Introduction: SIMPLE Parallel/Series Select Switch

Picture of 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

Picture of 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

Picture of 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,


Delltechnet (author)2017-04-20

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?

Delltechnet (author)Delltechnet2017-04-20

Sorry 1 motor (writing this on a phone)

scott.cairo (author)2017-03-29

great instructable

love thw first page on identifying switches.

JonathanCasey (author)2017-02-18

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

instructableskin (author)2017-02-17

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

esrapp21 (author)2016-11-07

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.

fkyc (author)2016-08-23

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~

TracyM106 (author)2016-06-26

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.

Kubert007 (author)2016-05-27

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

Kubert007 (author)2016-04-24

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!

AnthonyC152 (author)Kubert0072016-05-27

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

Kubert007 (author)AnthonyC1522016-05-27

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.

AnthonyC152 (author)Kubert0072016-05-27

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

DieCastoms (author)Kubert0072016-04-24

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!

Kubert007 (author)DieCastoms2016-04-25

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!

DieCastoms (author)Kubert0072016-04-25

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!

CoolRextreme (author)2016-05-04

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


miked2001 (author)2016-03-17

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.

IanW42 (author)2016-01-22

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.

fiveseven808 (author)2015-11-03

I knew this was possible but couldn't figure out how to do it in my head! Thank you so much!

TomB28 (author)2015-06-13

Awesome instructable. Can this work using 2, 12V power supplies instead of batteries? I'd like to use a DPDT relay instead of a switch, so I can use a PLC to control it. Can you send me/post the 'struct' on this?

APM5yhZGW3h0 (author)2013-05-21

This is great, makes sense to me now. Will let you know how it goes.

Since I am being greedy; and receive such quick/excellent feedback, I will continue with questions.

I would also like to wire the (3) 6v12ah batteries in such a manner that would allow me to switch between parallel for charging and serial for running. I have started to scribble out a simple schematic; however I would also appreciate your input. I would appreciate your thoughts.

DieCastoms (author)APM5yhZGW3h02013-05-21

You MIGHT be in luck! I have thought about this in the past but never sat down to try to 'do the math'.. but this afternoon, I sat down with a pencil and paper and I THINK I figured it out, with a double-throw FOUR pole switch... You could theoretically do it with two pole switches that have a center-off, but you would have to do it EXACTLY RIGHT EVERY TIME or you would be connecting two of the batteries to each other directly, positive to positive and negative to negative . . . SOMETHING would burn, quickly. . .

It will take me a while to do a diagram for this, and by the time I have a diagram finished, I might as well make another Ible out of it!

I will post a link here when that's done.


DieCastoms (author)DieCastoms2013-05-21

Ok, so I did some poking and diagramming . . . . and I figured out . . . . that the only limit to how many cells I can switch is the number of poles I can find in a double-throw switch!!!! 2 poles for two batteries, and add two for each additional battery, 4 for three, 6 for four, 8 for five, and so on. I currently have a diagram for 8 batteries with a 14-pole switch... and I've traced it a dozen times, I see no shorts and no faults, so long as EVERY pole is switched at the same time ... otherwise, Chernobyl.

elhnad (author)DieCastoms2015-03-19

I'm really surprised this hasn't been figured out yet in a safe way by other ppl on the webz. (maybe it has but i'm not sure how to search for it) sounds like it'd be very useful to have more than 2 packs go from parallel to S. Like these other guys i'm interested in this for an ebike.

JohnnyS3 (author)2015-03-05

This thread is spot on! :-) -I needed a series/parallel setup for an e-cigarette setup that vapes in series but charges in parallel. It works perfectly, thanks to the help from this thread. Many thanks!!!

graphixv (author)2015-02-26

I have two 12 volt solar panels that I want to be able to switch from 12 volt parallel operation to 24 volt series operation (to select whether the panels will charge a 12 volt battery pack or power an inverter at 24 volts). If I put in a disconnect switch first, followed by a DPDT switch, do I then need to put in an output selector switch? Or is the output going to be determined by the DPDT switch? Otherwise, I think this will wok.

aauliye (author)2014-12-09

OK this switch will go from parallel to series and vice versa?

richkenn (author)2014-08-27

I need to know how to wire a ozone generator.

Maybe you can help. I don't have a background in electrical design or even profess a working knowledge. I'm building an ozone generator for my own use and have all the components, I just need to determine the correct way to wire it.

