A simple glow plug driver for model engines

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A glow plug driver

A simple and free glow plug driver to start model engines with methanol
type fuel (with castor or synthetic oil).
Designed by Stefan Spännare. Latest update 1998-04-08.

Circuit layout:

Oscilloscope view of signal:

Red: Voltage over glow plug. Blue: Voltage over 1 Ohm resistor.
Max current: 4.5 V / 1.0 Ohm = 4.5 A. Frequency 450 Hz.

Advantages

• Very good glowing and starting properties.
• Works with all 1.5 V and 2 V glow plugs.
• The glow intensity of the glow plug can be adjusted with the potentiometer.
• Should be powered from a 12 V (starter) accumulator.
• Switched operation (low power consumption).
• Survives temporary glow plug short circuit.
• Survives reversed polarity.
• Very easy to build.
• Very cheap.

Disadvantages

• The glow current can not be easily measured because of the switching.
  Check the glow intensity with an unscrewed glow plug.
• Can not be used with normal small power supplies (only with accumulators)
  due to high (5 A) transient currents.

Instructions

• Be careful to not short circuit the accumulator when testing.
• The glow plug driver can easily be built on a normal laboration card.
• The function can be tested with a car lamp (12 V, 50 W) as "glow plug".
• The IC (NE 555) is a timer circuit, here used as switching oscillator.
• The transistor (BDX 34 C, Darlington) must have a small heatsink.
• The large diode must survive a current of at least 3 A on average.
• The LED (Light Emitting Diode) is of standard (20 mA) type.
• All resistors in Ohm or k Ohm (1 k means 1 kilo Ohm = 1000 Ohm).
• The potentiometer and small resistors must be of at least 0.25 W type.
• The 100 k Ohm potentiometer is of linear type.
• The large 1 Ohm resistor must survive 10 W (or at least more than 5 W).
• The capacitor is given in nF (nano Farad).
• The cables to the diod, transistor, 1 Ohm resistor and the glow plug
  should be quite thick (0.75 mm²) due to high (5 A) transient currents.