stepping up battery voltage

[Igor]

Hi.
I want to step up voltage of my AA 1,5 battery to 2.5V but i need to
limit the current to 500mA.

Ampmeter shows that the current of the battery is around 6A and dropping
to 3A.

How to make this 2.5 / 0.5A output ?

 

[Daniel Pitts]

On 4/6/13 12:08 AM, Igor wrote:

Hi.
I want to step up voltage of my AA 1,5 battery to 2.5V but i need to
limit the current to 500mA.

Ampmeter shows that the current of the battery is around 6A and dropping
to 3A.

How to make this 2.5 / 0.5A output ?

Usually, amperage is drawn by the circuit, not "produced" by the battery.

Remember ohms law, I = V/R. The ampmeter is design to have a low R, so
as not to effect the whole of the circuit. If you connected the meter
directly to the battery, you've basically shorted the battery. Which
AFAIK is dangerous.

If you want 2.5v with .5A, that means the rest of your circuit needs to
have a resistance of at least R = 2.5v/.5a = 5ohm. You'll be hard
pressed to find useful circuit with < 5 ohms.

In any case, are you *sure* you need to limit the amperage, and that the
circuit isn't going to just use what it needs?

 

[Igor]

On 04/06/2013 09:54 AM, Daniel Pitts wrote:

On 4/6/13 12:08 AM, Igor wrote:
Hi.
I want to step up voltage of my AA 1,5 battery to 2.5V but i need to
limit the current to 500mA.

Ampmeter shows that the current of the battery is around 6A and dropping
to 3A.

How to make this 2.5 / 0.5A output ?

Usually, amperage is drawn by the circuit, not "produced" by the battery.

Remember ohms law, I = V/R. The ampmeter is design to have a low R, so
as not to effect the whole of the circuit. If you connected the meter
directly to the battery, you've basically shorted the battery. Which
AFAIK is dangerous.

If you want 2.5v with .5A, that means the rest of your circuit needs to
have a resistance of at least R = 2.5v/.5a = 5ohm. You'll be hard
pressed to find useful circuit with < 5 ohms.

In any case, are you *sure* you need to limit the amperage, and that the
circuit isn't going to just use what it needs?
Yes I'm sure. The output should be 2,5V/0.5A. I want to make this as

simple as possible and as first step I want to see how will this work
with AA battery. However, if you know how to get this output from some
other source, let me know.

I do have 3v/5A AC/DC converter (12/9/6/3V) but again current is much
to big for such application. I can switch this ac/dc converter to 12V
(1A) and put some load , like some motor, so that the voltage and
current will drop to needed value..

 

[John Fields]

On Sat, 06 Apr 2013 10:29:32 +0200, Igor <igor@com.net> wrote:

On 04/06/2013 09:54 AM, Daniel Pitts wrote:
On 4/6/13 12:08 AM, Igor wrote:
Hi.
I want to step up voltage of my AA 1,5 battery to 2.5V but i need to
limit the current to 500mA.

Ampmeter shows that the current of the battery is around 6A and dropping
to 3A.

How to make this 2.5 / 0.5A output ?

Usually, amperage is drawn by the circuit, not "produced" by the battery.

Remember ohms law, I = V/R. The ampmeter is design to have a low R, so
as not to effect the whole of the circuit. If you connected the meter
directly to the battery, you've basically shorted the battery. Which
AFAIK is dangerous.

If you want 2.5v with .5A, that means the rest of your circuit needs to
have a resistance of at least R = 2.5v/.5a = 5ohm. You'll be hard
pressed to find useful circuit with < 5 ohms.

In any case, are you *sure* you need to limit the amperage, and that the
circuit isn't going to just use what it needs?


Yes I'm sure. The output should be 2,5V/0.5A.

---
If your load requires 0.5A with 2.5V across it, then it doesn't matter
how much current the supply can source as long as it's not less than
0.5A.
---

I want to make this as simple as possible and as first step I want to
see how will this work with AA battery.

---
Since the maximum possible voltage obtainable from a non-lithium AA
cell is around 1.5V, you can't use an AA cell to get 2.5V.
---

However, if you know how to get this output from some
other source, let me know.
I do have 3v/5A AC/DC converter (12/9/6/3V) but again current is much
to big for such application. I can switch this ac/dc converter to 12V
(1A) and put some load , like some motor, so that the voltage and
current will drop to needed value..

