Feb 262014
 

2009 VW Jetta

Dealer recently replaced battery and fuse/relay box. Now they are trying to sell me an alternator. My car has only 55k miles. Service adviser said they performed a load test while replacing the battery. They said alternator is producing excess ripple and will continue to work until diode burns out and car will no longer crank. They said I may have to jump start. Battery voltage 12.41; charging voltage 14.32 ; battery voltage after turning engine off 12.71.
Did AC ripple test at battery and read 0.047-0.051 volts AC or 47-51 mV AC.
The lights are not dimming, never had to jump car, battery light on dash never appeared. Why is the dealer trying to sell me an alternator?

  2 Responses to “2009 Volkswagen Jetta 2.5”

  1. My first thought for a reason they would try to sell you an alternator would be so they can make money. That is what they are in business for is it not?

    If you do not feel that you want to purchase an alternator, then don’t buy it. You are not required to buy it if you do not want to. This is an opportunity for them to up-sell…. you know, would you like fries with that?

    Battery manufacturers recommend that under normal float charge conditions, battery ripple RMS (Root Mean Square) voltage must be limited to <0.5 % of the DC voltage applied to the battery.

    Take a digital meter and set it to AC mode. Select a voltage range to read approximately 2 volts. Start engine and let idle. Negative lead to ground and positive lead to BATT+ lead on the back of the alternator. You should have less than 0.1 volt AC. The lower this value the better. Ideally, an oscilloscope would be a better instrument to use but not everyone has one.

    Yours read 0.047-0.051 volts well below 0.1 volts. You are right to question spending money when you don’t need to.

  2. I took the AC ripple measurement at the battery. Black lead to negative post, red lead to positive post. Those were the readings in AC volts. Is it as accurate as the positive lead to the back of the alternator. I have a digital automotive multimeter PDI.

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