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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:
http://www.instructables.com/id/SIMPLE-Polarity-Reversing-switch/
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:
http://www.instructables.com/id/SIMPLE-Polarity-Reversing-switch/
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Signing UpStep 1Selecting 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.
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.
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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,
cheers,
tony
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.
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.
Mike, at DC