how can I get 24v voltage by 9v battery?

suncq · Joined: 21 Jul 2006 Posts: 21

I'm building a pic-based data logger powered by a 9v battery. I need to provide a 24v(24ma) voltage for external sensor or tansmiter.
how can I get this voltage by just 9v battery?

thanks in advance

asmallri · Joined: 12 Aug 2004 Posts: 1635 Location: Perth, Australia

You need a DC-to-DC converter which is a switching regulator combined with an inductor and a handful of components. You can also buy switching regulator modules which are prebuilt assemblies.

Assuming an 80% efficiency, this will present a drain of about 80mA from the 9 volt battery. These types of devices typically have large inrush currents so you need to ensure your battery is capable of supplying the initial inruch current. Typical inrush current for this regulator / load combination would be about 500mA.

These are very crude guesstimates.
_________________
Regards, Andrew

http://www.brushelectronics.com/software
Home of Ethernet, SD card and Encrypted Serial Bootloaders for PICs!!

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

Look at the graphs for that level of current drain. See how long the
battery will last.
http://data.energizer.com/PDFs/522.pdf

suncq · Joined: 21 Jul 2006 Posts: 21

thanks to asmallri and PCM!

I hava found the telemetry product from the web,
Entire unit is powered by three CR123A lithium-ion batteries and for external pressure sensor it provider Output Voltage 24 VDC �5% output Current Rated from 0 - 24 mA.
I don't know how does it do. Do you know?
thanks!

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

Post a link to the website and give the name and model of the product.

suncq · Joined: 21 Jul 2006 Posts: 21

Thanks to PCM. please see the following:
http://www.tanklink.com/brochures/4000Brochure04C.pdf

asmallri · Joined: 12 Aug 2004 Posts: 1635 Location: Perth, Australia

The system is designed to send information at a very low rate, for example they quote 18 months life for the battery with one callout per day.

The sensors are not being driven continuously. I assume the unit must periodically power up, make a sample and shut down again. How efficient this is depends on the sensor and the sample interval. It may sample once a minute, once an hour, or once a day. The more often it samples, the shorter the battery life.

For example it make take as little as 100ms for the sensor output to be stable once the sensor is powered up so with a 10 minute sample interval the sensor is powered for only 1% of the time. If we assume the sensor typically reads around mid scale (14mA) the effective current consumption average over the sample interval is 140 microamps.
_________________
Regards, Andrew

http://www.brushelectronics.com/software
Home of Ethernet, SD card and Encrypted Serial Bootloaders for PICs!!

PCM programmer · Joined: 06 Sep 2003 Posts: 21708

It's clear that they're not running at 24 ma current usage all the time.
The micro-controller is probably in Sleep mode mode 99% of the time.
In that mode, it uses very little current.

The generic name for this type of product is a "data logger".
It records data from some sensor periodically. Then the user
can read the data at certain times or dates. Or, in the case of
this product, the device makes a cell-phone call once a day to
the central location and sends the data.

suncq · Joined: 21 Jul 2006 Posts: 21

thanks to andrew and PCM reply for detail explanation.
which DC-to-DC converter can I use to produce 24v(24ma) with a low shut down current? give me a tip!
input 9v battery
output 24v (24ma)
sample time: 3 second
sensor: differentail pressure sensor or tansmitter

Humberto · Posted: Thu Oct 26, 2006 8:52 am