Radar Shuts Down When Trim Tabs Activated?

[SkunkBoat]

something to consider after you find your problem...separate your House from your Start.
I won't go into detail but it can be done using an Aux Chargiing cable from your Yamaha or using a separate "battery isloator" or using a VSR/ACR relay.
What you get is a start battery that does nothing but start your motor and charge up while its running. None of your electronics are connected to it. You could power your trim tabs from it and separate them from your electronics also!
Starting your motor and running your tabs would not cause a blip on your electronics.
You get a House battery that runs your electronics/lights and charges whenever a motor is running. If you run it down it doesn't effect your ability to start.

Your switches would still allow you emergency start or emergency House from the other battery.

You would not have to remember to switch batteries to charge.

 

[seasick]

What a lot of folks miss is the test of the voltage drop on the negative feed conductor. It is as important as the +12v feed.
You might think that if you connect a voltmeter to a negative battery terminal and the negative bus bar lug at the helm, you would read 0 volts. If there is any current flowing you wont. There is a voltage drop in the negative also and that has to be in spec. The voltage you read will be the actual voltage drop as opposed to the actual voltage you read on the positive lug.
In your case, you stated that the voltage at the buss bar ( fuse block) dropped to around 8 volts. That is a lot of drop and most electronics would have a problem.
The question is where is that large voltage drop occurring; in the hot side or in the ground side. If the drop is the same for both the pos and the neg, you are either undersized in a conductor, have a weak battery, or have a bad wire/connection somewhere.

Assuming you have that big voltage drop when the tabs are running, a simple test to see if the batteries are bad is to measure with only one battery selected at the time and compare that to BOTH batteries selected. If a battery is bad, the measurements will be significantly different. If the voltage drop is the same, your issues are in the wiring (cable fuse block, battery switch and the accessory breaker)

 

[Sauza45]

I think you have a batter problem, you said you checked them I have seen battery do crazy things.
You said that the garmin blinks when you start the motor, that makes me think battery.

 

[seasick]

I think you have a batter problem, you said you checked them I have seen battery do crazy things.
You said that the garmin blinks when you start the motor, that makes me think battery.

My Garmins are voltage sensitive and will reboot if the voltage drops below a certain value. To fix, that I turned off the low voltage alarm and the unit stopped rebooting.Note that 8 volts will probably cause most MFDs to shut down. In my case voltage when cranking the motor was about 10 and a bit volts.
I am not convinced yet based on the info supplied that the batteries are the issue. It is more likely an overloaded buss or a bad connection/wire. The tests and measurements I mentioned would probably determine exactly what is going on.

 

[Mark DV]

Seasick. Yes I did voltage test with each battery individually. The results were the same.

 

[seasick]

That probably eliminates the batteries as the cause. ( but not the battery switch)
I don't know if the following was asked . To eliminate another possible source, can you start the motor on either battery? If so does it crank over normally on either battery?
I had another thought just to add to the pot.
If you can get your hands on a clip on amp meter, measuring the current when the tabs are activated. It is somewhat possible that the trim pump is drawing more current than it should. I don't think that is the issue but it can't hurt to cover all the bases

 

[Mark DV]

The engine starts well with either battery.