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Alternator not working (properly)?


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6 replies to this topic

#1 heebok

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Posted 12 January 2021 - 09:11 PM

Hi all. My 2002 mk3 mondy smart charge doesn't seem to be working, no idea how long it's been like it but I've only just noticed the other day when I was do some unrelated tests and checked voltage at battery terminals while engine was running; it was only putting 13.6v in when I've read it should be closer to 14.8v (or there abouts), even when revving the engine, voltage seems to be fairly constant around the 13.6v mark. Voltage drops if I put all the electrics on (heater, seats, lights et) and seems to fluctuate around the 12.8/13.2v mark.

 

I don't have battery light on the dash, nor any fault codes logged according to my code reader. I've checked the alternator fuse (7.5a, I forget the number f30 I think) that was OK, checked the earth points under battery, undid them anyway and gave them a touch up and put them back on, no dice. In the end I decided might as well replace the battery since the one on it was getting a bit old anyway, so I bought a brand spanking new silver calcium hoping my luck would be in. It wasn't.

 

So I'm left thinking this is the alternator. Its obviously working to some degree but its only putting out the standard "dumb mode" charge, but i've read that the 3 pin plug on the alt can cause this problem too, is that more likely? Best I can tell is on the 3 pin plug, one wire is the 12v supply, one is the pcm control and one is the sense wire. But if one or more was broken wouldn't the battery light come on (as I say mine isn't on, and no fault codes either)?


Edited by heebok, 12 January 2021 - 09:13 PM.


#2 mondy zetecs

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Posted 12 January 2021 - 09:48 PM

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Mine is same only puts out 13.8v with no fault codes been like this for 3yrs. 


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#3 mike4369

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Posted 13 January 2021 - 11:04 AM

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 Voltage drops if I put all the electrics on (heater, seats, lights et) and seems to fluctuate around the 12.8/13.2v mark

This would suggest that the alternator is working OK as it is able to supply enough power to run the electrics.


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#4 PURPLE_2L_LX

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Posted 13 January 2021 - 05:38 PM

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Check the orange/yellow wire from the alternator to the battery

and fuse F30 (7.5amp).

 

That is the smart charge cable, although it maybe the alternator, several

versions and some are underpowered without the smartcharge.

 

13.8v is fine if your doing longer journeys, with lots of shorter ones you may

notice it doesnt charge the battery enough.


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MK4.5 TDCI 140 Business Estate.

 

MK3 FUSE INFO CLICK HERE ... FORD WIKI CLICK HERE .... FORD ETIS CLICK HERE

Adding your location may find someone local who could offer assistance.

F-Super, Bluetooth OBDII (ELM) and a MS509 scanners (test subjects required).

ForDiag now available to victims.


#5 heebok

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Posted 13 January 2021 - 08:43 PM

I'll do some more checks then, tho this prompted me to search for info in particular about that wire and the fuse and I came across this thread about a transit with smart charge issue, but seems like it probably applies here given it's ford; the second poster in that thread says voltage at that fuse should be identical to battery (makes sense given it's the 12v supply) and a high resistance at the fuse terminals can cause voltage drop which in turns makes smart charge drop out. He doesn't say what sort of resistance is 'normal' tho.

 

How would I go about finding out what the correct resistance should be do you think? I can just measure the resistance at the fuse terminals but I won't know if that's a higher than normal value, but, I dunno, I guess since battery voltage is supposed to match that at the terminals if I read what the battery says and do that ÷ the amps at fuse I'd get a resistance value that it's supposed to be closer to.

 

Or I could just pluck some base figures out of thin air and do 12.6v ÷ 7.5 = 1.68Ω and assume that when reading the resistance at the fuse anything higher than 1.7Ω means that's the culprit for the low smart charge voltage, but it doesn't sound very scientific. Or correct:

 

ihave.jpg



#6 PURPLE_2L_LX

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Posted 14 January 2021 - 02:32 PM

I don't think its 1.7 Ohms, at 14.2v that would be 8 amps/ 100+ watts?

 

 

I can see what your thinking but not sure thats the right answer. 

 

Personally i would check the voltage at the battery and the fuse and

then with the fuse fitted compare the voltage drop at the alternator.

 

You could use a small buck/boost converter to feed different voltages

to the alternator and see how that alters the charge rate.

 

Any idea what brand the alternator is?  I have a feeling the cheaper

aftermarket units don't have the correct circuit for the smartcharge.

 

Their Amps rating is often lower than the original item also.


MK4.5 TDCI 140 Business Estate.

 

MK3 FUSE INFO CLICK HERE ... FORD WIKI CLICK HERE .... FORD ETIS CLICK HERE

Adding your location may find someone local who could offer assistance.

F-Super, Bluetooth OBDII (ELM) and a MS509 scanners (test subjects required).

ForDiag now available to victims.


#7 nicam49

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Posted 14 January 2021 - 07:07 PM

I'm writing from memory here without cross-checking for accuracy, but I seem to recall that the smartcharge control wire to the alternator can become open-circuit for reasons I don't remember, so if you can trace that wire or at least disconnect the plug from the alternator and check for corrosion on the connectors and also with a multeter on ohms, and the ignition OFF measure that wire to earth as you should get a reading of sorts, and if the wire is open circuit, you should get a very high resistance, or even infinity.
<p><p>nicam49 2002 Mondeo TDCi Ghia X Estate mk3 pre facelift Stardust Silver+Rust.[b] 308,000+miles, but been off the road since Nov 2019 after timing chain slipped during fuel pump transplant. Awaiting return of mojo




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