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Battery Failure Causes

Battery problems

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7 replies to this topic

#1 OFFLINE   kaptnk228


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Posted 06 November 2014 - 09:44 PM

6 Nov 2014


This is an update to my post regarding monitoring your battery.


After 2 weeks, we got our C-Max back from the dealer after our first battery failure.


Our Cause:


1. The Dc/DC converter that charges the battery seems to have failed and was replaced

2. The battery was dead and was replaced

3. They could not get the proper 14.4+ volts across the battery.  They were getting some where near 13.5 V  Cause: Replace a high power/amp fuse with the heavy cable.

After the fuse was replaced, everything worked again.  A thermal camera would have shown the component that was hot or dumping the battery power.


Outstanding issues:


Nothing here fixes the battery monitoring system and low battery setting of 12 Volts.  I suspect that this will require a software upgrade

Yes, the Engineering test mode has a battery or voltage monitor.  We are now getting 14.3-14.4 V.  You can't use it while using the standard instrumentation.  You can only access it

at startup while holding the ok button.  The coolant temp is also there but not much good unless you leave it in ETM.


So I still want an accessible battery and engine coolant gauge while I am driving down the road.


Ford has come through for us in fixing what appears to be the root cause of the battery failure ie a short in the fuse.  I will give you the name when I get it.


Trust all will be okay in the morning.  I am still going to use our 12 V battery monitor while driving to make sure  everything is working okay.  Way to go Ford.  Our lives are surely worth more than $2.40 as per GM while the GM pig CEO made $42 million a year.  Now fix the BMS alarm.


These may NOT be the only causes of a failed battery but they appear to most likely what is causing a lot of people problems.  One person related wires damaged from a leak of the water pump.

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#2 OFFLINE   Zathrus


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Posted 06 November 2014 - 11:11 PM

Just an observation...I think the 3 failures you list are related. I suspect failure 3 occurred first (and is something I have not seen reported in this forum yet). This high impedance wiring/fuse short most likely stressed the DC/DC converter components, causing it to fail. DC/DC converter's failure ultimately caused 12V battery failure. The 14.4V charge level you are now seeing is about right, The 12V resting voltage (with car off) should be 12.2 - 12.7 (= 50% to 100% SOC). I place my 12V battery monitor in rear hatch 12V outlet to montior battery resting voltage (this outlet remains connected to battery with car off). Let us know the fuse number/name when you get it. Thanks.

#3 OFFLINE   Bill-N


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Posted 07 November 2014 - 09:58 AM

So I still want an accessible battery and engine coolant gauge while I am driving down the road.


Coolant temp is available as part of MyView.  See owners manual for details.

#4 OFFLINE   ptjones


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Posted 07 November 2014 - 10:10 AM

You could get a ScanGauge II so you could monitor all ICE and Batt. #s, that's what I have. :)



#5 OFFLINE   SanDiegoDP


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Posted 06 March 2015 - 08:49 PM

I'm a bit new here.    Are there many cable junctions between the DC/DC converter and the 12V battery?


If there is no charging-system voltage monitor _at_ the battery, and the output of the DC/DC converter runs at a fixed voltage output of say at 14.4 V, and that voltage encounters any significant resistance on the way to the battery, then the DC/DC converter can run all it wants to, but it won't succeed in pulling the battery all the way up to full charge in a normal length of time if at all. 


Ideally, there would be a remote voltage sense _at_ the battery, and the DC/DC output would servo its output voltage to the value required to put 14.4V _at_ the battery.  That remote sensing is a standard practice in delivering high current to voltage sensitive loads for exactly the reason kaptnk228 experienced.  If you get even 0.1 Ohms at a cruddy connector or fuse junction, then your 10-20 amps of charging current yanks 1 to 2 volts off the applied voltage and the battery would see only 13.4 to 12.4 V during charging, and that won't keep the battery strong for long.


From the sound of it, having a voltage monitor in one of the 12V ports is a simple and effective way to detect the problem before the 12V battery dies from repeated insufficient charging.

