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Mark

Wiring FIA Battery Cut Off Switch

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Hi all

If anyone can understand the question I am trying to ask I will be impressed.  

I am Fitting an FIA type battery cut of switch to the Vitesse, it's the type with a resistor to protect the alternator from surges. I converted the car to alternator using Dave's guide on here and works perfectly.

No wiring diagrams came with the Switch but I have fitted them to a couple of cars in the past and was pretty straight forward. I printed off a wiring diagram from google showing the same two main connectors and four spades labled 1 and 2 as opposed to W Z as on some.

I understand to split the main supply from the battery to the solenoid (the diagram I am using says from the battery to the Main electrical feed), connecting each end to the two main terminals on the switch. Then wire the small resistor to the terminal marked 1 and then to earth, then another wire to the other small spade labled 1 to the main wire going to the solenoid. The two other small spades labled 2 break the Positive coil wire.

I can't understand how connecting the resistor to the main wire going to the solenoid can stop surges going back to the alternator if the switch is cut whilst the engine is running.

I suppose I am asking by wiring in an alternator and removing the old cut out box and related wiring do I need to fit the resistor to the circuit in a different way.

Sorry a dogs dinner of a question, that I am struggling to get my head around. 

Mark

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Should be a diode not a resistor and it’s there to stop the alternator current from keeping the engine running when the battery is disconnected 

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I hesitate to question the guru, but I have a 1 Ohm resistor on that subswitch fitted to SofS.    It says so on the side.     Been used a few times, but the alternator still working.

John

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Oops...... My bad.....  :pinch:

In my defence, both are possible.  I remember doing battle with one many years ago where we couldn't get the engine to stop, so did something fairly desperate involving earths and dead shorts. This worked with the dynamo fitted at the time but then came back to haunt us when an alternator was fitted instead.  Two dead of alternators later we worked out our stupidity and fitted a diode - which was a challenge to source as it needed to be fairly hefty.   I suspect that cut-off switch didn't have the supplementary low-current terminals that they all seem to come with now.  The extra terminals make it easy to get the engine to stop and the resistor is there to dump the residual current from the alternator.

4430-TERMINALS-WIRING-2-1200w.jpg

I think the point is that while the main switch and Z contacts open when the switch is turned off, the W contact closes and connects the engine side of the electrics (including alternator output) to earth via a resistor (usually 3 ohm 10W by the looks), which gives the alternator output somewhere to go while the alternator is still turning.

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I've just got a basic switch on the AH, fried a few alternators but think that because I've over revved them, even with reduction pulleys?

Same switch fitted on the GT6 and never had a problem. (thats an alternator problem not a GT6 problem )

RR

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Thanks Nick for the diagram, got a similar one but your version is labled clearer.

I think the doubt in my mind is when I  wired the alternator output, I took Daves preferred option to wire directly to the positive terminal on the battery and not to the solenoid. I think in order to protect the alternator from serge I am going to need to run the alternator output directly to the solenoid so that it is on the correct side of the cut out switch that incorporates the resistor. Does that sound right ?

Mark

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18 minutes ago, Mark said:

I am going to need to run the alternator output directly to the solenoid so that it is on the correct side of the cut out switch that incorporates the resistor. Does that sound right ?

Yes.  Or you could go to the engine-side terminal on the cut-out switch if it were more convenient - doesn't really matter provided it's not bypassing the switch - which it will be if you leave it where it is.

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Cheers that clears it up in my mind. Vitesse is running and driving, well a couple of miles so far after 13 years. Photos to follow soon.

Mark

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9 hours ago, Mark said:

Cheers that clears it up in my mind. Vitesse is running and driving, well a couple of miles so far after 13 years. Photos to follow soon.

Mark

:ohmy: :biggrin: :thumbsup:

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Great!  Just one thing to remember with the cutoff switch is don't ever connect another battery up to the car with the switch in the off position (unless it's directly to the your battery terminals i.e. never anywhere 'up-circuit' of the switch such as directly onto the starter solenoid e.g. to test something or try to jumpstart it) - otherwise you'll effectively be shorting the newly connected battery directly through your 1 Ohm resistor.  

Typically doesn't end well... (ask me how I know...) :)

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