Battery charge problems

Tiny
ATACAMA
  • MEMBER
  • 2002 HYUNDAI TERRACAN
  • 67,000 MILES
I have a 2002 Terracan with a new battery. The battery dealer on checking the charge for warranty validation informed me that it was not charging sufficiently. On removing the alternator, my mechanic/auto electrician found the voltage regulator burnt out, so that was replaced, along with new brushes (included with the new voltage regulator). Now all back together and still will not reach the required 14.2 volt charge required for the battery warranty. Any ideas why, even with a new voltage regulator, it would not charge enough? Currently showing around 13.7 volts, which can drop to below 13 with all lights on.
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Tuesday, May 7th, 2013 AT 11:28 AM

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Tiny
ASEMASTER6371
  • EXPERT
More failure in the alternator. Replace it with a new or rebuilt unit

Roy
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Tuesday, May 7th, 2013 AT 5:40 PM
Tiny
CARADIODOC
  • EXPERT
Low voltage is not the cause, it's the symptom. The generator should be professionally load-tested for current output and "ripple". What you're describing is typically caused by one bad diode of the six. That will reduce the current to exactly one third of its design rating which is not enough to run the entire electrical system under all conditions. The battery will have to make up the difference. For the common 90 amp generator all you'll get is 30 amps.

When the generator can't deliver the needed current it can't build up system pressure, which means voltage. The voltage regulator won't even kick in yet and do anything until system voltage gets to around 14.5 to 14.75 volts.

Think of a pressure relief valve on an air compressor or hot water heater. They open to release pressure only if the controls fail and pressure gets too high. If the pump can't develop the needed pressure you don't fix that by replacing the pressure-relief valve. You have to fix the pump. Your mechanic replaced the pressure-relief valve, so to speak, and expected the voltage to be higher. Voltage regulators can fail that way, but it is extremely uncommon. The weak pump, (generator), is almost always the cause of the low system voltage. The diodes can be replaced in a block of six or two blocks of three, but it's very time-consuming so it's always less expensive to just replace the entire generator.
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Tuesday, May 7th, 2013 AT 6:19 PM

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