Alternator connected to starter WTH

[transmitterdan]

Originally Posted by Wotname

The above does not explain how the output voltage is controlled. It explains how it is generated but not how the voltage is regulated. I have no issue with how the output voltage is generated, it is quite straightforward and I agree with your analysis above.

Let's stick to the original premise of a OEM engine fitted with a generic internally alternator. You posted that the diodes will be blown up if alternator output is disconnected before the engine is started. I disagree with this statement as I can't see why the output voltage would exceed the regulated voltage set point. Maybe I'm wrong but the regulator circuits I'm familiar with will not allow the output voltage to be greater than the set point (~14V).

At the heart of the issue is where the internal regulator senses the output voltage. If it senses it from anywhere else than the output terminal of the alternator, then I can see that the output voltage would keep rising if that terminal was open circuit. To what level, I don't know. I haven't seen such an alternator but of course, that doesn't mean they don't exist.

Attached are three different alternators all with internal regulators and although there are some differences, they all sense the output voltage internally from the B+ terminal and regulate the field current to maintain that set point. Although the other terminals vary from one to three, they work in the same manner using a zener diode to maintain the preset voltage. In all of these circuits, there is simply no requirement to have a battery connected to the B+ terminal before operation. The output voltage will rise to the set point and be held there by the regulator operation. It can't rise any higher because as soon as it does, the regulator removes the field current.

Take the middle diagram case with the key switch which is the most common. And no output connection to the battery. There will be power for the field circuit via the key. So the internal regulator will excite the rotor coil with current. The stator will try to create a current directly proportional to the rotor current. Coupled inductors don’t work on voltage, they work by induced magnetic fields which are proportional to current. Since there can be no current to the battery because there is no wire, the stator voltage goes to some really high value and the diodes avalanche and die.

This has nothing to do with how voltage regulation works. Even though an alternator produces current we can regulate voltage by measuring voltage and if voltage is too high, we turn down the current in the rotor. Likewise, if voltage is too low we can increase the current in the rotor which in turn raises the voltage. This is how all alternator regulators work.

But the regulator design presumes the presence of a battery at the output of the diode stack. Without the battery the regulator cannot work as designed. The output voltage will have high ripple from the rectified AC and the regulator will not be able to regulate very well.

[Wotname]

Originally Posted by transmitterdan

Take the middle diagram case with the key switch which is the most common. And no output connection to the battery. There will be power for the field circuit via the key. So the internal regulator will excite the rotor coil with current. The stator will try to create a current directly proportional to the rotor current. Coupled inductors don’t work on voltage, they work by induced magnetic fields which are proportional to current. Since there can be no current to the battery because there is no wire, the stator voltage goes to some really high value and the diodes avalanche and die..........

No, the stator voltage can not rise that high.

Once the stator voltage rises high enough (~14V), the zener diode conducts which turns TR2 ON which turns TR1 (pair) OFF which interrupts rotor current.

No rotor current causes stator voltage to drop to a value where the zener diode blocks again preventing the BE current of TR2 which turns TR2 OFF which turns TR1 (pair) ON allowing rotor current to flow again. The cycle continues regardless of current flow though the B+ terminal.

The internal capacitor across the output provides for some smoothing of the AC ripple if the B+ is open circuit but of course, a good battery provides enhanced filtering.

[transmitterdan]

Originally Posted by Wotname

No, the stator voltage can not rise that high.

Once the stator voltage rises high enough (~14V), the zener diode conducts which turns TR2 ON which turns TR1 (pair) OFF which interrupts rotor current.

No rotor current causes stator voltage to drop to a value where the zener diode blocks again preventing the BE current of TR2 which turns TR2 OFF which turns TR1 (pair) ON allowing rotor current to flow again. The cycle continues regardless of current flow though the B+ terminal.

The internal capacitor across the output provides for some smoothing of the AC ripple if the B+ is open circuit but of course, a good battery provides enhanced filtering.

The regulator cannot reduce the rotor current to zero instantly. The rotor has inductance and therefore it takes time to collapse the field. Once the rotor field builds up then the voltage of the stator breaks the diodes. Without the battery attached the regulator is quite often not a stable feedback system.

[Bycrick]

I can’t see it. The alternator is stopped. I apply field voltage, There’s now a magnetic field from the rotor, which is coupled to the stator. But since the magnetic field isn’t moving, there’s no output from the stator. As the alternator starts to spin, the magnetic field starts to move, the stator voltage starts to rise. As it approaches the regulator cutoff voltage, the field current is gradually reduced. I don’t see any collapsing field or inductance entering into this. I’ve run alternators without loads without problems. What you CAN'T do is disconnect the alternator load when the alternator is supplying current. Then the energy in the magnetic field has to go someplace, which will raise the output voltage until the field energy is dissipated. If it gets high enough, you’ll blow the diodes.

