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Electronics or Battery or What???

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I have a Mercury 115 Optimax with a large starting battery which was new last year. The starting battery is hooked up to the my Lowrance 522c GPS and depth finder and the lights, bilge pump, aerator and guages run off of this battery. My problem is that when I start the motor the Lowrance shuts itself off and I have to go through the process of bringing it back up. Any thoughts on what is causing the unit to shut off??



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put an isolator between the starting battery and the battery that you have the other things hooked to. when you start the engine, it will charge both batteries but won't pull power from the starting battery when you run the other items. Kind of like a one way valve or check valve for electricity.

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Despite being large and new, your starting battery may not be providing enough amps to supply the fish finder when you crank the engine. How much do you run all of the electronics? How long do run the motor on plane to recharge the starting battery? How big is/are the lake(s) that you fish? Do you recharge the starting battery after trips?

Your new battery could also just be a dud. Hook up a meter and see how many volts it's putting out at rest, during cranking, and at idle.

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All the answers above are more or less correct, but the actual culprit here is "Voltage Drop". When the starting motor kicks in, it draws a large amount of current (Amps) from the battery. When a large amount of current is being drawn from the battery,the voltage it is able to produce drops from somewhere around 13V to a lower value. When the starter motor is shut off, the voltage comes right back up. This is normal and happens with all batteries. A low battery makes this voltage drop greater, and a battery with a weak cell will be even worse.

In the manual for your fish finder, you will find an operating voltage range, and what you are seeing is an automatic shut off during the starting process when the system voltage drops below this range. The shutdown that you are seeing is normal in the low voltage condition.

To fix the problem here are some things you can do. First, clean all the contact points in the wiring, especially the battery terminals. Corrosion on the connections creates resistance which makes voltage drop problems worse. Next, charge the battery with a battery charger and try it again to see if the problem persists. If so, remove the battery and bring it in to be checked for a weak cell. If everything checks OK, your battery may simply not have enough amperage capacity to prevent the voltage from dropping too low during cranking and you may need to replace the battery with one that has a higher CCA rating. The CCA rating is how much amperage it can produce when cold. That will provide more amps during the starting process without dropping the voltage as much.

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Perfect, someone who understands DC electrical and how to explain it, pay attention to him and you will go far. One thing I might add regarding these types of concerns. As electronic goodies become cheaper and more available the open space on the dash board goes down, the problem, your electrical current demand goes up. Most boats are not designed or rigged with enough current carrying capacity to support all of the electronics that tend to end up on the dash. I have dealt with this problem on numerous boats and my solution has been to a a dedicated buss block, or terminal strip to supply power to everything that is added. Just connect an addtional battery cable to each terminal, anything from 4 gauge upto 2/0 gauge depending on how far and how large the demand, (for most small fishing boats common around here 4 gauge will suffice), and run them to the helm and connect to the respective positive and negative terminals on the buss block. Now when you add another accessory rather than tapping into an existing power wire, attach each power and ground wire to one of the open buss block terminals and the voltage drop will be so small that your voltage problems will be solved.

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