[TriEmbed] Battery Connection for Atmel Micro

[John Vaughters]

Looking at the efficiency chart for the LM259x you can expect about 80% efficiency from 9v to 5v. The 95% figures are peak figures and you can only get that if you are going from about 60v to 48v. The good news is the 7804 regulator is only getting you about 40-50% efficiency, so you are looking to double your time using a 9v battery. That does not seem to get you where you want, so you probably need to consider increasing your battery sizes. Either way for your application you will want to use the switching regulators to minimize your battery size. As I mentioned before, old car chargers are usually free because they are just laying around and you could test with that before you even buy anything.


The sleeping idea sounded like something worth investigating. That might get you where you want to be on a single 9v battery and a buck regulator.

Good Luck,

John Vaughters



On Friday, October 25, 2013 12:30 AM, "kschilf at yahoo.com" <kschilf at yahoo.com> wrote:
 
Hi Chip,

Paralleling batteries is a tricky business.  Batteries never have exactly the same 
voltage.  The highest voltage battery will discharge into the lower 
voltage cell.  If a battery in parallel experiences a shorted cell, that battery will rapidly discharge the other batteries.  In commercial 
installations, large batteries are only connected in parallel with 
protection (diode or more complex current sharing) to prevent power loss and/or fires.


I would suggest connecting the two Lithium batteries in series and then 
using a buck converter to regulate down to what you need for your 
project.  On-semi (was Motorola) and Texas Instruments both offer PTH 
controllers, but you have to add the other ingredients (output inductor 
and cap, input cap, catch diode, etc.).  It is also highly recommended 
that you lay these components out on a PCB instead of flywires.


The good news is that you can buy pre-made modules using TI's (formerly 
National Semiconductor's Simple Switchers) LM259x controller on Ebay for as little as $5 in single quantity or less if you buy 5 or 10 in a 
lot.  They are small, simple to use and have potentiometers built in to 
adjust the output voltage.  They are advertised as having 90+ percent 
efficiency but that figure is dependent on the load.  They are very 
handy for small projects and will get you running in less than five 
minutes.

Good luck,Kevin Schilf
Digital Telesis, Inc.
_______________________________________________
Triangle, NC Embedded Computing mailing list
TriEmbed at triembed.org
http://mail.triembed.org/mailman/listinfo/triembed_triembed.org
TriEmbed web site: http://TriEmbed.org
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.triembed.org/pipermail/triembed_triembed.org/attachments/20131025/93763208/attachment.htm>