what is the point of using rcr123 instead of 17670

Hi

what is the point of using rcr123 with 9v dropn in instead of 17670 with 2.8-4.2 drop in

2 rcr123 = 8 volts .. 750 mAmps

while 17670 = 1500 mAmps

so the 17670 will drive the flashlight for longer time .... is that write ?

edit: durr... I read the wrong voltage for some odd reason :thinking:

It depends on the driver used and efficiency thereof. If the drivers were 100% efficient then the following scenario would be applicable:

Vin x Iin = Vout x Iout = Pin = Pout

Therefore, if Vout = 3.5V and Iout = 1000mA (1 Amp)
then for:
17670 @ 4.2 V, Vin=4.2V & Iin=833mA
2 x RCR123 @ 8V, Vin=8V & Iin=437.5mA

In actual scenario the following formula is more applicable:
Vin x Iin x (efficiency % @ Vin for driver) = Vout x Iout

Hope this helps to clarify.

CampingLED said:

It depends on the driver used and efficiency thereof.

Click to expand...

Yup. While Ohm's Law is unshakeable, it's the way a driver is made and what's it best optimized for that makes the difference.

So another answer might be that it's not a simple battery comparison issue, but an issue of what batteries the light you want to use them in likes best.

Zenster said:

Yup. While Ohm's Law is unshakeable, it's the way a driver is made and what's it best optimized for that makes the difference.

So another answer might be that it's not a simple battery comparison issue, but an issue of what batteries the light you want to use them in likes best.

Click to expand...

But with 18650, the capacity gains usually outdo driver inefficiency and result in longer runtime than 2RCR123.

there are very few well regulated dropins for a single Li-Ion cell. That's probably the biggest thing.

Some Surefire E bodies won't fit protected 17670's...so I have to use two RCR123's instead.

Marduke said:

there are very few well regulated dropins for a single Li-Ion cell. That's probably the biggest thing.

Click to expand...

I have noticed this too.

Is it because the Vf of the emitter is higher than the nominal voltage of the cell? I have seen some reports of Cree emitters measuring over 4.6Vf. Is it asking the impossible of an electric circuit to regulate up to that voltage level, from a single 3.6V cell?

Furthermore... Is it true that part of the price for a higher end light goes into the manufacturer selecting emitters at the lower spec range for Vf?

If you had rcr123's you could also share them with your single cell lights, which the 17670 wouldn't let you do.

Dropins for a single Li-Ion cell ideally need to be both buck AND boost, making them complicated, expensive, and less efficient (in general). It's much cheaper and easier to make a buck-only dropin for voltages higher than about 3.9v

kramer5150 said:

I have noticed this too.

Is it because the Vf of the emitter is higher than the nominal voltage of the cell? I have seen some reports of Cree emitters measuring over 4.6Vf. Is it asking the impossible of an electric circuit to regulate up to that voltage level, from a single 3.6V cell?

Furthermore... Is it true that part of the price for a higher end light goes into the manufacturer selecting emitters at the lower spec range for Vf?

Click to expand...

The Vf is always around 3.6 volt, but so is the battery voltage. To do a good regulations your need some electronic that can do both buck and boost regulation and that is not very common.

The cheapest solution is only to use pwm regulation, then the max. light output will fall, when the battery is discharged.
A better solution is to do only boost and use pwm to regulate brightness, this means that the light will be a bit brighter on a fully charged battery, but maintain a good brightness, until the battery is empty (NiteCore D10/EX10 does something along these lines).
And the best solution is to have both buck and boost, then your can use a wide range of input voltages and maintain a steady light output.

This is what I love about CPF. A person asks a question for which he may expect a simple answer and we all take him to all the possibilities and variances, backed by theory and experience. :twothumbs

CampingLED said:

This is what I love about CPF. A person asks a question for which he may expect a simple answer and we all take him to all the possibilities and variances, backed by theory and experience. :twothumbs

Click to expand...

I must have missed something because I figured more along the lines that if we couldn't dazzle him with our brilliance, we could always baffle him with our BS.

The OP is fairly quite. perhaps we achieved both.

Where a 17670 can excel with a boost driver is running a Lux III emitter. Witness, the KL4 and KL5, and the U2. My KL4 and KL5 run just fine on one 17670 and in regulation.

Bill

waiit, so there is a differnence in flashlight performance other then runtime if you are using 14500/17500/RCR123A and so on an so forth?

Crenshaw

Crenshaw said:

waiit, so there is a differnence in flashlight performance other then runtime if you are using 14500/17500/RCR123A and so on an so forth?

Click to expand...

That will always depend on the led driver in the flashlight, for a well designed driver there will be no difference.

many information in here

Thank you ALL ... That was so nice and helpfull

i see most of you prefer the rcr123 for some reasons