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Calling any automotive electrical gods. Not 7 related


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Help required please. 

I’ve had since new a 2014 1.6 Transit Connect van. In cold weather it starts first time straight away which is a good thing, but the cranking speed is not brilliant. I checked the alternator charging voltage early one cold morning and found the following voltages.
9.58 volts Lowest reading during starting.
15.83 volts Max/Peak. Putting all electrical equipment on. Maybe a spiked reading.
14.74 volts average (approx 10 minute period)
14.90 volts live reading.
All these were pretty much at tickover.
Any technical bods that can say that this 14.90 volts is cooking my battery as I’m thinking that 14.2 volts Max would be the safe limit?
Thanks in advance.

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I am by no means a god, but I would think the battery has a problem if you see up to 15.83 volts.

What do you measure with?

There will of course be ripple on the battery, but 14.74 V also seem on the high side. 14.2 is as you say around the max voltage.

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Rj - Measured it with a Fluke meter with a min/max/avg reading, so should be accurate. 

I don’t want to buy another battery if the alternator’s voltage regulator is feeding the battery with too many volts as it will just fry the new one. My daughter has an older Connect van and this also has quite a high voltage output at 14.64 volts, making me think that this may be normal. 

Boss - I could check the voltage drop along the cables to the starter but it’s so tight and awkward under the bonnet. I’ll give it a go on Saturday.


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If you measure across the battery it's unlikely to be a loose connection that causes overcharging. The only way that could happen was if it was a reference wire that feeds back to the ECU that's broken.

You don't by any chance have access to a scope? I would be interested in seeing the curve and to see if the voltage regulator actually is regulating.

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I’ve just sent this reply to Johnathan Kay’s email.

Somebody from Pistonheads mentioned something about smart charging systems on vehicles nowadays which I’ve now read about. When needs arise the battery can receive up to 16 volts based on the outside and engine temperatures etc. I don’t know whether my van has this and I’ll need to check but it has given me some reassurance that it is possible for a lead acid battery to received up to 16 volts for a controlled amount of time. My van luckily does start first time otherwise I think I would be having problems a lot sooner. So it may be that my battery life is prematurely failing. I’ll probably just see how it goes and replace the battery as and when and maybe call into Fords and pick their brains. 

No access to a scope but I would say that the voltage is stable. I think I’ll perform the same min/max test etc with the engine hot just to see if the smart system (if it has one) drops the voltage down.



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I very much doubt it sould go as far as 16V.

There's a little about Fords smart charge here:


At 16V most batteries would be boiling - which you want for the batteries used in a forklift - I don't know the English term for it.

On the other hand, if your car has an AGM battery, then first time anything boils, the battery will be damaged.

If you want to push a healthy battery to 16V you'll need a significant current. If the battery is dead not. If you measure the voltage drop across the wire from the alternator to the battery you'll have an idea about the current. (or better still if you have a clamp current meter).


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