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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63 Discussions

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?

1 reply

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.


1 year ago

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!

6 replies

Agreed! I am wanting to do the same thing with my sons jeep hurricane. I have one other question though. Would it be possible to do this setup and be able to charge the batteries in parallel with a 12v battery tender hooked up? Kubert007, how do you charge your power wheels battery? Thanks in advance

Hi Anthony,
That's exactly what I do. I switch it to parallel and hook my shumacher charger up. Keep in mind that it will take twice as long but when charging in parallel. However the shumacher is way better than the PW charger and will shut off when full.

Cool, do you hook up the charger with the clamps onto the terminals or do you have it hardwired? I would like to have it hardwired if possible

Kubert! First, thanks for makin me smile, I am forever amazed that people still look at this 'Ible.

Second, I have looked your switch up on Amazon and based on the results I have seen there, the seventh pin should not matter, if you are not trying to get the lights in the switch to work. I do not THINK that you will be able to get them to work, and to be honest, I haven't studied the diagrams, they might actually burn out ... If your pin 2 of that switch (using it's own pin numbering) is connected to the POSITIVE side of one of the two batteries, you can ground pin 7 for the lights to work.

Third, if you wired exactly as in my 'Ible with the switch I have found in results on amazon (which happens to show the pin numbers in the same order as I used in my instructions :P ) I do not see why it would not work.

So let's see if we can fix this. You say in the 1-4 position, you get 12 volts but in the 3-6 position you get nothing? Did you remember to connect pins 3 and 6 directly to each other? Would it be possible to take a photo of your work for me? I'll do my best to figure it out for you!

Hi DC,

Thank you for your quick response! After getting your reassurance (from the master!) I went back and double checked everything because I knew it should work. I checked all the continuity on my wires and sure enough I had one bad connection. I fixed that and BAM! It worked!

Thank you so much for your instructable and your vote of confidence. And my son thanks you too!

I'm rally glad you found the faulty connection. Please, feel free to put up some pics of your project, I'd love to see!

Hey! I noticed this 'ible and got extremely excited about the possibilities it could open. Thanks so much for posting it!

I am working on a second Electric Longboard build; a 12S (44.4) volt system that powers two 63mm motors for a hopeful top speed of 45mph.

It runs off 4X 6S 10Ah. Wired in series then parallel to create one big 12S 20Ah battery.

There would be a switch to turn off one of the motors (cuts out about half the amp usage) for around double board range, be that with a bit less power/top speed as its only functioning off one motor.

Originally, I had decided that in order to switch series/parallel (either top speed with about 10 mile range, or around 20mph with 18-20 mile range) would have to be hand done: Stop, get off board, open battery housing, unplug the series or parallel adapter wire, plug in the parallel or series adapter wire, close the housing back up, get back on board, continue on my way.


Then I saw this, and it instantly occurred to me I would not even have to open the housing if I mounted a parallel/series switch on the side. I would just switch it and instantly double my range, albeit with a round half top speed.

This could also double as a 'beginner/extreme' mode switch, as I could (secretly) switch it to parallel before I gave it to someone not-as-experienced (I wouldn't want my younger brother to hop on a 12S system and instantly hit 45mph, and would rather him stay with a 6S system. speed safety and such ;)

Not only that, but I would USE the board in series, flip the switch to parallel, then CHARGE the board in parallel.


Sorry for the rambling, but thanks again for the idea. I am WAY excited! :D


Thank you, I will be doing this with a relay to switch an AC transformer output to switch between 120v and 240v out. The output coils must be parallel for current capability, other wise things would have been simpler.


2 years ago

Looking for a solution like this for... a 12v solar panel charging THREE x12v leadacids in parallel, then a switch to get the series 36v required for ebike.

Or would a DC-DC converter be easier? (12 up to the 36) - that would require some kind of balancing - would 12 to 13V zeners across each battery provide a bypass?

OR I guess i could connect in permanent series then charge each battery as needed.