Starting motor kills fishfinder

[Tilla]

I've had two different fishfinders and they both seem to turn off when I start the main motor. I'm sure that the current draw from starting the main motor lowers the minimum power threshold of the fishfinder.
I've even changed the location of where I get my 12v source.
Any solutions?

[Flatfish]

Has it always done this?

[Orca]

As you suggest, when you start up, you get a large voltage drop from all the juice required for the starter.

One solution is a starting battery and a house battery that are isolated from one another. I uesd a Blue Seas isolator, left my perko switch set to 1, and now I have 1 battery isolated from the starting battery.

Another option would be to put a big capacitor on the power feed to the finders. You could find these at the Stereo store. Not sure how big you would want, I would have to do some calculations. If you do the cap routine, you need a diode before the cap. 12000 f should do it.

[FastAction]

Optima battery???

[chucks electric]

hello, the only acceptable correction for this problem is to add a house battery that is dedicated for electronics, that will eliminate this concern.

[Catching Nemo]

Definitely another battery for the electronics. NW boat dealers should just start adding the second battery by default. Shouldn't even be an option.

[No Time]

A dedicated battery for electronic is definitely the way to go, but you might want to also check the fuse and fuse holders going to the units for corrosion/oxidation.
A little extra impedance and a drop in voltage is all it takes

[Tilla]

1.It has done this with both finders.

2. It is an Optima battery.

3. I have a 24 volt system for the e-motor so I have already have three batteries (Optimas), I guess I could make more room and take out some life preservers.:smirk:

4. Or can I get a 12 volt source from the 24 volt in series...sounds familiar......there is a thread somewhere?!
Aha! Boat dog has a drawing describing what the builder had mentioned once.

[klicknative]

Do you have an outboard or sterndrive? I'm thinking if it's a sterndrive and the sonar is powered off the ACC terminal on the key switch, when the key is turned to start, it shuts off the ACC circit. I know a lot of cars ect are set up that way but not shure about boats. If it's not, then check all the conections including the battery cables at both ends.

[Orca]

Sure, get your 12V for the finders from one of your 2 optimas used for the emotor. Hook neg and *** for the finders to the neg and *** of one of those 2 batteries. But then if you run this bank down using the emotor, then the FF is done also. But may not be a problem if this bank charges off the main engine.

[Tilla]

It's a tiller, 200 hp Merc.
74 lb thrust 24 vdc e-motor
15 hp kicker
I think I can tap off the 24 vdc system

[PRINCEMASTER]

Only other suggestion is a surge cap like one used by the stereo buffs. This may or may not do the trick.