---
If your load draws a _fixed_ 0.5A from a 2.5V supply, then you could
use your converter by setting its output to 3V and putting a one ohm,
1/2 watt resistor in series between the converter and the load, like
this: (View using a fixed-pitch font)

+------+
|~ +3V|---[1R]---+
| | |
| | [LOAD]
| | |
|~ GND|----------+
+------+

If your load draws a varying current, then that won't work and the
problem becomes one of regulating the voltage across the load
regardless of the current into the load.

Does your load current vary, and if so , how much?

--
JF

 

[Helmut Wabnig]

On Sat, 06 Apr 2013 09:08:30 +0200, Igor <igor@com.net> wrote:

Hi.
I want to step up voltage of my AA 1,5 battery to 2.5V but i need to
limit the current to 500mA.

Ampmeter shows that the current of the battery is around 6A and dropping
to 3A.

How to make this 2.5 / 0.5A output ?

Eaby 290590670347 step up converter
nominal input voltage 3 volt, but is works lower.

see also 290714206877


Run two of them in parallel:
Ebay 280711749967


w.

 

[Ian Field]

"Igor" <igor@com.net> wrote in message news:kjohtq$ug5$1@l01news1.ot.hr...

Hi.
I want to step up voltage of my AA 1,5 battery to 2.5V but i need to limit
the current to 500mA.

Ampmeter shows that the current of the battery is around 6A and dropping
to 3A.

How to make this 2.5 / 0.5A output ?

A popular method of stepping up low voltage is the blocking oscillator
(plenty on the internet) but you're basically at the mercy of the flyback
voltage developed by the collector winding, there's nothing to stop you
winding a secondary winding with fewer turns to make a lower voltage flyback
converter - might even be possible to have a secondary with more turns than
the collector winding (only works out if you're using a rectifier on the
output) to make a step up forward converter.

You can wind the blocking oscillator inductor on one of the bigger ferrite
toroids from a scrap motherboard, collector winding for 1.5V single-cell =
15T, same for the base winding. You can wind as 30T with a tap at 15T (for
B+) to give you a sense of how the winding is arranged - the base winding is
connected to the base via a 100 Ohm pot in series with a 15 Ohm limiting
resistor (which will probably give a fair bit of control over output
current) - the fixed resistor limits maximum base current with the pot at
minimum.

Experimenting with secondary winding ratio & configuration is left as an
excercise for the student.

 

[Jamie]

Igor wrote:

Hi.
I want to step up voltage of my AA 1,5 battery to 2.5V but i need to
limit the current to 500mA.

Ampmeter shows that the current of the battery is around 6A and dropping
to 3A.

How to make this 2.5 / 0.5A output ?

You are sitting on the border of not to many switch IC's that can

start up reliably at 1.5 volts. I do remember one that could start at .8
volts
but don't have the number at the top of my head..

you could make a blocking oscillator on a small hand wound
transformer, but regulation maybe a bit tricky.

Also, if I remember, the Cmos version of the 555 timer will operate on
a single cell. With that, you can make a buck boost supply.

I guess it all depends on what you're trying to do..

Jamie

 

[Phil Allison]

"Ignorant"

I want to step up voltage of my AA 1,5 battery to 2.5V but i need to limit
the current to 500mA.

** Makes no sense.

You cannot have a fixed voltage AND a fixed current limit too.

Ampmeter shows that the current of the battery is around 6A and dropping
to 3A.

** That is the current under near short circuit conditions.

Try measuring the VOLTAGE at the *same time* and I bet it is SFA.


..... Phil

 

[Daniel Pitts]

On 4/6/13 1:29 AM, Igor wrote:

On 04/06/2013 09:54 AM, Daniel Pitts wrote:
On 4/6/13 12:08 AM, Igor wrote:
Hi.
I want to step up voltage of my AA 1,5 battery to 2.5V but i need to
limit the current to 500mA.

Ampmeter shows that the current of the battery is around 6A and dropping
to 3A.

How to make this 2.5 / 0.5A output ?

Usually, amperage is drawn by the circuit, not "produced" by the battery.

Remember ohms law, I = V/R. The ampmeter is design to have a low R, so
as not to effect the whole of the circuit. If you connected the meter
directly to the battery, you've basically shorted the battery. Which
AFAIK is dangerous.

If you want 2.5v with .5A, that means the rest of your circuit needs to
have a resistance of at least R = 2.5v/.5a = 5ohm. You'll be hard
pressed to find useful circuit with < 5 ohms.

