'Minty' The 240 Wagon

Are you going for looking impressive or to have a practical daily? That turbo looks fine with a 90+ manifold and fits a 3" dump too ;)

Why does so much go into the switch? Wouldn't it be best to use the switch on the earth side of the battery?

It's a minor detail, but putting the switch on the earth side of the battery means you end up switching the starting current as well as everything else.

You're going to want something to ensure that switch never gets turned off with the engine running.

It's not the alternator "sending current back through the circuit" that is the danger. The issue with an alternator is it needs the "capacitance" provided by the battery to regulate. If you disconnect the battery you can (in some unpleasant circumstances) get wild voltage fluctuations and massive inductive spikes that love to eat electronics. So you always need a battery connected when the alternator is running.

Don't take this the wrong way, but it seems like an overly complicated solution to a simple problem. What is wrong with the ignition switch?

bgpzfm142;59394 wroteThere's also an interesting article on Swedespeed (#121) about the need to have a 12V light in the alternator charge circuit, as some alternators need a 'flash' of the field windings so that the voltage regulator operates properly.

A brief digression. The alternator requires power to the field coil to make power itself. Once it's "excited" then the regulator gets power from the stator coils and supplies it to the field so it's self sustaining. When you start from 0, there is no voltage coming from the stator, so you need an excitation voltage to get things started. This is supplied through the alternator warning light. This small current is enough to get things moving and then it's off an running.

If you don't have an alternator light then there is often enough "residual" magnetism in the field coil to get things going but it depends on both how much magnetism is there and how fast you are spinning things as to if/when it will excite. Most alternators seem to be geared about 2:1 off the crank and in general it seems you need in excess of 6000rpm on the alternator (3000rpm engine) to get it to excite with no outside power. I've seen it take close to red-line, and I've seen some excite at 2krpm (engine speed).

So you want (need) and alternator light wired between the D+ terminal on the Alt, and a switched 12V source to get the alternator to light up reliably. If the bulb blows you get no alt light at all and have to rev the crap out of the car to get it to excite. When the alternator is not spinning, the light supplies all the current to the field coil which is what makes the bulb illuminate.

Samman88;59443 wroteInteresting. So basically the field coils are electromagnets, and in order for the alternator to act as a generator these must produce a field, using power from the alternator itself? Why don't they use conventional magnets to produce a field?

How do you electrically modulate the output of a permanent magnet. That's how motorcycle alternators work and the regulators in those work by shunting the excess energy away as heat. You can do that on a bike because it has a small electrical system with a relatively predictable load profile. You want to shunt away 500W-1KW of excess energy in a car alternator ?

Plus, as you throttle the magnetic field down you reduce the energy required to turn the alternator so you save fuel.

Samman88;59443 wroteNot quite sure I understand why you need a light though - is this stock in a 240? Surely if you switch on the power to the feild coil and current passes through it then it should produce a field regardless of whether it has a light in the circuit? And then it switches to using the stators power output.

Dunno. Does your 240 have that little bulb on the dash board with a symbol of a battery on it? The only car I've had that didn't have one of those is a 1965 Triumph TR4A, and that had a generator. Function was determined with an ammeter. Lights are cheaper :)

The light is a cheap way of saying "the alternator is not working, you're going to roll to a stop at some point", and it doubles as the exciter. Best of both worlds.

The light will be so that the circuit actually draws some current through it, otherwise it's a loop with no (or close to no) resistance, and so will have no current draw (I=V/R) and therefore no magnetic effect, although if you get the alternator speed up enough you will excite it at some point.

As for the isolator switch, do you need this to be able to switch off the engine or just isolate the battery when the car is stopped? If you're just isolating the battery, the standard system of a switch of some kind on the positive side will work fine, and stop the car from being powered or started, if you wanted to kill the motor as well, maybe consider running a relay that breaks connection to both the normal ignition switch wiring, and the battery positive when the switch is thrown.

Please please please just switch the earth side and try not to destroy too much of the stock stuff if you actually want to use the car... thats the bottom line.

Let me know if you decide to swap the 18T out... my R needs some extra ponies

I hope you get a decent power gain over a ported 90+ with that manifold, otherwise its just badly designed to be used for rhd or upright mounting..