Technical Alternator trouble or worse?

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Technical Alternator trouble or worse?

JohnE222

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Hello.
I have a Fiat Ducato based camper. When I start the engine, after about 20 - 25 seconds the engine battery light comes on and the engine speeds up a little.

Also, during the first 20 - 25 secs. with battery light off, there is a discharge from the habitation battery until the engine battery light illuminates. The habitation battery then shows no further discharge.

I've checked the engine battery with a multimeter. The voltage across the engine battery terminals shows only 12.8 volts with the engine running so it looks like I have a faulty alternator. No charge to either engine nor habitation battery.

Have I just an alternator problem or is there more lurking?

Cheers, John
 
John. I don't know what model van you have but on my van when I start it and let it idle it does the same as yours but when I start it and a few seconds later plip the throttle it the starts charging and is fine.

I know this works on my van as I have a smart charger connector fitted that shows the battery state and it shows green or amber before turning the key then red on startup and turns green after giving it a few revs


Mike
 
I have a similar condition on my motorhome. Sometimes when I start the battery light stays on. I gently raise the revs to about 1000rpm and the light goes out and stays out when I let the revs return to idle. It never comes on whilst driving. I know the alternator is not charging when the lamp is on because the fridge 12v indicator is flashing that no 12v is available.
 
Saw this on the web; "Often not well known is that alternators do not produce voltage/current as soon as they start to spin. There is a zero-ampere speed at which the alternator reaches its rated voltage before it can generate any current. This is typically 1000 rpm (500 engine rpm). I came up which the second figure because the alternator pulley on the bus is half the size of the engine fan pulley and so the alternator spins at twice the engine speed. Next in the series of important events during alternator spin up is the idling speed: typically at 1500 rpm (750 engine rpm) the alternator must be able to satisfy the needs for long term consumers (basic electrical demands) without running down the battery.

Just above the idle speed is the cut-in speed at which the alternator begins to deliver current for the first time. The exact speed depends on the battery voltage, voltage from the alternator warning light (pre-excitation power), the rate of change of rotational-speed and the magnetic remanence of the rotor's magnets. If you've started your engine and "heard" the alternator slow down the engine at the beginning of fast idle warm-up this is the cut-in speed heard in action.
http://www.ratwell.com/technical/ChargingSystem.html
 
I've just had a thought, :confused:.

Although the van has only done 26000 miles, (an 08 plate), it still has the original engine battery.

Could it be that this old battery is not holding charge as well as it should and is therefore making the alternator work too much?

I'm trying to fathom a reason as to why the alternator failed.

I reckon a new battery at the same time as a new alternator is a good idea.

Thanks again to all you helpful folks.

John.
 
You could check out the earthing, negative terminal to bodywork, and to the engine block. Cable terminal connectors or the cables themselves can corrode over time?
IF this is the cause, it's cheaper than a new alternator!
 
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