In any case, are you *sure* you need to limit the amperage, and that the
circuit isn't going to just use what it needs?
Yes I'm sure. The output should be 2,5V/0.5A. I want to make this as
simple as possible and as first step I want to see how will this work
with AA battery. However, if you know how to get this output from some
other source, let me know.

I do have 3v/5A AC/DC converter (12/9/6/3V) but again current is much
to big for such application. I can switch this ac/dc converter to 12V
(1A) and put some load , like some motor, so that the voltage and
current will drop to needed value..


I think you're misunderstanding something. Voltage is typically an

"exact" rating for a circuit and power supply. Amperage is a "maximum"
rating, meaning it can't safely supply more than that (and still
maintain the voltage level).

So, if I have a device which came with a 12v 500mA power supply, I can
plug in a 12v 2A power supply with no ill effect (assuming the same
polarity is maintained)

On the other hand, if I plug in a 16v 500ma power supply, I could cause
problems to my device. Or, if I plug a 12v 250ma power supply, I could
damage the power supply, or the device would simply not work.

So. I ask again. Are you sure you need "exactly" 500mA, not "at least"
500mA? Perhaps you could tell us what you're using this for, so we, as a
community, could better help you.

 

[Phil Allison]

"Daniel Pitts"

Remember ohms law, I = V/R. The ampmeter is design to have a low R, so as
not to effect the whole of the circuit. If you connected the meter
directly to the battery, you've basically shorted the battery. Which AFAIK
is dangerous.

** Not if done only briefly.

he short circuit current of a AA cell depends on what type it is:

Heavy duty Zinc = about 3 amps.

Alkaline = about 9 amp

NiMH = 30 to 40 amps.

That last one is dangerous cos it can set the meter probe cables on fire.



..... Phil

 

[Tim Wescott]

On Sat, 06 Apr 2013 18:43:07 -0500, Jamie wrote:

Igor wrote:
Hi.
I want to step up voltage of my AA 1,5 battery to 2.5V but i need to
limit the current to 500mA.

Ampmeter shows that the current of the battery is around 6A and
dropping to 3A.

How to make this 2.5 / 0.5A output ?

You are sitting on the border of not to many switch IC's that can
start up reliably at 1.5 volts. I do remember one that could start at .8
volts but don't have the number at the top of my head..

you could make a blocking oscillator on a small hand wound
transformer, but regulation maybe a bit tricky.

Also, if I remember, the Cmos version of the 555 timer will operate on
a single cell. With that, you can make a buck boost supply.

I guess it all depends on what you're trying to do..

Jamie

It pretty much has to work down to 0.9V or so if you're going to get
everything there is to get out of the battery -- a dry cell only puts out
1.5V when it is very lightly loaded for it's charge level.

With a 100% efficient converter, 2.5V at 500mA demands around 833mA out
of a 1.5V cell, and the current required goes up as the cell voltage goes
down.

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com

 

[Tim Wescott]

On Sat, 06 Apr 2013 10:29:32 +0200, Igor wrote:

On 04/06/2013 09:54 AM, Daniel Pitts wrote:
On 4/6/13 12:08 AM, Igor wrote:
Hi.
I want to step up voltage of my AA 1,5 battery to 2.5V but i need to
limit the current to 500mA.

Ampmeter shows that the current of the battery is around 6A and
dropping to 3A.

How to make this 2.5 / 0.5A output ?

Usually, amperage is drawn by the circuit, not "produced" by the
battery.

Remember ohms law, I = V/R. The ampmeter is design to have a low R, so
as not to effect the whole of the circuit. If you connected the meter
directly to the battery, you've basically shorted the battery. Which
AFAIK is dangerous.

If you want 2.5v with .5A, that means the rest of your circuit needs to
have a resistance of at least R = 2.5v/.5a = 5ohm. You'll be hard
pressed to find useful circuit with < 5 ohms.

In any case, are you *sure* you need to limit the amperage, and that
the circuit isn't going to just use what it needs?

Yes I'm sure. The output should be 2,5V/0.5A.

Then you don't understand electronics very much at all, or you're stating
your needs very poorly. Because what you're asking for is physically
impossible.

The load on a power source determines the relationship between current
and voltage. Usually this means that there is a 1:1 relationship between
the voltage applied to the load and the current it pulls; never does it
mean that the source can dictate both the voltage at and the current
through the load. You can make a 2.5V source and apply it to a load that
will pull 500mA at 2.5V, or you can make a 500mA source and apply it to a
load whose voltage will ride at 2.5V at 500mA, but you absolutely
positively cannot make a source that will deliver 2.5V at 500mA to
anything at all.

