Electrical Math problem

[Spinalguy]

i am making a helmet cam. i want to avoid any moving parts from the recording source.
SANDISC has recently released a new product, the V-MATE. Its a video memory card recorder. It uses the same cards that a camera uses. The cool part is that a 2GB card will record 7.1 hours!!!
When i bought it, the salesman told me it was rechargeable lasting 12 hours on each charge cycle. He was WRONG......basically clueless and made it all up. It has to be plugged in to work.

The dilemma

i really, really want to make this work. It is perfect in every regard except it needs power. Can i cut the wires from the wall source and use auxillary battery power from a 12V rechargeable battery?

These are the specs on the AC/DC Adaptor:

Class 2 Transformer
input: 120V AC 60HZ 11W
output: 5V DC 1000mA


What if anything can i do to carry a battery that will last over 3 hours and is rechargeable that will not hurt the V-MATE.

Thanks

 

[stuckagain]

Is this for the mountain bike or the KTM?

[Spinalguy]

KTM but i will also use it for DH mtn bikin (if i ever go...again)

[DGenR8]

The recorder only needs 5 volts  @ 1000Ma, you should be able to find a cordless phone battery to make it work. The transformer takes the 120 volts from the outlet and reduces it to 5 volts @ 1000 Ma.

[bae146]

You have two choices on power supply.  If you want to go with a battery pack you will need to make yourself one with proper voltage to match your sandisk.  12Vwill kill it.  Do you want to build this battery pack to be recharged by your KTM's electrical system or a battery pack that will be recharged by 110VAC?  I am no electrical genius but we need to know exactly what you are after to help give you direction.  If you want to run it off you vehicles power supply you could wire this into your electrical system

http://www.thesourcecc.com/estore/Product.aspx?language=en-CA&catalog=Online&category=DC+AdaptorsandPlugs&product=2738864  
 

The dc converter from the source would be your easiest bet.

[Spinalguy]

bae146,
i thought about running an invertor thru the battery in the KTM (as it is 4 stroke electric start) but if i crash and almost every rider crashes once per race, i will be wired to the bike...so to speak, probably not a good idea for 2 reasons:
1/ unless things disconnect on impact, the camera to scandisc connection will be toast
2/ run enough length cable as the bike rarely lands more than 10 feet from impact but...........it would suck to spend all that time collecting cable to get going again as every second counts racing. Not to mention riding with long leads of cable thru dense bush and technical tree courses would be crappy.
Clotheslining comes to mind

So, it has to be portable power that resides in my backpack. My pack is not large for races as i carry liquid and thats about it. There would be room for the scandisc(smallish and very light) and battery power.

Mark,
correct me if i am wrong but i thought i had to MATCH the 5V 1000mA rating with a battery of identical ratings?
i have googled for such a battery but have had no luck but i may be inputting the wrong info?
Readily available are 7.2 and 6V rechargeable batteries from Radioshack for RC cars. The mA ratings are 1500 to 2000.

Thanks for the previous input and i appreciate further input regarding my reply.

TK  

[Spinalguy]

Here are some examples:

http://www.thesourcecc.com/estore/product.aspx?language=en-CA&catalog=Online&category=Cordless+Batteries&product=2317006

http://www.thesourcecc.com/estore/Product.aspx?language=en-CA&catalog=Online&category=RC+Toy+Batteries&product=2300430

http://www.thesourcecc.com/estore/Product.aspx?language=en-CA&catalog=Online&category=RC+Toy+Batteries&product=2300329

This pdf file may be the solution but i am not sure i understand it. Page 6 and 7 i think? is the solution?

http://www.oreilly.com/catalog/psphks/chapter/hack15.pdf

[Elsifer]

These are the specs on the AC/DC Adaptor:

Class 2 Transformer
input: 120V AC 60HZ 11W
output: 5V DC 1000mA

/quote]

I'm no electrician, but 1000mA = 1A.

