Honda BF9.9A DC Receptacle Concerns

[BrianAllen]

I am new to sailboat ownership. Our Hunter 25.5 came with a Honda BF9.9A with the DC Receptacle for charging the battery. The manual indicates the plug should output 12V @ 6amp. I am measuring a low varying voltage with no load at idle. My background tells me the voltage regulator/rectifier has failed or it is designed to have no output without a load

Does anyone have experience with feature?

Does it only have the 12V at speed? I'm concerned about connecting up to my battery only to have battery push back into the DC Receptacle to fry something.

- Brian

 

[Benny17441]

What is the output at cruising RPM? Oh, by all means connect the battery, it will not damage anything that already might be damaged. These alternators are weak and do not put out much Amps at idle.

 

[BrianAllen]

What is the output at cruising RPM? These alternators are quite weak, especially at idle. If the readings are the same at higher RPM then regulator/rectifier could be shot.

I didn't test that when I have a propeller off when doing the oil changes. It is back on the sailboat now so I will have to get some help to measure that while underway.

I was concerned about placing a 1 to 3 volt output onto a 12 volt battery's terminals.

 

[walt]

If I read correct, you measure that voltage on the plug.. but not connected to a battery.

Most small outboards have very little regulation so without the battery, it is just the coil trying to pulse some current through a diode. Since no load, no current and you just get an open load voltage spike. You are probably using a DC volt meter and it when it reads some DC voltage, it is expecting a constant DC voltage rather than very short duration pulses. So.. you cant trust the readings with a DVM. If you did the same test with an O scope, you probably would see fairly high voltage spikes (greater than 12 volts and the voltage doesnt mean much with no load) each time a coil went past a magnet. But the "duty cycle" will be low and DC meter only sort of averages this

How to tell if stuff is working... more complicated. But I dont think what you measured means anything is wrong. The low voltage also does not mean you should not connect to the battery. Things could be working just fine.

FYI, the rectifier diode set can be damaged if you have the outboard connected to a battery and running.. and then disconnect the battery while the outboard is running. Never disconnect the 12 volts from the outboard to the battery while the outboard is running. Some brands can tolerate this.. but best to just never do it.

 

[BrianAllen]

To Walt, thanks for the info. I had read about the disconnect concerns. I will go ahead to configure the batteries and monitor the current to confirm flow is into the battery. I wouldn't want to put a scope on the sailboat that would be just asking for something to go wrong.

 

[Johnb]

Recommend you install a fuse at the battery end of the wiring to the outboard. This should be commensurate with the size of the wire, or smaller if the ampacity of the wire is much greater than 6 amps and you wish to provide some protection to the outboard as well.