Install of Dual SeaGauge Remote Sensor units on older twin CAT 5000 with quad SeaGauge Displays
The M/Y Angle is a 120 ft motor yacht based in Fort Lauderdale Florida. It is powered by twin Cat 5000 engines. The existing instrumentation consisted of a set of mechanical gauges located directly on the engines and a separate set of dual station VDO analog gauges in the wheel house and fly bridge. Also in the engine room were twin Northern Lights 12VDC generators with analog VDO gauges directly attached to each Gen set in an instrument panel.
The owner wanted to convert the mostly non functional VDO style gauges to a digital instrument panel while still keeping the mechanical gauges in the engine room. The available space in the wheel house allowed for removal of the Port and Starboard analog gauges and replacement with dual 5.7” dia SeaGauge G12HD displays. The fly bridge had more available space to accommodate dual SeaGauge G24N 8.4” weather resist displays with glass touch screens. The fly bridge was partially covered but still exposed to the elements. A Plexiglas cover provided protection in case of rain. A canvas cover was also in place when docked.
The requirement to maintain existing mechanical gauges in the engine room was accommodated by separate dual station electrical senders for the wheelhouse and fly bridge analog gauges which consisted of tachometer, engine temp, oil temp, oil pressure, transmission pressure, and amps. A separate set was installed for Port and Starboard engines. The owner wanted to add twin EGT probes for each engine to monitor turbo temps, Fuel Filter Vacuum, and a set of gauges for each of the DC Generators (Temp, Oil PSI, and Voltage). A total of 12 gauges for Port and Starboard Instrument panels. It was determined that a dual set of SeaGauge Remote Sensor Interface units could be mounted on each engine and individually drive two SeaGauge Displays (Wheel house and Fly bridge) via wired serial connection. Four CAT5 network cables were run from the engine room to the Wheelhouse (2) and Fly Bridge (2). These small cables would replace the existing set of dual station sender wires (two 16 wire bundles).
Since there were no existing gauges in the Wheelhouse and Fly bridge for the Gen Sets, they were to be wired in from the Gen Set Analog panel to the SeaGauge Remote Interface unit to multiplex the gauges to both display heads. With a requirement to keep the existing Gen Set gauges in place in the engine room, it was determined to tap into the existing sender terminals and calibrate the voltage signals to appropriate Temperature and Oil Pressure readings. Terminal strips were easily accessible in each panel to tap into the gauge sensor input. The SeaGauge Remote sensor unit can accept both resistive type senders and voltage input. When a traditional analog style gauge is used, it provides a bias voltage (usually 12V) to a sender that converts temperature or pressure to a variable resistance. This in turns creates a variable voltage signal from 0V to about 10V that is proportional to desired reading. The Gauge uses the voltage to drive the needle movement. SeaGauge Remote Sensor unit can convert this voltage via 256 point calibration tables to create an accurate mapping of the sensor reading. While this is not as accurate as directly using a dedicated and separate sender due to variations in bias voltage from the analog gauge, it is usually more than adequate for most installations. The High impedance of the SeaGauge Remote Sensor unit in voltage sense mode prevents affecting the analog gauge when in parallel mode. Operational tests of the Gen Set analog gauges from cold start to max temp showed a voltage swing of 7.0 volts cold down to 2.4 volts hot. Therefore a 3:1 voltage divider was selected to achieve the best resolution.
