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AdrianM

Diagnosing Smart Charge

13 posts in this topic

Hi all. We Just picked up a used C-MAX 08 with nice low mileage. However OEM Battery was flat when we went to drive away so garage swapped in a new battery. As might be expected it wasn't a Silver Calcium, but they assured us it was OK. Now I know it isn't really. But that can be sorted. What I am really concerned about is why the OEM battery was in such poor shape in the first place. It shows a high internal impedance so wont take or hold a decent charge. This leads me to suspect the charging system which is different to most other cars.

I understand that the battery temperature is estimated and only when considered cold is a full charge applied. So far I have not seen anything higher than 13.6V - even when cold and after running down to 11.5V by putting on headlights before starting. I was hoping to see 14.4V or higher after starting the engine under these conditions but it generally holds at around 13.6V most of the time.

As another test I switched on all the heavy electrical loads I could with the engine running and the battery voltage was around 12.5V and seemed to be falling slowly. I would have expected the alternator to do better than this.

SO given that the charging voltage is variable, under what conditions should we be able to measure 14.4V or higher? To me it seems as though something has gone wrong and the alternator is just putting out a "safe" maintenance charge only. Wish I could see the back of the altenator to check the leads but it's pretty inaccessible. Is it necessary to get to it from below (i.e. drop the panel covering the underside of the engine bay)

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Thanks for that link mintalkin.

Next, put a meter across the battery. Remember when you remove the smart charge 3 pin plug from the back of the alternator, it reverts to a conventional alternator! If you do not have about 13.8 volts, carry out basic charging system checks and suspect the alternator, its not a smart charge fault !

That's slightly confusing - is 13.8V supposed to be seen with the 3-pin plug removed? I wouldn't think so because reverting to a conventional alternator should put 14.4V on the battery. So assuming that this test is done with the plug in, then yes there's approx 13.8V on mine. So, according to the author, the alternator is OK and it's the smart charge system that's under suspicion.

I've measured the terminal voltage on the battery under a wide range of conditions now (e.g. fully charged, mostly discharged, hot, cold) and never seen over 13.7V so I'm still thinking that the smart charge system has gone into its own kind of "get you home mode". Given that I'm not going to attempt further diagnosis - as all I want to do is present the fault to the garage that sold me the car, this will have to do.

With a convention charging system it would be much more black & white - the absence of 14.4V or more on the battery would indicate a duff alternator, or wiring defect.

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Still none the wiser. Correct Siver Calcium battery now fitted and garage assures us the charging system has passed every check. However, I still haven't seen more than 13.8V at the battery terminals under any conditions. Using a scope I can see that all three phases of the alternator are there (diodes OK) but even when I deliberately skim the charge off the battery using the generous number of electrical loads the car can provide, still nothing higher than 13.8V appears on the battery with the engine revving and all other loads off. What is the smart charge thinking?

One other unhealthy looking thing is that even with the engine revving, switching on fogs, main beam, heated front/rear screens and full cabin fan - the alternator can't keep the battery voltage up above 12.2V Now I appreciate that there is a limit to the alternator output current (not sure what the C-MAX can manage - it looks pretty puny) but I can see the winter scenario where this may be an issue. Of course, the PCM will step in and cut the heavy loads when the "low voltage threshold" is met (rather than fit an alternator with adequate capacity?). Perhaps someone here could repeat this little experiment? Those who know how to get battery voltage up on the info display could do this quite easily.

I managed to get my multimeter on the battery of another C-MAX and after a few seconds of starting it rose to a reassuring 14.5V

To me, that's a tick in the box that I just can't give to our car yet - despite assurances to the contrary!

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Finally got the scope on the Alternator Load Request/feedback PWM signals on the back of the 3-way plug as per mintalkin's link. The request signal (PCM telling the alternator how strong the field should be) is virtually stuck at 43% positive duty cycle all the time. It doesn't make any difference if I apply all the heavy electrical loads or not - the PCM doesn't vary the request. The feedback from the alternator varies alot, 98% positive with all the loads on, and hunts widely around 50% with electrical loads off.

