battery for a led bulb

[attchoum]

hi everybody

I just buy a strong led for a light project. This kind of led http://cgi.ebay.ca/ws/eBayISAPI.dll...MEWA:IT&viewitem=&item=110082006135&rd=1&rd=1

I need your opinion on what type of batterie should i use.

This led work on a 4v source. I was thinking about 3v lithium batterie, but i can find how llong i will be abel to turn on my light whit those batterie.
Any help are welcome.

thx
etienne

 

[ScubaToneDog]

Well, a lot depends on what housing you are using. You could make a pretty compact light with a 9V battery for instance. You would need to put a 270ohm resistor on the front side voltage. (I am approximating the current at 20 mA).

You dont want to over power or under power LED's. Your plan of under powering it by a full volt will not make it very bright. You would be using it at 3/4 of its potential and as the battery drains it will dim to a blue light.

A propos, votre anglais est mieux que la plupart d'affiches d'âne muettes ici.

I hope I said that correctly...My French is not very good! Hope this helps.

 

[attchoum]

thx
my fist idea was to put 2 3v lithium pile to get 6v and then put the right resistance.

i just don't know how to calculate the mh i need if i what to have 2hour burn time

 

[ScubaToneDog]

Ok, I looked at the specs on your LED. You need to drive it with 3.42V at 1500 mA. You will need at least four 3V lithium batteries if you want to drive it for 2 hours.

 

[senjaya_chang]

thx
my fist idea was to put 2 3v lithium pile to get 6v and then put the right resistance.

i just don't know how to calculate the mh i need if i what to have 2hour burn time

First you will need to know your batteries Ampere Hours (Ah), see your batteries detail for this.

To count your flashlight burn time follow this instructions

A 1500mA LED works in 3.42V will need 1500mAh for 1 hour operations
T x A = At
T=>Time needed (hours)
I=>LED Current

so, if you need burntime for 2 hours, then you will need 2 x 1500 = 3000mAh batteries.

However i suggest you to use Alkaline batteries, they are more stable and long live.
For example D cells Energizer Alkaline have 26.000mAh, so 3 of them will produced 78.000mAh.
3 batteries in series give you :
(78.000mAh : 1.500mAh) - 10% = 46.8 Hours

Dont be surprise, i know some people will say this is imposible but that is a brand new technology you have in hand. dont bother with your 2 hours time, you'll get more than that. I experience this and get more and more like this LED.

Since you have the burn time in your control, I suggest you to use 5 or more LED, It will give you the Brightess Flashlight you can find. Only one problem there, the light made by LED cannot penetrated well in water, it will only get 30% above the human visibility range in water. Well still it's more than enough for me.

But remember, 3 of them in series will make 4.5V, so you will need 1 Ohm resistor to hold the down time.
R = (VS - VL) / I
R=> resistor
Vs=>Voltage supply
Vl=>LED Voltage
I=>LED current (in Ampere, 1 Ampere=1000mA)p.s. I suggest you to have more complicated downstep circuit since the resistor only will give you some problem when the batteries are almost out of power. Send me a msg if you need the circuit.

 

[do it easy]

hhmm, I think I have a similar LED light in my PT LED upgrade-

I bought 4/5 sub C NiHM cells to power it. I can put 4 of these cells in the space that 3 regular C batteries take up. This brings the voltage up to a nominal 4.8v. The batteries are rated at 2000 mAh. Just for comparison, I burn tested them against some 3500 mAh C NiMH cells I had.

I put both lights in a bucket of ice water in the garage to test them under realistic conditions. To my surprise, the full size C batteries performed better! The 4/5 sub C batteries were slightly dimmer at 2 hours and less than half as bright at 6 hours. The full size C batteries at 7 hours were compareable to the 4/5 sub C batteries at 2 hours. I stopped the test since I had to go to work and I didn't want to take the chance of over-discharging my batteries.

So, in my experience, C size NiMH batteries will work fine and provide more than 2 hours of light!

 

[do it easy]

I forgot to mention that the new batteries are indeed new, so they might not be up to their full capacity yet. I'm running then through a few cycles to see if it improves. I'll let ya'll know if it changes materially.

 

[Charlie99]

To do it right, you should use a dc-dc converter circuit to drive it with a constant current. You should also solder the LED onto a printed circuit board with nice fat copper traces for good heatsinking. The cooler you keep the internal junction, the more light output you will get.

A constant current DC-DC converter lets you make full use of the energy in whatever battery you choose, and your battery choice is no longer limited to a specific voltage.

 

[Charlie99]

However i suggest you to use Alkaline batteries, they are more stable and long live.
For example D cells Energizer Alkaline have 26.000mAh, so 3 of them will produced 78.000mAh.
3 batteries in series give you :
(78.000mAh : 1.500mAh) - 10% = 46.8 Hours

You can add the mAhr ONLY if you have them in PARALLEL. Since they are in series, the three 26Ahr D cells are a 4.5V, 26Ahr battery, not 78Ahr.

But remember, 3 of them in series will make 4.5V, so you will need 1 Ohm resistor to hold the down time.
p.s. I suggest you to have more complicated downstep circuit since the resistor only will give you some problem when the batteries are almost out of power.

The other alternative is to go to 4 cells in series. Although this wastes more power, the current will be more constant over the life of the batteries. Since NiMH batteries have a flatter discharge curve, using 4 NiMH batteries will also give a more constant current, and therefore more constant light output.

 

[Charlie99]

hhmm, I think I have a similar LED light in my PT LED upgrade-

I bought 4/5 sub C NiHM cells to power it. I can put 4 of these cells in the space that 3 regular C batteries take up. This brings the voltage up to a nominal 4.8v. The batteries are rated at 2000 mAh. Just for comparison, I burn tested them against some 3500 mAh C NiMH cells I had.

I put both lights in a bucket of ice water in the garage to test them under realistic conditions. To my surprise, the full size C batteries performed better! The 4/5 sub C batteries were slightly dimmer at 2 hours and less than half as bright at 6 hours. The full size C batteries at 7 hours were compareable to the 4/5 sub C batteries at 2 hours. I stopped the test since I had to go to work and I didn't want to take the chance of over-discharging my batteries.

So, in my experience, C size NiMH batteries will work fine and provide more than 2 hours of light!

This result is what would be expected IF the "PT LED upgrade" has a constant current circuit built in. If it is a dumb/linear constant current circuit (such as 2 resistors, 2 diodes, and 1 transistor), then the burntime ratio will be the same as the Ahr ratings of the batteries ---- 2.0 to 3.5, i.e. about 75% longer life for the full size C cells.

If the LED module has a DC-DC converter in it, then the runtimes will be approximately proportional to the energy in the battery. 4 x 2.0 x V = 8V for the sub C's, and 3 x 3.5 x V = 10.5V watt-hours for the full size C cells. (V is the avergae cell voltage -- the same in both cases, about 1.25V). So with a DC-DC converter in the replacement LED module, the full size C cells would run about 30% longer (10.5/8 = 1.3, i.e. 30% increase).