[TG] [TG11] Sounder Supply Voltage Too Low

[Tom - Raymarine - Moderator]

Hello Mark,

Personally I'm not aware of any other cases, but that's not to say that other people aren't seeing it and if anyone else is I would be interested to hear about it.

Re. supply voltage: it's surprisingly difficult to say for sure that voltage is good:

• Voltage at the battery or at the distribution panel is not going to be quite the same as product supply voltage (there's always some degree of drop along the run of cable and connections) and if there's a bad link in the chain somewhere then that voltage drop can be significant
• Voltage measured at the display end of the cable is no-load: if there's a high-resistance connection somewhere (and this is a boat: high-resistance connections are very likely) then you will see a very different and much higher voltage with no load than with a few amps being drawn through the cable.
• A multimeter or distribution panel indicator will only ever show an average voltage, they will give no idea of the stability of the supply or the lowest voltage that will be reached when there are dips due to current being drawn by other products being powered through the same distribution system. Multimeters only measure voltage a few times a second, but I've seen voltage dips as short as 10 milliseconds cause product brown-out reboots. You can only see that kind of voltage dip on an oscilloscope, which is why we encourage all technical dealers to have one in their toolkit.
  

What I tell our technical dealers is that unless they've measured the supply on the end of the product's supply cable with an oscilloscope with a full operating load applied (everything on the boat on, in full at-sea conditions), then they can't be absolutely positive that the supply is good. Battery capacity and charge-state have very little to do with it: trust me, I know from long and bitter experience. I've seen product supply voltage dip below 9V on a new, 50' powerboat with 27V at the batteries.

I don't think that changing between equivalent transducers would be likely to affect this, unless the new transducer were faulty and had a much lower impedance (and so drew much more current) than the old one. The two part numbers you mention have the same nominal performance, and the same Sense resistance which is what the display uses to detect whether it's there or not. There should be no operational difference between them. Changing to a different type of transducer (e.g., on a different model display, changing from 600W to 1kW) could draw more current and prompt an alarm if the supply were marginal.

Regards,
Tom