Thread: Alternator Volts?

Originally Posted by Aaron IIA

The alternator should put out a constant voltage, providing that it's output is not exceeded and sufficient rotational velocity is maintained. It is the current that varies to suit the load. Measure the voltage at the alternator output terminal.
Aaron

are you sure it's not the other way around ... at least partially?

We're on the road ATM for 16 days ... So been watching the battery status daily. Morning Start and the voltage starts at about 14.4-14.6v .... After a short time it drops to 14.2-14.3v .... battery recovering after overnight lights, fridge,etc .... Then depending on what's charging like laptop, iPads, iPhones, camera, fridge running (set it to -5 while driving) after about an hour or so it floats between 13.8-14.2. When we stop for the night battery reads 12.7v .... All readings per nanocom and matched by the voltmeter at the fridge in the back.

Your readings sound way to low Pedro .... ???

Sent from our campsite at the Black Stump, Coolah.

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Yes. At least in standard systems. Some modern systems reduce the operating voltage after a while to reduce fuel consumption. This makes it hard to charge a flat second battery.
Aaron.

I will check the volts at the alternator terminals... I have figured out a way to charge the car from the vans solar panels😆

Mick---- the battery is about 12 months old

Originally Posted by Aaron IIA

The alternator should put out a constant voltage, providing that it's output is not exceeded and sufficient rotational velocity is maintained. It is the current that varies to suit the load. Measure the voltage at the alternator output terminal.
Aaron

That’s spot on the money, it’s the current that varies, to suit the load, but you should always take the voltage readings at the cranking battery’s terminals, not at the alternator.

It‘s of no importance what the voltage is at the alternator’s output, it’s the voltage at the cranking battery that is the actual charging voltage.

Newer vehicles now come with thick cabling between the alternator and the cranking battery so the voltage difference will be small, if the battery is not in a low state and the cable run between the alternator and the cranking battery is relatively short.

But with older vehicles, because they usually had thinner cabling between the alternator and the cranking battery, the voltage difference can be quite large

But by taking the voltage reading at the cranking battery, you get the correct charging voltage reading.

I have a plug in meter on the cigarette plug in the cabin. My current reads 13.9 when driving and drops when stopped. The alternator was rebuilt last year so I assume its running normally. Battery fully charged is 12.6 but usually floats above that. I understood the alternator's output didn't change but the current in the system varied dependng on load.

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on the D2(cos that's what we are speaking about here) there's no direct cable between the alternator and the battery, the alternator's output goes into the fusebox where it splits between all the systems and the battery cos it was conceived to bear the systems while the engine is running and charge the battery at the same time... its one subject what's the charging voltage at the battery positive terminal and other subject what's the alternator output voltage depends on what we are speaking here...at the alternator's output or at the fusebox before it splits to battery the voltage varies between 13.5 and 14.5 on a well working D2 charging system as it was built depending on system's load(current drain), engine revs and the stage of battery charge... that's how it happens in real life, any voltage reading which is out of this range means that something is wrong(could be many reasons) and investigations are needed