An immediate counter-example to what you're asking for is a resistor: a 5-
ohm resistor will pull 500mA from 2.5V, but if you exchange that for a 1-
ohm resistor, it will pull 2.5A from 2.5V. There's no way that your
source can make a 1-ohm resistor act like anything other than a 1-ohm
resistor other than magically changing the nature of the resistor.

I want to make this as
simple as possible and as first step I want to see how will this work
with AA battery. However, if you know how to get this output from some
other source, let me know.

There is no simple about what you are asking for, because the first step
in achieving your goal of a source that will always put out exactly 2.5V
and 500mA, regardless of what load is attached, is to move to a different
universe with different physical laws -- then figure out how to stay
alive there. Until you manage that, you need to obey the laws of physics
here.

I do have 3v/5A AC/DC converter (12/9/6/3V) but again current is much
to big for such application. I can switch this ac/dc converter to 12V
(1A) and put some load , like some motor, so that the voltage and
current will drop to needed value..

No you can't. What you are asking for is not physically possible.

Tell us what you're really trying to accomplish. Not the 2.5V/500mA bit
-- tell us what you're building, and what you expect to do. Something
along the lines of "I want to build a pocket electric cigarette
lighter..."

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com

 

[Jamie]

Tim Wescott wrote:

On Sat, 06 Apr 2013 18:43:07 -0500, Jamie wrote:


Igor wrote:

Hi.
I want to step up voltage of my AA 1,5 battery to 2.5V but i need to
limit the current to 500mA.

Ampmeter shows that the current of the battery is around 6A and
dropping to 3A.

How to make this 2.5 / 0.5A output ?


You are sitting on the border of not to many switch IC's that can
start up reliably at 1.5 volts. I do remember one that could start at .8
volts but don't have the number at the top of my head..

you could make a blocking oscillator on a small hand wound
transformer, but regulation maybe a bit tricky.

Also, if I remember, the Cmos version of the 555 timer will operate on
a single cell. With that, you can make a buck boost supply.

I guess it all depends on what you're trying to do..

Jamie


It pretty much has to work down to 0.9V or so if you're going to get
everything there is to get out of the battery -- a dry cell only puts out
1.5V when it is very lightly loaded for it's charge level.

With a 100% efficient converter, 2.5V at 500mA demands around 833mA out
of a 1.5V cell, and the current required goes up as the cell voltage goes
down.

Yes, very well understood..

Yes ago a made a concoction where I used a diode to isolate the Vcc of
a basic timer and had that drive a mosfet to buck switch a coil which
got its (+) before the diode. Then I back fed the final output of the
switch circuit which was 12 volts after regulation to the Vcc of the timer.

The source was a 6 volt arrogation battery system, a very large one
at that, however, there were some electronics that needed 12vs from that
and it needed to stay operating when the 6 volt battery drained down to
the point where it could no longer supply enough output in the buck
circuit to maintain 12 volts and back feed the timer. I had a comparator
switch in there to shut things down if the output reached 10 volts or less.

During the day solar panels were used to recharge this system if
possible and a emergency generator if needed. THe gen would start
if the buck circuit switched into shutdown.

The only problem with all of this of course, once the battery gets down
like that, you are not starting that circuit until it is up and happy
again

Oh the days of what I could do with timers, I also love the cmos
versions. I know there is more integrated IC's these days for that
and i've used a few, but those aren't as much fun!

Jamie

 

[Ian Field]

"Jamie" <jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote in message
news:Cm18t.18605$yV1.16318@newsfe29.iad...

Igor wrote:
Hi.
I want to step up voltage of my AA 1,5 battery to 2.5V but i need to
limit the current to 500mA.

Ampmeter shows that the current of the battery is around 6A and dropping
to 3A.

How to make this 2.5 / 0.5A output ?

You are sitting on the border of not to many switch IC's that can start
up reliably at 1.5 volts. I do remember one that could start at .8 volts
but don't have the number at the top of my head..

The PR4401 LED driver can start that low but probably won't shift as much
current as the OP wants - not sure whether you can buffer those with an
external transistor or not, but I think they've since released an upgraded
version anyway.

There is a variety of single cell inverter chips; probably LT, maybe maxim.