question about modifying a battery pack

[kq702]

Hi, I use a small security camera for watching over my work shop. I dont use it all the time, only when I know its going to be a busy day. I purchased a swann 3.3 micro camera and it works great, just the only problem is if I want to have the film record an entire day it takes about 3 or 4 9V batteries. Its very annoying because the batteries only last a few hours. I tried charging the batteries and they dont last very long so I came up with my own idea.

I have a bunch of small lion cell phone batteries and I charged up 3 batteries and made a custom battery holder, and wired it up so the batteries pop in and out of the battery holder box. When three batteries are installed, they are connected in a series. Each battery puts out about 4.15 volts (if fully charged). So my custom battery pack is just under 13 volts.

So I connected it to my camera and it lasted a while. The custom battery pack allows the battery to last all day without having to be replaced. However after about 30-40 full day uses the circuit blew in the camera (I assume from being overpowered with the 13 volts when the calling voltage is only 9 volts).

So I got a new camera but I was wondering if I can add a reisistor or something so it wont do damage to the camera this time? How would I do that (or is it even posable)?

 

[pattenp]

Yes, use a resistor. See link:http://www.play-hookey.com/dc_theory/voltage_divider.html

 

[aandpdan]

Even better, use a 7809 voltage regulator ic.

 

[kq702]

Hmm, if I post a photo of my battery pack can someone help show me where to place the components? (3rd battery is in the back, you can not see the third one at that angle)

 

[pattenp]

See the below link for using the 7809 voltage reg. It connects as follows, (battery +) to (+Vin), then (+Vout) to the (plug +). The (battery -) to the (-V/ground) and (-V/ground) to (plug -).

http://www.researchcell.com/general/7809-pin-and-circuit-diagram/

 

[kq702]

Ok great info!

The only problem is my local radio shack only has 12 v and 5 v regulators and I need this item for tomorrw if I can find it. I was wondering if I cant buy two 5's and double them up? (that would make about 10 volts)

 

[pattenp]

They step down the voltage. It's not like putting two 5V batteries in series to get 10V.

 

[justsam]

Perhaps only use (2) of your cell phone batteries. Voltage may be a little low, but should still work. The camera no doubt has it's own internal regulator, and internal circuitry may actually operate from +5VDC.

 

[kq702]

great idea! will give that a try this afternoon!

 

[nehog]

I'll only say that using lithium batteries in any application other that one designed for them presents some risks, and you need to understand the risks (of fire, for example) if you go this route.

I'd recommend a smaller 12 volt LA battery instead, such as one from a UPS, a charger made for sealed LA batteries, and a switching mode regulator if you absolutely must have 9 volts. Using a resistor or a series pass regulator is inefficient at best.

A couple of 9.6 volt NiCa batteries would work very well, and may be easier to charge.

 

[kspwski]

I like the two battery idea. If that doesn't work you can use two resistors to make a voltage divider to get your 9v Wikipedia Link. In the graphic on wikipedia Vin connects to the + side of the battery, vout to the + on the camera and the ground goes to the ground wire. This would not be regulated and the output would change relative to the changing input voltage while discharging.

 

[aandpdan]

How about an LM317, an adjustable regulator.

http://www.discovercircuits.com/DJ-Circuits/bat-elim2.htm