Stepping-up Voltage

[[email protected]]

Hi there,

I'm looking to build an adaptor to enable me to use my 7.2V batteries
(6AH Li-ion) to power 12V devices. The batteries are more than capable
than outputting the required current, if I can convert the voltage.
What is the easiest way to achieve this ...?

I've noted the existance of these components:
http://www.maplin.co.uk/Module.aspx?ModuleNo=5501&&source=14&doy=7m8

I'm not familar with them- but is this the kind of component that I
would have to use?

Any help and guidance would be appreciated, as I've been struggling to
find helpful information (perhaps I'm searching for the wrong terms!).

 

[Rich Grise]

I'm looking to build an adaptor to enable me to use my 7.2V batteries
(6AH Li-ion) to power 12V devices. The batteries are more than capable
than outputting the required current, if I can convert the voltage.
What is the easiest way to achieve this ...?

^^^^^^^

Buy a 12V battery.

But seriously, if the app notes and suggested circuits in the data sheet
give you what you want, then go for it. At worst, it will be a very
interesting learning experminet.

Good Luck!
Rich

 

[epicedium]

^^^^^^^

Buy a 12V battery.

But seriously, if the app notes and suggested circuits in the data sheet
give you what you want, then go for it. At worst, it will be a very
interesting learning experminet.

Good Luck!
Rich

Fair point .. this is still an option, but there are several good
reasons why using my large supply of 7.2V 6AH batteries would be a
major advantage ... I'm basically looking to power an LCD screen and
wireless transmitter (both 12v and relatively small current users).
Another audio transmitter is 3V, so ideally I'd want a 12V and 3V
output-- but obviously going up to 12 is more difficult than stepping
down to 3V!

These are used and charged almost daily, so moving away from charging
7.2V Li-ion packs, 12V battery packs *and* AA batteries for the 3V
transmitter would be a big help I'm hoping to mount 2x 7.2V
batteries-- one directly into the camera, and one powering the 12v and
3v devices.

Unless I can get any other advice/suggestions, I think I'll get that
component and give it a shot.

Cheers!
Kris

 

[Old Mac User]

I copied this from the link you provided. Notice this...

Output currents up to 3A are possible with this device, from a wide
range of input voltages (35V to 40V). Output voltages up to 60V can be
developed...

35V to 40V input and you propose to use 7.2V batteries to drive this?
OMU

 

[epicedium]

Cheers for noticing that OMU, but below that description it says-

Q) The description states an input voltage range of "35V to 40V" while
the data sheet provided says "3.5V to 40V" - I''m guessing the product
description is wrong? - Lloyd Williams
A) yes its an error in the description.
--

i.e., minimum input is 3.5V, not 35! Why they haven't ammended this I
have no idea,,,

This image shows it as part of a simple circuit:-
http://www.maplin.co.uk/images/full/5501i1.jpg

 

[sparc]

you need a DC to DC converter ....many available ...gewgle "DC/DC
converter"

 

[Guest]

7.2 + 7.2 = 14.4
Use your batteries in series
or series parallel

 

[jasen]

Hi there,

I'm looking to build an adaptor to enable me to use my 7.2V batteries
(6AH Li-ion) to power 12V devices. The batteries are more than capable
than outputting the required current, if I can convert the voltage.
What is the easiest way to achieve this ...?

connect two in series. many 12V devices will work from 14.4v too.

other than that, you could try a boost converter.

Bye.
Jasen

 

[epicedium]

I had actually ruled out running them in series, mainly due to the
weight, but if I could run both the Camera *and* peripherals off the
two batteries than that would actually be fine ...

How stable would it be to do the following? i.e., would it be safe
enough to run the sensitive equipment off ...

- Two 7.2V batteries connected in series
- Camera connected in parallel with One of the batteries (being fed
7.2V)
- The two batteries (14.4V) ran though a resistor & zener diode to give
me a regulated 12V output.

Sorry if this seems simplistic, but that's why I'm posting in basic
electronics ; )

many many thanks,

Kris

 

[Old Mac User]

How about two 7.2 V batteries in series with about four diodes to drop
the voltage about 4 x 0.5 volts?

 

[Chris]

I had actually ruled out running them in series, mainly due to the
weight, but if I could run both the Camera *and* peripherals off the
two batteries than that would actually be fine ...

How stable would it be to do the following? i.e., would it be safe
enough to run the sensitive equipment off ...

- Two 7.2V batteries connected in series
- Camera connected in parallel with One of the batteries (being fed
7.2V)
- The two batteries (14.4V) ran though a resistor & zener diode to give
me a regulated 12V output.

Sorry if this seems simplistic, but that's why I'm posting in basic
electronics ; )

many many thanks,

Kris

Kris has a good idea with putting two batteries in series and adding
series diodes, although I'd think 3 diodes in series (e.g. 1N5401s)
would be better -- your voltage drop at a couple of amps will be close
to 0.8V to 1V each. Radio Shack sells them as their Catalog #:
276-1661 for $2.49 for 4.

Either that, or if youu're very concerned about getting an accurate
voltage over load conditions, you could simply put a low voltage
regulator between the 14.4V source and your load to get a
well-regulated 12V for a wide range of load conditions. A good choice
would be the LM1084IT-12. It uses only 5mA(typ) quiescent current, can
crank up to 5A, and is available in the TO-220 package. Just add a
heat sink, two 10uF tantalum caps, and a 500 ohm load resistor if
minimum current is a problem, and you're good to go.

The diodes have the advantage here in one important way -- they don't
use any current when there's no load.

Good luck
Chris

 

[Rich Grise]

I had actually ruled out running them in series, mainly due to the
weight, but if I could run both the Camera *and* peripherals off the
two batteries than that would actually be fine ...

How stable would it be to do the following? i.e., would it be safe
enough to run the sensitive equipment off ...

- Two 7.2V batteries connected in series
- Camera connected in parallel with One of the batteries (being fed
7.2V)
- The two batteries (14.4V) ran though a resistor & zener diode to give
me a regulated 12V output.

Sorry if this seems simplistic, but that's why I'm posting in basic
electronics ; )

Please bottom-post.

That said, it sounds like your setup should work fine, with the caveat
that the bottom battery will need to be charged more often than the top
one, because of the additional current draw from the camera.

Good Luck!
Rich

 

[jasen]

I had actually ruled out running them in series, mainly due to the
weight, but if I could run both the Camera *and* peripherals off the
two batteries than that would actually be fine ...

How stable would it be to do the following? i.e., would it be safe
enough to run the sensitive equipment off ...

- Two 7.2V batteries connected in series
- Camera connected in parallel with One of the batteries (being fed
7.2V)
- The two batteries (14.4V) ran though a resistor & zener diode to give
me a regulated 12V output.

Sorry if this seems simplistic, but that's why I'm posting in basic
electronics ; )

If you need exactly 12 volts a LM7812 is generally preferable to a
resistor and zener as it wastes less energy.

Bye.
Jasen

 

[epicedium]

Thanks everyone, advice has been v v helpful!

I've measured the batteries and they actually range from 8.37 to 6.05v,
so the peak of 16.74v is probably too high to bring down with diodes
(well, unless I have loads of them).

I'm thinking that I'm going to try two approaches-- the zener/resistor
approach (maybe with a transistor to help regulate further), and with a
cheap IC regulator... I'd like to see how both work, and what kind of
efficiency I get.

thanks again!
Kris