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battery life extention

 
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lennyu
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Joined: 06 Nov 2008
Posts: 4

PostPosted: Thu Nov 06, 2008 8:49 pm    Post subject: battery life extention Reply with quote

ok I'm sure this information is available somewhere, but I've searched and searched and cant seem to find it anywhere. I'm probably just not using the correct keywords in my search.

Anyways, Here goes...

I have a wireless digital security camera with an internal lithium battery and a 5V DC input that powers the camera and charges the battery. The battery lasts approx 4hours... what I want is an external battery back that I can plug into the 5V input that will make the battery life much much longer like a day or 2.. or longer would be even better...

the idea i had was to make a pack that holds a few 9V rechargeable batteries...

so i can just go and switch out the 9 volts every couple days

How would I go about that? a voltage regulator? can I just hook them up paralell?

any help would be greatly appreciated ..

long story short any power source that could provide a constant 5V DC for as long as possible.

I've also considered solar as this is going to be outside, but the primary function of the camera is at night and I live in IL and this is going to be up through the winter so I kinda figured solar power would be out of the question.. could be wrong? but even if i could use solar to recharge I only get 4 hours out of the internal battery so I still need something additional to make it through the night

Thanks again,
Lenny
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Alan
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Joined: 29 Jan 2006
Posts: 1399
Location: Winnipeg, MB

PostPosted: Thu Nov 06, 2008 10:39 pm    Post subject: Reply with quote

This is able to be done. First thing you will have to do is calculate the size of battery you will need. I think we will find that it would take so many 9 volt batteries that it would not be practice.

Look at the existing battery pack and find its mAh rating. We will then have to multiply that number by about 12 to get the 48 hours of run time you desire.

I think that we will find that a small 6 volt battery will fit the bill. The battery I mean can usually be found in small items such as electric hedge trimmers.
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lennyu
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Joined: 06 Nov 2008
Posts: 4

PostPosted: Fri Nov 07, 2008 1:58 am    Post subject: alright Reply with quote

thats a great start... thank you very much... now to elaborate...

this is to power a small wireless camera primarily for temporary purposes (a couple months) therefore I want to use a battery that isn't useless after i'm done with this project. What I forgot to mention is that the camera really only needs to run at night (about 10 hours a night)...

What I've come up with...

I have a sony handycam (dcr-sr42)
the standard battery is 1700 mAh
the extended battery I just found is 2200 mAh at 6.8V
If I use that battery atleast I can use it afterwards in my camcorder

Specs for the camera I'm planning on using from the seller are as follows
(I know I originally said 4 hours, but that camera turns out to not offer the video quality I needed so.. now we're down to 2 hours runtime estimate)

Battery performance: >5V (DC)5%, 700mAh
Battery capacity: 250mAh
Working time: 2 hours
Consumption current: 80mAh

...now first thing I noticed... 250 mAh battery ... 2 hours working time... 80mAh consumption ... unless i'm missing something doesn't that mean that the battery should run more like 3.5 hours?
(250/80 = 3.5)

Also.. what is the 700mAh figure under battery performance?

now if the 80mAh is what i'm working with that means the 2200mAh battery will give me 27 hours which will work fine and allow me to change out the battery every 2 days...

My next question is can I run 6.8V to a 5V input without messing something up? and if not what do I have to do to step it down to 5V?
can I just use a rectifier diode?
is that safe for the battery can it cause any problems (limiting the voltage output)?

Also will lowering the output voltage give me more battery life?

i ask because the battery is actually listed as 14.96Wh

I conveted it using amp = watt / volt
14.96W/6.8V=2.2 Ah *1000 = 2200 mAh

So does that mean if i'm only running it at 5V...

14.96Wh / 5V = 2.992 Ah *1000
=2992 mAh
2992 mAh / 80 mAh = 37 hours run time??

Thanks again for your previous help it really pointed me in the right direction.. and sorry for so many (probably dumb) questions

Question summary for ease of answering:

Do the battery cap. / consumption / runtime numbers seem wrong?

What is the 700mAh figure under battery performance?

Do I have to lower the voltage from 6.8V to 5V?

What do I have to do to step it down to 5V?

Will limiting the output voltage damage the battery?

Will lowering the voltage to 5V give me more battery life?


Thanks again,
Lenny
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lennyu
Newbie


Joined: 06 Nov 2008
Posts: 4

PostPosted: Fri Nov 07, 2008 2:23 am    Post subject: quick addition... Reply with quote

ok I'm shopping around for different cameras and I'm noticing higher image quality cameras for lower prices if I buy one without an internal battery... and since I'm going to use an external battery back anyways this is looking like a better option...

The problem is they run higher voltage.. 8V seemes pretty standard a couple run as high as 12V...

