AA LiIon vs. RCR-V3

[bjn70]

I was interested in higher capacity AA's for my wife's digital cam and wondered also if these would be applicable for use in lights. I thought I read that LiIon have several times more capacity than NiMh but they are made to discharge slowly. Thus I'm wondering if they might be usable in a light using standard LED's.

Anybody know anything about 1.5V LiIon AA's or 3V RCR-V3's?

 

[Marc]

People have been using 14500 LiIon (same size as AA) in there lights, mainly in cutdown minimags with a sandwich (madmax/minipro3). Half a Duracell CRV3 will do the same since they're 2 3V in parallel.

I was wondering about the rechargeable CRV3, are they 2 3V in parallel or 2 1.5V in series like the Energizer? When they say that their capacity is something like 1100mah, is 1100 for each cell or for both (eg 550 each).

 

[djpark]

RCR-V3 (Rechargeable) I have has 2 14430 li-ion cells in parallel configuration. It has 3V 1100mAh marking on the casing.

Other RCR-V3 may have different design, but mine has separate charging and discharging channel to the negative contact of the battery. Battery+ and pack+ are common.

The charging channel seems no circuit, but direct connection to the battery. I can't really confirm it since the pcb is covered by 2 big chips which I presume FETs and can't see the thread. When measure between battery+ and the charge-, it gives the full battery voltage (mine shows 4.05V).

There is a p-channel FET at pack- discharge output and this is provably prevents the back flow of the current from the pack- connector to the battery in case it is connected to the charger (it shouldn't) or connected to the live circuit with reverse polarity.

The output from the pack+ and pack- is 3.75V without load and it drops to 3.2V when 5 ohm load is applied and 3.0V with 3 ohm load.

There is a sot-23/6 chip which I can't identify. Can it be a output voltage regulator to drop to 3V (I doubt) or the output control FET has rather high Rdson?

I guess a charge and discharge logging and charting is in order.

-- dj

 

[TrueBlue]

A 14500 Li-ion, AA size, cell has 3.7 volts with the highest capacity cell at 850mAh. A NiMH cell has 1.2 volts and anywhere from 1800 to 2500mAh. So a 14500 has 3.145 watts of power. A NiMH 1800mAh has 2.16 watts while a NiMH 2500mAh cell has 3 watts of power stored.

The mAh rating of the NiMH might have you thinking it has more power than the 14500- it doesn’t. The 14500 is AA sized but has more voltage, more power stored and can discharge at a higher rate than a NiMH cell. But your equipment has to be able to take the extra voltage.

 

[djpark]

To get better idea of RCR-V3 behavior, I measured the voltage of the cell with 5 ohm load. But instead of two 14430 li-ion cells, I used only one 14500 cell. This is done because I wanted to see how the protection circuit works rather than the run time.

I have been thinking that the 3 legged chip between the pack- terminal and battery- is p-channel FET, but it looks like a 0.7V zener diode. The voltage drop by the part is almost constantly 0.7V throughout the time.

So this is how the RCR-V3 can claim the output to be 3V with 3.7V li-ion cell.

The low voltage protection circuit cuts off the output when the battery voltage hits below 2.5V. At the time, the pack output voltage can be any value between 1.5V and 1.8V depending on the load.

As you can see in the chart, once the output is cut off, the battery voltage recovers back, but the output will not be restored. Just removing the load will not restore the output connection, it requires at least small amount of charging current coming in from the charge- pin before the output is restored.

Theres is provably no over-charge protection circuit built in. I may be wrong with this statement since I can't recognize the 6 pin sot-23 chip.

To conclude, RCR-V3 get full charge of li-ion and delivers output 0.7V less. So it may be quite safe to use on the equipment or light which is designed for 3.0V battery source and yet it can take full charge of the li-ion unlike other protected cell which has to be charged to 3.7V only.

-- dj