4 AA extra power pack for smartphones & other USB devices?

[Adam Funk]

Hi,

I recently came across a "Rayovac Rescuer" in Target or somewhere
similar. It has a USB power output which you can use to top up a
smartphone or similar device "in the field", & takes 4 AA cells ---
either alkaline or rechargeable, but you can put rechargeables in it &
use a USB cable to charge them up (I'm not sure if you use the same
USB port for charging the batteries up as for discharging them into
your phone). Can this thing be any good?

ISTR that you need a slightly higher voltage to charge cells up than
they provide, so can a 5 V DC input charge a set of rechargeables up
adequately so they can put 5 V DC out later?

Thanks.


--
There are some things that are not sayable. That's why
we have art. --- Leonora Carrington

 

[Jasen Betts]

On 2015-08-01, Adam Funk <a24061@ducksburg.com> wrote:

Hi,

I recently came across a "Rayovac Rescuer" in Target or somewhere
similar. It has a USB power output which you can use to top up a
smartphone or similar device "in the field", & takes 4 AA cells ---
either alkaline or rechargeable, but you can put rechargeables in it &
use a USB cable to charge them up (I'm not sure if you use the same
USB port for charging the batteries up as for discharging them into
your phone). Can this thing be any good?

ISTR that you need a slightly higher voltage to charge cells up than
they provide, so can a 5 V DC input charge a set of rechargeables up
adequately so they can put 5 V DC out later?

phones run on lithium polymer cells ( 3.6-4.2V ) and will charge from
anthing above about 4.5V

USB power is 4.75 to 5.25V DC

A series battery of 4 rechargable AA cells is about 4.4V when depeleted
and 5V when full, mostly about 4.8V

so you couild charge and discharge through the same connector, but
it's better to remove the cells and use a dedicated NiMH charger.

--
umop apisdn

 

[Adam Funk]

On 2015-08-01, Jasen Betts wrote:

On 2015-08-01, Adam Funk <a24061@ducksburg.com> wrote:
Hi,

I recently came across a "Rayovac Rescuer" in Target or somewhere
similar. It has a USB power output which you can use to top up a
smartphone or similar device "in the field", & takes 4 AA cells ---
either alkaline or rechargeable, but you can put rechargeables in it &
use a USB cable to charge them up (I'm not sure if you use the same
USB port for charging the batteries up as for discharging them into
your phone). Can this thing be any good?

ISTR that you need a slightly higher voltage to charge cells up than
they provide, so can a 5 V DC input charge a set of rechargeables up
adequately so they can put 5 V DC out later?

phones run on lithium polymer cells ( 3.6-4.2V ) and will charge from
anthing above about 4.5V

USB power is 4.75 to 5.25V DC

A series battery of 4 rechargable AA cells is about 4.4V when depeleted
and 5V when full, mostly about 4.8V

so you couild charge and discharge through the same connector, but
it's better to remove the cells and use a dedicated NiMH charger.

Interesting, thanks. I'll have to work out the mA¡h & energy values
for 4 AAs of various kinds versus the phone battery to see if the
thing is likely to be useful.


--
Dear Ann [Landers]: if there's an enormous rash of necrophilia that
happens in the next year because of this song, please let me know.
99.9% of the rest of us know it's a funny song! --- Alice Cooper

 

[Adam Funk]

On 2015-08-01, Jasen Betts wrote:

On 2015-08-01, Adam Funk <a24061@ducksburg.com> wrote:
Hi,

I recently came across a "Rayovac Rescuer" in Target or somewhere
similar. It has a USB power output which you can use to top up a
smartphone or similar device "in the field", & takes 4 AA cells ---
either alkaline or rechargeable, but you can put rechargeables in it &
use a USB cable to charge them up (I'm not sure if you use the same
USB port for charging the batteries up as for discharging them into
your phone). Can this thing be any good?

ISTR that you need a slightly higher voltage to charge cells up than
they provide, so can a 5 V DC input charge a set of rechargeables up
adequately so they can put 5 V DC out later?

phones run on lithium polymer cells ( 3.6-4.2V ) and will charge from
anthing above about 4.5V

USB power is 4.75 to 5.25V DC

A series battery of 4 rechargable AA cells is about 4.4V when depeleted
and 5V when full, mostly about 4.8V

so you couild charge and discharge through the same connector, but
it's better to remove the cells and use a dedicated NiMH charger.

Thanks for clarifying that. From googling around, it seems that the
iPhone battery (for example) is typically a bit under 6 W¡h, whereas a
set of 4 AAs should give up to 10 W¡h (rechargeable) or 12 W¡h
(alkaline). I might try one of these things if I see it again.


--
If hard data were the filtering criterion you could fit the entire
contents of the Internet on a floppy disk. --- Cecil Adams

 

[Adam Funk]

On 2015-08-01, Jasen Betts wrote:

phones run on lithium polymer cells ( 3.6-4.2V ) and will charge from
anthing above about 4.5V

USB power is 4.75 to 5.25V DC

A series battery of 4 rechargable AA cells is about 4.4V when depeleted
and 5V when full, mostly about 4.8V

so you couild charge and discharge through the same connector, but
it's better to remove the cells and use a dedicated NiMH charger.

So what would happen if I just wired 4 AAs in series between the
ground & power wires of a chopped USB cable & tried to recharge a
phone with it? How about a resistor in series to limit the current?

(I'm wondering how much "stuff" there is in the Rayovac Rescuer other
than the battery case.)


--
"It is the role of librarians to keep government running in difficult
times," replied Dramoren. "Librarians are the last line of defence
against chaos." (McMullen 2001)