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:
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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)  APM5yhZGW3h01 year ago
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)  DieCastoms1 year ago
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.

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.

JohnnyS323 days ago

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!!!

graphixv1 month ago

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.

aauliye3 months ago
OK this switch will go from parallel to series and vice versa?
richkenn7 months ago

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.

pimpyourstuff7 months ago

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)  pimpyourstuff7 months ago
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!7 months ago

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:


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.

DieCastoms (author)  charlessenf-gm1 year ago

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. :)

DieCastoms (author)  RehabIsForQuitters9 months ago

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. :)

DieCastoms (author)  RehabIsForQuitters7 months ago

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. :)

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)  APM5yhZGW3h01 year ago
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)  DieCastoms1 year ago
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!

amasegny1 year ago
Thank you once again. I use your instructable for a solar charger for the phone.
amasegny1 year ago
Thanks! Worked perfectly.
DieCastoms (author)  amasegny1 year ago
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.

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)  Nokjhnbvtyhj2 years ago

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.
judypalmer2 years ago
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!
DieCastoms (author)  judypalmer2 years ago
Your comment is greatly appreciated. I am glad to know that people are still getting use out of my rather-simple instructable, even when there are many others who have done the same basic instructable, both before and after mine.

My other instructable that you might find useful is the reversing switch. I would assume that your radiator fans and solar panels are all DC, so you could easily switch each fan for blowing in or out.

Mike, at DC.
SnoopKatt4 years ago
Thanks! Worked perfectly. It doesn't matter which side is which BTW, I tested it myself for that.
DieCastoms (author)  SnoopKatt4 years ago
Thank for the feedback! I am glad that it worked well for you.

Mike, at DC
SnoopKatt4 years ago
Thanks! I bought some 6A/125V switches for some guitar cabs I'm building, so I can switch between 4 ohms and 16 ohms :)
bennyb15 years ago
Will this work on a Jazz bass, to change the pickup configuration? I was going to put in a push-pull pot for this, but have several of this type switch on hand. Thanks for the info. BennyB
DieCastoms (author)  bennyb15 years ago
Before I answer that, let me point out that I have absolutely no idea about guitars. That being said, this switch will allow you to have the pickups in series or in parallel to each other. I have no idea if that is something you would or wouldn't want to do with the pickups on a guitar. Since no power is put into the guitar from the amplifier, I don't THINK anything can be damaged by wiring the pickups improperly, so I would say try it, and let me know!
I believe that will do what I want. It just alters the sound output of the pickups. Thanks. BB
DieCastoms (author) 5 years ago
I am sorry, but I do not have a camera with which to take any pictures. The few pictures I have were taken by a friend. It does not matter which pin is pin 1 in most switches. It MIGHT matter if you have a lighted switch, in which case it will matter where you connect the positive and there may or may not be an EXTRA pin for the ground. Follow the instructions that came with your switch if it is a lighted switch. Thank You for your comments! Mike, at DC.
PARKOUR1235 years ago
Does it matter how you hold it? I mean can you hold it the opposite way and still have the same meaning? Also how do you tell which one is pin 1?
Can you also add a picture of your DPDT slide switch after you have finished soldering as I am a little confused with how to connect it.
varun175 years ago
i know that sir but does that mean that we get parellel and series connections in a single switch connection means if we want to connect 2 motors in series and 2 in parellel then that wont be possible.....
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