So, to get your 5v, you could use 3x1.5v AA, C, or D cell batteries in series to get 4.5v, add a 4th one to get 6v. Which *shouldn't* harm the device.
I wouldn't use a 12v battery, with a resistor to bash it down to 5v. That resistor will get awfully hot. Like burning plastic or leather hot.

Do a test with 3xD cell batteries in series. That should be enough voltage to run the device. The current spec is prolly created by the devices own internal resistance (Ohms law says 5ohm on the device for 5v and 1A).
If the device doesnt work with three cells, add the fourth to bring up the total potential to 6v. The half volt won't make a difference. Perhaps a touch more heat in the device.

If the device works with three or four cells, then see how long they last. Should be more than enough to capture a race. Plus those are pretty cheap and disposable batteries. Those batteries are all 1.5v, AA, C, and D's. Just their capacity increases as the size of the unit increases. So a D cell will run for a lot longer than a AA.

RadioShack or TheSource has battery holders that work great for such a project. Good luck!

Once again, I'm no electrician! I know just enough to be dangerous!

[bae146]

You need to match the 5 volts but not the mA  The mA is just the capacity of the battery.  Just like the cca rating on an automotive battery.  Most battery packs do not put out 5v.  Battery packs are made up of cells witch normally put out anywhere from 1.2 to 1.5 volts.  The standard AA alkaline battery's put out 1.5 where the rechargeable battery's put out 1.25 volts.  Do you have access to a digital multimeter?  If so plug in your ac adapter and see what it is putting out for voltage.  You will probably find out it puts out more than 5v.     If you were to get 4 1.25v rechargeable aa batteries and hook them is series you would have about 5 volts.  Now most of the better nimihi batteries have a mA rating of 1200.  So for your simplest soloution this would work.  However for a longer usage time you would need maybe 8 batteries.  You would then hook them up in pairs together and then in series to maintain your 5 volts with a 2400 mA rating.  Same voltage just twice the capacity.  This is cheep to as you can get 4 aa batteries and a charger at costco for about 26 bucks.  I think you can still get battery holders at the source (radio shack)  You can get the adapter end to plug into your device there as well.  If you need any more directions as to how to build one of these let me know.  You will need a soldering iron and some wire but that is all.

[Vinman]

Go to London Drugs and get (4) AA NiMh batteries for digital cameras.

They are 1.2 volts so (4) connected in series totals 5V. I believe the batteries London Drugs carry are also about 2500 MA., which should last a reasonable amount of time.

Vince

[kenny kustom]

All rechargeable batteries are 1.2-1.3 volts. A regular alkiline is 1.5V.

[Vinman]

All rechargeable batteries are 1.2-1.3 volts. A regular alkiline is 1.5V.

Not quite all, I have a bunch of rechargeable alkalines that are 1.5 volts.

[Spinalguy]

Thanks all.
i will get the batteries from London Drugs, the holder and connections from Radio shack and maybe some help from bae146.
i'll update you all.
Thanks again
Tom

[shibby]

I've actually rebuilt my own laptop Battery using LI-ION cells. the cells were actually pretty cheap and would probabley last quite a while if you were only powering the video recorder.

something like this would work
http://cgi.ebay.com/4x1000time-CR123A-Li-ion-3V-Rechargeable-Battery-600mAh_W0QQitemZ300107928694QQihZ020QQcategoryZ40975QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

The device requires 5V but having a little extra voltage shouldn't hurt it , as long as you're not putting in ALOT of extra voltage. Usually if you measure the AC adapter, it can be +/- up to 1V.

If you take the above batteries (4) and wire them in up into 2 each in series, and then take the 2 pairs and wire them in Parallel. You will end up with a 6V 2400 mAh battery pack. Also keep in mind that just because the power supply says 1000mA (1amp) doesn't mean that the device will draw that much. the only way to find out how much it draws is to put an amp meter in series with the powered up unit and measure it. But say the unit draws 600mA (which is pretty high), the battery pack would last approx 4 hours.

[DGenR8]

5v Battery pack here...

http://www.bixnet.com/5v7libapa.html