Condenser, resistor, suppressor ? What is it ??

[The Moosehunter]

Upon removal of my fuel pump from the chassis, it would appear that either I am a clumsy buffoon or the wire going into a small metal thingymajig had already broken off.

I'll get a piccy later today, but it is shown on the top piccy on page 98 of a second edition of The Bible. But it does not say what it is.

Need to get a new one I guess, but electrics not being my stong point, haven't got a clue what it is, pretty essential when ordering a new one

If any one knows, then would they also per chance have a cross reference so I can get one at my local motor factors, as I need the car running by Wednesday.

Thanks chaps

[spend]

Dont think it will stop your car running - just suppressor for radio.

Dave

[steve-v8s]

When current is flowing and you open the circuit (with a switch or the armature of a motor for example) the current tries it’s absolute best to continue flowing via the air gap and forms a spark. The capacitor (or the very old fashioned term condenser) provides a momentary path for the current to follow which is an easier route than forming a spark across the air gap. This will reduce any possible radio interference but more importantly each time the contact suffers a spark, part of it will be eroded away. After a while the nice clean, low resistance contacts will become pitted, carbon encrusted and won’t work any more. So yes it is fairly important to have the capacitor fitted.

Where you are switching current via an inductive load (the coil in a motor for example) it is particularity important to have the capacitor fitted as when the magnetic field in the coil collapses a fairly high voltage can be generated. The higher voltage is a lot better at leaping the air gap and therefore a lot more effective at eating the contacts.

Apart from eroding the contacts and radio interference, some people may also have the opinion that it is not all that desirable to have sparks occurring inside a fuel pump.

[GreenV8S]

steve-v8s said:

Apart from eroding the contacts and radio interference, some people may also have the opinion that it is not all that desirable to have sparks occurring inside a fuel pump.

The sparks would occur at the fuel pump relay. It isn't usual to put a capacitor across every motor, and I wonder whether this is something that has been added to cut down radio interference?

[steve-v8s]

Sorry Pete have to disagree, think you will find most DC motors will have a cap across them. Not an automotive expert but it is standard practice in industrial applications. It prolongs brush life by preventing sparking at their point of contact on the armature. The pump on my 98 Griff certainly has a cap and it looks to be original.

[spend]

So are you saying we dont need to bother with Bosch fuel relays ~ just fit common or garden variants?

[GreenV8S]

steve-v8s said:

Sorry Pete have to disagree, think you will find most DC motors will have a cap across them. Not an automotive expert but it is standard practice in industrial applications. It prolongs brush life by preventing sparking at their point of contact on the armature. The pump on my 98 Griff certainly has a cap and it looks to be original.

Sorry, you're right, but that isn't quite what I meant. It's normal for DC motors to have small capacitors across the brushes. It helps reduce sparking across the brush/commutator junction as the coils come in and out of phase, just as you say. I expect you'll find the fuel pump has these internally. What isn't ime common is to fit an external capacitor at the motor to absorb the back EMF as you disconnect the supply to the motor. These sparks would occur at the relay not the pump. They could be reduced by a capacitor at either end, but they can also be reduced by a diode across the relay which lets the current through the motor 'free wheel' while it decays. Whichever way you cut it, it is not normal to see external capacitors strapped across fuel pumps and other similar sealed motors. Not in my experience, anyway.

[The Moosehunter]

GreenV8S said:

Whichever way you cut it, it is not normal to see external capacitors strapped across fuel pumps and other similar sealed motors. Not in my experience, anyway.

What a superbly detailed answer (even if most of it went over my head)

So in summary, should I bother replacing it ?

[seasider]

The Moosehunter said:

GreenV8S said:

Whichever way you cut it, it is not normal to see external capacitors strapped across fuel pumps and other similar sealed motors. Not in my experience, anyway.

What a superbly detailed answer (even if most of it went over my head)

So in summary, should I bother replacing it ?

Andy your about as good as me sparky bits

[steve-v8s]

It seems I would replace it and Pete wouldn’t. Have you tried the radio since removing it ?

[The Moosehunter]

seasider said:

Andy your about as good as me sparky bits

Definately

Give me something metal and something else bigger to hit it with and I'm OK

Cheers for your help Steve, no I haven't tried the radio yet as it's balanced on two axle stands at the mo, with no wishbones on it and am reluctant to fiddle inside until they are back on.

I think I may just fit the pump without for now, get some wheels on and then maybe do the radio test and take it from there

As long as it doen't go bang then I'm sure I can cope

To be honest, I only really noticed I had a radio recently. No need to have it turned on with my new "electric" exhaust

Demo on the Tunne Run for those who are interested. (assuming I get something to attach my wheels to soon)

Moose

[spend]

Theres a bit more room to fit the lower wishbone with the pump off BTW.... if you had'nt thought of it (I didnt - double refit of fuel pump....)

Dave