I am helping with a circuit that uses 8x AA batteries (10.2V max) to power a small BLDC motor circuit and an arduino microcontroller in parallel. Meaning the +/- wires are tee’d at the battery, and both “halves” of the circuit are powered from the same common source. The arduino controls the BLDC (pwm signal to ESC) and cannot reset or shut down during operation. The arduino circuit is powered through the Vin pin (7-12V tolerant) and draws between 18mA idle and 220mA max. The motor draw causes battery voltage to sag as low as 4.9V when the motor starts from stop under load and batteries are run down, and we’ve had intermittent issues with dropouts and over-voltages using cheap buck or LM2596 buck-boost regulators.
I am looking at #2869 S9V11MA to power the arduino circuit. It looks like it can handle the input voltage range (4.9-10.2V) and the datasheets suggest it can run reliably over the expected current range (18-220 mA) with the given input voltage and an output setting of 7.5V. Or might the #2118 S7V8A or #4967 S8V9F7 be a better choice?
Thank you in advance for any guidance you can provide. My guess is there are quite a few regulators that will work fine. I’d rather not over-spend when not needed, but dont want to buy twice either.
Any of the voltage regulators you mentioned should generally be able to handle the load of your Arduino circuit if the batteries can hold up, but a voltage dip that large suggests that your batteries cannot handle the load. So, while adding a regulator might help in some situations, it is not guaranteed to stop a brown-out, and I would recommend addressing the problem more directly. For example, if it is practical for your application, you might consider adding some acceleration limiting to reduce the current demand when starting up. Additionally, you could try adding some capacitance to the line to help smooth out the spike. Lastly, it might be worth considering a more appropriate power source (such as a LiPo with a high C-rating).
By the way, I’m not sure what type of AA batteries you are using, but the max charge should be around 1.5V per cell for brand new Alkaline batteries or freshly charged NiMH (which are 1.2V nominal), so an 8-cell pack should be around 12V max.
Appreciate the feedback. You are correct that asking more from the voltage regulator is just compensating for poor circuit design, and boosting output of a nearly max’ed out battery pack under high current draw remains a problematic approach. We will investigate a current limiter and better throttle control along with a new voltage regulator.
