What is an inverter?

[Terry]

They haven't here either since the car dynamos were usurped by alternators several decades ago and the 'dynamo' for cycle lighting seemed to go out of fashion long before LED lighting became available.

[Nowhere-Man]

Could be.  I haven't seen "dynamo" used here in decades.

The alternator on my Lister SR2 air cooled diesel boat engine is called a "dynamo" in the service manual. It's a Lucas.

A few weeks ago I was getting a bit frustrated trying to find a proper explanation of the so-called "dummy light" or "idiot light". I went through numerous automotive explanations and was left baffled because all were stating that "12 volts each side" of the light causes it to go out. Made no sense to me at all.

So, on the subject of charging and generating, here is how it works:

Inside the alternator there's a fixed delta winding (3 coils called the stator).

The rotor (a spinning coil) is an electromagnet and works just like the old HT chokes in vintage radio that smoothed the A.C. ripple while making a magnet around the speaker. With the rotor you need slip rings and carbon brushes so the AC output can be taken to the rectifier.

Here's the important bit: When ignition is turned the rotor field coil is energised by the 12 volt battery and thus becomes an electromagnet. At this point the lamp is wired between battery + and a negative potential terminal called D+ on the alternator. Therefore it's at 12 volts and lights up.

When the engine too is turned over the energised rotor spins between the stator windings and the electric field is produced. At this point mechanical generation makes the battery 12 volt supply to the rotor redundant and the field is now generated by the alternator itself. The D+ then becomes positive and with no opposite potential across the lamp, it simply goes out. Hence, dummy lamp - the alternator is charging.

Most people will already know the 3 stages of AC taken from the stator are rectified by six diodes. The D+ dummy lamp stage is rectified by 3 other diodes and provides the supply to the field rotor winding.

I don't know much about dynamos but assume you don't need a rectifier for a cycle lamp dynamo so maybe it's just an small AC generator.

[Kalee20]

Yes, most bicycle 'dynamos' are in fact alternators. No brushes, permanent magnet rotor, very simple.

Running an incandescent filamet bulb, it doesn't matter of course, AC is as good as DC.

[Alan Douglas]

Unless you're moving so slowly the lamp flickers.

[Crackle]

The alternator on my Lister SR2 air cooled diesel boat engine is called a "dynamo" in the service manual. It's a Lucas. ..............
.................
The rotor (a spinning coil) is an electromagnet and works just like the old HT chokes in vintage radio that smoothed the A.C. ripple while making a magnet around the speaker. With the rotor you need slip rings and carbon brushes so the AC output can be taken to the rectifier.

Hi
Not strictly true. The winding on the rotor in an alternator is simply an electro magnet, it does not smooth the AC or DC that is generated. It is used to "regulate" the output voltage of the 3 phase alternator winding and diodes, by varying the amount of current passing through the rotor winding, this is controlled by the alternator regulator circuit, they can be either "machine sensed" or "battery sensed". A machine sensed alternator does not take into account any voltage drop in the charging circuit and cables to the battery, it in effect just regulates itself. Whereas a battery sensed alternator will have a separate wire fed back to the battery so the regulator can monitor the actual battery voltage and state of charge.

By the way, in some of the larger uninterrupted power supplies, during normal operation the AC input charges the batteries and is regulated to keep the batteries at a constant voltage. The batteries are also connected to an inverter which then powers the "uninterrupted output"
This ensures there is no interruption of power in the event of a power cut, and also the equipment is totally isolated from the mains.
They will also have a series of bypass switches so the batteries can be taken out of service for maintenance.
Mike

[Crackle]

By the way, in some of the larger uninterrupted power supplies, during normal operation the AC input charges the batteries and is regulated to keep the batteries at a constant voltage. The batteries are also connected to an inverter which then powers the "uninterrupted output"
This ensures there is no interruption of power in the event of a power cut, and also the equipment is totally isolated from the mains.
They will also have a series of bypass switches so the batteries can be taken out of service for maintenance.
Mike

I thought I would just add, the description above is a very simplistic one. There would normally be complicated computer controlled circuitry and the "charger" would not only be capable of keeping the batteries at their float charge but of also supplying the full current in order to maintain the float voltage when the output of the unit unit was under full load.
They are in effect an AC to DC then DC to AC converter, and this type of UPS is called an "Online UPS"
controlled
Mike

[ex 2 Base]

The "Dummy light " or" idiot light" is the ignition warning light on a car. We had a car and the bulb was loose in it mounting which then stopped the alternator from charging. We were going home and the engine stopped for no apparent reason. When I tried to start the engine the battery was completely flat, no ignition warning light of course. Fortunately for us a neighbour saw us and stopped, he had a strong rope in his boot and gave us a tow home, just about a mile. After charging the battery the engine started, no ignition warning light , I checked the alternator, no output . I was a bit confused and then started to check the rest of the charging circuit and it was then I discovered the loose bulb. What a job to remove the dash to gain access to a simple bulb. The manual said you had to remove the steering wheel, with all that entailed. I managed without removing the steering wheel as so many controls are mounted on the steering wheel.
Finally I've done a few jobs on my friend boats and notice all their alternator are battery sensed. Ted

[Nowhere-Man]

The "Dummy light " or" idiot light" is the ignition warning light on a car. We had a car and the bulb was loose in it mounting which then stopped the alternator from charging. We were going home and the engine stopped for no apparent reason. When I tried to start the engine the battery was completely flat, no ignition warning light of course. Fortunately  for us a neighbour saw us and stopped, he had a strong rope in his boot and gave us a tow home, just about a mile. After charging the battery  the engine started, no ignition warning light , I checked the alternator, no output . I was a bit confused and then started to check the rest of the charging circuit and it was then I discovered the loose bulb. What a job to remove the dash to gain access to a simple bulb. The manual said you had to remove the steering wheel, with all that entailed. I managed without removing the steering wheel as so many controls are mounted on the steering wheel.
Finally I've done a few jobs on my friend boats and notice all their alternator are battery sensed. Ted

It excites the magnetic field. I was a bit frustrated over explanations  of dummy lights online but someone on a racing car forum cleared it up.

You'll find the D+ wire on the back of the alternator and it's thinner. That will cause the bulb to light but it should become positive on engine start and the bulb will go out. That's why they say 12 volts each side but really it's just zero potential between 2 terminals that are both 12 volts positive between each one and chassis.