How to shutdown the alternator ?

[transmitterdan]

Originally Posted by stormalong

That is only true with an internal regulator. An external regulator would still energize the field. It there is no alternator output what do you hope to accomplish by shorting to ground?

His alternator has an internal regulator. Shorting should accomplish the OP's stated goal of shutting down the alternator without using energy from the engine.

[SecondBase]

Mechanical option: add a 2 grove pulley so you can turn rotation on and off via belt tension.

Not the scientific test mentioned early in this thread but air conditioning in a car reportedly consumes 1 mpg at 65 mph.

I am considering eliminating my starter batteries to make space for two more lead acid house batteries. Starting would be accomplished by one of two jump packs with emergency starting via house bank. If I'm ok with the minor inconvenience any reason this approach wouldn't succeed?

[Maine Sail]

Originally Posted by transmitterdan

His alternator has an internal regulator. Shorting should accomplish the OP's stated goal of shutting down the alternator without using energy from the engine.

His solar is set for 14.8V his alt is set for approx 14.4V plus it will drop regulated voltage by 0.01V for every degree rise in temp above the 20C (68F) baseline. If the solar is doing its job the alt would be off anyway, except for some bulk periods. Because the system voltage on the bus, dictated by the solar controller, will be above the alts limiting voltage, the alt regulators only is to turn off the field.

These Hitachi alts can still self excite even with the L terminal disconnected or the lamp burned out... The "L" terminal helps excite it at low RPM but they can still self-excite when it gets to a higher RPM.

There are numerous options:

*Open the alt and tap into the brush circuit and insert an On/Off switch. Takes about 30-45 minutes. (least expensive, less than $20.00 in materials, no risk of alt self exciting)

*Open the alt and bypass the internal reg and use an external reg with an On/Off switch. (more expensive, more complicated, requires alt temp sensor and a regulator that can limit field output such as the Balmar ARS-5 or MC-614)

*Run the alt to the safety battery then use a simple ON/OFF switch and constant duty / heavy duty solenoid to parallel to house when needed. A simple ON/OFF battery switch could also be used for paralleling and is likely already there. Safety battery will always be at or near 100% SOC so load on engine is likely not even measurable or essentially zero. (inexpensive to moderately expensive, simple and straight forward)

*If concerned about continual absorption to safety battery simply insert one leg of a diode isolator in the B+ path with a switch to bypass the diode when full regulation voltage is necessary. (medium expensive, slightly more complicated)



If the OP is discussing an external rectifier he is certainly capable of tapping into the brush circuit to install and $8.00 On/Off switch and some wire....

[john61ct]

Originally Posted by SecondBase

I am considering eliminating my starter batteries to make space for two more lead acid house batteries. Starting would be accomplished by one of two jump packs with emergency starting via house bank. If I'm ok with the minor inconvenience any reason this approach wouldn't succeed?

Start from House and save the jump packs for emergencies.

[rom]

Thank you Mainesail for the very good summary of options available to shutdown the alternator or disconnect it from the house battery.

As the OP, allow me to say that if you are still searching for the answer: I am convinced, switching off the field is safe, works everytime, before or after you start the engine. You probably don't need to go any further than post # 108 from Mainesail.

And you probably don't need to waste your time on the rather suspicious alternative options we have been debating lately, unless like me you feel the need to educate yourself, and are ready to be asked for public apologies if you go to far

[transmitterdan]

Rom,

No need to apologize. If people cannot discuss technical topics for fear of offending someone then "they" have won.

But you are right that cutting the field wire will shut it down.

[john61ct]

Excellent to see an OP acknowledge that the horse is well and truly dead.

Maine Sail he da man!

[SOLAR SUPPORT]

Let me ask you three questions about the Alternators :

1 Which one is being electricaly excited, stator or rotor or both?
2 If they are being excited electricaly both, are they excited separetly?
3 Which exciter circuit can be cut with the help of a thermostad relay switch without any damage to the alternator and the whole electric system setup while the alternator is runing? Stator or Rotor?

[Wotname]

Originally Posted by SOLAR SUPPORT

Let me ask you three questions about the Alternators :

1 Which one is being electricaly excited, stator or rotor or both?
2 If they are being excited electricaly both, are they excited separetly?
3 Which exciter circuit can be cut with the help of a thermostad relay switch without any damage to the alternator and the whole electric system setup while the alternator is runing? Stator or Rotor?

1. Rotor
2. No, only the rotor is excited electrically
3. Rotor


The rotor is excited electrically. The current flowing through the rotor coils create a magnetic field. The rotor is turned by the engine thus turning its magnetic field.

This rotating magnetic field 'cuts' the stator windings (coils). This induces a voltage (AC) in the stator. The diode pack rectifies the AC to a DC voltage. If there is a load circuit connected to the alternator (as there should be), current then flows through the load circuit. Typically the load circuit on the alternator is the battery.

The DC output voltage of the alternator is 'regulated' within set values by the regulator which controls the current flowing in the rotor windings thus controlling the strength of the magnetic field surrounding the rotor windings.

[SOLAR SUPPORT]

Alternator's excessive inner heat becoming a threat to itself when lead acid batteries replaced with Lifepo4 battery.

