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I want to use a MOSFET that can handle high current use for switching, so I decided to use the external MOSFET for 3d printer. I tested it out on other loads such as motor, LED, relay it is able to conduct when I connect the control to a 12v voltage. But when it comes to a car bulb it doesn't seem to light up.

The car bulb is able to light up when connected directly to the 12V car battery, but cant light up when connected through the MOSFET.

The MOSFET power source is from a 12v battery, the load part is connected to the light bulb and the control pin is connected to a 12v dc source, and has also tried to connect it directly to the 12v battery. In which both cases are able to switch on other loads but not the car bulb.

The VGS of the MOSFET is 10V, in which when 10V is applied across the gate the source and drain of the MOSFET is suppose to conduct current.

the MOSFET connection

The MOSFET i use

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    \$\begingroup\$ Welcome to EE.SE! Please post a schematic. \$\endgroup\$
    – winny
    Dec 23, 2019 at 15:03
  • \$\begingroup\$ VGS is a voltage you can measure not a specification. Questions about undocumented modules are off topic here. You might however take a voltmeter and see where in the circuit most of the voltage is being dropped. Clear it is not across the lamp filament, is it across the module? What is the battery output voltage under load. \$\endgroup\$ Dec 23, 2019 at 18:14
  • \$\begingroup\$ Do you have a part number for the power switch (which is visibly more than just a MOSFET). It MAY be that it has intelligent protection and that it sees the very low bulb resistance and massive inrush current as a short circuit and "refuses" to turn on. The switch is labelled "50 ohms max" - suggesting that a load at 12V of under 1 Ohm would be tolerated. TRY adding say 1 Ohm in series with the bulb to start with. This increases the load's startup resistance from maybe 0.1 Ohm and may persuade the switch to operate. IF this works , see low low a series R it will work with. \$\endgroup\$
    – Russell McMahon
    Dec 24, 2019 at 7:50
  • \$\begingroup\$ Is this it? marvle3d.co.nz/parts-accessories/… \$\endgroup\$ Dec 24, 2019 at 10:50
  • \$\begingroup\$ What voltage do you measure across the battery and the bulb when attempting to to light it? \$\endgroup\$ Dec 24, 2019 at 10:58

1 Answer 1

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Do you have a part number for the power switch (which is visibly more than just a MOSFET). It MAY be that it has intelligent protection and that it sees the very low bulb resistance and consequent massive inrush current as a short circuit and "refuses" to turn on.

The switch is labelled "50 ohms max" - suggesting that a load at 12V of under 1 Ohm would be tolerated. TRY adding say 1 Ohm in series with the bulb to start with. This increases the load's startup resistance from maybe 0.1 Ohm and may persuade the switch to operate.

IF this works , see how low a series R it will work with.

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