DC (Direct-Current) generators are machines that rotate and supply an electrical output with current and voltage in the same direction. We use them to convert a mechanical input to a unidirectional electric output. That’s what makes them different from AC (Alternating-Current) generators whose pros and cons we covered. Regardless, we use both types of generators widely nowadays. The power demands usually dictate which one is a superior choice. If you’re considering getting one for personal use or your industrial project and have no one to turn to, don’t fret. Here are the advantages and disadvantages of a DC generator:
Advantages of a DC generator
You will quickly realize the simplicity and robustness of DC generators that make them so well-known and frequently utilized. Let’s dive into the pros of a DC generator:
1. It is relatively straightforward to understand
We know the concept of electric generators may seem complex to laymen. However, compared to modern electronics that use PCBs (Printed Circuit Boards) and parts you can barely see without a magnifying glass, generators haven’t changed principally. DC generator works based on Faraday’s law of induction which states that “Whenever a conductor is placed in a varying magnetic field, an electromotive force is induced.”
Thus, the energy conversion from a mechanic to an electric one is based on the simple principles of electromagnetic field production that is induced dynamically, meaning the conductor can also move in the magnetic field. We will explain that next. For now, you should know the basic EMF equation for a DC generator:
Eg = (P*Ø*N*Z) / 60*A
- Eg — Electromagnetic field generated across any parallel path
- P — The full number of poles within the EMF
- N — Armature’s rotational speed in rpm (rounds per minute)
- Z — The complete number of conductors for the armature in the field
- Ø — Magnetic flux that was produced for each pole
- A — The total number of armature’s parallel paths
2. DC generator consists of simple parts
DC generators have a simple design that can consist of roughly 9 to 12 parts such as:
- Rotor or armature core
- Field coils
- Armature winding
- Pole shoes
- End housings
A DC generator is essentially made of two parts, a rotating one (rotor or armature core) and a static, or stator. The stator houses the rotor at its code. The rest we mentioned are smaller components.
3. They vary and can be used for a wide variety of purposes
Look at any promotional leaflet and you’ll see tens of different uses. Add things required for commercial use, and you have a huge list. We will mention one that stands out from AC generators below. For now, without getting into the specifics, there are 3 types of self-excited DC generators:
1. Series wound generator
As the name suggests, the series wound DC generator has a field winding that is connected with the armature in the series. Therefore, it uses field coils with only a few turns of a wire with a large diameter. The coils have low resistance, thus helping increase the voltage output when the current draw increases. These are used whenever a stable current is necessary, such as in arc lamps that need lighting and booster.
2. Compound wound generator
Compound wound DC generators are those that combine series and shunt fields. Furthermore, we often use a cumulative compounded DC generator, meaning the magnetic flux the series winding produces helps the one the shunt winding produces. Those are frequently seen in uses such as remote offices, lodges, or hostels without a reliable electric grid.
3. Shunt-wound generator
Shunt-wound DC generators are those where the windings of the armature and the field are parallelly connected. Because they can provide unchanging output voltage, we can use them for most lighting purposes, battery charging, providing excitations for alternators, portable generators, and so forth.
4. DC generator is reliable for off-grid use
A separately excited type of DC generator can provide lighting and power via field regulators. That makes it suitable for off-grid use, as does the self-excited DC generator we mentioned above. Plus, the fact they can supply constant voltage makes them adequate for large motors and power supplies. Also, they provide power with little electric fluctuations. That means you can find DC generators in construction sites, remote locations, factories, welding machines, and massive industrial machines. Plus, the costs can be lower compared to AC generators since the inverter is unnecessary.
Disadvantages of a DC generator
Now is the time to move on to the drawbacks. Here are several cons of a DC generator:
1. DC generator is incompatible with a transformer
While there are many upsides to a DC generator’s ability to produce voltage at a specific level, low or very high. However, it cannot use a transformer, meaning it is unable to convert the current voltage to a different one, which AC generators can. Unsurprisingly, this makes the design simpler since there’s no worry of a high voltage discharge during conversion.
2. Its efficiency and durability are low
While the DC generator is stable and reliable, its efficiency can go down quickly. The simple ones are rather efficient and easy to maintain, such as powering lighting or home appliances. However, if the power demands require complex wiring, this reduces the efficiency of converted energy. Also, it uses brushes and commutators that must be maintained and replaced many times over the life of a DC generator. Plus, brushes create friction, smell, and emit carbon.
3. The current in a DC generator is subject to many losses
DC generator converts mechanical to electric energy, but it incurs great losses in the process:
- Copper loss — Happens when current passes through windings. Consists of field copper winding loss, brush resistance losses, and armature copper loss.
- Mechanical loss — Friction between the generator’s parts causes mechanical losses.
- Iron loss, magnetic loss, or core loss — The current that passes through the armature creates induction but suffers two types of losses: eddy current and hysteresis.
4. Unsuitable for providing stable voltage over great distances
This disadvantage of DC generators is tied to the absence of transformers. While they can generate a certain voltage level at shorter distances, the stability goes down when the distance increases. Thus, you often see professionals recommend AC generators when the wiring is longer than 100 ft or roughly 30.5 meters.