Understanding Fuel Pump and Coil Wiring

[RGUK]

Hi all

I'm trying to understand how the fuel pump is wired on a xv535. From what I've read, the ignition coil creates a spark by putting a current through the primary coil and then cutting the circuit at the desired time which collapses the EMF in the coil.

The attached diagram has the fuel pump connected to the negative side of the rear coil (orange wire) via a relay. I'm guessing if the ignitor unit is not pulling the negative to ground, then there's 12v feeding the fuel pump. If the ignitor unit pulls the coil to ground, then the pump stops.

How does the coil collapse the EMF if there's always a path to ground either through the ignitor unit or the fuel pump?

Thanks in advance
Rich
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SV650

[WD Forte]

electrickery always takes the path of least resistance

I'd say when the TCI switches on to ground the coil and collapse the field
it effectively shorts power to the relay coil as well, effectively pulsing it.
I assume this is so the pump only runs when the engine is turning so as not to flood it.
These pumps are only low pressure low volume types to keep the carbs topped up, not high pressure, high current types so may have a moderately high resistance which doesn't impinge badly on the coils primary winding.

Think of it as a voltage divider with
the primary coil at the top and the pump relay coil and pump itself as the bottom.
With the TCI as a switch to ground, when its open (in a non sparking state)
primary current would have to ground via the relay coil and pump coil
to collapse the field and they probably have enough combined resistance to prevent unwanted effects.

Thas my guess anyway assuming that diagram can be trusted
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bikers smell of wee

[RGUK]

Thank you WD Forte for the reply.

Just to confirm when you say

[WD Forte]

Doh!
Your right of course it does
It was late and I got somewhat fixated over the relay end.

Either way I still reckon any connection to the relay and pump must have a high enough resistance to not adversly affect the LT coil function, otherwise it could never work properly.

I never utterly trust any wiring diagram until I see for myself
and the picture of its layout may be misleading.
I suspect its connection to the LT coil may just be as a control signal and actual power for the pump comes from the red/white wire
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bikers smell of wee

[RGUK]

I think I've found the missing part of my puzzle (if it's not right, I'll just have to accept 'is works how it works'')

I couldn't get my head around how the pump could work when it's only gets a split second of power when the spark fires. (Coil not being pulled to ground).

I'm guessing (and hope it's right) the pump is kind of getting a PWM voltage. Even at idle say 800rpm, the spark happens approx 6 time per second (800/2)/60. I've tried to simulate it in a circuit simulation app and get the pump at 9v at idle.

If I ever get the bike running I might connect my oscilloscope and see what's happening.

Thank you for your time to respond.

Rich
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SV650

[Nobby the Bastard]

The relay doesnt get a chance to react to one pulse ending before the next arrives so the circuit to the pump stays closed the whole time there the pulses.
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trevor saxe-coburg-gotha:"Remember this simple rule - scooters are for men who like to feel the breeze on their huge, flapping cunt lips."
Triumph Sprint ST 1050

[RGUK]

Looking at the diagram, the control (switched) side is controlled from the key ignition switch, so it's not being switched with the spark.

Once the key is in the 'on' position, the relay links the coil to the pump until switched off.
____________________
SV650

[WD Forte]

[RGUK]