No loads:46620435.jpg Heavy loads:94046726.jpg

Yellow trace=feedback Blue=request

Now I'm trying to understand what this means. The PCM seems content with one fixed, moderate, rate of current generation no matter what. So the battery is taken to a middling 13.6V Adding electrical loads depresses the battery voltage but the PCM doesn't request more juice. This suggests that the PCM is making bad decisions!

I would still love to know what other people see when they monitor their battery voltage and progressively apply the big loads - something that can be done in under a minute while sitting behind the wheel ;)

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Hi Adrian, I´m a focus owner, so I have the same issue than you with the smart charging system. I made measures with a oscilloscope and I have the same results as you. The signal from de PCM never moves, with or without loads.

Please, could you tell me how did you solve this problem? did yoy change the PCM or Is possible to flash it??

Thanks

Greeting

Fede

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Hi Fede, well, this is still unresolved for us. The last attempt was to take the car to another Ford garage and have them run an independent test. The stupid answer was "It passed all the tests". When asked how it could "pass all the tests" yet remain stuck permanently at 13.7V nobody had a clue.

I finally used an OBDII tester to look up the PCM codes and sure enough the demand voltage is always the same so that explains what's seen on the PWM signals at the alternator. Like I concluded before, the PCM is making a seemingly odd decision to maintain a constant voltage at the battery.

Maybe this was an engineering decision on this year of vehicle - the silver calcium battery is less reliant on equalising charge according to some, I found one instance of them being used in a large array (for power line backup) and fed from a constant 13.8V to avoid the need for step-down conversion before the voltage was transformed (which hints at a dopey kind of invertor being used)

If so, it's a different stratedgy to that used with the same battery on a 2007 Diesel model I had my hands on. Not having a fleet of Fords to hand I turned to the next best thing (a Ford internet forum) but so far nobody seems to want to play.

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I have a 2008 1.8 TDCi C-Max and a multimeter. Can I help?

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I have a 2008 1.8 TDCi C-Max and a multimeter. Can I help?

Thanks. Good of you to offer! If your battery is the OEM silver calcium like ours and has the same charging strategy, then it would appear that you should never see more than 13.8V between the terminals when the engine is running

If however, as I suspect we will find, you measure 14.4V (especially with a warm engine) then we can say that there's either an unaccountable difference between charge regimes (for the same type of battery) on petrol and diesel models... or that our PCM has a fault that flies beneath the Ford diagnostics radar.

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Okay, I think I understand. I'll investigate tomorrow and post my findings.

Can I display battery voltage via the dashboard display then?

Dave

rafal_b likes this

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Hi Adrian, I've got Mondeo and similar alternator behaviour. After start voltage settles at around 13.7V (no load) then after switching lights, radio and fan goes down to 13.2V. During approx 45min trip from work it gradualy goes down to 12.7V (lights radio and heating fan on all the time.

I'm not an expert but in my opinion at 12.7V battery is not being charged at all. I'm bit worried that at some point my car won't start. Did your battery ever went flat because of that?

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Hi Adrian, I've got Mondeo and similar alternator behaviour. After start voltage settles at around 13.7V (no load) then after switching lights, radio and fan goes down to 13.2V. During approx 45min trip from work it gradualy goes down to 12.7V (lights radio and heating fan on all the time.

I'm not an expert but in my opinion at 12.7V battery is not being charged at all. I'm bit worried that at some point my car won't start. Did your battery ever went flat because of that?

sounds like your alternator is dying

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My multimeter measured 13.9V between the terminals with the engine idling.

I've had a starting problem twice in the last week, especially when cold. The battery was fine, there was just no ignition.

Not that it matters, the car was part-exchanged for a 2011 Titanium 1.6TDCi today....

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