Battery overcharging - Dash warning lights

[unofix]

Sorry wrong link posted: These are the real Ford schematics obtained via ETIS back in the day when that used to work.

This is for the S-Max 2013 schematics:

https://drive.google.com/file/d/1N-8lEMGMjmMMDkERSHuMddrUv2CbDfqB/view?usp=sharing

[unofix]

Not sure why you wouldn't have the option to reset the BMS in FORScan.

Next time you reconnect FORScan and it asks to load the vehicle profile it has already saved, answer NO and that will force it to a full rescan of all modules just encase something went wrong when it first scanned them.

There are 2 different methods of resetting the BMS depending on the vehicle and age. Don't be in a hurry for the battery light to flash, it can take a full 30 seconds before it does anything. Also make sure the drivers door is closed otherwise it often doesn't work.

 

[unofix]

How to reset the BMS - both methods:

 

[laserhalen]

Thanks, got the schematics.

Tomorrow i will get the alternator tested by a specialist. He questioned, same as you, how it is putting out 16v when the LINbus is disconnected. He was also asking why I didn't get a Ford packaged alternator from the main dealer considering I had to hand in my old core..anyway that is a different story.

If the alternator is bad then ill be buying a new one, albeit with a little trepidation in case there is something in my cars circuit that could be damaging it?

The alternator PN im getting on partslink is AG9T-10300-AA and the BMS cable is AG9N-10C679-DF (though it is AG9N-10C679-DE on the car)

Anyway ill keep you posted as to the results.

Thanks.

[unofix]

3 minutes ago, laserhalen said:

10C679-DE

The last letter is just the revision code. As long as the new harness has the last letter equal or higher than the original that's fine. 👍

[laserhalen]

Just back from the test - you were right i have a faulty alternator. A very sound guy who took my phone and recorded the behavior during the test. (Portlaoise Auto Electrical just in case anyone from midlands of Ireland is reading!) im pi**ed off that all this time it was a failed alternator after being reassured categorically that it was working fine. Im back to the main dealer now to see if they will replace it for a Valeo one.

At the same time I'm hoping as well that there is nothing on the car that has caused the damage to the alternator, though the Auto Electric guy said this is very unlikely.

so in the next couple of days ill post back to let you know how i get on, both in getting a new part and of course if that fixes the problem. lets see.

I don't think i can attach the video so there are a few screenshots of different stages in the test. if the video is of any value to you dm me and i could save it to a google drive or something.

thanks.

[unofix]

Thank you for the update on the alternator problem.

I'd agree with the guy that it is extremely unlikely that anything on your car could cause damage to the alternator.

The real concern is has the alternator caused any harm to electrical equipment on the car. After all the system is generally expecting 13.6V nominal with charging voltage rising to 14.8V what it is not designed to tolerate is  sustained voltages 17.2V or more.

Do get back and let us know how things turn out with a new alternator fitted. 😀

[Tdci-Peter]

On 4/2/2023 at 7:59 PM, laserhalen said:

Still the voltage at the battery is 16++

I posted this before I saw the 2nd page! Mistake I have made before. All major automotive electronics are specified to withstand a lot more than 16v, usually up to at least 24v for short periods. Things like radios and many add-on goodies may be more sensitive. So I am optimistic there will not be damage to any critical parts, but the battery will have had its life seriously shortened. I would ask whoever supplied & then failed to spot the failed part, to replace the battery as well as the alternator.

This is what I scribbled before seeing this page:

16v plus with LIN connected or disconnected sounds like an alternator with a dead regulator that is putting full voltage on the field winding all the time. Power transistors that fail usually go short circuit, so this is quite possible.

 

On 4/2/2023 at 7:59 PM, laserhalen said:

i'm not getting consistent resistance readings from this but the best i got was 3.4 3.5ohms at battery terminal direct and 2.5 from the other side of the BMS

Taking good readings of low resistances is almost impossible with any battery powered meter. You need to inject quite a big current (say 1A or so) to get a practically measurable voltage on a low resistance system. And use a 4 wire (Kelvin) connection, or you are just measuring test lead & contact resistance.

In circuits carrying a few 100 amps, anything over 0.01ohms is big. 100A times 0.01 ohms is 1v, and would give a 100W power dissipation in the resistance. If it was a bad contact it would get very hot. Assuming the BMS sensor can carry full alternator current & possibly starter motor current (600A to 800A quite often), I would expect it to have about 1milli-ohm (0.001 ohm) resistance. You won't measure that with any conventional meter.

The best way, (but not necessarily the safest or easiest!) to look for bad connections in high current circuits is trying to measure voltage drops with the alternator running. An infra-red thermometer is a safer but less direct way to look for the resulting hot spots.

 

[laserhalen]

thanks that's very good info there. i didn't drive 10 miles with the new alternator on and every time i was testing it in the interim i switched it off immediately (from idle) when i saw the overvoltage. (whether it was the message on the dash or my own measurement at the battery). but im noting your advice on the battery life.

i'm disappointed in the main dealer, but i'm telling myself its a genuine mistake!!

