Using boat battery with fish finder makes it un accurate?

[12thManFalseStart]

I noticed by trying to get rid of extra weight in this new boat I just purchased, that by using the battery to the boat engine to run my fish/depth finder makes it go nuts after 2 mph. jumps to 600 to 900 feet deep in 10 feet of water. I'm thinking it has to do with the engine rpm's and the magneto/alternator messing with the fish finder. Anyone else have this problem?

 

[Socal Pat]

Re: Using boat battery with fish finder makes it un accurate?

You sure it's not the transducer picking up turbulence over 2mph?

 

[12thManFalseStart]

Re: Using boat battery with fish finder makes it un accurate?

You sure it's not the transducer picking up turbulence over 2mph?

I'm not sure, but it doesn't do it while using a separate battery, and works at 35 mph. I was just wondering if anyone else had this issue, or if it's maybe just my brand of fish finder, etc?

 

[Fed]

Re: Using boat battery with fish finder makes it un accurate?

What is it like when you're stationary with the motor idling in neutral?

 

[MH Hawker]

Re: Using boat battery with fish finder makes it un accurate?

It sounds more like a bad connection.

 

[12thManFalseStart]

Re: Using boat battery with fish finder makes it un accurate?

What is it like when you're stationary with the motor idling in neutral?

It's working, until I start to move past about 2 mph, then goes haywire. Note, I didn't have any handy wire, so I used phono jacks. Red and white, cut off the jacks, and stripped them down. Might be the problem, but I thought wire is wire.

 

[Silvertip]

Re: Using boat battery with fish finder makes it un accurate?

If it works fine on a separate battery but not on the engine starting battery then you either have bad connections, are running the wires too close to other sources of interference or there is electrical noise from the engine charging system. Radio Shack stores can provide a filter for the 12 volt feed to the unit if it turns out noise is the issue.

 

[bruceb58]

Re: Using boat battery with fish finder makes it un accurate?

What happens when you have the engine in neutral and increase the RPMs? Does it do the same thing?

 

[12thManFalseStart]

Re: Using boat battery with fish finder makes it un accurate?

If it works fine on a separate battery but not on the engine starting battery then you either have bad connections, are running the wires too close to other sources of interference or there is electrical noise from the engine charging system. Radio Shack stores can provide a filter for the 12 volt feed to the unit if it turns out noise is the issue.

I'm willing to bet it's noise, and need a filter. Kinda what I thought the whole time, but could be wires too close to other sources. They all are hooked together on the batery leads.

Being an older engine, and it doesn't always start up on the first few cranks, it's probably best to just bring and use the spare battery anyways. lol, can't push start a boat. Thanks guys.

 

[ThrottleBack]

Re: Using boat battery with fish finder makes it un accurate?

It's noise because a seperate battery doesn't do it. Example some cars have a port in the radio face where you can hook a 2 sided headphone cable so that your phone or ipod plays music through the stereo. If you then plug in a charger to the phone from the cig lighter the higher the rpms in the car the more "whining" you will hear in the speakers.

The reason in my example is you basically established a loop in the system, at least how i understand it. In your case I'm betting the issue is when the motor is under that power the alternator is pushing power into the battery, causing a higher then expected electrical response to the finder. The filter will likely solve the issue.

 

[dingbat]

Re: Using boat battery with fish finder makes it un accurate?

Electrical "noise" manifests itself as clutter on the screen. It would be unusual for noise to affect depth readings because of the design of the transmitter circuit. Electrical problems with the depth readings are typically voltage related with some units being far more sensitive to voltage fluctuations than others.

But.......if I understand you correctly, you've removed weight from the boat and the unit works fine above 35 mph?

A battery is a lot of weight to a boat that size. Removing a battery would have changed the interaction between the hull and the surface of the water, i e transducer is not as deep in the water as before. For kicks, I would put the battery back in but leave the finder connected in its current configuration and see what happens.

 

[Fed]

Re: Using boat battery with fish finder makes it un accurate?

It does sound like the attitude of the boat has changed enough to put the transducer past the tipping point, if the water flow under the transducer face goes into the negative zone then the bubbles take over.

Lower the trailing edge of the transducer a few millimeters or make a passenger sit on the transom.
You'd be surprised how much rake you can run with no ill effects.

 

[ThrottleBack]

Re: Using boat battery with fish finder makes it un accurate?

That would be truly interesting if the issue is that one battery made all that difference in depth.

 

[Fed]

Re: Using boat battery with fish finder makes it un accurate?

It's not the depth I mean TB it's the angle of the transducer face.