Another Alternator Question

[CRS51]

With a 24 volt alternator does the wattage of the warning bulb have any effect on the charging output or excitation of the alternator ?
Would there be a difference in alternator behaviour between using a 5 watt bulb and a 21 watt bulb or even no bulb at all and direct feed from ignition switch ?
Just a question that’s been bugging me and one I cannot find a definitive answer too
Thanks Chris

 

[Chippie]

I would say no difference…the warning lamp works by differential voltage between the battery voltage and the alternator output….

 

[Guineafowl]

The warning light circuit connects 24V to earth via the rotor, which is an inductor (electromagnet), and the bulb, which lights. Once the alternator is spinning, the rotor produces its own 24V in opposition, cancelling out the 24V feed so the voltage across the bulb drops to zero, so it goes out.

When you first switch on (key I), the rotor builds a magnetic field. The speed of this is determined by the circuit resistance R and the inductance of the rotor windings L. Multiplying R.L gives you the time to charge to 63% of what’s left to charge, so you can see the (magnetic) charging fades with time.

After about 5 RL time intervals, the rotor will be near enough fully charged. After this, the current is limited only by the rotor resistance, which is low. You need a bulb to limit the current as well as indicate charging. A resistor is sometimes used instead.

With a direct feed, no bulb, the rotor will heat up rapidly. A 5W bulb has a higher resistance, so will take longer to excite the rotor than a 21W one. Other than that, there should be little effect on alternator performance.

 

[Chippie]

Thinking car alternator…

What is the 24v alternator from?

 

[ajlelectronics]

Thinking car alternator…

What is the 24v alternator from?

The physics is the same.

 

[CRS51]

Thinking car alternator…

What is the 24v alternator from?

It’s from my old Quasi Arc welding set
Cheers Chris

 

[CRS51]

The warning light circuit connects 24V to earth via the rotor, which is an inductor (electromagnet), and the bulb, which lights. Once the alternator is spinning, the rotor produces its own 24V in opposition, cancelling out the 24V feed so the voltage across the bulb drops to zero, so it goes out.

When you first switch on (key I), the rotor builds a magnetic field. The speed of this is determined by the circuit resistance R and the inductance of the rotor windings L. Multiplying R.L gives you the time to charge to 63% of what’s left to charge, so you can see the (magnetic) charging fades with time.

After about 5 RL time intervals, the rotor will be near enough fully charged. After this, the current is limited only by the rotor resistance, which is low. You need a bulb to limit the current as well as indicate charging. A resistor is sometimes used instead.

With a direct feed, no bulb, the rotor will heat up rapidly. A 5W bulb has a higher resistance, so will take longer to excite the rotor than a 21W one. Other than that, there should be little effect on alternator performance.

Thankyou for the answer
Chris

 

[Chippie]

As in this example….the warning lamp lights because the battery volts is higher than the alt output….