Small battery

[bee]

I have a project that is powered by a 9volt battery pp3 style and i need to reduce the size of the battery and not sure what is the best option avaliable , The current drawn is 18 Ma,, The circuit is a strain guage circuit
I have tested the voltage down to 3.5v on the bench power supply and it seems to still work okay,, Starts to drop out below about 3v,, Any ideas appreciated

List of items in circuit

1x 78ls05 reg
1x ad623 op amp 550uA~ 2.5-6v
1x mcp6292 op amp 1 Ma~ 2.5-6v
1x 12f675 pic 100uA~ 2v-6v
1x 433mhz transmitter 10Ma ~ 2-12v

These values taken from data sheet

Thanks
bee

 

[MikeMl]

Get rid of the 7805 and replace it with a modern low-dropout, low min-current regulator. Can you do anything to reduce the duty cycle of the device; i.e. put it to sleep, and only wake it periodically?

 

[peufeu]

Yeah, if you don't need continuous transmission, you can use a battery which has enough voltage to run the PIC (whose power draw is very low) and periodically wake the rest of the circuit to transmit a burst.

 

[bee]

It has to transmit about every .5 second at max so it would not be worth going to sleep would it ?
What i am looking for is a smaller battery as the space this has to fit is very small
I will look into a low drop out reg ,, Any part numbers Mike

Thanks for your advice guys
bee

 

[cr0sh]

Have you considered a few N or 1/2AA cells in a holder? You might also look at this list, to see if anything else might work:

List of battery sizes - Wikipedia, the free encyclopedia

Something else to consider: Internally, a 9V battery consists of 6 AAAA cells wired in series - each cell is about 600 mAh in capacity; now - if you used a low-dropout regulator, and could have a 4.5 volt battery made in the same form-factor as a 9V battery, but with two pairs of 3 series-connect cells wired in parallel...

 

[bee]

The 1/2 AA sounds like it might be okay,,
Given me some ideas thanks

bee

 

[Diver300]

It has to transmit about every .5 second at max so it would not be worth going to sleep would it ?

It would be worth going to sleep. I had a design that went to sleep 16 times a second, and significantly reduced power consumption by doing so

 

[MikeMl]

It matters not how often it goes to sleep per second; it matters how long it takes to send one data burst.

 

[bee]

The Transmitter would be the one to put to sleep as its dragging 10Ma
I am not sure how long it takes to fire back up,Will have to do some research on that one
When i say 500Ms it could get out to 1 sec, So a fair bit of time ,And it is triggered so it could stay off until it is needed
Just depends on how long to settle the circuit,Bit more testing needed
Have just ordered some CR 2477 button cells 3v@1000mAh,and plan on using 2
And looking for a low drop out reg
I am not sure how long for the transmission to take place iam sending 8bits in a manchester routine

bee

 

[crutschow]

There are several 6V non-rechargeable lithium batteries that are quite small, and have a high energy capacity. You might consider one of those in place of the alkalines.

 

[bee]

Carl
I will check them out Thanks ,,
I just grabbed the 2477s as they were only 2bucks each just to get it going on a lower voltage and smaller battery
Have located a Ldo reg 3v local store just have to go pick it up

bee

Edit: The cr2477 are lithium batterys