# How to Power 2 devices at different voltages with the same set of power source(batteries)

I'm just curious if it's possible to power 2 devices at different voltages with a set of batteries while making sure that the 2 devices makes use of all the batteries. I have here an illustration of the connection that I would like to get verified.

Each battery is rated n volts

I used dashed lines in 2n volts connection for ease of seeing. I want to power each device with 4n volts and 2n volts

An Alternative Illustration^

The solution that I propose is to connect 4 batteries in series first to power 1 device. Then since there can be 2 sets of batteries in series already I can connect these sets in parallel for the Voltage to not add up. However, just by looking at the circuit I think some portions are actually shorted.

Any help would be appreciated. Please don't be harsh if this is a dumb question.

• Can you draw batteries in a straight chain, it's so difficult to imagine what you have drawn. Jun 1, 2018 at 3:42
• Yes, you can do that but batteries that power two devices will die faster. Jun 1, 2018 at 3:44
• – user152966
Jun 1, 2018 at 3:54
• I have done it. My bad
– user152966
Jun 1, 2018 at 4:06
• :( It still looks awful. Jun 1, 2018 at 12:59

No. Your attempt to power a 4n load, and and 2n load from balanced batteries, shorts out each 2n battery.

You have two (or three) options.

a) Power the 4n load, and a 4n->2n converter to power the 2n load. This could be a linear regulator if the power level is low enough for you to not worry about the inefficiency and heat. Better though would be a buck regulator.

b) Configure the batteries as 2n, and power the 2n load, and a 2n->4n boost converter. Choose (a) or (b) depending on which load draws more power, or the convenience of having a buck or boost converter to hand.

c) Power the 2n load from a battery tap, and tolerate the consequences of the imbalance (replacing batteries earlier, or charging differently)

d) Power the 2n load from a switchable battery tap, so you spend 50% of the time powered from the 'top' batteries, and 50% of the time from the 'bottom' ones. Obviously you cannot common the grounds if using it like this.

e) Use a 2n set and a 4n set of batteries. You need more batteries, but get complete freedom.

Ok, so 5 options.

Wouldn't adding a pair of diodes solve the issue? If the current isn't something massive I think it would be fine no?

• no <+ extra letters to make up the comment length> Jun 1, 2018 at 12:50
• @Neil_UK how so?
– user152966
Jun 2, 2018 at 7:56
• Hello Red, and welcome. If you don't describe the issue, we cannot answer to your question. Jun 11, 2018 at 7:07