On Tue, Dec 14, 2010 at 1:33 PM, Bob Blick <bobblick@ftml.net> wrote:

>
> On Tue, 14 Dec 2010 12:17:47 -0500, "V G" said:
>
> > > Is this for the iPhone charger? If so, I think you can get away with
> > > 4-AA nimh cells, a polyswitch fuse, and four resistors(to trigger
> > > charging). At the very least, you need to try it to see if it will
> > > deliver much charge to the phone. Do the test a day after charging th=
e
> > > batteries so they are not at their peak voltage, get out your
> > > multimeter, see if it charges your phone.
> >
> >
> > I know for sure that the Eneloops can deliver more than 1 A of charge, =
so
> > why WOULDN'T it work? I also know what resistor values to use, so the
> > bare
> > batteries and resistors should work, given that the voltage range is
> > appropriate.
>
> The voltage of the batteries under load and as they discharge will
> effect how much charge they can actually get to the phone and how much
> is left in the batteries. Also, it may be that your phone does something
> interesting, like disconnecting, if there isn't enough voltage for 1 amp
> to flow.
>
> So I'd have to say that you really don't know it will "work". At least
> not satisfactorily. So it makes sense to test the idea.
>
> > That's true. But the biggest issue is that I don't know what voltage wi=
ll
> > damage the iPhone. The batteries can initially supply 5.8 volts, so tha=
t
> > may
> > be a little too much for the phone to handle.
>
> "Initially" is the key, that is why I suggested letting the batteries
> sit for a day to relax from their peak voltage. You can also pop them
> into a flashlight for a minute or two before your test, just to pull
> them down a bit. Remember, I am just suggesting you do a test, not make
> this part of a regular process. Do a test in a situation you control.
>
> Of course, what most people would have already done is test with an
> adjustable bench supply and the four resistors. And lacking an
> adjustable bench supply, gone to Radio Shack, gotten an LM317 adjustable
> regulator and potentiometer, and made one. Might come in handy for other
> projects.
>
> Cheers,
>
> Bob
>
> P.S. I can pretty much guarantee that you will not be able to get 1 amp
> for any length of time if there is anything besides a fuse between the
> batteries and the phone. So you will never be able to use an LDO unless
> it is so overspec or custom that it is ridiculous. Any method you use to
> limit the voltage will need to be a shunt. But 5.8 volts is nothing to
> worry about, so you don't even need that.


You're right. I really need to get myself a bench supply. Ordering one now.
--=20
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