3 volt regulator question

[dannich]

I have small digital video camera that runs off of 2 AA batteries 3 volts.
I want to be able to run this from a 6 volt SLA battery with a 3.3 volt 1.5 amp regulator. I have been told that even with the camera off that this regulator will continue to draw power from the SLA battery.
will this be a huge draw on the battery or will it be minimal while the camera waits for the signal form the PIR sensor to turn on???
If it will be a huge draw on the battery, does anyone know of a fix for this to keep from draining the SLA battery.
My whole reason for this is to be able to keep my camera in operation for a greater period of time without need for a battery change. I am hoping for 3 weeks or longer battery life. The camera will probable draw 1.5 to 1.9 Ah
when in operation.

Thanks for the help

Dan N

 

[blueroomelectronics]

Modern NiMH AA batteries can have a capacity of 2500mAh, what's you SLA rated for?
PS a linear regulator will simply burn off half the power.

 

[Gayan Soyza]

As suggested the solution is high capacity NIMH cells.I don't think batteries will run longer than 3 weeks even though you use SLA ones.

Use NIMH rechargeable cells the latest I have is 2700mAH.Don't for get to recharge them from a descent charger accept by the manufacturer.

 

[mneary]

If your small digital camera runs off "2 AA" cells, it is NOT the same as 3.3V. 2 AA cells (NiCd, NiMH, or Alkaline) will produce 1.2V for most of their lives; 2xAA will be 2.4V.

The camera will probable draw 1.5 to 1.9 Ah

Do you mean 1.5 to 1.9Ah per hour, or day, or week, or total for the 3-week period? Or 1.5 to 1.9A when active?

 

[dannich]

If your small digital camera runs off "2 AA" cells, it is NOT the same as 3.3V. 2 AA cells (NiCd, NiMH, or Alkaline) will produce 1.2V for most of their lives; 2xAA will be 2.4V.

Do you mean 1.5 to 1.9Ah per hour, or day, or week, or total for the 3-week period? Or 1.5 to 1.9A when active?

Well the camera will burn up a set of AA batteries (regular alkaline) in about 90 minutes. a person from another forum suggested the 1.5 Ah rating.
Seeing as the AA battery states it is 1.5 volts I assume it will output 1.5 volts x2=3 volts. So I want to use the 6 volt SLA to increase the time in use between battery charges. If the camera draws 1 amp while in use it should use a 2700mah battery in 2.7 hrs?? I am looking for more run time. A 6 volt SLA has I believe 4 to 6 AH rating

 

[Blueteeth]

Well, if you are certain you wish to use an SLA battery, then a 'buck converter' is what you require. This steps down a voltage quite efficiently (80-90%).

As for preventing the system draining power form the battery when the camera is off (ie: its not drawing power) then a simple switch between the battery and your regulator circuit??

Battery life of your current AA's (alkaline) depends on not only the current draw, but also the minimum voltage the camera can accept. Alkalines are generally considered 'dead' when they get to 1V...and so their mAH ratings is until they get to 1V...I doubt your camera can accept that and so would probably consider something like '1.3V/cell' as 'dead'. Also battery capacity depends on current drain...alkalines have lower capacity for higher current drains.

Not trying to confuse you, just saying...its a bit 'ish' to judge battery life of alternate batteries.

My suggestions for an external battery pack:

Battery type: NiMH tend to have a better 'capacity/weight' ratio than SLA's, Perhaps 4-6 D size cells would be ok? But Of course, cost is a consideration. You will have to decide on weight, size, capacity.

Regulator: in order to get the voltage your camera wants (2.9-3v?) From another voltage source - usually higher voltage, but using a lower voltage is also possibile - I can see two options.

Linear regulator - will waste power when on and when the camera is off. Unless the battery you choose will hold just over 3v over its discharge..then even an LDO regulator would be quite inefficient.

Buck regulator (switching regulator) Quite efficient, and usually has a 'power down' mode that will draw only uA from the battery when not in use. Check ebay for MC34063 modules - premade.

Well I hope thats food for thought at least.

Blueteeth

 

[mneary]

Seeing as the AA battery states it is 1.5 volts I assume it will output 1.5 volts x2=3 volts.

They are only telling 10% of the truth. A "1.5V" Alkaline battery will supply nearly 1.5V for the first 10% of its life, then it spends the next 80% of its life supplying about 1.2V. During the final 10% of its life it's falling from there to 0.8V. See energizer.com or duracell.com.

I'd expect, considering the difficulty you'll face in adapting an SLA, that a pair of "C" size NiMH will best suit your needs. You might even use "D" size, but beware that some manufacturers just package "C" cells in "D" outlines.

[edit] The figures I gave (80% at 1.2V) assume discharge rates of C/20 at most. The alkaline really falls flat at high current levels. You may find a dramatic improvement in battery "life" just by switching to NiMH just because they can better handle high current.[\edit]