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Author Topic:   Quiescent Current of Electronic Devices
mpbspb posted 04-14-2009 10:26 PM ET (US)   Profile for mpbspb   Send Email to mpbspb  
I have a two-battery set-up in my [Boston Whaler DAUNTLESS 15 boat]. Battery ONE powers then outboard. Battery TWO powers the trolling motor, a [LOWRANCE] combination GPS-chart plotter-SONAR, and [a sterophonic audio reproduction system]. [Battery TWO] has something drawing current all the time, it seems. [The stray current] completely discharges the battery after three days. I notice a spark when touching the [power lead] from the LOWRANCE unit and [audio system] to the battery, but [I do] not [notice a spark when touching the power lead] from the trolling motor [to the battery]. Should these two units draw [current from] the battery when powered off? Or is there another problem?
HAPPYJIM posted 04-14-2009 11:36 PM ET (US)     Profile for HAPPYJIM  Send Email to HAPPYJIM     
The stereo may have power going to a clock or maybe a standby mode. That still shouldn't drain a fully charged battery in good condition.
mpbspb posted 04-15-2009 08:04 AM ET (US)     Profile for mpbspb  Send Email to mpbspb     
I thought that about the stereo. Do you think the gps antenna pulls power when the unit is off. Should I put these units on an acc. switch?
HAPPYJIM posted 04-15-2009 07:58 PM ET (US)     Profile for HAPPYJIM  Send Email to HAPPYJIM     
I don't think GPS antennas use any power but I would have all electronics on an accessory switch.
jimh posted 04-15-2009 08:27 PM ET (US)     Profile for jimh  Send Email to jimh     
You should mention the model of your LOWRANCE unit, as it will be important in assessing what is happening.

Measure the quiescent current drain on the battery when all devices are in the OFF state. It is not particularly unusual that there be a drain of 0.001-ampere to perhaps 0.003-ampere from electronic devices in their OFF state. This current is used to sustain the voltage on memory chips in order that certain user settings are maintained.

The instruction manuals for the electronic devices should make clear if they draw any quiescent current in their OFF state.

A typical battery used in a 15-foot boat for engine starting ought to have a capacity of at least 20-Ampere-Hours. In order to drain the battery in a period of only 72-hours, the current drain would have to be on the order of

20-Ampere-Hours/72-hours = 0.278-ampere

A current drain of 0.278-ampere is much higher than I would expect the current drain associated with maintaining a memory chip.

I suspect you have a wiring error in your LOWRANCE device wiring which is maintaining power to the MNEA-2000 network bus that is used to connect the chart plotter unit to the GPS receiver. Read the instructions for your LOWRANCE unit carefully to see how to handle this wiring.

high sierra posted 04-15-2009 11:29 PM ET (US)     Profile for high sierra  Send Email to high sierra     
Lowrance GPS antennas use power all the time if hooked to a power source. I noticed my antenna draining the battery over a period of time. Install a separate switch for the electronics. high sierra
Chuck Tribolet posted 04-16-2009 09:00 AM ET (US)     Profile for Chuck Tribolet  Send Email to Chuck Tribolet     
HAPPYJIM: Modern GPS "antennas" aren't just the antenna. The
whole receiver is in there, and does need power.

By packaging the receiver with the antenna, they eliminate
the signal loss in the coax, and the cost of coax and RF-grade


jimh posted 04-16-2009 08:06 PM ET (US)     Profile for jimh  Send Email to jimh     
If we knew the LOWRANCE device, we could have a more informed discussion.
HAPPYJIM posted 04-16-2009 11:59 PM ET (US)     Profile for HAPPYJIM  Send Email to HAPPYJIM     
Thanks, Chuck.
All of my GPS's are 5+ years old so I had no idea.
jimh posted 04-18-2009 10:08 AM ET (US)     Profile for jimh  Send Email to jimh     
If we could find out what type of LOWRANCE device is being used, we could help discover if there was an error in the wiring which permitted the GPS receiver to remain constantly powered.
mpbspb posted 04-18-2009 08:05 PM ET (US)     Profile for mpbspb  Send Email to mpbspb     
Thanks for all the replies. The Lowrance is a LCX 25c. There is a note in the owners manual and power drain when off. Also the stereo manual has the same note. I will be installing a switch to eliminate this problem. I have since added a engine mount minn kota em55 trolling motor as well. Went out today and the battery did not last long at all. The battery is new and is the same battery powering the lowrance as well. It is a cheaper deep cycle but I thought it should last longer than 45mins. of run time.
jimh posted 04-19-2009 09:46 AM ET (US)     Profile for jimh  Send Email to jimh     
Start a new discussion to investigate the amount of stored energy in a battery and how long it will last when powering a trolling motor.
jimh posted 04-19-2009 11:52 AM ET (US)     Profile for jimh  Send Email to jimh     
The LOWRANCE LCX 25c uses a GPS receiver that is connected via a NMEA-2000 network. If your wiring configuration leaves the NMEA-2000 network powered at all times, the GPS receiver will continue to operate even when the LCX 25c display unit is powered off. This may account for the higher than normal quiescent current drain you are seeing on your battery.
davej14 posted 04-19-2009 04:24 PM ET (US)     Profile for davej14  Send Email to davej14     
The installation instructions for a NMEA 2000 network from Lowrance specify that the network should be powered via a switch so it can be powered down when not in use.

The quiescent current for your radio memory should be insignificant.

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