175 HP Black Max Not Charging, Voltage Varies

[llliquid]

My '96 175 HP Black Max does not seem to charge the batteries (the voltage does not rise when running). The stator shows near continuity between each of the pairs of yellow wires and is not shorted to ground. I measure about 25 VAC across the yellow wires with the motor running. It has 2x 5 wire regulators. When I measure the voltage on the red wires (going to the battery) I get a voltage that varies from about 6-13 VDC. This should be a more stable 14.5 volts or so I believe. Seems like the rectifier/regulator is not quite doing it's job, however not too long ago I replaced both of these units when the tach. stopped working (now works). Any help would be appreciated? Or any other points I should measure?

Note the boat has a battery isolator (large diode). The red lines from the voltage regulators go to the A port (alternator input) terminal of the isolator and then the 2 batteries are connected to the ports B1/B2 on the far side of the diode. I was curious if this was preventing the charging system from sensing a low battery voltage and have now bypassed the isolator. I still did not see a rise in the voltage when running at idle, but will try at WOT later today.

 

[Texasmark]

Re: 175 HP Black Max Not Charging, Voltage Varies

Most silicon diodes will give you a forward drop of 0.7v to 1.1 or so depending upon current flow. Shottky would produce half that drop. So, subtract those numbers from what you are supposed to have and you have the answer to that.

What do you need this diode for anyway? The input voltage seems right to me, the regulators are in parallel with the outputs summed to provide up to 40 amps to the battery.

One thing you might do is remove the output from each and see what the battery charging voltage is to the battery just running on one.

Additionally you could switch to AC voltage and see what you get. If a diode were shorted you could get AC and it would alternately charge and discharge the battery making for some screwy readings.

HTH,

Mark

 

[llliquid]

Re: 175 HP Black Max Not Charging, Voltage Varies

The voltage going to the diode varied rapidly from 6-13 VDC almost like a poorly rectified signal. So yes my concern is that this should be a nice constant DCV instead of varying. It's not going to charge very well as it is now, I wouldn't think. Maybe I could add on a third party rectifier hmmm... Or try groundign the regulator better.
The battery isolator is supposed to allow you to charge 2 batteries at once and protect the motor's electricals. It was just there when I bought the boat 3 years ago, so I never changed the rigging.