This is an ozone generator that is cooled by a fan. The ozone must be switched off first and than, after a few minutes of cooling the ozone components, the fan can be switched off. The question is; how do I correctly wire this so that the fan can run anytime but the ozone can only run when the fan is running and than be shut off first? The unit runs on 110 and I am using toggle switches with indicator lights.

pimpyourstuff (author)2014-08-26

I want to charge four 12V 12aH sealed lead acid batteries in parallel. Then, while running/discharging, the batteries should be in series to get 48V to power a hub motor. How do I do that?

DieCastoms (author)pimpyourstuff2014-08-26

the wiring will be MUCH more complicated, and you will need a probably-very-expensive switch who's contacts will have to be very synchronized or you're going to have a very short-lived switch.

I do have the diagram worked out, I did figure it out, but have not yet physically tested it, since I do not have a switch, and thus have not published the information, since I cannot be 100% positive about it.

RehabIsForQuitters made it! (author)2014-08-21

Finally got around to putting this thing together. Thank you for all your help with this. Next version will output 12v, 24v and 36v with no switch(es) to mitigate the risk of mechanical failure. Here is the link to it:

charlessenf-gm (author)2014-02-14

Curious to know if this will work if one substitutes batteries for the motors? Could one, then, switch from two batteries in serial to two in parallel to power a single motor.

It will absolutely work for that! In fact, it will work for switching two batteries into parallel for charging at 12 volts, and into series for use at 24 volts!! Will, of course, take twice as long to charge as getting a 24 volt charger, but a switch is much cheaper than a charger ;)


This is exactly what I need to get my battery pack for my bike to give me 12v for an inverter on long bike trips that require camping. Thank you! I do wish your graphical diagram was clearer but it will do. Thanks again. :)

Do keep in mind that while using it as 12 volt for your inverter, you cannot also use it at 24 volt (or 6?) for your bike.

If you are running two 12-volt batteries to make one 24-volt pack, I would suggest running your inverter off of one of the two batteries at a time but alternate between the two batteries so they are both used equally. This way you can still have 24 volt for the bike AND 12 volt for the inverter. The 'danger' here would be drawing enough off ONE of the two batteries to unbalance the voltages between the two.. which is why I suggest having a way to swap between them.

If you are using two 6 volt batteries in parallel for the bike, and swapping to series to get 12 volts for the inverter, BE CAREFUL not to supply the bike with the full 12 volts, EVER, as it has the potential of burning out a lot of stuff . . .

All that being said, if it is working out for you, and you're not hurting your stuff, then GREAT! I am glad my Ible is still being useful after so many years :)

Mike, "DieCastoms."

I've come back because I need to ask you a question. I have come across the need to do this with 3 batteries. It turns out that my ebike motor performs outstanding with 36v so I have 3 12v batteries. Can this be worked to get 3 batteries to go from series to parallel? Any info is better than what I currently have and thanks in advance. :)

The short answer is yes, it can be done, I've done it.

The long answer is .... you MUST have the right switch or you are going to burn things up. You MUST have a "break before make" switch that completely breaks all to connections from one setting BEFORE making any of the connections for the other setting, and ALL the 'poles' (individual sets of contacts within the body of the switch) must stay synchronized. It really is not safe to do with individual switches, in my opinion.

that being said, as soon as I find my drawings, I will post them. If you look through the comments on this Ible, I spoke to

APM5yhZGW3h0 about it. I just am not sure if I can still find the solution.

Mike, from DC.

So the 4P2T switch came in today. it's a bit more complex than I thought it would be and needs a bit of research. here is a pic of what I'm up against. Know of and g9od places to get a schematic? lol.

I ended up finding a 4PDT switch. Is this one that could work in this application? I've been considering just wiring it up as 36V all the time and then use a regulator like this:

... if I need to use the batteries for other applications. I do like the 12/24V DPDT setup that you detailed and I still need to do that post, I have the pix. Having it setup with regulated power the whole time is not a bad idea as regulated power is preferable. I'm not sure which direction is best at this point. Are you familiar with 4PDT switches? It is scheduled to arrive in the mail early next week.

My e-bike adapter kit runs at 24V and it uses 2 x 12v 10Ah Li-Po batteries. I love how little they are for having so much capacity!! :D If the controller is fed 12v (Parallel mode) then it won't operate since it isn't enough. If it's 24v then it works fine. Since posting that comment I've changed the concept and the battery is becoming separate from the bike and is going to be used for many applications. I'm going to post the instructable for it very soon. I'm doing up the wiring tonight and will probably post this weekend and you can see the excellent impact that this instructable had years later. It's actually really cool, can't wait to share. Thanks for all the help. :)

APM5yhZGW3h0 (author)2013-05-20

DieCastoms, your instructable was very helpful/interesting. However, I would appreciate your thoughts and others regarding the following desired design.

