What batteries to power a 24 volt LED

I am going to build a portable flood light using a 50 watt LED it's a street lighting type, I would like it to be carried like a torch so batteries will have to be in iternal, and the voltage is 24 to 26 volts @ 2200ma. Output should be 4,000 to 4,500 lm. I would like a burn time of 1hour.

What do you think would be the best way to power this led, keeping the cost reasonable?

What is the internal battery space? internal to what, light housing or backpack?
What driver do you plan on using?

A 6S1P/2200mAH R/C flight pack will do it. Inexpensive (about $30), lightweight (13-14oz.), small size (113x33x52mm), easy and very safe to balance charge using a hobby charger.

The 6S1P/2200mAH R/C flight pack seems to be a 22.2 volt I see you can get them in a 3800ma model too, the led need 24 to 26volt I am looking for a drive thats my next task, the housing is not made I would build it to fit the pack. could I raise the voltage in any way that would work?

It will work without any additions. The voltage will be between 22.2 and 25.2 volts depending on its state of charge. You can get them to 9000+mAH.

What LED? in what housing?

Variable voltage will give you variable output. It'll start out bright and start dimming as the battery voltage drops. Do you want full light output for an hr? Or, do you want ~.8 watts of light lost every minute?

It won't work without additions!

You need to find a boost driver to take 12v up to the 2200ma @ whatever voltage the LED needs.
Or, you can build a 30+V battery pack and buck it down to your needed voltage for 2200ma.

http://cgi.ebay.com/250859161445
http://cgi.ebay.com/220697691827

Or, send an email to taskled.com and see if you can run a couple of their drivers in parallel. Two of their drivers set to 1100mah in parallel(if parallel works) will get you the 2200mah and pretty much a fixed light output for that 1hr IF you have the battery capacity(minimally 5+ 18650's or a 10ah 12v AGM).

Without a driver, you can 'maybe' get away with a 24v 7ah AGM scooter-type battery. Fully charged, the battery is at 26 volts and dead by 20v. 7ah should get you the 1hr run time. You'll be cooking in the 60+ watt range and as the voltage drops, your LED power will too. But, I doubt that you'll dim below 40w in that 1hr time frame. You can use something like a dropping diode or resistor IF you don't want that initial 60+w output when you 1st turn on the LED with a fully charged 26.4v battery. You'll have to use your DMM to monitor both voltage and current to make sure you're where you want to be.

This sounds like it's going to be one of those DX flat panel led's. If so I would suggest looking elsewhere for led's. 5S XM-L's would cost about the same, be more efficient and be easier to run off of 6S lipo's. All you'd need is a buck driver, or if you go 6S XM-L and 6S lipo you could actually get away with direct drive using a resistor.

I found the led on ebay it's No 390245307832 not shure of it's origin yet, the first DC to DC converter you listed seems to fit the bill? how will the 60watts effect the LED? Just started this project so I am looking for other emitters that fit the bill, cant find the 5s XM-Ls that you sergest, thanks for your help,

No you simply buy 5 Cree XM-L leds and wire them together in series. It'll output much more light. You can get them on a 14mm board so you can arrange them in a nice compact pattern.

I looked at that led and yeah you're not going to get 4000 lumens out of it and at a color temperature of 12000k you're going to get one really really blue led. It won't look pretty. And it'll dim rather fast as these generate tons of heat.

No matter what you do you'll need massive heatsinking and possibly a fan. Led's do not like heat.

I have 2 sst-90 and drivers I brought I could use them then, and drive them separately or together? I take your point about the flat panel led's. the heat and running at 12,000k would be a poor idea. Thanks for your help again, keeps me thinking!

Drive them both together in series as it's kinda hard to find a 9 amp led driver. Then all you need is at least one 2S lipo battery and you can run these in parallel to get more capacity. You can run these direct drive with a simple resistor setup.

