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Simple Motor Control from AC
By Stan Leech
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Control your Meccano models (or anything else) from your Windows PC!
Take a look at my new MECControl project at meccontrol.com

If you need to control a DC motor, but only have an AC power supply, the simple circuit shown in figure 1 might be just right.  It uses only two diodes and an Single Pole Double Throw (SPDT) centre-off switch and will allow you to switch the motor on and off, and change its direction.

The AC supply from your power supply transformer needs to be 1.5 to 2 times the voltage required by the DC motor that you use.  This is because the diodes, which each form what is known as a 'half-wave rectifier' when they are active, waste half of the power in the process.

Further Information Rectification - Includes a description of a half-wave rectifier

You will need to use diodes that can pass the current that the motor will consume, at the voltage you will be using.  1N4001 diodes can pass up to 1A at 50V, whilst 1N5401 diodes can pass up to 3A at 100V.  In figure 1, 1N4001 diodes are used because the power supply voltage is 12V AC and the motor runs at 6V DC.

Figure 1: Simple motor control from an AC supply

 Shopping List

Details of both 1N4001 and 1N5401 diodes are given below - two of one type only are required for the circuit in figure 1.

Part
Description
  Quantity
Required
  Rapid
Code
  Unit
Price
  Total
Price
1N4001 Rectifier Diode   2   47-3130   0.05   0.10
1N5401 Rectifier Diode   2   47-3144   0.11   0.22
Miniature SPDT Toggle Switch Locking with Centre Off   1   75-0084   0.66   0.66
Grand Total   0.98

Full printer-friendly parts list

Order the above items from Rapid Electronics via our Circuits Shop and help support the Electronics in Meccano website, without affecting the price you pay! Just click on an item for information about it and/or to add it to your Rapid order.

Orders can also be placed by telephoning Rapid on 01206 751 166 or visiting their website at www.rapidonline.com. Prices quoted include VAT at 20%.

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Article Information
Topic: Controlling Motors | Created: 30/12/2002 | Last modified: 11/02/2007 | First published in EiM: Issue 5 (September 1999)

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