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 slow.fast 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:
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,
3 People Made This Project!
- m6233555m made it!
- jamesbunnjr made it!
- RehabIsForQuitters made it!
1 day ago
Perfect solution for my need to switch two 12v batteries from 12 parallel to 24v series. Search Ebay for "Heavy Duty Knife Switch DPDT" for a nice selection including 100amp.
2 years ago
Thanks for this - your diagram helped cage my brain for wiring two 12v batteries to output either 12v (in parallel) or 24v (in series). I needed a high amp for starting airplanes at either 12 or 24 volts. For those also looking for this type of switch, type "high amp DPST switch) in Amazon. There was a nice inexpensive 63 amp blade-type (breaking - meaning breaking the the circuit between throws) switch on there for about $13.
DieCastoms, you may want to add that this works for switching between batteries by switching the batteries for the loads on your diagram - I think more people are interested in doing this with two batteries in series or parallel.
Reply 1 day ago
Exactly my need and purpose thanks for the high amp switch idea.
Question 6 days ago
I have two boat trolling motors that want to control for steering - one forward, the other reverse for left and right. But I also figure I can connect them in series for slow speed and parallel for fast. Any suggestion of the switching circuit for all that? 😊
Question 1 year ago
I'm building a headphone amplifier and I can use this at the output transformer for selecting different headphone impedances..
But I have 3 output coils to play with.
Is there a solution for the 3?
Otherwise, I could use two switches - one for two coils and the other for the third..
All X2 because it's stereo.
Question 5 years ago on Introduction
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??
Answer 2 years ago
You realize that would be perpetual motion, which is impossible. You'd need almost 14 horsepower to run a 10kw generator. This would in turn take almost 14kw to run the motor if it were 100% efficient (most are 80-95%). And that's running. Starting would probably be 18kw.
2 years ago
Thank you. Exactly what I was hoping. I am using 140mm 12 volt fans above the bedroom doors to circulate air (the return being the gap at the bottom of the door). I have mounted the fans in a rotatable assembly to blow the warmer air where you want it. Out for summer (sucking cool air in under the door) in for winter (forcing cold air out under the door). This is cheaper than installing ductwork. The switch will be to change how much air you need moved.
Question 2 years ago
Anyone tried paralell / serial switching betwen a transformer's primary side? The schematics are easy, I'm only afraid what happens when i flip the switch under load accidentaly.
On paper, nothing should happen, if one side of the DPDT slightly quicker than the other, it lands on an open circuit.
Answer 2 years ago
As someone already mentioned, a "break before make" switch would ensure a dead zone through the middle of the switch's action to prevent exactly what you said.
Answer 2 years ago
That's why you need a "break" switch
2 years ago on Introduction
Hey - I was looking at this, and it's great, but I think your initial statement is incorrect... Series batteries will increase voltage, whereas parallel batteries with maintain the voltage, but increase the current.
Therefore 2x100ah 12v batteries in series will give you 24v at 100ah, where as the same batteries in parallel will give you 12v at 200ah (not including losses or types of battery of course.)
This is REALLY important... could you please check and update!?
Reply 2 years ago
He's talking about two LOADs on one one battery. You're talking about two BATTERIES on one load, so therefore they ARE opposite.
5 years ago
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?
Reply 5 years ago
Sorry 1 motor (writing this on a phone)
5 years ago
love thw first page on identifying switches.
6 years ago
Is there any way to do this with transistors rather than a mechanical switch?
6 years ago
I like it!
I'm going to use this for my heated seat pads. Low/Off/High. Thanks!
6 years ago
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.
6 years 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~