Honda BF90 Electrical Interference

[sutor623]

Hey guys, haven't worked much with Honda outboards.

Got a good friend that has a 2002 Honda BF90 (four-stroke carbureted). He has an HDS-10 with sidescan. For some reason, when the gas motor is on he will pick up electrical interference on his side scan sonar. The longer the Honda is running, the worse it seems to get, up until a point. He has re-routed his wires as far as possible with no luck, and even put in a choke on the transducer wires. He is running a separate battery for his electronics.

I think the stock spark plugs for this motor are the DR7EA. Any ideas what he can do to silence all this noise? Are these motors just electrically noisy?

 

[gm280]

Well sutor, for starters, I don't understand the "choke" on the transducer cable. I would think that is counter productive to the single myself. I would first try to determine if the noise is coming from the power lines, hence battery feeds, or over the air from RFI the engine is making. If the noise is over the air, then changing plugs is one way, and maybe shielding the inside of the engine cowl with some type aluminum tape could help out. If he is going to install noise filters, do it to the battery feed lines to the unit, not to the transducer cable. The filter will try to keep the transduced single from feeding back and forth thereby reducing the capability. JMHO!

 

[hondam]

These motors are not typically noisey, the dealership I work a sold dozens of them. You probably have a ground issue.

I agree the ferrite needs to be on the power supply wires for the HDS not the transducer cable. And make sure all the grounds are good in the boat and the two batteries are sharing a common ground.

The charging system on the Honda needs to be tested too. I used a midtronics battery diagnostic system for this, it would inform you of a damaged rectifier.

Those NGK plugs are the right ones I would not substitute them.

Also want to make sure the interference isn't being caused by the tubulence/cavitation of the prop. You probably would have noticed if it was this but want to make sure it want overlooked.

 

[sutor623]

Ok thanks for the pointers guys. I will double check for cavitation. It is a Carolina Skiff, very flat hull. Water does strange things coming off the back of that thing!!!

Aluminum tape inside the cowling is a great idea!

 

[sutor623]

Ok so the sonar still makes the "noise" when the motor is on muffs, so no cavitation. We checked all grounds and they look good. Continuity is strong with ground from all sections of the motor. Battery charges well but other than that I wouldn't know how to check the rectifier. And I was mistaken choke is on power wire not transducer cable. Should we try some shielded power wire? Also I wonder why the noise doesn't start until the motor has been run for a few minutes. Thanks for any ideas guys.

 

[gm280]

Ok so the sonar still makes the "noise" when the motor is on muffs, so no cavitation. We checked all grounds and they look good. Continuity is strong with ground from all sections of the motor. Battery charges well but other than that I wouldn't know how to check the rectifier. And I was mistaken choke is on power wire not transducer cable. Should we try some shielded power wire? Also I wonder why the noise doesn't start until the motor has been run for a few minutes. Thanks for any ideas guys.

Okay you did add a bit more info of your problem. And that points to the alternator or charging system to me and here is why.

You stated that it doesn't start until the engine is running for a while. And my thinking is because as you crank the engine, you drop the battery voltage a little. And then after the engine cranks up, the charging system starts to charge the battery back up. Once it gets the battery back to full again the charging system is outputting pulses that the battery doesn't absorb anymore and therefore those spikes are causing the issues.

I would take a good DVM (multimeter) and see how the output looks. Check the DC voltage level AND then switch the meter to AC voltage and see what it reads. I'm betting you will see an AC voltage riding on the DC level. And that IS your interference. I would most certainly check the rectifier and/or regulator pack and if that checks good, I would install a good quality filter in the battery line to the locator. JMHO!

 

[hondam]

Do you have a battery cable going from the neg on one battery to the neg on the other battery? Did not mention that in your responce, that i an important part of everything being grounded properly.

A midtronics battery diagnostic system is a common automotive tool, it will help diagnose the charging system if anything is wrong. If you have any friends/family that works on cars they may have access to one. I have one i got off ebay and is how i do it and usually get very accurate results.

This may be a problems to take into an expert, the reg/rec on that engine is expensive and not returnable so if you guess and order one that is not needed you just wasted a lot more money then it would have took to have the person look at it in the first place.

 

[sam am I]

Think I'd take a "carry-on" battery, sit it on the deck, run the + and - from the FF to it and power it up totally isolated from the motor/boat's system's...........IMO, this would be fastest path to resolve the issue of "radiated" or "conducted". Go from there (step B) depending on what this particular test shows.

Still noisy = Radiated (unit is picking up noise/emissions/RF from airways. Cables, PCB etc., acting as antenna)
Quiet = Conducted (Power source issues, EMI from ig. radiating onto and conducting up on power wires, bad rec perhaps [I'd suspect you'd have low DC though if rectifier was open], etc )

GM...........Depending of bandwidth of his/a DMM meter (most higher-end fluke's are 100Mhz) and the freq. of the noise/RF (could be in G/Mhz's..........dv/dt ---> ~), he might not see anything switching over to AC....Fast'ish scope might otta do the trick there tho