2010 Honda BF90XR charging issue

Quick run down: 3 batteries on boat. 1 starting battery, 1 house battery, and 1 additional house battery. The third (additional house) battery is on a separate switch but they are all in series, its a 12 volt system. I had the starting battery blow up (battery fluids all in the battery box/case) so went ahead and replaced all three batteries. Been running on that for about a month, no problem. Started noticing the volt meter on the tach showing only about 12 volts and in some cases 11.8 volts while making way. Pretty unusual because it typically runs around 13 to 13.4 volts when making way and usually hold around 12.4 in idol. The other day, after having run the boat hard all day, anchored up to get some shut eye, upon waking up, the batteries were run down and would not crank the motors. Had to emergency pull start the starboard motor and then was able to crank the port. Shortly after making way for 10 min, went to idol and the low voltage buzzer went off, was around 11.4 volts. Had to make a long run back to the dock and did so hovering around 11.8 to 12 volts. At the dock it dropped voltage again in idol before loading on trailer.

I have removed the 3 batteries that were run down and was able to charge them up on an AC charger. I did replace them with brand new Optima batteries (dual purpose) just to rule out batteries. I was thinking its the alternator/s but upon testing them per instructions in the service manual (checking resistance between 0.09 to 0.14 ohms) they test fine, right around 0.1. I was doing some testing with the boat out of the water today, it seems if I just run the port motor, my volts hold at about 12.4 and that's with all my equipment turned on and running the motor at about 3000 RPM. When I add the starboard motor it will drop it down to 11.8 volts and putting it up to 3000 RPM it will maybe jump back to 12 but back down to 11.8 volts. It seems like something in that starboard motor is draining or the alternator isn't charging? I'd love some ideas if anyone has any before I put it in the shop. Would love to avoid that as there aren't any good Honda dealers around anymore.

Sort of confusing.
You describe an undercharge condition but having a battery boil over or "blow up" as you say, often indicates high OVER charging. Although, batteries do "blow up" for other reasons.

Another confusing statement you make is; "they are all in series, it's a 12 volt system".
Batteries connected in series provides for doubling or tripling voltage. I'm thinking you simply meant to say they are in parallel?

Anytime a 12 volt charge system falls beneath the battery static volts....in this case 12.4 to 12.6 volts....its considered not charging.

Most systems will accept all loads (within parameters) and continue to charge the battery with around 1 volt left over. This isn't a hard and fast rule but is illustrative of "desired".

You may want to do some voltage drop testing on this system. Volt drop tests are a quick and usually easy way to pinpoint and remove excessive resistance in electrical systems. There are many excellent tutorials on volt drop testing online in various formats. A crucial bit of knowledge for anyone with a digital volt meter trying to troubleshoot electrical issues. It is extremely valuable in diagnosing bad multistrand wiring including battery cables. Very accurate and reliable results when used properly.

The reason I suggest that you do this is because you have new batteries and from your description the system may have excessive resistance between the alternator(s) and the battery bank.

Always check charge voltage at the alternator output terminal and then at the battery posts. This too might give you an idea of what may be being lost due to resistance in connections and cables.

A boat will always need more electrical system care due to the environment. Disconnecting and literally polishing electrical connections regularly will prevent problems off shore.

Goodluck.

Thank you for the reply. Yes I believe the battery "boiled over" or blew up due to age (~4 years) and excessive heat this summer. That was about a month prior to this charging issue.

Yes the batteries are in parallel, my apologies.

I'm not quite sure where to hook my multi-meter to test the alternator output directly. The stator harness has the the three white wire terminal connector that hooks into the regulator. Should I stick the positive to one of those terminals and ground the negative?

Good question. I might have some info on this but I can't get to it at the present. But, until someone can tell you for sure, you can probably find it by looking at the starter moter. The main positive post from the battery should be connected to the starter solenoid terminal. Find and trace the wire from the starter to the alternator and that should be the main charge wire from the alternator.

If it's not wired like that then a wiring schematic will probably be need to be accessed.

Although, one other way to identify the correct wrire would be to find the wire at the alternator that is hot with the ignition off.

I don't work on the larger outboards so my knowledge of how they are configured is sometimes lacking. I have to fall back on my automotive experience lacking the pertinent documentation.

Sorry.

