On my current project, my company was required to install pole lights for a temporary employee parking lot to be used during the construction of a new building. The service from the utility for the pole lights would not be installed until after the parking lot began to be used, so a rental generator was ordered as an interim power solution. In order to run the pole lights at night, a time clock was needed. Expecting a standard time clock, I was surprised when the generator rental representative presented the Teco SG2 PLR.
- Multiquip DCA70USI WhisperWatt Ultra-silent Generator (it is amazingly quiet) with a set of terminals for the autostart feature
- Teco SG2 12HR-12D v3 PLR (programmable logic relay)
- Pole lights in a parking lot
Thankfully I was familiar with the Teco SG2. I had experienced it as a side-project at IEC’s school, as well as in one of its alter-ego forms, the Allen-Bradley Pico, at Red Rocks Community College. The generator is equipped with a 2-wire terminal block for its autostart feature, requiring a dry set of a contacts from a relay controlling the condition of the autostart. One of the output contacts (Q1 in the picture) on the Teco SG2 PLR would suffice.
Only a few steps needed to be done to configure the SG2 to start the generator. The first step was the physical wiring. The SG2 required 12V DC power, so I connected the negative power input of the SG2 to the generator chassis and took the positive power input from the hot side of the autostart terminal block. I then connected a second wire from the hot side of the autostart block to the common of the Q1 relay output on the PLR. The normally open (NO) side of the Q1 relay was wired to the other side of the autostart terminal block allowing the Q1 output relay to control the autostart on the generator.
The next step was to program the SG2. Although I had never programmed it from its front panel (I had always used a computer as an interface), the procedure proved to be quite intuitive. The keys are self-explanatory, and the menu system is straight forward. I checked the system time on the internal clock and set it to the current time. Then I went into the ladder program and went to work. There was an existing program which I erased. I added a real time clock (RTC) on line 1 to regulate the start and stop times of the generator so as to control when the pole lights in the parking lot were on or off. The RTC comes with several modes. I chose mode 1 (daily timing), entered Sun-Sun (Sunday through Sunday), and set the on and off times (7pm to 7am).
On line 2, I added a NO contact tied to the RTC’s internal coil, and on the same line as the NO contact, the Q1 relay output coil. So, when the RTC activated, its NO contact closed and activated the Q1 output relay, thus starting the generator. We put a couple of test times in the RTC for testing and it all worked as it should. All was well until…
One of our foreman stopped-by later that night to make sure that the lights were on. They were not on. Upon inspection of the generator, it was in a fault condition. He switched the generator to manual and went home.
The next day, we did some tests and found that the timer was working properly. The generator had an internal fault that manifested itself one other time when we switched it to manual which showed us that we could not rely on the autostart feature. Since we were using the generator for only a couple of weeks, the easiest path was to change the start time to 10 minutes before we left at the end of the work day so that we knew the generator had started.
That said, I decided to write a program that would handle this fault and be more fault-tolerant in general, just for fun. I incorporated a way to handle any glow-plug preheating and any condition where the generator did not start in 10 seconds, such as the internal fault we are facing. Below are images of both LogixPro (a good program for quick program prototypes) and Teco SG2 ladder logic programs. I did not find a way to access the enabled bit for the timers in the SG2 (though I did not look very hard, nor did I look at the timer files), so I just used their done bits, which changed the way I implemented the logic in the SG2 version from the LogixPro version. I also added a message to the screen of the SG2 to show when it went into a fault condition.
The SG2 program basically does the following things:
- Controls the generator autostart and run with a real time clock (RTC)
- Attempts to start the generator for 10 seconds
- If the generator does not start in 10 seconds, it rests for 50 seconds and tries to start again
- The start procedure is attempted 5 times. If it does not start on the 5th attempt, the SG2 displays a fault message.
- If the preheat indicator light activates on the generator, the 10 second start timer is stopped so that the generator can preheat for as long as it needs without affecting the 10 second start window. I02 would be connected to a NO set of contacts on the same relay that turns-on the preheat indicator light on the generator.
- A voltage monitor (could be a phase monitor or as simple as a 277v relay) connected to I01 monitors the status of the generator to indicate if it is running or not.
- The fault counter is reset either by pressing the up arrow on the SG2 interface or when there is a successful start of the generator.
Here is a zip file containing both ladder logic programs: Generator Auto Start Timer. You can download the SG2 programming software, load the ladder logic program, and start the emulator to see how it works. You can interact with it by activating the I01 and I02 inputs (preheat and voltage monitor). You can change it and play with it all you like.