Battery Voltage Confusion!

[TelcoLou]

Um, don't know why I haven't noticed this until just now ... must be the drugs :wacko:

Anyway, why is it that my NiMH rechargeables are 1.2v and regular non-rechargeable alkalines are 1.5v?

If my remedial math is correct, there's a difference of .6 volts using rechargeables ... the performance is the same, or so it seems; I notice no difference in speed, screen brightness, etc. using these different types of batteries, so what gives?

 

[Robster]

You are right that the fully-charged voltages of the batteries are different. So well done

The battery voltage isn't used as it is, though. It is fed to a switching, step-up regulator that produces 3.3V. This is used to power the LCD, RAM, etc, and also feeds two more regulators, one that produces 5V (not quite sure what for) and one that produces 1.8V for the CPU core. The 3.3V step-up regulator can work with battery voltages down to around 1.5V.

Now, most batteries will produce something like their rated voltage when fully or partly charged, and then when the battery is flat, the voltage will drop quickly. Because of this, the step-up regulator works just fine until the batteries are nearly dead, then the voltage gets too low for the step-up regulator to work and things start going haywire

The exception to this is the *really* cheap and nasty non-rechargeable batteries, the kind you buy 50 for $10 or whatever. They have high internal resistance, and so the voltage falls as soon as you connect any sort of load. As we have seen on these boards, some of these batteries can't run a GP32 even when they're brand new. They are really only good for running low-drain devices like clocks or whatever.

 

[TelcoLou]

Wow. I understand. Thank you so much ...

(... now if only I could discover what makes women tick, I could rule the world ...)

 

[Steve-O]

My RC Car Cells are rated 1.2volt and I use 4 cell packs (Total of 4.8volt). When Fully Charged they Read a total of 5.8 - 6.0 Volts (Around 1.5Volt per a cell) and when the Car is flat the pack reads 4.7 - 4.9