What does "inductive loads must be diode suppressed" mean and what diode should I try?

Thread Starter

daytona

Joined Jan 15, 2021
41
I need to incorporate an optic level switch in a radiator tank to determine when the water level drops low. The paper that came with the Gems sensor says "inductive loads must be diode suppressed" what does that mean and what diode should I try? They give a schematic that shows SENSOR WIRING.jpg
 

MrChips

Joined Oct 2, 2009
23,535
A coil of wire, a solenoid or motor for example, is an inductive load.

When current flows in an inductive load a magnetic field is generated. This represents energy.
When the current through the inductor is removed (i.e. driver or switch is turned off) the magnetic field collapses and the stored energy has to be released somewhere. This results in a large reverse voltage (back emf) across the coil of wire. This voltage spike can cause havoc in electronics and may even destroy your electronics. A diode (snubber circuit) is placed across the inductive load or across the active driver in order to suppress the back emf.

If your application is not switching an inductive load then you can omit the snubber diode.
 

MaxHeadRoom

Joined Jul 18, 2013
23,115
. The paper that came with the Gems sensor says "inductive loads must be diode suppressed" what does that mean and what diode should I try?
Gems sensors often are used to pick up a relay, if this is the case with yours, then you need it.
They usually are reed relay style switching devices.
Max.
 

Thread Starter

daytona

Joined Jan 15, 2021
41
A coil of wire, a solenoid or motor for example, is an inductive load.

When current flows in an inductive load a magnetic field is generated. This represents energy.
When the current through the inductor is removed (i.e. driver or switch is turned off) the magnetic field collapses and the stored energy has to be released somewhere. This results in a large reverse voltage (back emf) across the coil of wire. This voltage spike can cause havoc in electronics and may even destroy your electronics. A diode (snubber circuit) is placed across the inductive load or across the active driver in order to suppress the back emf.

If your application is not switching an inductive load then you can omit the snubber diode.
Thanks, I don't think it is an inductive load. It goes into an engine controller switched input.
 

MaxHeadRoom

Joined Jul 18, 2013
23,115
The Gem sensors I have used generally have used a PM magnet in the float and reed relay style switch, this will not require a BEMF diode, only in the case of the switch operating a relay, then the diode is needed.
Max.
 

Thread Starter

daytona

Joined Jan 15, 2021
41
The Gem sensors I have used generally have used a PM magnet in the float and reed relay style switch, this will not require a BEMF diode, only in the case of the switch operating a relay, then the diode is needed.
Max.
Thanks, it not a float. Ours is an opto device with open collector output of 18 mA sink max installed in the radiator. I think the engine controller is not an inductive load. I do have a dual float in the fuel system and it is just two switches
 

MaxHeadRoom

Joined Jul 18, 2013
23,115
Thanks, it not a float. Ours is an opto device with open collector output of 18 mA sink max installed in the radiator. I think the engine controller is not an inductive load. I do have a dual float in the fuel system and it is just two switches
OK, then if it inputs into a semiconductor circuit, Opto IC etc, then the diode is not needed.
Max.
 
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