As is typical in most retrofit projects, the first step is to determine the existing wire schematics and trace where the analog senders were located on the engines. Since the CAT 5000 had a completely separate mechanical Instrument panels, there were dual locations for the Temperature senders. Both mechanical OIL pressure and Transmission Pressure are sensed from Hydraulic lines. Fortunately, the sender wires for the analog Wheelhouse and fly bridge gauges were routed to a terminal strip located behind the mechanical gauge set in the instrument box. Removing the 8 bolts from the panel allowed access behind. With no schematic available to trace the sender wires, investigation was required to determine which positions were to be isolated and disconnected. One technique was to first take voltage readings and with power off and determine if there were any live circuits. Then power was applied to drive the existing analog gauges and voltage readings taken. Being a 24VDC system, any terminal going to a sender with power on and engine cold would produce a voltage less then 12VDC. Once these locations were found, the sender wire could be disconnected from both the Wheelhouse and Fly Bridge gauges to see if the voltage dropped back to 0V. For example, Engine Temperature may read 7VDC on a cold engine, disconnect the sender wires from both Engine Temp gauges and it will drop to 0V. This was repeated for Oil temp, Oil pressure, and Transmission Pressure to isolate the sensor wires and label the location on the terminal strip. Fortunately these were all located together and were actually part of a jacketed cable bundle routed up to the Wheelhouse and then on to the fly bridge. The bundle contained the four senders plus sensor ground. The sender wires were disconnected from the terminal strip and replaced with color coded jumpers to the SeaGauge Remote Sensor Unit terminals. It would have been desired to also disconnect the sensor ground wire going up to the wheel house but no other suitable ground was found to supply the 12VDC power for the display head so it was retained for that purpose.
The one gauge that was not retained or replicated was the AMP meter. Mechanical Current measurement was done via shunt in the engine room and via embedded shunts in the Wheelhouse and fly bridge. Shunts require passing the heavy gauge cable carrying the load under test through the sensor and then amplifying the very small voltage to achieve a reading. The complexity of Amp measurements was replaced by the relative simplicity of Voltage measurement which gives a very similar indication of alternator charge status. Therefore AMP measurements were removed from the Wheel House and Fly bridge and replaced with alternator voltage. However, it is very important to jumper the two wires that feed the existing analog gauge when removing them or else the circuit will be open and not function.
During the survey of existing senders installed on the engine it was determined the temperature senders were very difficult to access and of unknown origin or type. Since resistance readings of cold and hot showed they were operating correctly, it was decided to keep them in place and simply load a corresponding Dual Station calibration tables. Dual station senders are used to drive dual analog gauges from one sender and have a different resistance curve then single station. When disconnecting both analog gauges (wheel house and fly bridge) and connecting to SeaGauge Remote Sensor unit, it applies a single station load. However this easily accommodated by loading a dual station table. Resistance measurements of the OIL pressure senders and transmission pressure senders (with terminals disconnected) showed an open circuit and there in need of replacement. These senders were very accessible and easy to replace. Given the age of the vessel and heat of the engine room, all pressure sender wires were cut, stripped, cleaned and re-terminated to ensure good electrical connections.
New instrumentation consisted of adding dual EGT probes to monitor the twin turbo on each engine. There are already plugged mounting holes on the exhaust to place the K-Type probes so installation was very simple. 14 feet of K-Type extension wire was need to route back up to the SeaGauge Remote Sensor Unit and feed directly to the K-Type amplifiers built into the unit. It is very important to always use matching K-Type wire when installing EGT probes. K-Type probes have a temperature range of 1600F.
One unique gauge added to the system was a Fuel Filter Vacuum gauge. The engine room already had a mechanical filter gauge to detect clogged filters and the owner wanted to replicate the gauge up in the wheelhouse. A OMEGA sensor part number PX209-30VAC was chosen with an operating range of 0 to -14 PSI (30 Hg). This sensor is accurately calibrated to produce a proportional voltage output of 0-5V. The SeaGauge Remote Sensor Unit has a regulated 5V terminal to power this type of sender. The theory is that the filter will draw less vacuum as the filters become dirty. The sensor voltage output was feed into the high impedance voltage sense on the SeaGauge Remote Sensor unit.