Alternator should be protected against the excessive heat generated in itself when charging Lifepo4 battery since Lifepo4 battery pulls max current that Alternator can deliver.

When the Alternator's working power gets higher,
Rotor's exciter current should be high to produce the max current needed.
Alternator's inner heat is geting higher when generated power is high at the same time. Cuting exciter current to cut the power that alternator generates seems to be a simple solution to let the alternator cool itself, but it is not safe. Because of the high inductive electric energy which traped inside the alternator may damage the alternator and/or boat's voltage sensitive electrical instruments when the rotor's exciter current cut.

[lateral]

“ Cuting exciter current to cut the power that alternator generates seems to be a simple solution to let the alternator cool itself, but it is not safe”.

Not correct.

I often cut my field current at max current with engine running. No problem.
Obviously, as load is still connected. Gives me more power on cold engine.
Besides rotor is low voltage /current amplified by high ratio windings in stator.
As I see it anyway.

[waterman46]

Originally Posted by SOLAR SUPPORT

Alternator's excessive inner heat becoming a threat to itself when lead acid batteries replaced with Lifepo4 battery.

Alternator should be protected against the excessive heat generated in itself when charging Lifepo4 battery since Lifepo4 battery pulls max current that Alternator can deliver.

When the Alternator's working power gets higher,
Rotor's exciter current should be high to produce the max current needed.
Alternator's inner heat is geting higher when generated power is high at the same time. Cuting exciter current to cut the power that alternator generates seems to be a simple solution to let the alternator cool itself, but it is not safe. Because of the high inductive electric energy which traped inside the alternator may damage the alternator and/or boat's voltage sensitive electrical instruments when the rotor's exciter current cut.

You are saying that if the alternator field current is suddenly cut off, that the alternator may produce a voltage spike. I think you are confusing a disconnect of the field, which is fine, to a disconnect of the battery from the alternator B+ output, which should never be done with engine running.

As long as the battery is still connected to the alternator output, nothing will be damaged by switching off the field current. Since the battery is still connected to the alternator B+ output, it acts somewhat like a huge capacitance to absorb any such spike.


My very old Balmar smart regulator includes a thermocouple device to protect the alternator from overheating.

[SOLAR SUPPORT]

As you say, if it is not harmfull, I want to try it. Can you show me which terminal will be pulled out to cut the exciter current on my Mitsubishi 115A Alternator? Below picture shows back view of the alternator.

[lateral]

For your level of understanding I suggest take it to an auto elect shop and they should do it for sfa.

Or I would take the cover off brush set/ internal reg behind
“W” and “B” terminals isolate one of the brushes and reconnect
Thru a switch on the outside paying attention to insulation/ strain relief etc.
At a guess, as I haven’t been inside a Mitzi.

Mine is simple, just turn the ignition off as the external reg is powered from ignition and manual motor kill. ( which I rarely use and only for short periods like
Low rpm manoeuvring) Bosch 115A. Force cooled. Temp derating.

[Wotname]

Originally Posted by SOLAR SUPPORT

As you say, if it is not harmfull, I want to try it. Can you show me which terminal will be pulled out to cut the exciter current on my Mitsubishi 115A Alternator? Below picture shows back view of the alternator.

Lateral as given you good advice so allow me to expand on it.

Making the assumption your Mitz alternator still has it's internal regulator, it won't be possible to interrupt the field (rotor) current by removing anything from the external connections. You would have to open it up to get access the field circuit wires.

In normal operation, the alternator does need to be externally excited before it will start providing an output. However as soon as it begins to provide an output, it will self excite internally and continue to do so until the engine is stopped.

The function of the terminals on this alternator are...

B+ --- the positive output terminal, goes to Battery +ve.

B- --- the negative output terminal, goes to the negative bus or engine block as applicable

W --- connected internally to one stator winding before the diode pack and provides an AC output of about 7VAC. This can be used to pulse (drive) a tachometer as the frequency of the AC is proportional to the speed of rotor thus proportional to the engine speed. W stands for 'waveform'.

S --- Sense terminal. This provides the voltage of the battery to the internal regulator to determine how much field current to push through the rotor. The regulator compares the sense voltage to it's preset value and attempts to make both the same (in simple language). Often connected externally to the B+ terminal for simplicity.

D --- goes to the warning light. Often designated as D+ and stands for ‘Dynamo Positive’ on old style generators (AKA dynamo). It is through this terminal that the alternator is initially externally excited as mentioned above. Before an output is established, the current flow through the rotor winding is from the battery +ve, via the key switch (ignition switch), through the warning light, to the D terminal and then through the rotor winding via the brushes and finally to B- (ground). At this point the warning light has current flowing through and thus is illuminated. Note, this is the same current that is flowing through the rotor windings at this point.

However once an output is established, the output voltage is supplied (internally) by the regulator to the D terminal. This causes the the current to cease flowing through the warning light and so it is extinguished. The alternator is now self exciting i.e. it provides it's own rotor voltage/current internally. The regulator is continually adjusting the rotor voltage/current internally to hold the output voltage to the preset value.

Now let me be blunt - if you don't understand the above after reading it a few times and giving it good thought, then you should get professional advice before messing with you alternator. However if it does make sense and you are feeling brave, go for it.