TurboTommy

I know basically that the alternator uses engine power to turn and create a charge. I'm thinking that the regulator tells the the alternator when to draw power from the engine in order to do the work.
Is this true?
What determines this to happen? (important question)
Is the regulator a sensor of some sort?
Therefore with a strong/new battery the regulator should tell the alternator to work less often or less hard?
Is it totally an on/off scenario, or can there be various degrees of work drawn from the engine?
If its the on/off scenario and the alternator is in its "non working" mode shouldn't the in car voltmeter read only about 12 volts because there is no charge being produced on top of a 12 V battery? It almost always reads more than 12 V.

Sometimes when I start a cold engine the voltmeter will read almost 14 V, and sometimes it will read barely 13 V. on a cold engine. In both cases it's the same ambient temp and no accessories on.

I have a new battery and new aternator. I think the regulator comes with the alternator? My voltmeter reads correctly (had it checked).

If anybody is bored and feels like answering these questions; that would be great.

brad-cam

I have exactly the same problem. The voltmeter seems to have a mind of its own. It reads anywhere from about 12.5 to 14 under exactly the same conditions.

I'm also interested to know if there is anything I need to worried about. Everything is working fine otherwise.

Bengt Sweden

The regulator will keep a steady voltage around 14v. If the battery is low then the current to the battery will be high. When the battery is charged the voltage difference will be small and the charging low. The alternator has a limit though so if battery is low and lots of power consuming accessories are switched on then it can take some time to reach 14v.
Bengt

dmsog

There is no non-working mode. Amperage is the current going to the battery, and voltage is the pressure required to get it there. Picture this as water flowing from a faucet; the rate of flow would be the amperage, and the pressure would be the voltage. When you first start the car, you've used up some of the electricity in the battery, therefore not as much 'pressure' is required to send current to the battery. As the battery becomes fuller, more electrical 'pressure' (voltage) is required to get the battery charged to the set point of the regulator.
Since various electrical items (computer, radio, etcetera) always have a draw on the system, there is always some output from the alternator, even when the battery is fully charged.
The easiest way to test the in-dash voltmeter is to hook up an accessory voltmeter to any 12v source inside the car within sight of the driver. Even the cheapest Radio Shack voltmeter is good enough for this. Compare the readings over time and you'll see how accurate the dash gauge is.

Doug

TurboTommy

I'm not really interested wheather or not my voltage gage is working. It's working fine; had it tested several times. And since I can apparently rely on the info given by the gage, I'm questioning why the charging system is doing what it's doing. I'm wondering why I get inconsistant readings all over the place.

So, what is the alternator putting out; pressure or flow? (in your example)

The gage in the car is a voltmeter so I guess it's measuring electrical pressure. It almost always reads higher when you first start the car, which would be the opposite of what you said. Or, did I misunderstand?

Jaak Lepson

The voltage regulator is as the word applies ... it regulates the voltage (and to some extent, current) to the battery. When the car is cold at first start-up the regulator allows a higher voltage to pass through and charge the battery to replace the "voltage lost". As the car warms up, the voltage does drop down to about 12.8 volts to maintain a charge.

When the temperature rises the battery requires a "lesser charge" . If If the voltage was higher, it would boil the battery dry ... bad! When the ambiat temperature is cold, below -5 degress C, the battery required a higher voltage to maintain it's charge. The voltages you read will be anywhere from 12.5 to 14.5 VDC depending on the ambient temperature (under the hood) and the load on the battery.

If you look at the voltmeter on the dash it will read close to 14 volts when you first start up. As you drive the temperature under the hood rises and the alternator has replenished the charge in the battery, you will read above 12 volts. If the meter does not move and stays near 12 volts or less, the system is not charging the battery! Bad! If the battery cables have not been replaced on your car, I would replace them soon. The cables have deteriorated and there is a poor connection reducing the voltage/current flow.

To sum up .... there are two types of charges to the battery: Float, which maintains a small charge (voltage is less) to the battery, and Equalize which tries to replace the large draw (higher voltage). If you use a lot of accessories and lights, the system will work to replace/maintain the voltage.

You should NOT see 12 VDC off any auto battery. It should always read over 12.5 VDC and in some cases 13.8 VDC. Any decent voltmeter will work.

Hope this ramble makes sense ... I used to work on standby power supplies in the field and taught this for 7 years as a Technical Trainer/ Night School College Instructor 7 years ago.

On another note ... batteries over time have a calcium build up on the plates, sulfates. You would need a "best charger" to rid the plates of this buildup. These chargers put out 16 volts with an O/P current of 2 Amps to clean off the plates. This is what kills batteries early, sulfation!!!


Jaak Lepson

dmsog

The alternator can only output amps, which is flow. You understood me correctly. I can't begin to guess why your voltage reading would be higher on startup than while running.

Doug

TurboTommy

I think I need to go back to school to learn electricity.

If the alternator is putting out amps, why is it kept in check by a VOLTAGE regulator?

What confuses me is what is the gauge actually measuring: the voltage at the battery, or the voltage that the alternator is putting out?

I thought it was at the battery; but why then is it almost always higher right after you first start the car, even after the car has been sitting for awhile (battery should be lower), even if the alternator is working to replenish.

