Alternator wiring - Ford 2G, advice required

[Julian West]

I'm looking to wire in my alternator, from searching the forum & finding this thread Alternator 3? wire connections & this link Ford Fuel Injection » Alternator Files

I've identified the alternator as a Ford 2G.

Trouble is, I don't have the right connectors & I dont' really understand this wiring diagram...... what does 'hot in run' mean?? Is this a ballast resistor & if so what sort???

Is there a source in the UK for these connectors??

What type of 'fused link' should I use??

Thanks in advance, & Any advice gratefully received!

[Ron Earp]

I think that should read "Hot On Run", meaning it has 12V when the key/switch is in the "Run" position. All that does is activate the field coil so the alternator will work.

Ron

[Mal]

I would agree with Ron about the Run In Hot section. This basically connects to the Run output of the Ignition switch to energise the regulator and provide the warning lamp circuit (both active when the engine is expected to run, isolated when expected not to run).

The fusible link is a type of fuse usually moulded into the cable linking the alternator to the battery. It should be rated about 150% of the rated alt output current, so that it will not blow if the alternator is supplying its rated power.

The fusible link is incorporated to protect the system by blowing if the diode pack in the alternator fails. In this case the diodes have a high probbability of failing to a short circuit, allowing enormous currents to flow throught the wiring harness, and melting all circuits in close proximity greating a fire hazard. The link blows and isolates the alternator from the balance of the wiring. The alternator would be destroyed electrically (but not mechanically) by the time the link blows.

Do not substitute a fuse or circuit breaker for the link, as if it blows or is switched open while the alternator is operating, the sudden load loss will cause the alternator output voltage to soar to the point where it destroys the diode pack. This is the reason the fusible link is rated much higher than the alternator.

The fusible link is always located outside the loom wrap, so that if it does blow the loom is not damaged.

You should be able to source matching connectors via an auto electrician.

[Julian West]

Gentlemen,

Thank you for your input, I understand much better now. I just need to source a fusible link & I'm there.

Thx again,

Regds

[Julian West]

Malb,

Thanks for going into such detail... The alternator will produce 75A, so will a 100A fuse will be about right?

Is a 'fusible link' different to a fuse?

Thanks in advance!

[Tony Hunt]

Julian,
A fused link is a fuse in the UK sense, but take care. The risk of an open circuit if you use the conventional fuseholder is far too high - see malb's comments.
A 12 gauge fused link is an inline fuse of around 160amps rating (often 2x 80amps in parallel). See this URL.
A quick check of the Internet brought up a picture - Sherco Auto Supply and a possible source, but there doesn't seem much this side of the pond.
Regards,
Tony Hunt

[Julian West]

Thanks Tony,

Reading the article you very kindly linked, it talks about replacing the fusible link with a 'Maxi fuse', & these are sold by VWP VWP - fuses about a third of the way down the page.

They also list midi fuses & mega fuses... are these the same??

In the mean time I've found that Reel Steel do the connector blocks for this alternator... Maybe the Fusible link will be part of the connector?? (here's hoping!)

Regds,

[Julian West]

I just found this aswell Land Rover Freelander 120 Amp Fusible Link - GENUINE on eBay, Land Rover, Car Parts, Cars, Parts Vehicles (item 120152372984 end time 26-Aug-07 22:55:19 BST)

Would this be any good?

[Mal]

The link in late 70's Fords (in Australia) was part of of the loom, but alternator output B+ to battery cable stepped out for a few inches where the link was moulded into the cable to protect the balance of the loom.

The Land Rover part that you linked to would be a good choice, provided that you can also obtain the housing that it fits into from somewhere. Housing needs to enclose the unit so that terminals cannot be shorted by tools, and insulate the unit from the chassis. The current rating would be in the right ballpark.

With this approach, you end with a unit that is easily replacable, but unlikely to get pulled out while the altenator is working by a zealous trouble shooter. Overall, that is the major consideration, the altenator must not have the load disconnected while it is running and energised.

[Julian West]

Mal,

Thanks for the advice, I'll do some research on a housing & maybe have a look at a mega fuse aswell.

Is it correct to say that the danger with using a fuse (as opposed to a fusible link), is that it could be accidentally puled out whilst the unit is running & this would destroy the alternator???

Regds,

[andy loveday]

Hi Julian

glad your sorted, RCR should be in about 8 wks, tried to send pm, but your box is full, needs a clear out, best of luck the rest of your build, Andy

[Mal]

Julian,
The issue is breaking the B+ to battery line with the alt energised and spinning. This iis why I am not advocating using a fuse. The LR fusible link, mounted in a suitable housing, would be a much better deterent to this than any type of push in/pull out fuse.

If you refer to your wiring diagram in the original post, they are three sets of (fixed) coils providing the output current/voltage for the alternator. They are arranged similarly to a 3 phase power unit. Following them is three pairs of diodes to convert the 3 phase variable frequency (with RPM) AC from the coils to DC voltage. The diodes are a high frequency capable type, not mains frequency units.

To control the DC voltage, the regulator adjusts the current in rotating exciter coil. (Voltage is a function of frequency and strength of the rotating feild which is in turn dependant on the exciting current).

Think for a moment of a bog standard coil ignition system. A current flows through the coil primary, increasing from zero until it reaches a constant level when the coil is magnetically saturated. This means that the coil is storing the maximum amount of magnetic energy that it can.

At some time after this, and timed carefully to the needs of the engine, the points open and stop the current flow. The result of this is a very rapid collapse of the magnetic field in the core, producing a high voltage pulse in the output of the coil, which then fires the spark plug.

Now, in the case of the alternator, if the alt is excited (field energised) and running, open circuiting the load terminal by blowing or removing a fuse, will create a pulse of substantial voltage, in a similar way to the ignition system but in hundreds rather than thousands of volts. This pulse will exceed the reverse voltage (blocking) capacity of the diodes and destroy them, most likely producing a short circuit and burning out the output coils of the alternator within a very short period ( 10 secs).

Hence the link must be of a type that is replacable but not subject to mans interference. Hence my reccommendation of the Land Rover type you suggested.

[Julian West]

Thanks again Mal,

I'm grateful for your taking the time to post in such detail. The 'fuse' I've gone for is a 'Mega fuse' which is a bolt-in 125A fuse & comes with a dedicated & properly insulated holder, so there is no chance of any shorts, or more importantly, there is zero chance of the fuse being 'pulled' whilst the engine is running. You need spanners to get the fuse out!

Regds,

[Mal]

Sounds great, as long as the holder is fully insulated all round to keep tools and other odds and ends out.