Installing a timer in the electrical circuit of the main engine turning gear

Greetings! With this post I propose to start the section “reading electrical diagrams on a ship” and examine one of the interesting questions regarding the shaft turning gear of the main engine.

This article is primarily suitable for those who already have some knowledge of reading electrical circuit diagrams.

In my practice, I often come across the fact that the shaft turning device is not equipped with timers (time relays) for automatic operation from the factory, and engineers complain about this, that it is inconvenient.

For example, recently, a engineer forgot to turn off the turning gear and it rotated the crankshaft of the main engine all night, while no lubricant (oil pumping) was supplied to the cylinders. Judge for yourself how critical this is.

Let's look at the diagram of the shaft-turning device of the main engine.

Electrical circuit diagram of the shaft turning device of the main engine

Diagram of the main engine shafting device (if necessary, I can upload a separate pdf file with very good quality)

The scheme is typical for most ships, but there are no timers for AHEAD and ASTERN operations. I will not describe in detail how the circuit works. If you really need it, I can write. Write in the comments to the article. Even if one person writes that this is necessary, I will be happy to describe her work in accessible language.

I once planned to write a separate post on how to read electrical circuits on a ship, but I never got around to it. In addition, I don’t like writing general theoretical articles; I prefer practice, as in this case about circuit modification.

Turning gear starter panel inside

I also would not like to start the question of the feasibility of modifying the circuit. To be honest, this cannot be done! Therefore, if you were forced to do this, it is advisable to do it in a written form.

Installing the timer for the AHEAD operation

In fact, to set the timer for the “Forward” operation, we are not interested in the entire circuit, but only in its separate section with the 1KM contactor, which is responsible for the “Forward” operation, and the 2KM contactor, which is responsible for the “Backward” operation. Why do we need a 2KM contactor? The fact is that its normally closed contact (NC) is involved in the power circuit of the 1KM contactor coil. This is done to interlock the contactors in order to protect the motor in case the operator presses two buttons at once or the circuit of buttons fails.

Mutual interlocking of contactors 1KM and 2KM

Thus, when the command is activated (by pressing the S3 button) “Forward”, the contactor 1KM receives power - the motor rotates forward, while the NC contact 1KM in the circuit of the contactor 2KM opens and it will not receive power when the S4 “Backward” button is pressed.

Circuit with a timer (numbers are the numbering of cables and contacts)

The timer circuit is very simple. Thus, the T timer coil is connected in parallel with the 1KM contactor coil, and the normally closed NC contact of the T timer is connected in series with the 2KM NC contact.

Regarding the designation of the timer and its NC contact. In the diagram I depicted them schematically, without using international standards; in different diagrams of different equipment manufacturers they can be depicted differently.

Thus, when you press the S3 “Forward” button, the contactor 1KM and the timer T receive power - the motor rotates forward according to the timer for 15 minutes. After this time, contact T opens, contactor 1KM loses power and the motor stops.

Turning gear starter panel inside

By the way, pay attention to the normally open NO contacts 1KM and 2KM, which bypass buttons S3 and S4, respectively. Thus, when the “Forward” or “Backward” button is pressed, contactors 1KM and 2KM receive power and, with their contacts, bypass the supply circuit of their coils.

Interlocking of buttons and contactors

And another element of protecting the circuit and motor from incorrect operator actions, in addition to the mutual interlocking of the contactors, is the S3 and S4 buttons with mutual interlocking of each other. Thus, when S3 is pressed, it (meaning its contact) will close the 1KM circuit and at the same time open the 2KM circuit. And when you press S4, it will close the 2KM circuit and open the 1KM circuit at the same time.

We figured this out, but let's move on to connecting the timer in practice.

Circuit with timer

From the diagram above you can see how much needs to be changed in reality. Necessary:

• pass the supply wire from contact A2 of the 1KM coil to contact A2 of the timer T coil;
• connect in series the wire from contact 16 NC of the T timer and the wire of contact 109 NC of the 2KM contactor;
• pass the wire from contact A1 of the 1KM coil to contact 15 NC of timer T;
• pass the supply wire from contact 15 NC of timer T to contact A1 of the timer T coil.

Thus, a timer has been added to the scheme for the operation of the shaft turning “Forward”.

When you press the S3 “Forward” button, the contactor coil 1KM will receive power (the motor will start working) and at the same time the timer T coil will receive power, which will begin counting the time (15 minutes). After the set time, timer T will open its normally closed NC contact T and the 1KM contactor coil will lose power (the motor will stop).

Video of the timer working (such a timer was installed in the turning gear circuit)

By the way, the video shows the operation of the normally open NO contact of the timer. In the circuit we use a normally closed NC contact.

Timer in control circuit

Using the same principle, you can add a timer to the circuit for the “Back” operation.

The scheme turned out to be quite simple. Of course, it can be complicated by additional locks, and you can also connect the timer in a different way. Write about this in the comments to the article.

I hope this post was useful for you. Thank you for your attention!