I currently have (3) 6v12ah batteries wired in parallel on a Barbie power wheels jeep. I previously was using a 12v18ah battery. I would like the ability to run “both” power supplies via a switch. I.e. I would like the switch to operate similar to how you described; however, with the difference that there are two power sources. For example the switch in the up position would be 18v via the (3) 6v12ah batteries, the middle position “off” and the down position would be 12v via the 12v18ah battery. Your input clarity would be helpful.


DieCastoms (author)APM5yhZGW3h02013-05-20

An excellent idea indeed! And thank you for the comment. Let me think on it for a moment. The switch in this set of instructions WILL NOT work for that, but i am sure that a set up can be figured out easily enough.

Just to be sure I am answering your exact question.. You want to switch between a single 12v battery -or- a bank of three 6 volt batteries?

Again, this switch in thise instructions, as it is wired, will NOT work, but give me a few minutes and I think I can come up with something for you :)

DieCastoms (author)DieCastoms2013-05-20

Oh, geez, the answer just slapped me in the face like a trout!

Connect your load, that's the car-side of everything to the two center pins (in my instructions, pins 2 and 5). To pins 1 and 4, connect the 12v battery, with the polarity matching the connection of the car. To the remaining two pins, 3 and 6, connect the series of 6 volt batteries, again, with the polarity matching that of the car.

Switching the switch one way will connect pins 1 and 2 together and also connect pins 4 and 5, which will connect the 12 volt battery to the car as if there was no switch involved and no other batteries present. Switching the other way would connect 2 and 3, and also 5 and 6, connecting the 6 volt batteries as if there was no switch and no other batteries.

Having an "off" position in this set up depends ENTIRELY on the switch you choose.

BE SURE that the switch can handle the current needed for the car. If you have a heavy duty amp meter, connect it between the positive battery lead of the 18v series, and the car. Prevent the wheels from turning, and power the car and read the meter. If you do not have a heavy duty amp meter, look online for a "Shunt" and the directions on how to use one. They are expensive if you're only going to use them once, though, so maybe finding a local shop that will help you measure the current would be best.

The DC motors in the car will pull the most current when they are 'stalled' like this. If your switch will handle this amount of current, you should be fine no matter how the car is driven.

The switch in THIS instructable can STILL be used to switch the motors between series and parallel. This will give you 6 volts (half of 12 volts, but full current available) to each motor, or 9 volts (half of 18 volts, but all of the current available), or 12 volts (but half of the current available from the 12 volt battery), or 18 volts (but half of the current available).

The switch in my other instructable can be also be used to switch motor directions. Just, again, MAKE SURE you have high-enough-rated switches.

I HOPE this is clear for you, if not PLEASE feel free to ask questions and I will answer them! I'm proud that this is still helping people!


amasegny (author)2013-05-03

Thank you once again. I use your instructable for a solar charger for the phone.

amasegny (author)2013-05-01

Thanks! Worked perfectly.

DieCastoms (author)amasegny2013-05-02

Four years (and two weeks) later, I am glad that this instructable is STILL helping people!!

Out of curiosity, I would like to know what you used the switch in? What was your application?

Mike, at DC.

Nokjhnbvtyhj (author)2012-04-20

Hi Mike,

Would what youhave described work as a torch dimmer if i were to implement your instructions?

DPDT Relays, - can i use a solid state DPDT to "create" a parallel or series power circuit using only

1 power source and use the DPDT to selct between the 2 at will?

any ideas please,

i am quite a novice,

Thanks for your instructable anyway,

many thanks,



DieCastoms (author)Nokjhnbvtyhj2012-05-09


Any means at all of switching the two switches at the same time (double pole) to one position or the other (double throw) without causing a short will work. Switches, relays, transistors, other electronics ...

As for your other question, if you have only one power source, you will have to have two separate loads (your torch bulbs). If your power source is 12 volts, for example, you can switch to parallel and have both bulbs receive 12 volts and light brightly. If you switch then to series instead, the same two bulbs will get 6 volts each and only light "half as brightly".

There is, to my knowledge and logic, no way to switch a single source and a single load from series to parallel. There really isn't anything to switch with one and one..

Mike, from DC.

judypalmer (author)2012-05-09

Your first instructable, my first time commenting! Wonderful instructable! I'm converting an AC swamp cooler to run on solar panels using two radiator fans. I spent hours trying to figure out how to run the fans in series or parallel (low or high) with a DPDT. By following your directions, I wired it up in about 15 minutes. Thanx, I'll look at some of your other instructables!

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