Battery basics

[MikeC]

6P runs on [email protected] ea= 7.4v. Why/how can we run 16650 which is rated at 3.7v? What am I missing?

 

[aznsx]

6P runs on [email protected] ea= 7.4v. Why/how can we run 16650 which is rated at 3.7v? What am I missing?

I don't have a 6P (yet) and don't know, but it's gotta be lumens &/or run time I guess(?). I suppose some of the LED 'drop-in' modules people use (vs incandescent 6P) make up for some of that. I've wondered myself.

 

[hamhanded]

6P runs on [email protected] ea= 7.4v. Why/how can we run 16650 which is rated at 3.7v? What am I missing?

123s are nominally 3v but sag in voltage under load. A single 16650 can deliver more current and will have less voltage sag.

For example, at 2.4A, you can expect 2x123 to run at 2.2-2.5 volts per cell. That narrows the difference between them and a single 16650.

https://www.candlepowerforums.com/threads/123-battery-shoot-out.67078/

 

[chillinn]

6P runs on [email protected] ea= 7.4v. Why/how can we run 16650 which is rated at 3.7v? What am I missing?

Not really. What you're missing is voltage sag. CR123A only test ~3.24V new when not under load. They can't actually put out that much voltage under a P60 lamp's 1.13A, more like 2.7V—2.5V (or two of them, 5.4V—5V), and as their capacity is depleted, their combined voltage under load drops below 4V. A Li-ion is nominally 3.7V under load, but fully charged under 1A load will put out 4.2V for a short time, but as capacity is depleted voltage, again, drops.

Look at the discharge curve for 1A (in blue), voltage stays above 4V for 20 minutes:

source: HKJ Test/Review of Sanyo UR16650ZTA 2500mAh


Here is a CR123A (look at what 1A does. It barely holds 2.5V for 30 mins, remaining 60 mins is below 2.5V):

source: HKJ Test/Review Panasonic Lithium Industrial CR123A

 

[kerneldrop]

6P runs on [email protected] ea= 7.4v. Why/how can we run 16650 which is rated at 3.7v? What am I missing?

You're missing the driver.
Think of the battery as a garden hose and the driver as an adjustable nozzle.

A 3 volt driver will limit the volts hitting the LED to 3 volts max. It'll be less though.

An LED can light up with less than 3 volts.

That's why a 3.7 volt battery works with the right driver

 

[Olumin]

Why/how can we run 16650 which is rated at 3.7v?

You can, but it'll run much dimmer. To my eyes about half as bright, which sounds about right.
You can run incandescents at any voltage you want, just that you'll dim it at lower voltage & overdrive or potentially blow it at higher voltage. Running a incan at higher voltage increases brightness but decreases lifespan of the bulb. Lower voltage increases lifespan but decreases brightness, often significantly.

LEDs are more complicated because it depends on the specific driver.

 

[MikeC]

Not really. What you're missing is voltage sag. CR123A only test ~3.24V new when not under load. They can't actually put out that much voltage under a P60 lamp's 1.13A, more like 2.7V—2.5V (or two of them, 5.4V—5V), and as their capacity is depleted, their combined voltage under load drops below 4V. A Li-ion is nominally 3.7V under load, but fully charged under 1A load will put out 4.2V for a short time, but as capacity is depleted voltage, again, drops.

Look at the discharge curve for 1A (in blue), voltage stays above 4V for 20 minutes:

source: HKJ Test/Review of Sanyo UR16650ZTA 2500mAh


Here is a CR123A (look at what 1A does. It barely holds 2.5V for 30 mins, remaining 60 mins is below 2.5V):

source: HKJ Test/Review Panasonic Lithium Industrial CR123A

This is helpful, I did fail to take sag (voltage drop under load) into account. BUT, I don't see a curve showing 2xCR123 drop vs. the 16650. ITSM that 2xCR123 starts with a higher voltage and has more "room" to drop. OTOH a single rechargeable cell is more attractive than feeding CR123 batteries.