With a 2S led setup you need to drop .66v total, at a running current of 9 amps that's a power dissipation of 5.94 watts. Pretty efficient to just use a resistor as there's no voltage overhead like a driver so you can still use 2S lipo with a driver you'd need to be running 3S. Calculating the ohms gives me approximately .073 ohms. So you're probably safe to direct drive it but just to be safer I'd put a .1 ohm 10w resistor inline with the led's as 5000+ mah lipos have ridiculously low internal resistances and could possibly overload the led. Plus as the led dims you know the battery is running low, with a 3S and driver setup if you could find it, you'd have constant light and then it'll turn off all of a sudden as voltage protection kicks in.

That should give you a good place to start.

Thanks qwertyydude, I have two new sst-90 would a 5000mah 2S 20C lipo drive them ok? what would be the run time? How do you rate the lipo batteries I have never used them? I like the fact you can get a 12volt car charger too, the size of the lipo's is good for the job and would make a small flood to use. thanks.

At a 9 amp draw you're looking at about 33 minute run time. But in reality it starts at 9 and then slowly the current drops down. It's almost not noticeable in the led because as current goes down the led efficiency goes up so realistically you'll get about 45 minutes of continuous runtime before you notice the led dimming significantly.

But you can always buy another. Hobbypartz.com has excellent deals on sky lipo 5000 mah 20c batteries. $20 and if you spend $25 on the site it's free shipping so buying 2 for $40 is a great deal.

If you truly do have .66V excess voltage, a .1 ohm resistor would limit you to 6.6A. Forward voltage of the leds varies some so it's impossible to say exactly what voltage they will draw at a given current. Also your battery voltage will sag and have a pretty significant effect on output. Checked the Mouser catalog real quick, they have Ohmite .075 ohm 7 watt resistor, in stock for $7.56. They also carry the SST-90 and SSR-90 (the SSR-90 will be easier to work with.)

A 20C 5000 mah lipo battery won't sag very much under these light loads. I tested mine at 10 amps and the voltage only went down about .05 volts under load. So don't expect that lipo pack to provide you with a safety margin.

For the body I am geting some 2.75" ally tube to try and I have ordered two Lipo 20 C5000 that I think will fit inside nice, if the tube is too tight I will have to go up to 3" dia. Charging the two Lipo's is a problem I can see coming as they will be linked to provide 7.4 volts at 10000ah I could seperate them with a two pole switch when in the off position for charging but it's getting messy to do that? Still not clear what to do to control the forwards voltage? I have never used a Lipo so what chargers will charge the two Lipo's in 6 to 10 hours? thanks for your help.

I've run parallel packs before in remote control cars. Balance both packs before putting them in then you can charge them in parallel. Parallel charging is perfectly safe. Although I suppose if you have a charger that has to have the balancing ports plugged in while charging it could be trouble. I use a Pro-Peak Prodigy 2 it doesn't balance so it doesn't need the balance port plugged in to charge.

Lipo's are new to me and I have spent a lot of time reading up on Lipo batteries and can't find out weather I can charge them in the unventilated body of the torch? I have ordered two 7.4volt C20 5000mah Lipo's and I am not sure how to charge them. I can not remove them for charging each time; it will take too long, and corrupt the seal. I have read about a "Blinky Balancer" that can be connected to allow charging without balancing, can this be left attached within the body of the torch after charging?

The blinky will drain the battery while it is attached. It balances by draining the high cell. What charger will you use to charge. Like I said once you balance and charge both packs you're good to leave them in the light and simply charge both packs in parallel. I've had packs cycled dozens of times and they never got more than .03 volts out balance.

It's usually not a good to charge lipos in a sealed case because in the unlikely event of failure you have to watch out, the batteries will vent violently and can cause an explosion. If at all possible it would be safer to charge the batteries outside or at least make sure the thing isn't air tight.

I haven't brought a charger yet, the flood light is for underwater use and would be kept sealed except for a 12mm hole for the charging lead to be fished out of during charging, this 12mm hole is the only way the torch can vent, and it will be sealed with a "O" ring on a threaded plug when ready for use, this my not be any good for Lipo's then? I could increase the size of the charge plug to 25mm if needed would that be enough?