How many mA - 3 CR123 batteries

[Rattleakak]

When I see LED ratings of 120 lumens @ 700mA , I want to know if 3 CR123's will run it at that lumen output. Someone please expain, equations work well too. What is the output in mA (mAH?) of 3-CR123's in series so I know what ranges I can work within. Thanks so much for the help. Yep I am a noob:grin2:

 

[Ragiska]

Re: How many mA - 3 C123 batteries

do you mean mAh? same as a single cr123 cell.

 

[Rattleakak]

Re: How many mA - 3 C123 batteries

do you mean mAh? same as a single cr123 cell.

When I see LED ratings of 120 lumens @ 700mA , I want to know if 3 CR123's will run it at that lumen output. What is the output in mA (mAH?) of 3-CR123's in series so I know what ranges I can work within. Thanks so much for the help. Yep I am a noob:grin2:

 

[gcbryan]

Re: How many mA - 3 C123 batteries

When I see LED ratings of 120 lumens @ 700mA , I want to know if 3 CR123's will run it at that lumen output. What is the output in mA (mAH?) of 3-CR123's in series so I know what ranges I can work within. Thanks so much for the help. Yep I am a noob:grin2:

Let's say the led requires 3.6V and 700mA so 2.52Wh

3 Cr123's in series will be 3 * 3V which is 9V at 1Ah so 9 Wh

9wh/2.52wh means it will run it for 3.57 hours (this is approximate and not allowing for inefficiencies).

However, you would need a driver to "buck" the voltage down to 3.6 V or so.

If you used a rechargeable RCR123 the voltage on those is 3.6 V and you could potentially go direct drive with either one battery or three in parallel.

 

[Rattleakak]

Re: How many mA - 3 C123 batteries

Let's say the led requires 3.6V and 700mA so 2.52Wh

3 Cr123's in series will be 3 * 3V which is 9V at 1Ah so 9 Wh

9wh/2.52wh means it will run it for 3.57 hours (this is approximate and not allowing for inefficiencies).

However, you would need a driver to "buck" the voltage down to 3.6 V or so.

If you used a rechargeable RCR123 the voltage on those is 3.6 V and you could potentially go direct drive with either one battery or three in parallel.

Awesome, do you have the equations? How did you you come to 2.52Wh from 3.6V and 700mA. Thanks again. I am learning......Does there happen to be a calculator online? Thanks!!

 

[McAllan]

3.6 V * 0.7 A = 2.52 W

Over one hour that accumulates to 2.52 Wh.

But I agree people should get their units right ;)
Else it's like saying. That's a very fast car - it drove 120 miles! It doesn't make sense.

 

[old4570]

When they quote 700mA ,

It mean's that the driver is rated to such ... SO the driver is feeding the LED 700mA . As for batteries , they are usually listed with the light , as in ,
2 x CR123A / 1 x 18650 etc .

Voltage range is usually also quoted ..

3.6-7 volt Batteries fully charged usually go 4.2volt [ Yeah confusing ]
3v Rechargeables are 3.6v fully charged
and 3v Primaries are 3volt

Takes some getting used to ...

3 CR123A is series = ?? Primary 9volt , rechargeable 12.6v
Voltage goes up not mA , but current drain will go down due to more voltage .

 

[gcbryan]

Volts * Amps = Watts

When you are talking about batteries you are talking about Watt Hours

Remember that 700millamps is simply .7amps

To figure out most of these problems this is mainly what you need to know

Most Cree brand led's are in the 3.2 Volt to 3.6 volt range and many are either at .7amp or 1 amp

You just need to learn the specs of the common batteries
Alkaline are all 1.5 Volt and AAA are 1A hour, AA are 2 AH,
CR123 are 3 Volt and 1 Ah
18650 are 4.2 V and come in different Ah sizes with 2.5 Ah being common

The idea is to try to match the batteries as closely as possible to the led

Regarding run time, you simply figure out how many Wh a led is (for one hour) and then do the same for the batteries and divide one by the other

When the battery specs and the led don't match exactly then you need either resistors or drivers to make them match. "Buck" drivers buck the voltage down to match the led and "boost" drivers boost the voltage up to match the led.

There's also constant current drivers that allow a led to burn at a constant brightness until the end of the battery life as opposed to gradually getting dimmer over a long period of time.

I hope this at least gets you started in the right direction.