Voltage Divider to control Current in a Circuit

[thoth_the_atlantean]

I need 3.3V to power a micro controller which drives a strip of WS2812. I have been using one 14400 3.7V 1200mAh battery to power the circuit, but after a short while the voltage drops to the brown-out level for the arduino and the program stops running. I'm considering running two of the 14400 batteries in series, and then utilizing a voltage divider to bring it back down to ~3.7V to increase the running time. Is this feasible? Am I wrong to think this way? Does anyone have any experience or comments they could make to help me on my way?

Thank you,
Thoth

 

[Mongrel Shark]

I'm considering running two of the 14400 batteries in series, and then utilizing a voltage divider to bring it back down to ~3.7V to increase the running time. Is this feasible?

Not especially feasible. You wont be increasing the amp hours by putting the cells in series and the voltage divider would have to sink a heap of current to ground to have enough at the middle to run the micro. Plus the resistors are dissipating heat. You'd be taking the same storage space and adding a lot of extra load. So it will go flat faster.

Placing a second battery in parallel will double you amp hours and run time. With no extra parts needed.

 

[(*steve*)]

a voltage divider won't work.

you could use two batteries in series followed by a regulator. for efficiency a switch mode power supply would be best.

you could also use a single battery followed by a boost switchmode regulator.

whatever way you go, you need to be very careful you don't over-discharge the batter(y/ies)

 

[Mongrel Shark]

I thought about suggesting a step down. But why would you use one? The op already mentioned having extra battery's. While you could get a very efficient step down unit, its not going to be as efficient as simply adding the extra cell in parallel. less parts for a better result is usually better IMO.

 

[(*steve*)]

I guess the question is whether 2.8V (or whatever you decide is the discharge limit) is sufficient to operate the device.

 

[BobK]

Putting 2 cells in series and using a buck converter allows you to get a constant output voltage until the batteries reach their fully discharged state, which means they will last longer than twice what you would get out of 1 battery with no step-down.

Bob

 

[hevans1944]

Wiring batteries (or cells) in parallel is risky business. The one with the greater charge will discharge into the other one. Sort of like getting a battery-jump to start your car. Works for a short while. Best to do as @BobK suggested: two cells in series with an efficient buck converter to get back down to 3.7 (or whatever) voltage.

 

[Mongrel Shark]

Ok good points there. Especially considering the op clearly needs some low voltage protection to avoid damaging those batteries.

 

[(*steve*)]

Wiring batteries (or cells) in parallel is risky business

Cells in series have different but equally serious problems.

if the cells differ in capacity, one will (if you only look at the pack voltage) get damaged by virtue of being over charged and over discharged. This will lead to the failure of the pack, possibly in a pyrotechnic fashion.

 

[hevans1944]

Cells in series have different but equally serious problems.

if the cells differ in capacity, one will (if you only look at the pack voltage) get damaged by virtue of being over charged and over discharged. This will lead to the failure of the pack, possibly in a pyrotechnic fashion.

Yep. That's especially important multiple, super-duper, high-current, re-chargeable Li-ion batteries like the IMR 18650. You need a battery management circuit to keep everything balanced, especially while charging.

 

[Petkan]

I need 3.3V to power a micro controller which drives a strip of WS2812. I have been using one 14400 3.7V 1200mAh battery to power the circuit, but after a short while the voltage drops to the brown-out level for the arduino and the program stops running. I'm considering running two of the 14400 batteries in series, and then utilizing a voltage divider to bring it back down to ~3.7V to increase the running time. Is this feasible? Am I wrong to think this way? Does anyone have any experience or comments they could make to help me on my way?

Thank you,
Thoth

Thoth,

Li Ion batteries are supposed to be discharged from 4.2V (fully charged) to 3.3V (not below)
Your 3.3V regulator may have too narrow input voltage headroom (say from 4V).
Apart of the well known step down (buck) and step up (boost) switching mode regulators - there is another category Buck-Boost. These regulators can make say 3.3V from a voltage ranging from well above the required output (say 12V) to way below it (say 2V). . Here is an example:
http://www.ebay.ca/itm/2in1-Buck-Bo...902863?hash=item3f6de8a54f:g:mzYAAOSwXeJYEEj8