SIMPLE Parallel/Series Select Switch





Introduction: SIMPLE Parallel/Series Select Switch

In this Instructable, I will explain how to use a simple double-pole, double-throw (DPDT) switch to select series or parallel wiring for two loads on one power source.
Wiring two loads in series will provide the full current available to both loads but only half of the available voltage, whereas, wiring the two loads in parallel will provide each load with the full available voltage, but only half of the available current.
Using this switch can effectively allow you to choose two power settings for your two sources. In the case of light bulbs, this can give you a bright or dim setting, without needing two different wattage bulbs.
In the case of electric motors, this can give you and high/low power settings.

This uses the simplest Double Pole Double Throw switch. This requires nothing more than the switch and some creative wiring. Please note that the "off" position only works if you have a "center off" switch! A DPDT relay can easily be substituted if you have one. If you want a 'struct' on this, leave me comments.

Please note that this instructable is intended to go with another of my instructables. Some of this instructable has been copied from my other instructable, since it will use the same type of switch.

You can find my other instructable here:

Step 1: Selecting Your Switch

You need to decide if you want to purchase a switch or salvage one from something else. if you purchase one, you have more options as there are many out there. if you salvage one you are limited to what you can find.

Make sure the switch you use can handle the amount of current you need
Decide if you want an off position or not.
Decide if you want a sliding switch, a toggle switch, rocker switch, or even a spring loaded switch that returns to off when released.
If there is a junk car around, check it for power window switches or electric seat adjusters. Both are most often DPDT switches. Don't forget to steal the motors or sometimes linear actuators out of the seat adjusters, if you can!!!!
Broken stereos commonly have one or two switches in them

If you salvage a switch, the first thing I would do is test ACROSS the switch to be sure it is double pole. The switch has two rows of contacts with three pins per row. NO pin in one row should have continuity to ANY pin in the OTHER row. In the "center off" position, if equiped, NO TWO PINS should conduct.

In the case of a sliding switch: You should find that the center pin in each row conducts to the pin at the same end that the slider is on, but will not conduct to any other pin in the same row or to any pin in the other row.

In the case of a toggle switch: You should find that the center pin of each row conducts to the pin at the end OPPOSITE to the toggle lever, but will not conduct to any other pin in the same row or to any pin in the other row.

In the case of a rocker switch: You should find that the center pin in each row conducts to the pin at the same end of the switch as the RAISED side of the rocker, but will not conduct to any other pin in the same row or to any pin in the other row.

Step 2: Wiring the Switch

Wiring for this switch is deadly simple.

To make my instructions a little more easy to follow, hold your switch in such a way that you are looking at the pins and they are arranged 2 pins wide and three pins tall. Imagine that the pins are numbered as below:

1 4
2 5
3 6

Begin by connecting pins 3 and 6 directly. The shortest piece of wire you can use will be best. You will need no other access to these two pins.

You will need to connect two wires to each of pins 1 and 4. These pins will be your two power supply wires, as well as one wire from EACH of your motors. As this switch WILL NOT change polarities, make sure that your positive wire from one motor (we will call this one Motor "A") is connected to the positive power source wire, and pin 1. Connect the negative from your other motor (Motor "B") as well as the negative from your power source is connected to pin 4.

This is the tricky part. You now should have only 2 free wires, one from each motor. These wires will get crossed in this step. This is intentional. Connect the wire from Motor "A" to pin 5, (not 2, like you would expect). Connect the wire from Motor "B" to pin 2 (not 5).

In my other instructable, I note here that there are many different combinations for the connections to that switch, however, there are some things that you MUST be careful about in this switch. You CANNOT connect your power source to pins 2 and 5 in this switch. The motors will be wired in series in one position, however the switch will cause a short in the other position.

Step 3: Enjoy, and Leave Me Comments

I hope you have enjoyed, and gotten something useful out of reading my first Instructable. Please leave comments if there was anything that was unclear or anything I should change as I will not know unless you tell me. Flames or non-constructive criticism WILL BE DELETED (if I have that option.. ignored otherwise).

Thanks for reading,



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I have a 3hp motor that I want to start running on existing house power to run a 10kw generator then once the generator is running I want to switch to the power from the generator to to run the motor.

I want a maintained on/off/on 30 amp 230V switch??


I've got on motor and 2x 18v batteries and 1 motor, in one setting I would like it to string the two together and make 36v and in the other I would like them to string together and make 18v. Is this possible?

Sorry 1 motor (writing this on a phone)

great instructable

love thw first page on identifying switches.

Is there any way to do this with transistors rather than a mechanical switch?

I like it!
I'm going to use this for my heated seat pads. Low/Off/High. Thanks!

would it be possible to do the exact opposite with 2 sources and 1 motor? Just swap each of the motors with a Battery and vise versa? I have 2 6s batteries to power a motor, and want to be able to run the two in series or Parallel.


like one of the cooment bellow, i too need to use 3 batteries but 4P2T seems too scary for me but i hope someone can help me out with an alternative for my requirement. using DPDT (on-on-on) switch, how do i wire up to achieve the following positions (P) for batteries connected in parallel: P1 > 1 battery, P2 > 2 batteries, P3 > 3 batteries. so far i only have the image below to refer to and i hope someone here can show me how. thank you~


I have a project where I will have (80) 3,2VDC 90 AH Life-YPO4 cells that I would like to set up to be in one of two configurations.

The first configuration would be 2 parallel strings of 40 cells each for 128 Volts and 180 Ah (23 kWh) of capacity.

The second configuration would be 5 parallel strings of 16 cells each for 51 Volts and (5x90=450) Ah (23 kWH) of capacity.

Maximum load will be 16 kW at 120 VDC (130 Amps) for config. #1

Maximum load will be 12 kW at 48VDC (250 Amps) for config. #2

I would love any thoughts you have on this scenario.

No I just hook the charger up when it's time to charge.

Hey Mike,

Not sure if you're still commenting on this really AWESOME instructable, but I am having a problem. I saw your instructable and I was really excited to trick out my son's jeep hurricane power wheel. I added two 12v12Ah batteries and wanted the option of running the batteries in parallel and series so they could run it for awhile or tear it up at 24v. I bought a bandc marine dpdt switch and wired everything as you described (swapping batteries for motors in your diagram) and the 12v works but can't get the 24v to work. The question I have is I regards to your diagram, everything works in the 1-4 or "up" position, but in the 3-6 or "down" position the switch doesn't work. The switch has a 7th pin, so maybe that has something to do with it. Please help!