Most of the installation time was spent on routing and terminating the sensor wiring into the SeaGauge Remote Sensor terminal strips. All ends were labeled and terminated with spades and then secured to the screw down terminal posts. Cat5 cable was used to route data from the Gen Sets to SeaGauge Remote Sensor Unit. It was important to include the Ground from the Gen Set so that the voltages were common referenced. The 4 display CAT5 cables we pulled through without end connectors which were applied afterwards. The Displays uses RS232 serial signals but CAT5 serves as an inexpensive choice. The RS232 TX (green/white) and RX (orange/white) wires are twisted with the ground (Green and Orange) to provide some shielding. It is very important to always use stranded CAT5 and not solid wire. The Solid wire will easily break at the connector ends.
The Power for the Remote Sensor Unit was taken from the RUN terminal on the Engine Instrument panel. This was a 24VDC. When the RUN is active, 24VDC power is also supplied to Wheel House and Fly bridge Instrument panels. When investigating the power taps in the Wheel House it was observed that different ground points had non-zero voltages from 0.5V up to 2V. It was also noted that the Main Volt bus as high as 28VDC. Since the Displays nominally run at 12VDC and also because over voltage drop during Engine start – it was decided to add separate 24VDC to 12VDC converters for each of the 4 displays. The DC converters provide better power conditioning and are much more efficient then adding a ballast resistor which was used to power the previous Analog gauges. It is noted that the analog gauges operated at 12V but only (24-28V) was present. Therefore ballast resistors were used to drop the voltage down to 12-13V which wastes much power and generates significant heat. The inefficient use of ballast resistors multiplied by the number of gauges (24) is a significant load on the Voltage and Ground bus. For example, a pressure Gauge with a 55 OHM load at 28V draws 500 mA or 12Watts. Multiple that by 24 gauges and that is over 280 watts. Compared to a SeaGauge G24N display and DC-DC converter running at 90% efficiently, results in 10 Watts per display. Therefore the Digital Display panels use much less power and thus do not affect the ground as much as the analog gauges.
The initial system check was done after power was connected to displays and Remote Sensor Unit. Engine switch was in RUN but not started. Both Wheel House Displays (Port and Starboard) became active with default dial gauges for RPM, Eng Temp, Oil PSI, Oil Temp, and Tran PSI. Since new senders were installed for the pressures, readings showed 0. When the Sender wire was disconnected for the pressures, they switched to max which is expected. The Temperatures showed the ambient air tem in the engine room of 85F. Voltage showed 28V (due to charger). Next, the display screens were modified to add both EGT probes and Fuel Vac in Digital Data Mode. The EGTs read the same temperatures as the other temp gauges. The Fuel Vac read 6.5 Hg (engine off). An additional display page was added for the three Gen Set gauges. The Temp and Oil Pressure read OFF since the generator was off and therefore no voltage was being produced. Next, the Gen Set was started and voltage readings taken at the terminal strip and matched with the readings from the analog gauges as the motor warmed up to operating temperature of 180F. Oil Pressure was steady at about 70 PSI. The voltage readings were used to create new calibration tables to correctly match the digital gauge values to the analog Gen Set values.
Once the initial readings were confirmed, the Main Engines were started and warmed up. As engines neared operating temperatures, readings were confirmed with the Mechanical gauges and inferred gun on the water cooling jacket and Oil Pan. Oil and Transmission pressure were as expected (60 PSI oil and 200 PSI transmission) Oil temperature appeared to be lower than water jacket by about 20 degrees but matched the Mechanical gauges. Port and Starboard EGT probes showed about 200F to 230F at idle. The RPM calibration was modified to match the digital tach on the Mechanical Panel of 600 RPM at idle. The procedure was repeated for the starboard Engine and Gen Set.
At the owners request, the existing analog gauges were left in place until the captain approved the digital panels were functioning as expected. Once the captain OKed the displays were giving the correct readings, the old gauges were removed and wire harness cut and terminated. Again, when removing the AMP gauge – it is important to jumper the existing wires. Once the old analog gauges were removed, the carpenter was able to proceed and cutout the holes for the new panels and rework the dash for final installation.