In the past we often got questions about the usability of existing ignition switches, customer would like to use, but did not work with our DIS ignition systems.
We picked up this issue and analysed it. From this, the following text was created.
The mystery of ignition switches
Around the ignition switches, a lot of rumour, myths and half knowledge is present.Most of the model pilots did not know that the named ignition switches are no switches.
We are expecting from an ignition switch, that it switches the connected input voltage without any losses to the output and do not limit the necessary current. Same, as a mechanical switch do.
So far, so good.
Mechanical switches are not used anymore as they are sensitive to vibrations and can not be remote controlled. Digital switches are substituting mechanical switches by using a digital module (e.g. a n-channel or p-channel FET). This module is controlled by a small micro controller, which reads a channel of the radio system to control the FET and to switch the ignition system on or off.
The FET’s in our applications can switch a current of 5A to 20A, some can handle more than 100 Amps.
Some in the market available “ignition switches” are programmable and can reduce the input voltage, e.g. 2S LiPo, to 5,5V. These units can be programmed to output = input voltage. This works so far, but these units can usually supply just 2 A of current. And here is the problem.Programmable “ignition switches” do not have the a/m FET, which is part of real digital switches. They use a programmable voltage regulator, which can be set to different output voltages via different reference voltages or resistor ratio. By the use of an enable/disable input the voltage regulator can be switches on and off.
If the reference voltage/resistor ratio has a defined value, the voltage regulator is used out of its range and does not limit the output voltage anymore. The voltage regulator is still existing and limits the maximum current.
Programmable “ignition switches” do not act like a switch but as a switch voltage regulator with current limitation. In most cases the max. current is limited to 2A and the current control is very fast. In case of exceeding the current limit by some milli seconds the output voltage is reduced by the regulator as long as the maximal allowed current is reached. This can end up in an output voltage of 3V, which is too low for the ignition system. The micro controller will not start and no stable conditions are set in the ignition system.This issue can end up in a destroyed ignition system.
Please use real digital switches like our DZS_2. This is a real digital switch, output voltage = input voltage and it can handle currents up to 10A, short-term load up to 50A.
We kindly ask for your understanding that we can not know all ignition switches in the market and can not answer all the questions around them. The above description should enable you to sort out the differences and to select the right ignition switch for your application.