having trouble with my new depth finder

i have 24volt motorguide (70some thrust) trolling motor, and connected my depthfinder to trolling motor batteries.

two 12 volt batteries connected in series, only tapped into one side of battery of course....depthfinder 12v syst.

my depthfinder works great until i turn on the trolling motor, then the screen goes black suddenly.....

only my depth feature is on....whole screen moves but in black.....

any suggestions??

is it frequency interference?? cause of wireless trolling motor or do i need to get separate battery for depthfinder??

thanks guys!

Sgt

If you are running electric only with no cranking battery, yes, you realy should get a seperate battery.  When I use a deptfinder in my jon with just a TM, I use one of those $20 lawn mower batteries.  

Which TM do you have, the one with variable/infinite speed control or one with the set number of speeds.  This makes a huge difference.

If you have the variable speed, do you have the xducer mounted on very near the TM?  If so, unplug the xducer and see if the black screen clears up.   There's is also the chance of the problem being radiated and picked up by the xducer cable or the xducer.   This is a very common problem with the variable speed TM, the ones with infinite speed control and not the five speed switch.  These are also the ones that usually cause the most feedback through the power cable.   Lowrance has a whole list of things you will need to go through and try to cure the problem and still may not fully cure it.  

If you find it is coming through the power cable, you might see if Lowrance offers filters you can buy and you could try some low pass filters from Radio shack made to remove altinator noise from your car radio, but there's the chance you will spend a bunch of money and still not totally cure the problem

I have spent hours and hours and doing all kinds of grounding and sheilding just to keep my xducer mounted on the TM from blacking out or causing interterence on my screen.

The only thing hooked up to your trolling motor batterys should be the trolling motor.

lowrance is real reliant on a steady 12v. All kinds of crap happens when you have a voltage drop. Wire it to your primary or use another battery.