Wonky Alternator

Absolutely it could be that.

When I had lost the feed to the reg on my car, it would run ok due to self excitation from the altenator residual flux, but when I loaded it (Like turning on the headlights), the engine would skip a beat and the voltage of the whole car would go down.

No reg = no field current = low voltage under load.


Chay

That's more a sign of a busted voltage regulator (Stuck on boost).

 

An altenator requires higher field current for the voltage to go higher. This could only happen with good connections, and a reg stuck on boost, maxing out the field current.

 

Your voltage should not exceed 14.2 or so. Higher and your bat will cook.

 

Chay

Romeo wrote: Well, I took a reading of the new alternator and it's at 14.7V Maybe the battery will take that?

Did you measure open circuit...?

kharmata wrote: Romeo wrote: Well, I took a reading of the new alternator and it's at 14.7V Maybe the battery will take that? Did you measure open circuit...?

If you measure it when you first start the car (battery connected) - and perhaps the battery is not fully charged - the voltage will be higher for a short time and as the battery builds up bit more of a voltage drop the volts will drop.  If the battery is fully charged and you have this high...hmmm not sure. seems high.

To me, that's too high a voltage. Over the long term, my opinion is that it will cook.

Start the car and idle. Measure the voltage. Rev up the car slowly to 2500rpm or so. Does the voltage level off, or keep climbing incrementally over the next minute or so?

What does it top out at?

My experience is that the voltage works like this:

1) Before starting, lowest voltage at the battery
2) Start. Idle. voltage is sub 14.2. voltage increases as car is reved indicating increased ability to send current to the battery as the engine speed increases
3) Voltage tops out quickly (On a decent battery) at a max of 14.2 or so. Voltage should not creep. There should be a hard limit on the upper voltage

I found this after looking for a bit. Maybe 14.4 before it gasses...

I've never seen one top out that high though.

Voltages for common usages

These are general voltage ranges for six-cell lead-acid batteries:

• Open-circuit (quiescent) at full charge: 12.6 V to 12.8 V (2.10-2.13V per cell)
• Open-circuit at full discharge: 11.8 V to 12.0 V
• Loaded at full discharge: 10.5 V.
• Continuous-preservation (float) charging: 13.4 V for gelled electrolyte; 13.5 V for AGM (absorbed glass mat) and 13.8 V for flooded cells

1. All voltages are at 20 °C (68 °F), and must be adjusted -0.022V/°C for temperature changes.
2. Float voltage recommendations vary, according to the manufacturer's recommendation.
3. Precise float voltage (±0.05 V) is critical to longevity; insufficient voltage (causes sulfation) which is almost as detrimental as excessive voltage (causing corrosion and electrolyte loss)

• Typical (daily) charging: 14.2 V to 14.5 V (depending on manufacturer's recommendation)
• Equalization charging (for flooded lead acids): 15 V for no more than 2 hours. Battery temperature must be monitored.
• Gassing threshold: 14.4 V
• After full charge, terminal voltage drops quickly to 13.2 V and then slowly to 12.6 V.