Help me buld a battery pack please!!! Student on a budget here

[kleme]

Hello everyone,

Sorry in advance for the noob question, but i have a health background not engineering, so I need some help. I bought a headlamp for work with a 3 watt Cree LED in it and its pretty good on the 3 AAA batteries that it accepts. I want to build a battery pack for it to not only boost the brightness of it a bit, but most importantly extend the run time to at least 8 hours, it currently only lasts for 3. I've come up with plans for a pack that would include a 700ma driver, a potentiometer, and a 7.4v 2600mah li-ion battery, but the battery is almost 40 bucks alone on another site. I was wondering if thats a good set up battery wise. Am I using to much power or not enough, does anyone have any suggestions on a buying a pack on this site but cheaper? Im also up for trying to build one myself. So far i figure i need 2 18650 3.7v 2600mah li-ion batteries, a PCB, and some soldering skills....... any suggestions on getting some cheap batteries like the ones on the dewalt battery tear down or maybe a battery that includes a charger.

Im so lost on this, just because there are so many options and I don't know what to pull the trigger on.....

Any suggestions would be greatly appreciated

 

[Mr Happy]

You are probably trying to make things too complicated here.

Also "increasing the brightness a bit" is probably not advisable. The light will be designed to operate as it is. Attempting to push more current through it is likely to lead to overheating and premature failure. The way to get a brighter light is to buy a brighter light.

Now, do you get three hours run time from rechargeable batteries, or from alkaline? In any case, to go from 3 hours to 8 hours you need to treble the battery capacity. You could do that by going from 3 AAA batteries to 6 AA batteries in a 3s2p arrangement. Some rechargeable AA NiMH batteries should do nicely. Buy a some simple plastic battery holders, wire them up the right way, and use regular AA rechargeables like eneloops. That will be a much more reasonable cost.

The only other thing to worry about is the current through the light. Lights that use 3 AAA cells may rely on the feeble batteries to limit the current. As soon as you put a bigger pack in there the light could be over driven and be in danger of overheating. You might need a low value resistor in the supply just in case.

 

[HarryN]

Hi, I would avoid solding to batteries unless you are really experienced, and then never to a Li based cell.

If your project is not super size / weight limited, you can get a very good quality, 6S, 7.2 volt, 5,000 mah NiMH pack from cheapbatterypacks.com for around $ 50 - with connectors. (sub C based cells, premium quality welds) I use a pair of them in series to run my son's r/c car - they just go and go. A 9S setup in a triangle format would be even better, and only nominally more $s.

As for a driver, 700ma is not really that much - for less than $ 20 you can get a 1 amp driver with pot from ledsupply that is fully sealed.

Li cells are great for performance and weight, but cost wise, they will bleed you dry.

 

[Mr Happy]

As for a driver, 700ma is not really that much - for less than $ 20 you can get a 1 amp driver with pot from ledsupply that is fully sealed.

But bear in mind you can let the magic smoke out of the LED or worse unless there is adequate heat sinking. If the original installation was not designed to run at 700 mA it will likely not have heat sinking for 700 mA...

 

[qwertyydude]

Hmm a good battery pack that's nice and cheap, how about just sticking with alkaline but getting a 3 D-Cell holder. It would probably be a good idea to put a 1 ohm resistor inline with the pack. And simply run a wire up to the contacts of your headlight. This way voltages match and it's cheap to do. You should get 40 hours or more out of a set of batteries. Oh and the easiest battery pack to use would be an RC car 7.2 volt battery pack if you're going the regulated route. 40 bucks can get you a higher capacity 3000 mah rc car pack and even a charger for it.

 

[greenLED]

I'm with qwertydude - go to Radio Shack and get a 3AA or 3C battery carrier and wire it into your headlamp.

Have 6 rechargeable cells and you can rotate 3 of them at a time.

 

[Marduke]

At $40 you can probably get a whole new headlamp that meets your requirements.

Knowing what you already have would help.

 

[kleme]

At $40 you can probably get a whole new headlamp that meets your requirements.

Knowing what you already have would help.

I have the H7 Lenser:
http://www.dealextreme.com/details.dx/sku.29435

It only costs $20, so i wanted at least an option that would cost me around that much more to modify it.

Im a dental student, and I am using it as a headlamp that is attached to my loupes. I needed a very focusable light that is light and powerful, and this one fits the bill. So i took off the strap and attached only the light to my loupes and extended the battery pack to fit on my belt. So now im looking to make it last longer and look neater than a couple of batteries strapped together. So yea maybe a battery for R/C would work?

 

[kleme]

Thank you guys for your help so far,

Ive found all the power supplies I need. Im going with a lipo that has a PCB, which will hopefully save me if I ever need saving. I wont be abusing the pack in a high draw application though so I'm not worried. One more question though. Is there any cheaper places than LEDsupply.com to buy a driver like this one http://ledsupply.com/03023-d-e-700p.php?