#6 OFFLINE   Adrian_L


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Posted 06 March 2015 - 09:13 PM

I've been a year and I think we've ruled out bad batteries and, slow parasitic drains, but nobody has figured out why the SE model seems most vulnerable and the SEL and Energi (all SEL) are less prone to the problem.


If the battery does die from repeated insufficient charging, then why has nobody reported dead cars after being in Walmart for two hours or after the morning dentist appointment.  They ALL seem to be after the car has been sitting through the night.


Certainly no harm in hooking up a voltmeter (there was a thread on $2 cig.lighter ones before) and monitoring the results.


SPL Tech

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Posted 07 March 2015 - 12:01 AM

FYI the Cmax does have remote voltage sensing. There are sensors on both the + and - battery terminals. I dont know what the ECU does with that information though, and I do not know where the voltage value that shows up on the dash is measured from.

#8 OFFLINE   SanDiegoDP


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Posted 08 March 2015 - 01:31 AM

Hi Adrian,


I'll put forth a hypothesis as to why the SE is more susceptible to these failures than the higher end models...  The SE does not have the Ford My Touch Electronics system, correct?  So with that missing, and maybe a few other less fancy power consuming options, it probably has a significantly _smaller_ current load on the 12 V system.   Am I correct in assuming that most of the electrical equipment in the vehicle runs off the 12 V system regardless of whether the vehicle is on or off?  Restated, everything runs off the 12 V system, and the 12V is fed by the DC/DC converter from the HV battery as required.  Right?


That's a lot of current to supply.  So the DC/DC is a pretty high current output device.  Right?  (Anyone know it's output current rating and/or architecture, i.e. PWM or zero-crossing type?)  I will assume that Ford hasn't done anything fancy with the systems design of that device, and used a single converter (although the converters are getting pretty sophisticated these days).  Most DC/DC converters require a minimum load to operate nicely, and are not designed to handle a really wide range of load currents.  They may be optimized to handle the heavy current load well, but at some compromise to the low current end of performance.  I'll assume that Ford chose (logically) to optimize the performance at the high-current end of operation.  The voltage output, the voltage ripple, and the switching noise (in the case of a PWM system) all vary as a function of load current.  I'm going to speculate that the SE current draw is frequently low enough that when the vehicle is trying to charge the battery, the DC/DC converter is only marginally nice about some aspect of it's output; maybe it's output voltage is not well regulated, either a bit too high or low, or the voltage noise and ripple on it is too large.  All of these deviations would be bad for a lead acid battery over time.


Too high a voltage will corrode the positive plate of the battery and lead to premature capacity failure (and also electrolyte loss).  Too low a voltage will undercharge the battery, lead to sulfation of the negative plates, and again premature capacity failure of the battery.  Too much voltage ripple, and you might get both symptoms.


My speculation is the the extra current draw of the systems in the SEL and fancier models puts a heavier load on the DC/DC converter, and thereby puts that converter into a more favorable portion of its design window (higher current output) where it operates more efficiently and with better tolerances on its output voltage, voltage ripple and noise.  The lighter load of the SE vehicle may put the DC/DC converter close to its lower current limit on decent operation where it fails in some way to keep the battery properly charged.


This hypothesis might be tested by putting an oscilloscope on the 12 V system and recording not only the DC value of voltage, but also the ripple and switching noise on it as well.     Just a hypothesis....  (Note that this issue is independent of the other issue that kaptnk228 experienced which may be the unwanted resistance in some cable connector or fuse somewhere in the charging system which probably also lead to the prolonged undercharging and capacity loss of his battery.)


I'll also take a stab at why the failures occur primarily overnight, and not after just a couple hours in the parking lot at work...  If the vehicle is not charging the battery properly, and the battery is progressively losing capacity over time, then the normal drains on the battery as the vehicle periodically uses current in the off state (as people have seen) become a more serious challenge for the battery.  Now assuming the vehicle experiences more total "wakeup and use some current"  events over an 8 hour night than a 2 hour stop at the shopping mall,  then the first time the battery will fail to hold sufficient voltage to boot the vehicle is naturally going to occur after the longer overnight string of drains rather than just a 2 hour string of drains (regardless of whether these drains are normal or otherwise).  It's simply a consequence of the slowly diminishing capacity of the (12V) battery.



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