They offered me a same make replacement, but I want a Valeo one. That's 140 more expensive (roughly the cost of my new battery!) so i'm going back to the AutoElectric guy, I want to give him a turn anyway hes doing the Valeo one cheaper than the aftermarket brand I was originally sold. plus he tests everything he hands over even if its brand new!

all going well ill have it back on the car Friday morning. lets see how it goes.

[laserhalen]

hi, i'm late posting but only got a chance to get it all back together yesterday.

Fitted the alternator Friday afternoon, car hasn't been driven yet but dare i say it so far so good!

So the new new alternator wasn't a Valeo turned out it was a Bosch, as I said I fitted it Friday, literally threw it on and run the car was all I had time to do. Yesterday evening went back at it, I had a few things to do, fit back both wheelarch liners (I had the one on the passenger side off checking wiring to the ECU), refit battery, air filter, covers etc around the fuel filter and lastly the aforementioned M12 engine mounting stud I had to run a tap through it as I had cross threaded it way back.

Car has run about 10 mins in total since. I can say a number of things that mean the signs are good:

• Voltage measures 14.8 by multimeter at the battery
• Engine is not hunting.
• Lights are behaving normally when you rev the car (interior footwell lights were varying in brightness when you rev the car, and daytime running lights would flicker)
• Traces are normal, see attached. I wouldn't know anything about this only for@unofix comment about the noise on my earlier ones.
• No overvoltage warning. yet.

I wont get to drive it until next week and Ill hopefully be able to confirm then that all is ok but regardless of the outcome I want to say a strong thanks for the help I received here. I don't care how simple the fix might have turned out to be, if it wasn't for the advice I got I don't know how long id stay messing with it! And the brains/expertise that turned up was excellent, I learned a few things.

Thanks.

After starting this originally as my own thread I hijacked this one as it was a similar post. If it helps anyone in the forum I could put up a single post on symptom cause and fix? 

[unofix]

2 minutes ago, laserhalen said:

Traces are normal, see attached.

Those traces are excellent, nice and clear with no noise. Alternator is outputting 'pure' DC without any extra bits 😀

[Tdci-Peter]

11 hours ago, laserhalen said:

I could put up a single post on symptom cause and fix? 

The simplest thing would be to put a link in your original thread across to this one.

Just copy the link that is where it says "Posted (date)" at the top of any post in this thread, and paste it into a new post in the other thread. Then anyone following the other thread can get straight here.

If you prefer to do it the other way, copying relevant info from this one into the other thread to make a simpler, edited thread, that would be fine too, but is more work!

The new traces look do much better, the C_Volt trace looks rough, but is actually only 0.1v, boosted up by Forscan's crude auto-scaling.  I guess that is some sort of regulation or feedback control signal, and shows the alternator is giving a steady output.

 

[laserhalen]

Thanks done that!

Now I have a few questions which aren't relevant to the issue anymore so there's no problem if you don't answer them.

I wondered whether C_Volt was the voltage commanded from the ECU or the actual charging voltage achieved by the alternator?

The guy at the main dealers referred to the signal from the ECU to the Alternator as the PWM.. I didn't go into it with him but I know a little about PWM from control of hydraulic valves. its not PWM in my car is it? - i thought it was a command sent via LINBus to a module to the alternators module or "receiver", is that correct?

[unofix]

C Volts (Computer Controlled) or (Charge Control) This terminal is an input signal from the ECU which controls the charge rate. This signal will tell the alternator when to stop/start charging.

It is PWM when the signal is high the alternator is in charge mode. The PWM ratio changes depending on the load on the vehicles system. The bigger the load the longer the signal will remain high.

[Tdci-Peter]

11 hours ago, laserhalen said:

I know a little about PWM from control of hydraulic valves. its not PWM in my car is it? - i thought it was a command sent via LINBus to a module to the alternators module or "receiver", is that correct?

Yes. And Unofix is virtually correct, but the physical implementation is a bit different on a 1 pin (LIN) alternator.

C_Volts must be a software value in the ECU, stored in a register there, and that is what is read by Forscan. The ECU converts it into a packet of digital information in LIN bus format, and sends it to the alternator. Here the little LIN processor will receive the packet, recover the stored value, and generate a PWM output with the set % of duty. Then it is the same as an older smart alternator I guess, and the Field coil is simply PWM modulated by that output to control the voltage output.

LIN is just a version of the old COM port or RS-232 style serial data interface that has been used since the 1960s, at least at a basic level. It is the protocol used that makes it LIN. It is cheaper, simpler & slower than CAN or other bus systems like USB or ethernet.

In cars, and almost all electrical equipment, power circuits will be controlled by some sort of PWM system, the old Triac light dimmer is a crude & simple example. Most resistive and inductive loads respond well to direct PWM control, it saves wasting a lot of energy compared trying to drop the voltage in a continuous manner using a dropper resistor or power transistor, and saves expensive heatsinks etc. Capacitive loads like most LED lighting power supplies and electronic compact fluorescent lamps may not work at all well with direct PWM, and would require a filter.