Dynamo vs Alternator

[Volfandt]

True, the Kubota Dynao is a low wattage alternator in that it makes AC voltage and uses a standalone rectifier/regulator to convert the voltage to DC and control the dynamo's output.

I don't have much of a demand for more wattage out of my BX23 but if I needed more light's etc., I'd be upgradeing to the alt kit mosh-kosh /forums/images/graemlins/grin.gif
Volfandt

 

[Keoke]

Techman, you are right in that no one makes DC generators anymore. There is no difference between an alternator and a dynamo. The Japanese and Europeans have called alternators dynamos for a long time but here in the US the dynamo name has never took hold.
Small (low amps) alternators on tractors tend to have their rectifier diodes external mounted (often in voltage reg) while large units will mount diode's internally to take advantage of fan cooling.

 

[djg]

I was taught in tech school that what we call an alternator was invented by chrysler when they put air conditioning in cars. The common DC generators of the time had insufficient output at low RPMs, and the battery would discharge if the A/C was used around town. This alternator has a rotating field coil that requires an input of electricity, which is fed through two brushes. There are three coils spaced around the rotating field that produce alternating current. This current goes through a diode matrix to produce DC. The dynamo as used in Kubotas is a permanent magnet rotor rotating inside a coil that produces AC, which is rectified by an external unit. It has only two wires coming out of it, and they can be attached either way, which is to say they have same color code. If you spin a dynamo by hand, you will feel a rythmic resistance as the magnet spins. It feels like a magneto when you spin it. The dynamo does not require any input of electricity, it has no brushes, it is weak at low RPMs. It is not the same as an alternator, as these terms are commonly used today.

 

[techman]

Actually as a device, the alternator is a very old device, predating the auto industry.

Alternator by definition produces an "alternating", or AC output. The technology uses some sort of magnet, usually as the rotor, although the magnet as the fixed coil was used in a number of designs. The rotating magnet is commonly known as a "rotating field" design.

The magnet can be a perrmanent magnet, as mentioned, or an electromagnet. The latter is known as as wound field or rotor design. Wound rotor units have the advantage of being able to vary or regulate the output voltage of the alternator by varying the magnet's strength. This comes at greater complexity and cost. A permanent magnet design is cheaper to make, but the output voltage varies with the RPM of the shaft. Some smaller AC power generators use permanent magnet rotors, since the RPM is basically constant, for 60 Hz output.

The king of the alternator is the brushless alternator. It has an electromagnet field coil that is fixed, which energizes (excites in correct terms) a small alternator coil on the rotor. The output of this small alternator is rectified by diodes on the rotor and feeds DC to the wound rotor of the main alternator which is down the shaft a bit further. The main alternator output comes off of the coils in the stator that are coupled with the main wound rotor. To vary the output voltage, the electromagnet field voltage of the small alternator (known as an exciter) is varied. This varies the resulting DC voltage to the main rotor field, and thus the AC output. Complex and expensive, but no brushes to maintain and the ability to regulate the output voltage.

I do not know who was the first, but the use in cars was to meet higher power demands (perhaps due to the A/C). The alternator design can produce more current as lower RPMs, if it is designed to due such. The other advantages were a smaller size and lower production cost. I suspect that the latter issue was what motivated the automakers.

paul

 

[Keoke]

Dig, you are correct, Chrysler introduced the dynamo in 1960 and called it an alternator. I guess it is because they felt it is an AC generator that changes (alters) that AC current to a DC current.
The difference between the PM (permanent magnet) and a variable magnet (electro magnet field) alt. influences the ability to vary the charge output of the dynamo/alternator.
Both of these units (fixed or variable fld) can be called dynamo's or alternators, use which ever handle you prefer.
If you look European or Japanese manuals printed for home use you will see alternators referred to as dynamo's.
Also, if you look at Bosch service manuals you will see their both their PM and EM alternators frequently referred to as dynamo's.

Current flow on fixed fld (PM rotors) is regulated by the CEMF put out by the battery. When battery is low or load is high flow will be high as battery offers no resistance to flow from alt.. Current flow will taper off as battery voltage climbs and counters alternator voltage.
This type of control is adequate for low load electrical systems but not for high amp units.

 

[midlf]

Alternators with DC output were not practical until the development of high current solid state diodes. The permanent magnet alternator, referred to here as a dynamo, uses an external regulator to interrupt or shunt the fixed output of the alternator. This is a common system on motorcycles, and I suspect ATV's. The "alternator" upgrade referred to here uses a regulator that controls the field current to the alternator to regulate the output, like an automotive alternator.

 

[Bearman1977]

I have a Kubota (Year 2016) B2601, and I just completed installing the Alternator Upgrade Kit (Kubota Part Number 6C040-9530-6, this kit contained everything needed to "Finally" have the electrical power (14.5 amps to 40 amps) for external work lights. It was well worth the investment of $210.00, next day shipped to me, and took me 1.5 hours to install in my own garage. Exceptionally easy to install. One thing I immediately noticed when I started it up, was a noise reduction, and a quicker start up. Strange but true. I would recommend to anyone owning a B series Kubota to invest in the Alternator upgrade, it's worth the additional money! Lastly, Many thanks to the folks over at Messicks Tractor Supply for taking the time and ensuring that I received the right upgrade kit. :drink: