"Nominal" vs. "Charge" voltage?

[ohaya]

Hi,

I see references to "nominal" voltages, and "charge" voltages, e.g., the tables in post #1:

http://www.candlepowerforums.com/vb...eview-of-Measurement-on-Soshine-SC-S7-Charger

From my initial newbie-ish messing around with my new (TR-003P4) charger and some 14500 and 18650 batteries, I know that they charge to 4.2V +/- .05V, so I get the "charge" voltage thing (i.e., the chargers should charge TO that voltage), but where does the "nominal" voltage come in, and what is the ramification/significance of the nominal voltage for lithium batteries (e.g., 3.7V for Li-ion, and 3.2V for LiFePO4)?

It doesn't seem that lights would be designed to work at a max of the "nominal" voltage, because if I charged a battery to 4.2V, and the lights only could accept a maximum of 3.7V, it seems like we'd be blowing LEDs all over the place?

Thanks, and apologies if this is a stupid question :(...

Jim

 

[TEEJ]

Yeah, the 4.2 v is what the cell charges TO, and the 3.7 v is what its at under load.

So when adding up cells to see if you're over an LED's specs, its the 3.7 v you use.


The load voltages are really a by product of the chemistry used.

That's why the CR123's are at 3.0 v, and the Nimh and Alka-Leaks are at 1.4v or 1.5 v, and so forth...and you'd use their load voltages in the same way you'd calculate the LED's supply for the rechargeable lithium ions.

Their chemistry dictates their voltages.

 

[SilverFox]

Hello Jim,

If you look at a discharge curve at a light load you will find that the nominal voltage is roughly the voltage half way through the discharge. This applies to secondary cells that can be charged back up. Primary cells list the nominal voltage as the voltage you measure right out of the pack.

That's why an alkaline cell is listed as 1.5 volts and a NiMh cell is listed as 1.2 volts.

Obviously that voltage will drop under higher discharge loads.

Tom

 

[ohaya]

Teej and Tom,

Thanks for the clarifications!

Jim