Garmin Voltage Discrepancy

[Jon magowan]

I have upgraded all the Garmin stuff with brand new Garmin stuff (GPSMAP 723, GMI 20, Reactor 40, GHC 50). All professionally fitted and connected via an NMEA 2000 network.

The system voltage is displayed on my Chartplotter. I’ve checked it and very happy that it’s correct.

The voltage at the GMI 20 instrument is consistently exactly 1 Volt below the system voltage.

The autopilot GHC 50 flagged up a low voltage alarm briefly on my last outing.

The reactor 40 autopilot is frequently but randomly flagging up an issue with the rudder sensor calibration (troubleshooting message suggests we check the voltage at the autopilot ECU).

What on earth would account for this voltage discrepancy? The cabling has all been replaced with the cables that came with the new devices.

 

[KompetentKrew]

Voltage drop on the cable to the GMI 20 - maybe much more convoluted wiring than to the plotter? - or a bad connection.

Is the GMI 20 being powered off the NMEA 2000 network? If so, is the NMEA 2000 network being powered off the autopilot? I can't be arsed to check if this is an option for your autopilot, but I think it is with some models. If so, then a bad connection or voltage drop to the autopilot would cause lower voltage on the NMEA 2000 network.

 

[Sandy]

The voltage at the GMI 20 instrument is consistently exactly 1 Volt below the system voltage.

I think Garmin are asking rather a lot of this dinky wee instrument. I have a GMI 20 myself and must try this when I am on the boat.

They are taking a voltage off the power feeding the NMEA 2000 network where there are a whole bunch of data packets flying about and somehow capturing the voltage from somewhere on a network of unknown length to allow the GMI 20 display a figure that is neither calibrated or validated. Perhaps, at best, a useful guide.

I don't even trust the voltage or amperage on my switch panel as checked against the Victron kit it can be as much as 1.5 amps and 1 volt difference! It's a quick guide as I pass the nav station that the batteries have some charge in them.

 

[PaulRainbow]

Voltage drop on the cable to the GMI 20 - maybe much more convoluted wiring than to the plotter? - or a bad connection.

Is the GMI 20 being powered off the NMEA 2000 network? If so, is the NMEA 2000 network being powered off the autopilot? I can't be arsed to check if this is an option for your autopilot, but I think it is with some models. If so, then a bad connection or voltage drop to the autopilot would cause lower voltage on the NMEA 2000 network.

It is powered from the N2K network. Some Raymarine autopilots can power the network, but not Garmins

 

[Jon magowan]

Thanks guys.
Actually the GMI 20 doesn’t appear to be sensitive to the voltage. I really like it (despite being blooming expensive!). It works solidly and consistently.
What bugs me is the autopilot randomly failing. I sail solo quite a lot and having an unreliable autopilot is crippling.
My feeling is that the rudder sensor is much more sensitive to the voltage it’s getting. I’m no electronics expert. Does this seem like a likely scenario, ie the GMI 20 working reliably with a lower voltage but the rudder sensor being much more sensitive?

 

[Sandy]

Thanks guys.
Actually the GMI 20 doesn’t appear to be sensitive to the voltage. I really like it (despite being blooming expensive!). It works solidly and consistently.
What bugs me is the autopilot randomly failing. I sail solo quite a lot and having an unreliable autopilot is crippling.
My feeling is that the rudder sensor is much more sensitive to the voltage it’s getting. I’m no electronics expert. Does this seem like a likely scenario, ie the GMI 20 working reliably with a lower voltage but the rudder sensor being much more sensitive?

From memory I think the voltage range on the GMI 20 is 9 - 16 volts.

When your autopilot 'randomly failed' what was the voltage and do you know how many amps you were drawing? If everything is switched on your voltage can drop to about 10 volts.

I run as little as I can when sailing, basically instruments, coms and navigation lights to minimise the power draw.

 

[Jon magowan]

Thanks Sandy,
Voltage was about 12.2 on GMI 20, about 13.3 on Chartplotter last time the autopilot failed. Domestic batteries are healthy and fully charged (recently checked at Plymouth Battery Centre). No big drain on the battery bank (sorry, no idea of the amps). Autopilot failure seems to be totally random. Perhaps next time I’m onboard I’ll engage the autopilot and load up the batteries with as much as I can to see if I can trigger a failure.

