NoLand RS11, analog to NMEA 2000 engine monitoring
What follows is a first time guest entry by regular Panbo commenter Adam Block, who is planning a 2011 Pacific crossing aboard his Nordhavn 47 Convexity. Adam says "he had no idea what he was getting into when he started a recent electronics upgrade," but he did manage to convert analog (generator) engine data into NMEA 2000 for display in the N2KView software above and elsewhere. He's also written a clear explanation of the options available for this tricky task, and the specifics of the NoLand RS11 he used...
Today I'm thinking about engine data. Though Convexity has a single primary engine, we actually have three diesel motors on board. The other two are a wing (get-home) engine and a 12 kW generator. Getting engine data onto the NMEA 2000 bus (and from there onto one of those displays) can be easy or hard, depending on the kind of motor you have. Owners of larger outboards have it easy: Mercury, Suzuki, Yamaha, Evinrude, and Honda all output lots of engine parameters in NMEA 2000 format, though you may need a funky wiring harness or digital gauge to make the backbone connection.
In general the same can be said for modern electronically-controlled diesel prime movers; most support an engine data protocol called J1939 that runs over the familiar industrial CanBUS (which happens to be the same wiring and communications standard on which NMEA 2000 is based). J1939 can be used to exchange data between two engines (to synchronize RPMs on a twin-engine vessel, for example) or to drive physical gauges -- Convexity's analog-looking engine gauges actually receive digital signals via CanBUS. J1939 engine messages aren't the same as NMEA 2000 engine messages, but Maretron offers the J2K100 converter box to bridge the two networks together. (It's a one-way bridge: the J2K100 passes J1939 data from the engine network to the NMEA 2000 bus, but no information flows the other way).
That's all fine for folks with brand new boats, you say, but what about the thousands of sail- and powerboat owners with older engines that lack electronic fuel injection and the engine computer needed to output digital performance data? Or in my case, what about my Lugger wing engine and Northern Lights generator, neither of which supports digital gauges? If I'm adding a complete monitoring system to the boat, it seems wrong to exclude them. (This is especially true of the generator, as its gauge package is in a hard-to-see location near the top of the stairs to the staterooms.)
It took some research, but I came up with three possible solutions for getting NMEA 2000 data out of my analog engines:
- Maretron EMS100: This analog adapter is designed for Yanmar engines, and Maretron doesn't currently certify its use with motors from any other manufacturer. They did helpfully send me a Yanmar engine wiring diagram in case I wanted to try and make up the required harness on my own, but one look at the diagram's maze of lines quickly put me off that idea.
- NoLand Engineering RS11: Browsing through the 2010 Gemeco catalog, I stumbled on a product (and manufacturer) I'd never heard of. NoLand is a small Florida outfit that makes a variety of mostly NMEA 0183 splitters and multiplexers. Their new RS11 converts the voltage signals many analog engines use to drive gauges into NMEA 2000 PGNs. The RS11 can be configured for a range of different input types and at $230 is a relative bargain.
- Albatross
ALBA-Engine:
Albatross is a Spanish company that makes some interesting NMEA 2000
sensors
and interfaces (they also appear to distribute NMEA 2000 devices from
nearly
all the other big names in this category, including Actisense, Maretron,
and
Airmar). Unlike the RS11, the ALBA-Engine works with either resistive or
voltage senders. But Albatross is hard to find in the U.S., and their
stuff is
correspondingly expensive - the ALBA-Engine costs nearly $500. {Panbo discussion and slide show here.}
Based on price and capabilities -- my gauges are voltage-based -- the RS11 seemed a good fit. I ordered direct from the NoLand web site, and the unit arrived about a week later. In the box was a small circuit board with a terminal strip on one side and an attached NMEA 2000 drop cable, a serial cable (the RS11 needs to be programmed before use via Windows PC), a somewhat flimsy-feeling plastic circuit board cover, and one of those business card-sized CD-ROMs that only work in slot-loading drives.
You can wire the RS11 directly to your engine, but I found it much simpler to connect to the back of the engine gauges themselves; all of the pickups are in one place, and I prefer to work in the comfort of the pilothouse than the confines of the engine room. I started on the generator first. All of the gauges have standard male disconnects on the back. The quick and dirty approach for small gauge sense wires -- I used a short length of 8-conductor 18-gauge Ancor data cable -- is to just bend the conductor over the disconnect tab and then press the female connector on the engine wire down over the tab. This approach won't pass any good electronics installer's muster, though, and probably violates half a dozen ABYC regulations; the right way is to use a standalone piggyback adapter, or a female disconnect with a piggyback connector as shown in the photo below. The RS11 needs only a single sense wire per gauge, which normally connects to the 'S' pin on the gauge body; as a ground reference it uses the ground pin of the attached NMEA 2000 cable. The NMEA 2000 bus supplies power to the unit.