Additonal questions...

can I step up the previously mentioned 6.8V battery to power an 8V device? and how would I go about doing that?

will stepping UP the power consumption hurt the battery?

is it possible that the camera would run off of the lower voltage?

the one for example (probably the one i'm gonna use)...

Power Supply: DC 8V 200mA
Power Consumption: 80mA / 120 mA with IR on

Note: I have no use for the IR so the consumption will be 80mA @ 8V

thanks again.. again sorry for the quantity of questions
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lennyu
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Joined: 06 Nov 2008
Posts: 4

PostPosted: Fri Nov 07, 2008 2:41 am    Post subject: ok... one more Reply with quote

...i know.. i know you're thinking this guy just never stops...

it just dawned on me I have 12V power tool batteries already they're a little big but thats not really a problem..

they are 1200 mAh ..they are NiCad not LithiumIon (is that a problem... advantages disadvantages?)

and going back to my previous question kinda... if I'm drawing 8V off a 12V battery...

Sorry again for all the different questions i'm kinda weighing my options here and trying to find the best solution....

thanks,
Lenny
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Alan
Site Admin


Joined: 29 Jan 2006
Posts: 1399
Location: Winnipeg, MB

PostPosted: Sat Nov 08, 2008 12:05 am    Post subject: Re: alright Reply with quote

lennyu wrote:
Do the battery cap. / consumption / runtime numbers seem wrong?

In general it sort of works that way but depending on how much current you pull it can work out different than expected.

lennyu wrote:
What is the 700mAh figure under battery performance?

Not exactly sure the battery performance number is?

lennyu wrote:
Do I have to lower the voltage from 6.8V to 5V?

You can check the camera specs to see what type of voltage range it will take. If all it states is 5 volts then I would feed it something very close to that. You should be fine with the rated voltage plus or minus 10%.

lennyu wrote:
What do I have to do to step it down to 5V?

You can use a voltage regulator or 3 series diodes.

lennyu wrote:

Will limiting the output voltage damage the battery?

No.

lennyu wrote:
Will lowering the voltage to 5V give me more battery life?

Generally not, with most methods since the additional voltage will be disposed as heat.
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Alan
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Joined: 29 Jan 2006
Posts: 1399
Location: Winnipeg, MB

PostPosted: Sat Nov 08, 2008 12:21 am    Post subject: Re: quick addition... Reply with quote

lennyu wrote:
ok I'm shopping around for different cameras and I'm noticing higher image quality cameras for lower prices if I buy one without an internal battery... and since I'm going to use an external battery back anyways this is looking like a better option...

The problem is they run higher voltage.. 8V seemes pretty standard a couple run as high as 12V...

Additonal questions...

can I step up the previously mentioned 6.8V battery to power an 8V device? and how would I go about doing that?

will stepping UP the power consumption hurt the battery?

is it possible that the camera would run off of the lower voltage?

the one for example (probably the one i'm gonna use)...

Power Supply: DC 8V 200mA
Power Consumption: 80mA / 120 mA with IR on

Note: I have no use for the IR so the consumption will be 80mA @ 8V

thanks again.. again sorry for the quantity of questions


There are DC to DC converters that can increase the voltage of your battery but this is not a simple process and I would not recommend it. You should always attempt to use the correct battery voltage or a bit higher and use some simple electronics to drop it.

I would just use a 12 volt battery and use a regulator with a heatsink.
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Alan
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Joined: 29 Jan 2006
Posts: 1399
Location: Winnipeg, MB

PostPosted: Sat Nov 08, 2008 12:25 am    Post subject: Re: ok... one more Reply with quote

lennyu wrote:
...i know.. i know you're thinking this guy just never stops...

it just dawned on me I have 12V power tool batteries already they're a little big but thats not really a problem..

they are 1200 mAh ..they are NiCad not LithiumIon (is that a problem... advantages disadvantages?)

and going back to my previous question kinda... if I'm drawing 8V off a 12V battery...

Sorry again for all the different questions i'm kinda weighing my options here and trying to find the best solution....

thanks,
Lenny


That would work fine. Battery type will not matter in your application.

I would use something like a LM317 regulator with a large heatsink (or bolted to a large piece of metal since this is a temporary install)
http://www.national.com/mpf/LM/LM317.html
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Tekwiz
HG Contributor


Joined: 20 Oct 2008
Posts: 36
Location: Vancouver Island

PostPosted: Sat Nov 08, 2008 3:47 pm    Post subject: Reply with quote

Yes, a voltage regulator & 12V battery is the way to go. The LM78xx series of 3 terminal voltage regulator ICs are cheap, easy to use, & virtually foolproof. They are available in a wide variety of output voltages, including 5 & 8 volts. If you are concerned about battery costs, you might be best off using disposable batteries. A pack of 8 AA sized batteries will give you 12vdc @ 2500mah, if you use alkaline cells. D sized batteries will give you 4500mah capacity or better. Smile
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