# stepping up battery voltage

Discussion in 'Electronic Basics' started by Igor, Apr 6, 2013.

1. ### IgorGuest

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 ?

2. ### Daniel PittsGuest

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?

3. ### IgorGuest

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..

4. ### Helmut WabnigGuest

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

Run two of them in parallel:
Ebay 280711749967

w.

5. ### JamieGuest

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

6. ### Phil AllisonGuest

"Ignorant"

** Makes no sense.

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

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

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

..... Phil

7. ### Daniel PittsGuest

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

8. ### Phil AllisonGuest

"Daniel Pitts"
** 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.

NiMH = 30 to 40 amps.

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

..... Phil

9. ### JamieGuest

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