Engines and their gauges vary widely, so before it will output accurate data you have to calibrate the RS11 using the somewhat rudimentary Windows application shown below. The terminal strip has two tachometer inputs and four analog inputs. With some limitations, the analog inputs can be used to monitor any of the following: oil pressure; oil temperature; engine (coolant) temperature; coolant pressure; fuel pressure; alternator voltage; turbo boost; and tilt/trim. Not all engines will output all of this data, and with only four inputs you'll have to choose which of these are most important. (The RS11 can also be connected to two separate engines, in which case you divide the four inputs between the two engines.)
Monitoring RPM requires knowing the number of "pulses per revolution" output by the engine. This varies depending on the engine type, and the RS11's manual does a pretty good job explaining what information you need to properly calibrate the unit. In my case I needed to know the number of teeth on the flywheel; a quick inquiry to Lugger provided the answer (126), which I entered into the configuration utility.
Analog calibration is a bit more complex. The RS11 operates on the principle that there is a direct straight-line relationship between voltage at the back of the gauge and the actual value being monitored. In order to determine this relationship, you enter two voltages and actual values into the calibration software, which then derives the proper formula (in the form value = m � voltage + b, where m and b are constants) from the supplied data. For example, in the case of engine coolant temperature my measurements were as follows:
Actual temperature #1: 58� F
Measured voltage #1: 6.20V
Actual temperature #2: 110� F
Measured voltage #2: 2.33V
Collecting these numbers can be a bit of a chore, especially if they are changing as you measure them. In the case of the engine temperature, I assumed that "actual temperature #1" was simply the ambient temperature of the engine room before I started the engine (it had been shut down for a few days). I turned on power to the engine and probed the back of the gauge with my multimeter to determine "measured voltage #1". For "actual temperature #2" I started the engine and waited for it to warm up enough to show a reading on the analog gauge. I probed the voltage at the same time as I read the temperature off the gauge, and entered the second set of numbers into the configuration utility. Needless to say, analog gauge accuracy, parallax, and timing all contribute to the quality of the calibration. Values that don't change much over time, such as oil pressure, are easier to calibrate.
With the calibration data entered into the
configuration
utility, it was time to download it to the RS11. I had some trouble
here: the
RS11 refused to accept the new settings. NoLand's head engineer
suggested that
a reboot or two (disconnect the NMEA 2000 cable to cut the power, then
reconnect) should fix the problem, and it did. Seconds later my
generator's temperature,
oil pressure, and output voltage popped up on the Maretron N2KView
screen (seen at the top of the entry).
As you can see, my calibration was pretty good, as the displayed values closely track the analog gauges:
Final mounting of the RS11 interface was easy due to its small size (3" x 3.75") and light weight; I simply mounted it to the back of the breaker cabinet and cinched down the cables:
With a little patient calibration, the RS11 is easy to install and works as promised, though I did have a couple of issues. First, on at least one occasion the RS11 seemed to lose its sensing capabilities. After I left the engine shut off for a few days (but the NMEA 2000 network, and thus the RS11, still powered up), when I restarted the engine the unit sent no engine data. Rebooting the RS11 cleared up the problem but it's something I'll be keeping an eye on.
My
other issue arose from the nature of the algorithm the RS11 uses to
calibrate
analog voltages. Some analog gauges use inverse voltage; that is, when
the
voltage from the engine's sender drops, the value displayed on the gauge
increases. This is the case for our generator's coolant water
temperature. When
the RS11 is calibrated, the formula it derives for this kind of gauges
has a
negative slope (that is, in that equation above, y is negative).
The
problem arises when the engine is turned off, and the voltage measured
by the
RS11 is zero. This zero voltage is spurious - it's not a true output
from the
engine, but an artifact of the engine being off - but based on the
formula in
the RS11 it appears that the temperature is very high. In our case the
N2KView
gauge reads 254� when the engine is shut down. I spoke to NoLand about
this
issue, and suggested that the unit sense when it the attached engine is
off.
Their chief engineer confirmed they would like to add that feature - one
I
believe the ALBA-Engine does have - but that working within the
limitation of
the small amount of memory on the RS11's circuit board was a challenge.
How about a Panbo round of applause for Adam Block {ed}
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at May 26, 2010 11:50 AM
Adam,
congratulations on this great, and detailed not only presented but more important tested RS11.
Thanks!