I am working on a portable project. I need to pull 3,500mA average with 10,500mA peak at 3.6v-4.5v. I see that "D" Alkaline Batteries are rated for 1.2-1.5v and 12,000mAh. So I am looking at using a 3 "D" Alkaline Battery Pack to achieve the 3.6v-4.5v supply.
Question:
12,000mAh / 3,500mA = 3.43 hours is a reasonable amount for this project.
But, I have not been able to find anything on the maximum safe discharge rate of Alkaline Batteries. Is it possible and safe to pull 3,500mA average (and possibly 10,500mA at peak) from Alkaline Batteries?
If not, can I solve the problem by putting multiple battery packs in parallel?
Best Answer
Somewhat related (though answer pertains to AA batteries, not D): Short Circuit Alkaline Batteries
It looks like 3.5A might be safe for continuous draw and 10A is just about do-able during peaks, though I might be a bit worried that the internal resistance of the battery will prevent you from reaching the peak currents required, especially when the batteries are nearly dead. It will also vary from manufacturer to manufacturer, and possibly even battery to battery.
You can employ a similar solution to those used by camera flashes and other systems which have large surge currents: use capacitors. The lab down the hall from where I work uses them to discharge many MA (yes, mega amps) for extremely short time periods to provide high power bursts. Your low current supply can be used to slowly charge the capacitors up to the correct voltage, then when demand requires capacitors can be discharged extremely quickly because they have very low internal impedance. You'll need to size the capacitance as needed for however large the spikes will be. Keep in mind that some electrolytic capacitors have quite high ESR (an equivalent concept to internal resistance), and may have lower current ratings than what you'll require. Checking the specs/datasheets is always a good idea. Putting a current limiter between the battery and capacitors also wouldn't be a bad idea since shorting the battery to the capacitor is close to just as bad as shorting the battery itself (especially for larger capacitances).