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Story of Punto's sudden battery death

Discussion in 'Engine Compartment' started by RaviHegde, Apr 7, 2014.

  1. bhai

    bhai Esperto

    Messages:
    1,183
    Ahmednagar
    Grande Punto 1.3 90 HP
    Thanx Ravi to writing this useful & informative topic. You did it DIY.

    Today I checked my AC button. I killed engine without putting air-con OFF.

    After that I gave turned key to MAR position only gave ignition.I didn't start engine.
    Blower of Air-con didn't came ON.

    As per your statement blower ought to have started after giving ignition due to its memory function
    But didn't happened as per statement quoted by you. If I am not wrong other cars also has same feature.

    I mean if I forget to put OFF Air-Con of my M SX4,it also restart at next ignition. But battery of my SX4 doesn't discharge.
    If this is common in all cars then battery of other cars should also discharge. Please clarify.

    P.S. :- Still I will check again. Because battery of 4 month old SX4 discharged within 3-4 hrs due to some unknown reason.
    Last edited: May 1, 2014
  2. RaviHegde

    RaviHegde Regolare

    Messages:
    299
    Karnataka
    14.62°N 74.85°E
    Grande Punto 1.4
    I am not referring to the memory function. Let me explain so that it is clear. Please bear with me if this is too much information.

    Under normal circumstances (when the AC relay is functioning properly) car electrical switches off the AC relay, and that in turn disconnects the compressor clutch (which is a pretty powerful electro magnet) and that in turn disengages the compressor from the engine. When we switch on the AC this relay connects the AC compressor electro magnet to the battery and that in turn engages the compressor to the engine. AC relay can malfunction in 2 ways:

    1. A conventional mechanical relay has a small actuator electro magnet inside it for moving the contact points. This actuator electro magnet winding may burn out causing the relay not to turn on. Or the relay contact points may burn out. Any of these will end up in one end result - it will fail to switch on the compressor clutch electro magnet when the AC is switched on. End effect is no AC cooling. On the dash you see AC is on, but no cooling because the compressor is not running. I have not experienced this situation in my car (yet!). [Note: Latest generation of relays called solid state relays don't use any electro magnet or moving parts. They use semi conductors like transistors/triacs/FETs. This discussion does not apply to them completely. However, solid state relays can also fail to turn on leading to similar end result.]

    2. Relay contacts may short circuit ending up with a permanent connection to the compressor clutch electro magnet, whether the ignition is on or not or the AC is switched on or not. Nothing matters in this situation. As long as the battery is connected to the car electricals, AC relay keeps the compressor engaged to the engine! I have experienced this mode of AC relay failure.

    Please relook at what I told with this background. This is what I mean when I say it is a design defect: Ignition switch is not a master switch disconnecting everything in the car (except crucial circuits like the remote lock and security system - they should be always on for obvious reasons). Battery is connected to many relays even when ignition is switched off. Any of them going bad can connect the load to the battery and kill it when the ignition is switched off. This is a major design defect in my opinion. Either Fiat should put good quality relays that don't short circuit OR they should install a master relay to disconnect everything in the car (except remote lock and security system) from the battery when the ignition is switched off. Former is an easier and better solution than latter needing very high quality and very high current rating relay.

    Another possible solution is - alert the driver when there is more than a threshold current flowing from the battery when the engine is switched off. This takes care of not only failed relays, it is also useful to alert the driver when s/he leaves a cabin light on or a bad switch in the boot keeps the boot light on without the driver knowing about it. This should be fairly simple and low cost to implement with today's electronics. It takes a very small sub-set of multi-meter circuit to implement this. A reasonably good digital multi meter costs less than 1000 Rs. today. At Fiat scale it should not cost more than 250-500 Rs. to implement this. A small cost but big advantage. Hope Fiat considers this!
    1 person likes this.
  3. puntosat

    puntosat Superiore

    Messages:
    588
    Bangalore
    I experienced a dead battery couple of days back...

    The car had run about 200 kms 2 days before the dead battery day...

    I had to jump start...
  4. RaviHegde

    RaviHegde Regolare

    Messages:
    299
    Karnataka
    14.62°N 74.85°E
    Grande Punto 1.4
    Finally after almost 4 weeks waiting experimental relay I ordered from Kits n Spares arrived. On the website they say delivery time is 2 weeks. But they conveniently forget it. I had to remind them over email several times and also call them to follow up. Looks like Kits n Spares is a sleepy company. Their partner element14 seems to be the worse because Kits n Spares responded to my queries quickly. Their queries forwarded to element14 (cc'd to me) were not responded by element14 at all. So, be warned - element14 is very bad to deal with.

    Though website has displayed Panasonic relay, what I got is not from Panasonic. It is made in Japan manufactured by Matsushita. This is the data sheet: CB1A-12V pdf, CB1A-12V description, CB1A-12V datasheets, CB1A-12V view ::: ALLDATASHEET :::. I am very happy about relay quality because this is a top quality relay. Sorry, I cannot post the internals here because it is totally sealed water tight and air tight with a small rubber plug in the only small hole it has on the base. Outer casing is so nicely moulded and fused to the base. Contacts have nice shiny coating. Everything screams quality! Only catch is - this relay has a different pinout. I knew its pinout is going to be different, but still ordered it to try a small DIY project. My idea is to solder the wires from old relay base to appropriate contacts of this relay to convert it :) I will try my hands on it in a few days and post the result.
    Last edited: May 9, 2014
  5. kirenh

    kirenh Regolare

    Messages:
    421
    Mumbai/Pune
    Pune
    Grande Punto 1.3 90 HP
    AFAIK Matsushita is a Panasonic company only.

    Kiran
  6. RaviHegde

    RaviHegde Regolare

    Messages:
    299
    Karnataka
    14.62°N 74.85°E
    Grande Punto 1.4
    I did not know that. Thanks for the information Kiran :)
  7. asimpleson

    asimpleson Esperto

    Messages:
    2,999
    Heptanesia
    Linea 1.3
    Yes Matshushita is even better. More authentic.. :D

    IIRC, they imported and sold Washing Machines under National brand initially in India.
    Incidentally, they do have a plant at Ranjangaon for many years where Fiat manufactures cars. :)

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