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Sharas

Ford Mondeo High Alternator Voltage

6 posts in this topic

Hi today my alternator caught on fire.

I had some issues before, when driving in hot day London traffic felt burning smell. After inspecting noticed wires in alternator had plastic melted. Next day I went to a garage and they tested my alternators voltage which was to high. Engineer told me that alternator is faulty and will pack up soon.

Which it did today (after 8 months).

I did get a new alternator and fitted today, but when I tested it had 16V on idle and 15.7 with lights and con on. My mondeo have a heated seats, factory fitted xenon lights, and so on.

After running for about 3mins it started smelling burn again and alternator is to hot to touch.

What could be a reasons of that?

Please help

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sounds like your fitting the wrong type?

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sounds like your fitting the wrong type?

I double checked part numbers for my model and its a right one

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The alternator runs a smart-charge system so it runs at over 12v at certain times

The fuel filter sits on top of the alternator, often changing the filter can drop fuel on the alternator, this can stay on/in

the alternator and has the potential to ignite

there may be other electrical problems (eg- like a short in the wiring) that could cause a replacement alternator to fail. And the next one, and the next one, and the next..... you get it

An extra heavy load can put the SWR (standing wave ratio) up, like all the items you mention (a short can too) - this can make the alternator get hot - it is difficult to tell if it gets that hot normally or it is overheating

A car with a smart charge system must have a silver-calcium battery

Also, sometimes new things smell as the paint/ stickers etc burn off

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Sounds like theres shortage in a circuit. Any advise on where should I start to look for or how do I check if there is a shortage for shure?

Thanks

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Hi today my alternator caught on fire.

I think we can agree that flames coming out of the alternator isn't exactly desirable. Some things can be a bit marginal, but actual flames coming from the alternator isn't usually a good sign.

I did get a new alternator and fitted today, but when I tested it had 16V on idle and 15.7 with lights and con on. My mondeo have a heated seats, factory fitted xenon lights, and so on.

After running for about 3mins it started smelling burn again and alternator is to hot to touch.

While those voltages are a bit high

  • You can certainly get differences of 0.1 - 0.2 volts (possibly a little more), depending on where you measure and what you measure with
  • Something like 15.5 volts can be a voltage that exists for a short period in a smart charge system

the degree of equipment fitted to your Mondy is essentially irrelevant, if those bits of equipment are turned off (and only of partial relevance when they are turned on). All Mondys of a given series (Mk IV, etc) have a fair amount of electrical equipment, and, as far as I know, the same capacity of alternator, etc, so the same thing should apply to all. The biggest individual loads are the heated screen, front and rear, so those are useful for testing what happens under load (and are fitted to all trim variants).

I think one of the possibilities for a fault is the feedback signal to the alternator. The 'traditional' alternator set-up uses the power lead from the alternator to the battery to measure the battery voltage (which has inaccuracies dependant on the current flowing). The more modern system has a separate feedback line, along which high currents do not flow, and so should be more accurate. However, if you have a fault on that line, it can cause faults that could not occur in the traditional system.

You have something like a three or four way connector to the alternator, and one of those lines ought to connect to the battery (there would be a separate, thicker wire for the high current path to the battery). If there is a series resistance (which you can measure with a meter, but you'll be best advised to take the battery out of the circuit to do it), then the voltage may go up. Also, if there was a parallel resistance to, eg, ground, that would also do it (also measurable with a meter, just about, with the battery out of circuit, depending on the other electrical equipment in the car; with the ignition off, the measured resistance ought to settle after a while - it is possible that it doesn't, though, if you have, eg, an ultracapacitor on the head unit supply).

Also, it would be a good idea to check that the connections to the battery are clean and secure, given that you are messing around with the battery terminals, because high and non-linear resistances there can cause weird problems, and make measurement difficult. If you have, say, 0.5 volts drop at a battery terminal, then the battery voltage is probably 0.5 volt, or more, different from what you measure it as, depending on exactly where you connect the DVM leads.

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