Just run the motor at 2500rpm and check voltage on the stater hot stud, just as you would on a motor car, the voltage should be above 13, usually the alarm beeps and battery warning light. comes on if the motor is not charging

Hey guys, I just wanted to follow up with my situation and provide some helpful information for anyone that stumbles on to this thread with the same or similar issue. It ended up being blown stators on both BF90 motors. Here's what we learned in the process:

• Like I stated, I was using a multimeter to test the resistance between the terminals on the stator but unless you have a pricier multimeter suitable for measuring resistance in milliohms, you aren't going to be able to measure down to a hundredth of an ohm. In fact multimeters have resistance themselves, you can see this by holding the two prongs together which in my case was a 0.1 ohms. So accurately reading 0.09 to 0.14 ohms was not going to happen.
• We also learned that a blown battery can fry a stator. Its possible that the blown battery we found at the beginning of June occurred while the boat was underway, I don't think this was the case but its possible.
• We went ahead and changed regulaor/rectifiers on both motors also because we were unsure if they were damaged or bad. We read that a bad regulator can also blow a stator so we decided to change both components.
• Rotor removal was tough but it finally came off. The 50 mm crankshaft/pulley holder is a must have for the job. The bolt on the 2010 Honda BF90D is in fact a normal, right handed thread. We were unsure after failed attempts to remove the bolt as the shop manual does not state it as left handed but we dug up some information on other forums to confirm (confirmation needed before we really torqued on her). We used a 750 ft/lb impact wrench at first with no success (yes it was on a capable air compressor). We ended up using the engine hoist on the opposite engine to wedge the breaker bar with the 50 mm crankshaft holder into place and hold it firm. We then used another breaker bar with a 2.5 ft steel pipe for more leverage to pop the bolt loose. We did soak it in Seafoam Deep Creep for about an hour also.
• Once you have the rotor off, the rest is a breeze running the stator harness through the electronic parts case. Remove the parts as needed.
• One step we did skip that the manual said to do was the removal of the CKP sensor. I'm not sure why that must be done as it is in not in the way of the rotor or removal of. I disconnected the wire harness to the sensor during the process but did not remove it. I don't think its necessary but maybe someone can correct me on that and we just got lucky?
• After new stators and regulators, both motors are charging the batteries once again, the voltage on the speedometer reads at 13.8 at idle with both motors running. In fact with only one motor running it charges to 13.7 volts at idol.

So the question becomes why/how did both stators blow???

My theory is that one motor/alternator setup is perfectly capable of charging all 3 batteries on our boat, with all equipment and computers running. Perhaps one stator has been out for sometime and we wouldn't notice because we are always running both motors simultaneously and like I said, one motor is perfectly capable of charging our system. It wasn't until the other stator went out that we knew we had a problem with charging.

I suppose it could have been the blown battery as well or it could have been bad regulators/rectifiers. Again, these are 2010 motors with just under 2300 hours on them. I have read over posts on different forums of people having to replace alternators at much lower hours and younger motors so I don't feel like its totally out of realm of possibility that ours just wore out.

Wow, tough stuff!
Considering that you are confident one outboard will meet your charging needs, I would think about isolating the the two alternators from each other. You can do this through an AB switch or probably get fancy and do it through an isolater. Although, I'm no ace with electonic hook ups like that I'm sure a bit of study or consultation with someone that is would get you there pretty easily.

The reason I think that's the way to go is that it's very likely one alternator failed and took out the other. Because, as they are now, they are both constantly connected to each other.

I read some stuff about using two alternators to charge the same bank of batteries and they were saying that you shouldn't use the internal regulators for control. It's because the set points of each regulator will always be slightly different and the one with the higher voltage setting will sort of "take the lead" and make both alternators charge at inefficient rates.

They were recommending an external regulator made for combining two charge systems.

While I thought that makes sense, it sounds expensive while the
A-B or 1-2-BOTH switch could isolate the two from each other and you could simply switch back and forth manually on each trip if you mount the switch in an easily accessed location.

Then, if you do have a failure with one system while on the water you can be assured that it's not taking out the other and you have a back up for keeping the starters cranking and running lights lit.

I'm sure there are "fancier" ways to go but I see that as possibly the simplest.

Thanks for the reply jgmo. I have thought about this as well but I am leaning toward just continuing as is. The boat/motors are 9 years old and ran for 2300 hours as is. I guess I am just leaning toward if it aint broke dont fix it.....yes I know it was broke but I think it may just have been normal wear. I guess time will tell and if we blow out the stators again soon then we will need to look at other options. We honestly may re-power soon anyway.

Yes, I see your point. I don't like "futzing" with anything that has a good track record but was throwing in the old 2 cents because I had been following your saga.

Good luck and fair winds to Ye!

Much appreciated my friend, fair winds and trailing seas to you as well.