[Wotname]

Originally Posted by transmitterdan

The regulator cannot reduce the rotor current to zero instantly. The rotor has inductance and therefore it takes time to collapse the field. Once the rotor field builds up then the voltage of the stator breaks the diodes. Without the battery attached the regulator is quite often not a stable feedback system.

Reducing the rotor current to zero instantaneously would be a bad thing causing large reverse polarity spikes in the stator which is why the regulator circuit prevents it happening.

When TR1 turns OFF, the rotor field begins to collapse cutting the rotor winding causing a EMF to be developed in the rotor coil. The polarity is the opposite of the previously applied EMF (normal inductor function). The rotor at this moment becomes a source of EMF rather than a load. Diode D10 conducts which tries to maintain the rotor current as the rotor field decays. Of course very shortly later TR1 turns on again suppling the usual rotor current and the rotor becomes a load again.

The battery is still attached to the stator and the regulator via the R terminal and to a lesser extent via the field diodes and the L terminal. The system remains stable and the diodes don't blow.

Attached is one method measuring the 13V rise speed of an alternator. In essence, this is the minimum RPM needed to maintain a 13V open circuit output or put another way, the RPM required for rotor self excitement to overcome the various internal losses. While not technically purely self excitement, it is the speed required for the alternator to maintain internal excitement (via the stator and field diodes) after an initial external excitement.

This test calls for running the alternator completely open circuit (after initial excitement) and measuring the output voltage. It remains stable.

Disregard the variable resistor in the diagram as it remains open circuit for this test. It is shown only because it is needed for other tests (not shown).

[transmitterdan]

What happens to the voltage if you run the speed up to 2,500 RPM as if it was on a real engine? Does it hold 13V?

[Wotname]

Originally Posted by transmitterdan

What happens to the voltage if you run the speed up to 2,500 RPM as if it was on a real engine? Does it hold 13V?

I don't know. The test described is to determine the minimum speed that the alternator will remain self excited.

My suspicion is that it would rise to ~14V but I have never tried it.

However I cannot see any reason in the circuit we are currently discussing why the B+ voltage would exceed ~14V if the B+ is left open circuit before starting. If the B+ voltage stays around the regulated voltage, the diodes are safe.

Empirical experience so far aligns with the circuit theory (as far as my understanding of the theory goes).

[Wotname]

Originally Posted by Wotname

................
When TR1 turns OFF, the rotor field begins to collapse cutting the rotor winding causing a EMF to be developed in the rotor coil. The polarity is the opposite of the previously applied EMF (normal inductor function). The rotor at this moment becomes a source of EMF rather than a load. Diode D10 conducts which tries to maintain the rotor current as the rotor field decays. Of course very shortly later TR1 turns on again suppling the usual rotor current and the rotor becomes a load again. .................

Transmitterdan will surely know the following but I feel it is important enough to explain further for other readers as it is easy to get confused at this point.

When an external voltage is applied inductor (say rotor winding), current flows though the inductor from +ve to -ve (using conventional current flow theory). When the current is interrupted , the field around the inductor collapses and this collapsing field induces a voltage that is in opposite in polarity to the original voltage - usually called the "back EMF". If a diode (or similar) is placed across the inductor (in a suitable direction), this back EMF allows current to continue to flow though the inductor in the same direction as the previous current. But the polarity of the back EMF has changed yet the current direction does not.
Why?
Because conventional current (+ve to -ve) considers the external current in a load, not the current flow in the source. Inside a source, conventional current flows from -ve to +ve.
So it the situation described, the current direction though the rotor winding remains the same because when the current is supplied by an external EMF, the rotor is the load but when the rotor becomes the source (with the voltage polarity inverted) , the conventional current flows within the source from -ve to +ve. I.E the same direction as previously.

[transmitterdan]

Yes, I know how inductors work. The simplest explanation for what happens when trying to stop current in an inductor is to remember that an inductor stores energy. The energy in an inductor at any given moment is 0.5 times inductance times current squared. If you want to stop the current you have to make the energy in the inductor zero. So the energy stored in the inductor has to go somewhere else. However you do that is up to the engineer designing the circuit. And the voltage will do whatever it has to do to get the energy out of the inductor.

With a diode in the correct direction across the inductor the energy is dissipated in the wire of the inductor and the diode. The current goes to zero when all the energy has been converted to heat. If a resistor is placed in series with the diode the energy can be removed much faster from the inductor due to the increased losses of the resistor and the current decreases much faster.