That would suggest the gauge measures alternator output. But then it should read higher when it's working hardest (high electrical draw); but it reads low.

This leads me to believe that the gauge is measuring some sort of net voltage of what's left after the alternator's work, and the draw on the system.

What I observed for sure: the hotter the engine compartment, the lower the voltage reading.

Can I assume that the lower the voltage reading, the less work is drawn from the engine?

TurboTommy

I don't know, but I might have a problem. Today, my voltmeter is has very inconsistent readings, jumping around a bit.
I don't know if this is normal, but my alternator feels quite warm to the touch. It's a little bit too hot to keep my hand on it. This is after ten minutes of low speed driving (in town) on a fairly cool day. Radiator fans have not come on. I have the AC delete with alternator mounted low (don't know if it's really supposed to run cooler there).
Does the alternator generate that much heat?

Jaak Lepson

Tommy ... there should be a duct that goes from the front spoiler to the alternator to keep it cool. If it is missing you will blow the diodes in the alternator ... make sure the cooling duct is there. The alternator does heat up as well as it gets heated from the engine.

As for where it measures the voltage ... it is from the output of the alternator. When there is a high current draw (Amperes) the voltage will drop! The only common value that stays the same is the resistance.

Ohms Law E (V) = I (current) x R (resistance)

or V / (I x R)

When the voltage drops, there is a higher current draw. When the voltage rises, there is less of a current draw. The battery has a certain charge it can hold and the alternator in conjuction with the voltage regulator controls the flow to the battery. You must match the battery type/rating to what the manufacturer recomends. If the voltage gauge fluctuates (jumps around a bit) it could be a sign of a loose connector or the alternator going. Make sure the cooling duct is there.

Jaak Lepson

Laust Pedersen

The voltage regulator (mechanical in the old days, now solid state) keeps the voltage out of the alternator at about 14V in spite of the engine’s rpm span from 800 to 6500 rpm. If there were no control, the voltage would be approximately proportional to the rpm. Alternators are AC generators (hence their name) that also need to be rectified.

Laust

TurboTommy

Jaak, I'm very confused between the relationship of current and the voltmeter in the car.

Can I assume, then, when the voltmeter in the car reads on the lower end (lets say between 12.5 and 13V), there is less work done by the alternator (also less power consumed by the engine) and yet more current available to supply the ignition coil, lights etc.?

Jaak, as far as your last post on the heat issue; it sounds like it's normal for the alternator to get quite warm.
My ducting somehow got lost during engine mods. This one of the reasons I went with the lower mounting position.
Anybody here know if this lower mounting (with the AC delete bracket) helps in keeping the alternator cooler?
A few people have told me that the original duct didn't do much especially at low speeds.

Jaak Lepson

Tommy ... when the voltmeter reads a lower voltage, it is putting out less current IF you have a standard load on the system to maintain the battery charge. No headlights, no defroster and other high current items.

When you first start the car the system will work on replenishing the lost charge and will read a higher voltage. After driving for 10 or so minutes the battery should be relenished and the alternator O/P's less current and the voltage will drop. The alternator starts to put out a higher charge above 1200 RPM and less of a charge at 800 RPM.

When you turn on the headlights and other high current draws (H4 draws more), the alternator works hard to replenish the charge at the same time as the sytem draws more. The voltage will read lower due to the draw. You may notice your dash lights dim a slight bit as well. That's why there is a 15 minute timer on the defroster circuit. This keeps the system from drawing too much, especially our cars as they where designed for standard lights.

If you want more current O/P from the alternator to overcome the draw, one has to replace the voltage regulator with a higher O/P or get a higher O/P alternator.

I use H4 headlights in my car with the standard system. I did replace the positive and negative battery wires as well as cleaned up the grounds. Due to the nature of our cars these cables must be replaced as the starter is located at the bottom of the car. The cables are exposed and are badly corroded! Icesharke does sell a set of replacement cables as well as the dealer.

As for robing power from the engine ... it is very little and will not affect the performance. AC will rob power. The PO of my car had removed the duct and I did notice a difference at low speeds. Once the duct was in the O/P of the alternator was better. Any air flow that is cooler will help. Heat is one of the bigest killer of the diode pack. Best to rig something up to keep it cool.

Hope this helps,

Jaak Lepson

dmsog

This is absolutely wrong. After starting the car, the voltage will be lower (and the amperage higher). As the battery becomes refilled, amperage is reduced and voltage is increased to the set point of the voltage regulator. The battery is maintained at the set point of the voltage regulator after replenishement and should never drop significantly while driving.
When the amperage is high, the voltage is low and vice-versa.

Doug
ASE Certified Automotive Electrician and 28 years owning a starter-alternator rebuilding business.

brad-cam

I drove around today with a digital voltmeter connected to the cigarette lighter and compared its reading with my dash voltmeter. The dash meter moved around from time-to-time, reading anywhere from about 12.5V to about 13.5V. The DVM was pegged on 13.90V pretty much constantly.

Looks like my dash gauge is faulty, or there is some bad wiring in the circuit to the gauge.

I'm not going to worry about it anymore. Looks like my charging system is working just fine.