sonar iterference

[J White]

This will only be of interest to those of you, who like me, are
picky, picky, picky about sonar - but I thought it really good reading.
Check out http://home.comcast.net/~cwebb56/TM_Intf.html
Of particular interest to me was the test info on built-in transducers,
ala MinnKota. I got interested in this when I noticed that if I slowly
motored across a flat with the outboard, it might show no fish -
but if I stopped and fished anyway, the screen would show fish after
I cut the main engine - I am running off the main cranking battery for
a power source, and believe I am experiencing alternator noise causing
my auto sensitivity to ratchet down - when I kill the motor, it increases
the sensitivity and reduces the filter effect - I think Lowrance/Eagle
calls it ASP. Jeff

[Barnacle Bill]

Most older outboards (and maybe the newer ones too) have unregulated charging circuits. A bad or dirty connection can cause voltage to go way up. In fact I blew 2 Garmin 240s before I found my problem (bad battery). The were nice enough to replace both of them for me although I didn't tell them what was going on. Anyway, since I now have a 24V trolling motor system I run both my Garmin and Lowrance off the trolling motor batteries. I have had no problems whatsover. If I had a high thrust 12V trolling motor, I could see where it could cause problems. (shutting off) as the battery got depleted. The Garmins were suppose to have over voltage protection but obviously didn't work. I didn't make these decisions out of the clear blue as I do have some electronic background. Not to the extent Canepole has but enough to keep me out of too much trouble. If I had a regulated system I would probably move one to the starting battery. Regulators/rectifiers can be added for about $150 on my motor and if I ever encounter anymore problems, I'll probably add one. Hope I made some sense.

[J White]

Yes, I think the older, unregulated output is what caused a
situation I have witnessed on older boats - I you turned on the stern
light at night, say to let your partner see his way into the boat, and THEN
cranked the motor, lots of times it would blow the bulb - to this day, I turn
off my lights momentarily when I first crank up - old habits. I have thought
seriously about some type of switch to change from one battery to the
other so as to have the sonar operating off of which ever one is not doing
anything, off crank bat when on electric power, then switch to troll bat(s)
when using the outboard. What would be nice is a switch that would make-
before-break so to speak, so you would never lose power to the unit and
have to re-start it. I do know for a fact, if you have both a trolling battery
and a cranking battery connected to different circuits of an on-board
charger, any interference seen by one battery will cross through to the
other, through the charger. At least it did with my Dual-Pro/Lowrance outfit.
Like I said, you've got to be nit-picky to notice this, but I have spent hours
playing with the sonar seeing how it will react to different conditions.
It will still show bottom and some bigger fish, with the auto filter jacked
way up, but there is a lot being missed.

[papasage]

i ran my depth finder on the troling battery just used the cranking battery for cranking . then i noticed when i was troling the finder would go crazy . so now i run the finder on the cranking battery . and i use a deep cyckle battery there also now .

[Eager Beaver]

I also use to run the front depth finder off my deep cycle battery which was for 12 volt motor. Now that I switched to 24 volt trolling motor I have all electronics running off my starter battery and only the trolling motor off my 2 deep cycle batteries up front and in the back I have a cranking battery and a 12 volt Minn Kota battery that can either be used for a trolling motor or starting the big motor. I use it to run my 3 horse elecric trolling motor on the back of the boat when I fish either South Dakota or Minn. for Walleye, when I back troll. I use the 4th battery for a back up in case any of the other 3 fail. When I don't have the back trolling motor on the boat. Works great for me.

[stray]

This will only be of interest to those of you, who like me, are
picky, picky, picky about sonar - but I thought it really good reading.
Check out http://home.comcast.net/~cwebb56/TM_Intf.html
Of particular interest to me was the test info on built-in transducers,
ala MinnKota. I got interested in this when I noticed that if I slowly
motored across a flat with the outboard, it might show no fish -
but if I stopped and fished anyway, the screen would show fish after
I cut the main engine - I am running off the main cranking battery for
a power source, and believe I am experiencing alternator noise causing
my auto sensitivity to ratchet down - when I kill the motor, it increases
the sensitivity and reduces the filter effect - I think Lowrance/Eagle
calls it ASP. Jeff

I’ve used a capacitor to stop alternator noise when using electronics in auto motive applications before; wouldn’t it work in this instance?

[J White]

I’ve used a capacitor to stop alternator noise when using electronics in auto motive applications before; wouldn’t it work in this instance?

I'm no gee-whiz when it comes to electronics, but
I think that is what he's talking about as one of the solutions, maybe
calling it something else, probably just so they can charge more for it
The Vexilar website has some good info on this too. Think they sell a
"noise filter" too, probably just a capactor, but for me, buying one for
the application would eliminate some of the guesswork as to what size
and type capacitor.