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Author Topic:   Humminbird SONAR Sensitivity to Input Voltage
ronniet posted 06-28-2009 07:41 PM ET (US)   Profile for ronniet   Send Email to ronniet  
I always knew my [2003--please express years in four-digits] Johnson 175 put out more than 14.5- volts. I can see the voltmeter pegged on the console gauge. I never really had much concern because automobile alternators produce an excess voltage as well. I recently purchased a new Humminbird 788ci SONAR and Chart plotter. It keeps flashing a screen message that says, "High input voltage." Is my fish finder in jeopardy? Is my engine and boat in jeopardy?

Some INPUT ON VOLTAGE would be appreciated. Thanks Ron.

jimh posted 06-28-2009 07:45 PM ET (US)     Profile for jimh  Send Email to jimh     
An output from the battery charging circuit of 14.5-volts is not excessive. That is a typical voltage necessary to deliver charging current to the battery.
ronniet posted 06-28-2009 08:03 PM ET (US)     Profile for ronniet  Send Email to ronniet     
I am aware that is normal
ronniet posted 06-28-2009 08:06 PM ET (US)     Profile for ronniet  Send Email to ronniet     
Can someone offer any advice on my situation

Thanks Ron.

jimh posted 06-28-2009 11:32 PM ET (US)     Profile for jimh  Send Email to jimh     
If the HUMMINBIRD is going to spend the rest of its useful life complaining about being operated by a 14.5-volt source, and your outboard motor is going to keep on providing that much voltage when charging the battery, you are at something of an impasse.

To make the HUMMINBIRD happier you could insert a bit of voltage drop in the battery lead to the unit. A regular silicon rectifier will produce a voltage drop of about 0.6-volts. You can use any silicon rectifier with a PIV of more than 100-volts and a current rating suitable to run the SONAR, which I imagine would be likely to be less than 5-amperes. Such a diode ought to cost about a dollar. You might get one with higher current rating on the chance that the SONAR draws more current when it is pulsing the transducer and the peak current could be quite a bit higher than the average current. If 0.6-volts is not enough, wire two diodes in series and you will get about 1.2-volts. The SONAR probably won't mind running an 11-volts when the engine is off, or you could put a small switch to bypass the diodes when needed.

jimh posted 06-28-2009 11:34 PM ET (US)     Profile for jimh  Send Email to jimh     
You might also consider checking the outboard motor. I would expect that a modern motor like a 2003 Johnson 175-HP would have a voltage regulated charging output. Typically it should not put out much more than about 14.5-volts. If it is putting out significantly more voltage there is likely a problem with the voltage regulator in the motor.
Chuck Tribolet posted 06-29-2009 12:33 AM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
I don't see where the input voltage has actually been
measured. I had one H'bird fish finder that had a voltage
display buried somewhere down in the menus. Or just put a
real digital voltmeter across the power supply to measure


ronniet posted 06-29-2009 06:59 PM ET (US)     Profile for ronniet  Send Email to ronniet     
I have yet to test the voltage as this is a recent problem and I don't posses a voltage meter!If my current voltage gauge is correct I know it is in excess 14.5 volts!Is the voltage reading on my gauge{higher than 14.5 Volts}and the warning from the sonar/chart plotter indicative of an underlying perpetual problem involved with owning a boat?LOL!

In reference To inserting rectifiers into my power lead to my sonar/chart plotter I would consider this once I was sure that that the excess voltage from my alternator was not detrimental to my to the heath of my boat or engine!

It is in my nature to help others maybe that's why I find it so easy to ask others for there's!

Thanks Ron.

jimh posted 06-29-2009 08:12 PM ET (US)     Profile for jimh  Send Email to jimh     
Battery charging output voltage greater than 14.5 is excessive.
PeteB88 posted 06-29-2009 11:38 PM ET (US)     Profile for PeteB88  Send Email to PeteB88     
Digital VOMs are pretty cheap. Great to hve in tool box

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