My Echomap UHD 9sv doesn’t read my battery voltage correctly. My battery is located in the back of my 16 ft. boat, and reads 12.6 volts. However, the voltage on my Echomap reads 12.2 volts.  I assumed the discrepancy was due to the voltage drop in the cable, but I read the voltage at the connection of the cable and the Garmin power cord, and it was 12.6 volts—same as at the battery.  Anyone have any ideas?

I am not sure what the issue is but I can say that on a full charge, my Echomap UHD reads 13.1v for a few minutes then drops down to 13.0v for a hour or so and will remain at 12.9v for the next several ours. I am using the stock cable. I am using a 18ah lithium battery from Amped Outdoors.

Thanks for the info.  My battery only gets to about 12.8 volts max.  That’s enough for me, as I don’t fish more than about 4 hrs per trip anyway. 

There will be some voltage drop in your wiring.  The smaller the wire,  the more resistance it has.  Voltage drop is a function of the resistance in the wire and the current going through it.   Voltage (in volts) =  current (in amps) X resistance (in ohms).  When you read the voltage with a meter there is virtually no current so there will be almost no voltage drop.

 

The Garmin website says your unit pulls a maximum of 1.5 amps.  Doing the math backwards, a 0.4 volt drop at 1.5 amps would mean roughly 1/4 ohms resistance.  Checking the resistance of wire on the Internet, 32 feet of 18-20 gauge wire would have about that much resistance.  

Thanks! IOW, I should have a voltage drop. My wire is (I think) 18 ga. I’ve got about 20 ft. of wire to my Garmin line, which is another 3-4 ft. , so this voltage drop is to be expected?

22 minutes ago, Maggiesmaster said:

Thanks! IOW, I should have a voltage drop. My wire is (I think) 18 ga. I’ve got about 20 ft. of wire to my Garmin line, which is another 3-4 ft. , so this voltage drop is to be expected?

Ya - you'd want 14 or even 12 gauge to reduce that voltage drop to 3%...with 18gauge over that distance, you're getting near 10% drop.

 

I'm running 16gauge for the electronics in the F-9...but my longest run is around 12'...which falls into the 3% category.

According to the Garmin website the voltage requirements for your unit are 9-18 volts.  12.2 should not be a problem.

It’s not a problem with the Garmin, but I use the voltage indicator to check the charge of my trolling motor battery; it powers both the Garmin and my trolling motor.

Do you check it when the TM is operating?

 

I seem to remember that my Striker 7CV showed a drop in voltage when I was running the TM on the canoe (only one battery ran everything)...came back up when the TM was shut off.

 

The F-9 will have a dedicated TM battery, and another battery to run everything else.

Garmin gave you a bad unit. Call them for a replacement that is accurate.