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ContinuousWave: Small Boat Electrical
Setting LOW VOLTAGE Alarm on Garmin Model 498
|Author||Topic: Setting LOW VOLTAGE Alarm on Garmin Model 498|
posted 04-28-2008 10:24 AM ET (US)
After reading the manual for the GARMIN 498 I learned you can set an alarm for when [the input voltage to the device is] low. To what voltage should I set the [alarm on the GARMIN 498]?
posted 04-28-2008 01:42 PM ET (US)
The manual for the Garmin should give voltage specs for the unit. It should be in the specs. I would set it at the lowest voltage that the unit will operate.
posted 04-28-2008 02:16 PM ET (US)
I could not care less about the Garmin operating - instead, set the alarm when the voltage drops to where you still get the engine running - probably around 11 - 12 volts. -- Jerry/Idaho
posted 04-28-2008 06:07 PM ET (US)
It's actually a pretty nice feature, my Garmin sonar unit has it and it's set at 11 volts. A good reminder when you're drift fishing with the VHF, GPS and sonar running that the battery is getting to a discharge point where you might have a starting issue.
posted 04-28-2008 07:41 PM ET (US)
The accuracy of the voltmeters in devices like a Global Positioning System receiver (GPSr) or a SONAR is usually not precise. You will have to compare the reading from the internal voltmeter of the device with the actual battery voltage as measured by an accurate voltmeter right at the battery terminals. This will give you some basis for choosing a lower alarm level for the device.
The circuit feeding the device may have some inherent voltage drop in it, too. This will also be reflected in the readings the device provides.
Once you develop a table of actual voltages versus measured voltages from the device, you can select the alarm level you are comfortable with based on the state of charge chart for a flooded cell lead-acid battery. See
A reasonable choice might be 12.2 volts, or 50-percent charge. Again, that is 12.2 volts at the battery, and there is no telling what the voltmeter in the Garmin might read.
posted 04-28-2008 10:32 PM ET (US)
Thanks for the info.
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