In the case of an alternator there is another place for the energy to go and that is the battery. Without the battery it takes longer for the regulator to make changes in the rotor current. Too long in some cases to prevent damage due to over voltage.

[wsmurdoch]

Originally Posted by Wotname

At the heart of the issue is where the internal regulator senses the output voltage. If it senses it from anywhere else than the output terminal of the alternator, then I can see that the output voltage would keep rising if that terminal was open circuit. To what level, I don't know. I haven't seen such an alternator but of course, that doesn't mean they don't exist.

Many internally regulated alternators have external sense terminals that can be used to sense voltage at the battery. Their use greatly reduces battery charging times.

What are Remote Sense Alternators | Delco Remy

For example on Delco alternators: It is the 2 or F terminal on SI series alternators and the S terminal on CS series alternators.

http://www.delcoremy.com/documents/a...12si-15si.aspx
https://alternatorparts.com/cs130-sbpage2.html

Bill

[rslifkin]

Originally Posted by wsmurdoch

Many internally regulated alternators have external sense terminals that can be used to sense voltage at the battery. Their use greatly reduces battery charging times.

What are Remote Sense Alternators | Delco Remy

For example on Delco alternators: It is the 2 or F terminal on SI series alternators and the S terminal on CS series alternators.

http://www.delcoremy.com/documents/a...12si-15si.aspx
https://alternatorparts.com/cs130-sbpage2.html

Bill

My Motorola-type alternators have a sense terminal as well.

[Charlie]

I didn't quite finish my rewire before leaving on my trip to So Cal. The battery system worked fine. Now that I'm home I want to get the wiring correct.

The problem I am having now is peculiar. I have a Hitachi 60 amp alternator on a Yanmar 4JH4E engine. I have a cable that I want to connect to an always hot positive bus bar as per design by Maine Sail.

The problem is that when I do this the low oil light and sound come on. In reviewing the wiring diagram I don't see that there is a connection from the oil sensor to the alternator. Does anyone have any ideas as to what would cause the sensor to sound by connecting a cable from the positive bus bar to the output stud of the alternator?

[Wotname]

Originally Posted by Charlie

I didn't quite finish my rewire before leaving on my trip to So Cal. The battery system worked fine. Now that I'm home I want to get the wiring correct.

The problem I am having now is peculiar. I have a Hitachi 60 amp alternator on a Yanmar 4JH4E engine. I have a cable that I want to connect to an always hot positive bus bar as per design by Maine Sail.

The problem is that when I do this the low oil light and sound come on. In reviewing the wiring diagram I don't see that there is a connection from the oil sensor to the alternator. Does anyone have any ideas as to what would cause the sensor to sound by connecting a cable from the positive bus bar to the output stud of the alternator?

I don't have the 4JH4E wiring diagram nearby but many Yanmar engines have a power wire (usually fused) going from the alternator output to the key switch on the panel. This will always be hot when the start battery is connected to the engine. Usually the oil light/alarm should only occur after the key switch is turned on and before the engine is started. .

Maybe your's is mis-wired or the key switch is ON or ......

[transmitterdan]

Originally Posted by Charlie

I didn't quite finish my rewire before leaving on my trip to So Cal. The battery system worked fine. Now that I'm home I want to get the wiring correct.

The problem I am having now is peculiar. I have a Hitachi 60 amp alternator on a Yanmar 4JH4E engine. I have a cable that I want to connect to an always hot positive bus bar as per design by Maine Sail.

The problem is that when I do this the low oil light and sound come on. In reviewing the wiring diagram I don't see that there is a connection from the oil sensor to the alternator. Does anyone have any ideas as to what would cause the sensor to sound by connecting a cable from the positive bus bar to the output stud of the alternator?

You have connected 12V battery power to the “ignition” circuit that powers the alternator regulator/field. That circuit is not supposed to be always “always on”. This circuit is activated by turning the key switch from off to the first position. That enables the oil pressure, temp alarm and instrument panel lights in addition to powering the alternator regulator.

In simple terms, you need either to read the wiring diagram or find a qualified marine electrician. You’re doing it wrong.

[Charlie]

Wotname thanks for your comment your nudge helped me to understand the problem.

Trans from your last paragraph I guess you got out of the wrong side of bed this morning. OTOH the first one was very helpful.

I didn't touch any of the wiring in the start/ignition circuit. This confused as to why the oil light/alarm would turn on. I assume what is happening is that the alternator wire that is connected to the panel is being backfed by the always hot cable.

Now that I know the likely problem I can check to see if my theory is correct. Then scratch the family brain cell for a solution. Probably involves adding a relay.