> I hear you John. If it doesn't work, then I'm no worse off than I am if I
>>> can't get it. Having it lets me use my iPhone for more things is all. If
>>> the
>>> PEG fails, I'll probably use one of those devices that lets you charge it
>>> from AAs. I've pretty much ruled out solar.
>>>
>>> The iPhone isn't critical. My safety won't be at risk or anything. My
>>> wife
>>> is also going, so between us, we have 2 iPhones. If we are conscious
>>> about
>>> conserving battery, we should always have one available for things like
>>> being a GPS.
>>>
>>> I mostly want the PEG so I can create a GPS trace of the whole trail. I
>>> know
>>> several hikers have already done this, but the more data we collect, the
>>> more accurately we have the trail mapped.
>>>
>>> On Fri, Mar 25, 2011 at 5:55 PM, John Abela <
>>> pacificcresttrail2011 at gmail.com
>>> > wrote:
>>>
>>> > I am still going to question the viability and reliability of this
>>> > product to keep an iPhone powered.
>>> >
>>> > Do I love the concept - heck yeah. I would even buy one IF it proved
>>> > to actually provide enough power to recharge the power-hungry iPhone.
>>> >
>>> > But, I just don't know Kevin... seems like a huge risk at this point.
>>> > You've got what... 20-25 days left to get your gear in order... and
>>> > you want to go out on the PCT with something that will have very very
>>> > little trail proveness (guess I have to make up that word).
>>> >
>>> > While I am a huge fan of solar systems, even the high dollar ones are
>>> > still risky.
>>> >
>>> > If you are planning to use your iPhone for everything you have said
>>> > you are going to use it for Kevin, it will be a primary piece of
>>> > equipment for you. Why put yourself at risk with some product that
>>> > just had a circuit board issue. We both know what that means... and we
>>> > both should know that is not something that should be screaming red
>>> > flags - considering your time line, considering the inability for
>>> > anybody to get this product under review and actual on-trail miles.
>>> > Sigh, a whole host of red flags here Kevin...
>>> >
>>> > As much as I may not like them, nor you like them, maybe those things
>>> > you throw batteries into and plug it into your device is the better
>>> > way to go at this point in time.
>>> >
>>> > Just some things to consider.
>>> >
>>> > John
>>> >
>>> >
>>> > On Fri, Mar 25, 2011 at 4:14 PM, Kevin Cook <hikelite at gmail.com>
>>> wrote:
>>> > > When I spoke with Ann this morning, she said they had a problem with
>>> the
>>> > > circuit boards and had to change suppliers. She said all backorders
>>> would
>>> > be
>>> > > out next week and that I should also be able to get one shipped next
>>> > week. I
>>> > > bet you get yours sooner than you think!
>>> > >
>>> > > I was getting pretty worried about how to power my iPhone. It was
>>> > probably
>>> > > my biggest gear concern that was still unresolved. So relieved to
>>> have
>>> > that
>>> > > taken care of!
>>> > >
>>> > > On Fri, Mar 25, 2011 at 12:57 PM, Halfmile <list at lon.net> wrote:
>>> > >
>>> > >> Kevin,
>>> > >> I ordered one on 9/13/10, so far it has not shipped. Your post
>>> > >> prompted me to call for an update as I have not heard about my order
>>> > >> since a 1/4/11 email. They said they had a parts problems and had to
>>> > >> change a supplier. It's suppose to ship in a few weeks.
>>> > >> -Halfmile
>>> > >>
>>> > >> On Fri, Mar 25, 2011 at 11:55 AM, Kevin <hikelite at gmail.com> wrote:
>>> > >> > Did anyone get their hands on an nPower PEG yet?
>>> > >> >
>>> > >> > Finally spoke to someone there and they said they are shipping
>>> this
>>> > week.
>>> > >> I think Halfmile had one ordered.
>>> > >> >
>>> > >> > Misspellings and typos brought to you by iPhone.
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