 

[Sandy]

Thanks Sandy,
Voltage was about 12.2 on GMI 20, about 13.3 on Chartplotter last time the autopilot failed. Domestic batteries are healthy and fully charged (recently checked at Plymouth Battery Centre). No big drain on the battery bank (sorry, no idea of the amps). Autopilot failure seems to be totally random. Perhaps next time I’m onboard I’ll engage the autopilot and load up the batteries with as much as I can to see if I can trigger a failure.

Your autopilot should be OK on that.

Plymouth Battery Centre are well respected round these parts.

 

[vas]

as already stated, GMI get its power from the N2K bus, plotter, a/p get it directly from the el.panel (at least should!)
My boat is 24V, have a 24->12 dropper that feeds the N2K bus which sits constantly at 11.9V (got the wrong dropper...) as I have close to 20devices on the N2K bus. Still all work fine!
Other devices and a/p is happy, my guess is some dodgy connection of the a/p ECU or dying batteries. GHC controller should report exact voltage to the ECU (iirc, was playing with the settings a couple of weeks ago) and you can configure the voltage for the low voltage error. Mind the warning doesn't disconnect the a/p.
Maybe post the exact message next time? is the digital compass properly configured? What rudder sensor have you installed?

V

 

[Jon magowan]

Thanks Vas,
Here are the messages that I’m getting on the Chartplotter.
Rudder position on the GHC 50 appears to be correct despite the message.
Rudder sensor is very unusual……..details to follow…..


H

 

[Jon magowan]

Here is the steering system looking forward. The rudder sensor is mounted on the Lewmar Integra drive unit.
Lewmar initially denied that this sensor was anything to do with them but after a bit of back and forwards they conceded that this was their design that never went into production. They have no idea how it got on my boat, and neither do I.
It’s a potentiometer connected by a small belt to the Lewmar drive.
I’ve removed the drive and checked the potentiometer. It seems to be working ok and the rudder position on the helm control always seems to be correct.
But yet, it keeps failing, absolutely randomly.

 

[vas]

doubt I can be of any help as I'm only familiar with hydraulic A/P systems using a garmin A/P pump...
Wonder, how this rudder sensor contraption is connected to the system?
Does it somehow "mate" with the Garmin A/P, is there a converter that brings the data to N2K bus?
and how is the steering motor thing whatever that is connects to the garmin ECU?

I wonder if the A/P system would work without the rudder sensor?

TBH, I'd be tempted to unplug the thing and see what garmin thinks of it
maybe it's going to work better
May have to rerun the config of the A/P

V.

 

[Sandy]

Do you have a 'autopilot' computer between the rudder sensor and the chart plotter?

Whoever fitted my autopilot went down the Raymarine route, there is a course computer (big box hidden in the bowels of the boat) and the rudder indicator is only displayed on the one Raymarine instrument onboard.

 

[Jon magowan]

Yes, there is a ECU (electronic control unit) which is the brains of the autopilot which is connected to the rudder sensor as well as the Chartplotter, helm control and CCU (course computer unit). All talking to each other. Very clever….if it works !

 

[PaulRainbow]

Thanks guys.
Actually the GMI 20 doesn’t appear to be sensitive to the voltage. I really like it (despite being blooming expensive!). It works solidly and consistently.
What bugs me is the autopilot randomly failing. I sail solo quite a lot and having an unreliable autopilot is crippling.
My feeling is that the rudder sensor is much more sensitive to the voltage it’s getting. I’m no electronics expert. Does this seem like a likely scenario, ie the GMI 20 working reliably with a lower voltage but the rudder sensor being much more sensitive?

I don't think rudder sensor is voltage sensitive. But, i'd carefully check the voltage at the ECU as well as checking all connections.

The Lewmar unit is a rotary drive, commonly fitted to Bavarias. If it's faulty you might be able to fit a Garmin rudder sensor to the steering quadrant at the transom.

 

[Jon magowan]

I don't think rudder sensor is voltage sensitive. But, i'd carefully check the voltage at the ECU as well as checking all connections.

The Lewmar unit is a rotary drive, commonly fitted to Bavarias. If it's faulty you might be able to fit a Garmin rudder sensor to the steering quadrant at the transom.

Yes, my plan is to fit a Garmin GRF 10 rudder sensor to eliminate that as a source of the fault.

 

[Pye_End]

deleted.