Relays and diodes

[Harry in Ky]

I've been studying the circuit diagrams and operation of various electrical functions in the service manual for the Kioti DK 35 45 50 tractor.

I see a number of relays (not all, but some, including the start relay) that have a diode placed in a loop around/between the terminals for power and ground on the coil circuit. Having dealt with this style relay for years, I don't understand the need for a diode in this application. Maybe someone can give me a "nutshell" explanation for why that might be needed?

I'm not looking for long winded breakdown on the theory of diodes/rectifiers, atoms and molecules, protons and neutrons or any of that. I know what a diode does. I just don't see why there would be one here.

 

[repete]

Can you post a circuit diagram?

 

[Harry in Ky]

Not really. I don't have anything I can post and am not computer literate enough to make one up.

 

[Agvg]

Diode Connected in Parallel to a Relay Coil – Relay diode - Electronics Area

The purpose of a diode connected in parallel to a relay coil (flywheel diode or freewheeling diode) is to avoid damaging some nearby components sensitive to high voltage.

electronicsarea.com

 

[5030]

Diodes only allow one way passage of power. My Kubota's are the same way actually.

 

[Harry in Ky]

From that I'm picturing something on the order of induced voltage as in an automotive ignition coil. Points open and close, circuit in primary coil winding generates voltage in secondary winding, that sort of thing. Maybe not precisely the same, but some of the principles overlap a bit.

 

[TractorTech]

An extra layer of protection

 

[etpm]

From that I'm picturing something on the order of induced voltage as in an automotive ignition coil. Points open and close, circuit in primary coil winding generates voltage in secondary winding, that sort of thing. Maybe not precisely the same, but some of the principles overlap a bit.

The voltage is induced the same way as an ignition coil. When power is removed from the relay coil the magnetic field collapses just like in an igniton coi.
Ericl

 

[WranglerX]

If your tractor has a computer the diode is there to protect computer from a voltage spike as magnetic field collapse when relay is deenergizes....

 

[Harry in Ky]

How about that? I've installed more of those relays than I can count, on all sorts of tractors, for all sorts of reasons. A good many with computers. No one has ever accused me of damaging their computer because of a diodeless relay. You learn something new every day, whether you want to or not.