Chasing help with Lipo Battery...

[mIKe-]

Hey guys.

What I'm looking for is a 11.1V (3S) lipo pack, with say 3000mAh+, but it needs to only have a very low discharge rate, the pack is only to power a few LED lights.

Smaller is better too, but anything will beat the 12V sealed lead acid most guys are using.

If anyone knows where I could find a cheapish pack that fits the description please let me know!

Thanks
-Mike

[eichkay]

Have you looked in the LHS at the cheap E-sky lipo's ? also why 3000mah ? Thats allot of capacity for LED's

[mIKe-]

Had a quick look around online but could only find like 20C+ lipo packs.

What I had the light set-up in mind for was a helmet light for night riding (actual downhill and trail riding, not just up and down the street) and getting several hours would be quite nice.

And these arn't just a normal LED, they chew some juice. But nothing like brushless juice.

[nexxus]

try www.hobbycity.com (http://www.hobbycity.com)

[eichkay]

You could run 2x 3s lipos in a smaller capacity in parallel

[KingBob]

Or use resistors.

[mIKe-]

Not sure how to use resistors as I'm not that smart.

Looks like 2 in paralell will be the keeper. Why that never occured to me if beyond me.

[KingBob]

LOL, dude, no offence, but if you cant work out how to use a resistor, then you shouldnt be strapping LiPo's to your head!

[mIKe-]

LOL, dude, no offence taken.

Battery doesn't go on the head, it goes inbetween my legs on my frame.. so much more care needs to be taken.

[Dazz 68]

Ebay for the batteries theres a heap of really cheap ones similar to what you were chasing for around $30 shipped from Hong Kong.
If your light hooks straight up to a 12 volt battery you wont need any external resistors to limit current as they are already built into the light .The C rating of the battery wont make any difference to how fast it will discharge.The LED's will only draw what they require having a lower C rating wont make them discharge slower it is purely an indication of the maxinmum power they can discharge if needed.

[SuperRoo]

I see there is a comment about "taking care" so what are you planning on using as a voltage cutoff for the LiPo?

LED's will go well below the voltage cutoff point of a LiPo before they start to dim and I'm sure you don't want a puffing LiPo between your legs while riding at night.

[KingBob]

Sssshhhh... dont tell him that! We might be able to do the gene pool a favour if they do blow up! :D

[mIKe-]

As for the resistor comment before KB, I thought it had something to do with the batteries, not just running it in the circuit.

As for a resistor in the circuit, I have a LED driver (glorified and expensive resistor) that can run 6 LED's up to 18V, so that isn't an issue.

As as for lower C value packs last longer, I know they don't aswell. I was just saying I'm chasing a lower C value as they are cheaper and I know the LED's won't have a fast discharge rate.

Lipo cut-off.. bit of trial and error at the start (at home with volt meter) to see how long I can get from a full pack while staying in a safe voltage, then I will use it for about half that to be on the safe side (I don't want fryed nuts). Depending on how long it lasts, I may need to get a second pack.

[remotebandit]

I use an 11.1V to run the dash on my go kart as the pack the dash came with was nicad and only lasted a days run , now i cant even tell you how long the lipo runs as it hasnt gone low yet in over 4 meets .

As you said Mike , just bench test it off a full charge , see how long it runs and then back it of for safety sake about 30% from your timed time .

Worst case takes you an hour to charge it .

[mIKe-]

Least someone is half positive on the idea...

[remotebandit]

i reckon its a great idea as lipo is the future , just watch the low voltage and if your gonna use it between your legs put it in your sack .... lipo sack that is .

[mIKe-]

Well I have a few option with what to do with it.

Most people don't know about Lipo's and other small high voltage and decent capacity that are cheap, so they are using huge batteries in an empty water bottle on the frame. So I could do that, or just make a full unit on the helmet.

[KingBob]

I'd avoid putting the LiPo on your helmet especially since you're looking at soft shell packs. If you stack your bike and hit your helmet you could damage the pack.

Depending on the kind of mA the LEDs draw, a 3000mAh pack could last you ages!

[mIKe-]

The LED's are fairly insane in terms of brightness, but they are still only a LED, don't pull current like halogen globes do.

I was thinking of a small lipo sack (if they even make small ones!?) inside a sealed plastic container for the battery.

But I'll have to look once I get the battery and see how it all goes together. I'm not going to do something dodgy, I have seen how Lipo's can go bang. And I cherish both my face and my nuts.

[KingBob]

A really bright LED (say 20000mcd) will likely only draw 20-25ma @ 3V which is bugger all for a Lipo, should last ages.

[SuperRoo]

Have you considered getting a multimeter and measuring the current draw of the LED's?

This little bit of info will help decide what you really need as far as capacity goes and will be a little more accurate than checking the voltage with your multimeter for several hours, possibly days.

[mIKe-]

Nah sounds far too intelligent SuperPoo... trial and error is more my style :)

Thanks for your help though guys!

[KingBob]

The LEDs didnt come in a package or anything with their specs written on them?

[mIKe-]

Nope.

The LED's are CREE R2 ones.

Rated to about 18V, and can pump out over 500lumens, thats as much as I really know.

[micmac]

SuperPoo... !

Is this something you do after a good night at an Indian restaurant ???

Great typo mate :-)

[mIKe-]

Nah, more like a big night after you found out Jacks stubbies were on special!

You had to quote it too so I can't just edit it out...

[KingBob]

Nope.

The LED's are CREE R2 ones.

Rated to about 18V, and can pump out over 500lumens, thats as much as I really know.

Just the LED or the flashlight bulb assembly? Dunno where you're getting 500 lumens from, most i can find is 275.

[SuperRoo]

Just the LED or the flashlight bulb assembly? Dunno where you're getting 500 lumens from, most i can find is 275.

I'm assuming thats an array of LED's since the R2's on their own are only good for 114 lumens @ 3.49 volts on their own.

[Dazz 68]

Could try putting one of these in the circuit ,it gives an audible warning when the batteries reach the cut off point.There are also heaps of cheap Lipo cutoff devices on Ebay that could easily be wired into yor project

http://cgi.ebay.com.au/ws/eBayISAPI.dll?ViewItem&rd=1&item=220357311574&ssPageName=STRK:MEWA:IT&ih=012

[remotebandit]

if its the 1 im thinking of they are single LEDs but they draw about half an amp .

Heavy duty mothers