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so it was very cold in my country last week and my car alternator died. I took it out and I found that one coil wire, which connects to rectifier is broken and there is no contact (I guess it could break because of -22 Celsius freezing cold). I added picture with alternator wiring diagram ant point where the solder joint is broken. I can't understand how it affects working of alternator? Isn't it just one coil not working or does it affect inductivity of stator since three coils are joined together? Also I tried to read resistance of voltage regulator (two pins where it connects to 12 V) with multimeter and I had no resistance reading (resistance was above "1" on 2 mega ohm position of multimeter). So my question, is it normal to have no resistance reading on voltage regulator while it isn't connected to 12 V or do I have two problems (my voltage regulator died and I need to re-solder that joint)?

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So my question, is it normal to have no resistance reading on voltage regulator while it isn't connected to 12 V or do I have two problems (my voltage regulator died and I need to re-solder that joint)?

  1. high impedance is expected for linear regulators without bias.
  2. Solder joints worked in -40 'C in Winnipeg so they should work where you live. Just fix that with resin-core solder and check the rest. (marginal defect)

It appears you only lost 1 of 3 phases but that reduces efficiency to less than 1/3 max power for delta windings. I guess the car may have detected/indicated the fault or perhaps you did with the rear windshield heater and headlights or dead starter.

p.s. in my retirement, I moved to warmer climate.

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  • \$\begingroup\$ Thank you for your answer and comment about impedance. One automotive repair shop last year was changing brushes and slip-rings, so they did that soldering job and I guess they did it not so well. And yes, you guess it right, battery light came on, I checked charging voltage and it was below 12V. Well, I have been slightly missing winters this cold, but it turns out to be extreme conditions for automotive, not mentioning starting problems in the mornings. \$\endgroup\$
    – Vytautas Sirautas
    Jan 21, 2021 at 21:09
  • \$\begingroup\$ ah well it's a dry cold... we used electric heaters as std . equipment in the engine block "frost plugs" when needed < 30'C unless weak battery @ -20'C.. Nothing like crisp cool air in the warm sun. \$\endgroup\$
    – Tony Stewart EE75
    Jan 21, 2021 at 21:19
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Is it normal to have no resistance reading on voltage regulator while it isn't connected to 12 V?

This is possible. Automobile alternators come in many variations, over many decades, and it is not possible to say what measurement methods will work with yours. Could try asking on https://mechanics.stackexchange.com or similar. They will need to know the exact make and model, with photos.

or do I have two problems (my voltage regulator died and I need to re-solder that joint [too])?

That is also possible. The whole alternator may have catastrophically failed. Generally these are just replaced nowadays as servicing them is seldom successful. Try resoldering the broken phase and see if the battery light goes out. If that doesn't fix it (regulator bad also), get a new alternator. Note there is a chance in more modern cars that some of the circuitry is moved outside the alternator.

If there is an auto service center or auto parts store near you, call them and ask if they can test this removed alternator. They might test it at no cost (especially if they think it might create a purchase.)

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