Blown 3 amp fuse and interferance

[lpugh]

Interference issues

03 Cougar
36 volt Ultrex 112...… HDS transducer with down scan on the trolling motor (not using the US2)
HDS 2 Touch at the bow
HDS 3 and Hook at the consol
Cranking battery is isolated from trolling motor bateries
Genius NOCO four bank charger
This boat has a 24 volt circuit and a 12 volt circuit ran to the front and is bridged at the connector for 36 volts
Thinking there may be some improvements by changing it to just two cables to the front for 36 volt

Running it at about the number 2 speed level it is the worst with minor interference when steering
I found the fuse to be blown, replaced and it ran for about five minutes and blew again. Disconnected the battery charger from the cranking battery and no longer blew the fuse. Reconnected the charger still does not blow the fuse... When the fuse is pulled the interference is horrible
I did find It has 1.8 ohm of resistance between the case sections of the TM. I Don't think that would be normal!

Since there has always been some interference, I decided to take steps to address several issues and put this to rest:
1. Ran a twisted pair 16 gauge wires directly to the cranking battery, opposite side of the boat from TM battery cables
2. Added ferrite rings to the transducer and power cables
3. rerouted transducer cable
4. Will install ducer standoff clamps on motor shaft
5. Will install choke on power cable to HDS when it arrives
6. Connected the number 1 charger output to the cranking battery instead of the #4

I would really like to know the circuitry of the brown 3 amp circuit and why it is only 3 amps. I talked to minnkota and they were not much help. Only that it goes from the brush plate to the battery ground on the board and not to or thru any other circuitry. Being 16 gauge this circuit should be able to handle at least 10 amps I think?
I also have seen mention of not grounding the TM and cranking battery together, This makes no since to me as I do understand when not grounded to earth the ground level voltage could be different

Does anyone have a good diagram that would clarify this 3 amp circuit for me, I can see how this fuse could blow on the charger without the cranking battery being grounded to the ground of the 36 volt side when using the us2
The way my mind thinks this would be a resistance in the ground circuit of the lower portion causing increased current thru the fused circuit

Thank You gentlemen

[CatFan]

The fuse only conducts if there is a connection between TM and cranking batteries so the smaller the better. It protects the internal transducer. The circuit creates a reference that is different from TM battery negative for noise reduction and the circuit is disabled if the fuse blows.

[Jonestrollingmotor]

On the Ultrex, the brown wire is considered a bonding wire. The US2 is grounded internally to the trolling motor case and this ground carries through the transducer into the transducer cable and, if using it on the depthfinder, onto the ground of the depthfinder, which is grounded to the cranking battery. On the other side, the bonding wire is attached to a screw that is holding the brushplate to the comcap, connecting it to the motor housing. The other end is fused, then goes to the control board. When the control board is activated, the bonding wire carries a ground circuit to the motor case causing it to "shunt" the ground, or make the case of the motor ground, much like the ground webbing in coax cable. If the US2 is used, the trolling motor ground and the cranking ground are connected through the transducer/depth finder to also help eliminate an interference issue. If for some reason, the batteries are sharing a ground somewhere else and the US2 is connected through the depthfinder (I understand yours is not) then it could cause a short between the cranking battery and a trolling motor battery and blow the fuse to keep from destroying the transducer and depthfinder. Hope this helps.
John

[Ann-Marie]

If the main negative cable supplying the trolling motor gets disconnected or unplugged while the motor is running, all the motor current attempts to go through the alternate ground via the negative bonding of the depth sounder. The fuse is there to protect the small gauge wire from melting due to this overload.

[Jonestrollingmotor]

If the main negative cable supplying the trolling motor gets disconnected or unplugged while the motor is running, all the motor current attempts to go through the alternate ground via the negative bonding of the depth sounder. The fuse is there to protect the small gauge wire from melting due to this overload.

Maybe, but not sure how. The bonding wire doesn't connect to the brush or armature in any way to have a load applied. It originates in the control board and supplies ground to the case of the motor. If the main negative cable disconnects, then no ground would be supplied to the control board. Since the trolling motor is isolated from the cranking battery, the ground feed to the depth finder would create a ground into the back side of the control board, but there is no positive from that battery to complete the circuit through the trolling motor.

[rfdong]

Could the “shared” ground be the other graph that is networked? Sharing a common ground to the cranking side via the NEMA network power? Or am I thinking about this wrong?

[Jonestrollingmotor]

Could the “shared” ground be the other graph that is networked? Sharing a common ground to the cranking side via the NEMA network power? Or am I thinking about this wrong?

Shouldn't be. The NMEA ground should be the same ground that your depth finder is using going directly back to the cranking battery. Both depth finders should be using this ground, as is the US2 (if it was connected) Since you're not using the US2, the bonding wire "circuit" ends at the termination of the US2 cable that goes to the depth finder.
John