Simrad 7 Cruise - Low voltage

[SaylorMade]

I have a Simrad 7 Cruise, that for some reason shows about 1 volt lower voltage than the actual battery voltage, and sometimes when the autopilot works hard, it starts to give low voltage alarms.

I figured it must by my own connection between the wire fom the panel to the wire in the Simrad, so I cut it, and soldered a new one.
Still the same.

I have measured at the connector from the panel, which gives me 12,8 V (Simrad says 11,8).
I even measured at the end of the Simrad cable just where it plugs into the instrument with a result of 12,7V and still the display says 11,8.

The two pins that connect + and - to the cable look pristine. (But they got a gentle cleaning anyway.)

No difference wether the sonar cable is plugged in or not.

Any ideas?

There does not seem to be any newer firmware, and no results from folks with similar problems appear in a google search .

[Statistical]

Since it measures fine on the device end of the cable unless the device is simply malfunctioning the connector on the device itself is the last possible place. To be clear I am talking about the connector on the device itself. Did you try cleaning the connector on the device with alcohol. Any signs or corrosion or charing?

[SaylorMade]

Originally Posted by Statistical

Since it measures fine on the device end of the cable unless the device is simply malfunctioning the connector on the device itself is the last possible place. To be clear I am talking about the connector on the device itself. Did you try cleaning the connector on the device with alcohol. Any signs or corrosion or charing?

Yes, the connector on the device is two thin gold "needles", they look pristine, but I did try and clean them gently with some contact cleaner.
But honestly they look like new.

I think it has been like this from the beginning (2+ years old), but never got to it until now. I always assumed that it was some of my work downstream from the instrument.

[wholybee]

First, measuring the end of the cable when not plugged into the device will always read full voltage. Voltage drop only occurs when there is a load. So, you would need to measure at that connector while plugged in and device is turned on.

Then, to find _where_ the problem is, measure voltage at various points between the battery and the device, while the device is on. Start at the battery, which you know is 12.8. Then move to the main fuse. Then the main disconnect, etc. Work through the main DC panel, breaker the chart plotter is on, etc.

When you get to the point where there is a significant drop, there is a problem between that point, and the previous point you measured with no problem. Because the autopilot affects it, there is a good chance the problem is somewhere in common between the two. Perhaps in the main DC panel somewhere, or a common ground.

[Statistical]

Originally Posted by SaylorMade

Yes, the connector on the device is two thin gold "needles", they look pristine, but I did try and clean them gently with some contact cleaner.
But honestly they look like new.

I think it has been like this from the beginning (2+ years old), but never got to it until now. I always assumed that it was some of my work downstream from the instrument.

Well the fact that you measure it as 12.8V at the panel when the device is connected and powered on would indicate to me it probably isn't your fault. The only remaining step would be measuring voltage at the device under load. A custom connector instead of push terminals or ring terminals makes that a bit more tricky but it can be done. You can use a terminal strip or stud or some other connector with exposed conductor. You could even remove part of the insulation on a the wire as a temporary test.

DC positive panel <-- existing wire-----> terminal strip or terminal post <---- temp wire ----> device connector. Same thing with the DC neg side. Now you have a pair of test points. If that still shows ~12.7V under load the issue is the device. If it shows 11.8V or whatever the device is showing and the panel shows 12.7V then the issue is the wiring between panel and device likely at the connectors. Possiby a bad crimp?

[SaylorMade]

A follow-up:

Thank you everyone in this thread for good advice.
For one, I was not aware that without load, it will always show the voltage from the battery.

It is impossible to meassure at the end of the cable that goes into the device, while plugged in, so I decided to go back to the panel, and follow the cable from there, and man... it turns out that it get it's power from a USB plug, that is powered by a cable from the busbar that also has one or two places where it is assembled.

Just by twiddling the connections I got the drop down to 0.2 to 0.3 volts, so I now know that I have a project on my hands. That mess (the other stuff look almost equally ..... up) needs to be dealt with soon.

I do meassure full battery voltage on the panels busbar itself though, so I take that as a good sign, that when I clean up that panel-mess, I should be in much better shape.

Am I right, or just optimistic?