Maker Pro
Maker Pro

Voltage Divider to control Current in a Circuit

thoth_the_atlantean

Jul 6, 2016
1
Joined
Jul 6, 2016
Messages
1
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

Jun 6, 2012
260
Joined
Jun 6, 2012
Messages
260
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*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,510
Joined
Jan 21, 2010
Messages
25,510
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

Jun 6, 2012
260
Joined
Jun 6, 2012
Messages
260
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*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,510
Joined
Jan 21, 2010
Messages
25,510
I guess the question is whether 2.8V (or whatever you decide is the discharge limit) is sufficient to operate the device.
 

BobK

Jan 5, 2010
7,682
Joined
Jan 5, 2010
Messages
7,682
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

Hop - AC8NS
Jun 21, 2012
4,878
Joined
Jun 21, 2012
Messages
4,878
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

Jun 6, 2012
260
Joined
Jun 6, 2012
Messages
260
Ok good points there. Especially considering the op clearly needs some low voltage protection to avoid damaging those batteries.
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,510
Joined
Jan 21, 2010
Messages
25,510
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

Hop - AC8NS
Jun 21, 2012
4,878
Joined
Jun 21, 2012
Messages
4,878
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

Feb 9, 2011
19
Joined
Feb 9, 2011
Messages
19
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
 
Top