Alternator Question

Rich Stidger · Nov 17, 2013

More info please- What type of alternator? Internal or external regulator? Is there a battery combiner in the circuit?

One possibility is that if you have a relay that connects the alternator output to the house batteries when charging, that relay may be bad. I have this type of connection on my h40.5, and I have had the relay fail. When it does, the house batteries are not charged but the starting battery is charged since it is connected before the relay.

If you have a connecting relay like I have described, when the engine is running there should be less than 100mv across the relay terminals. If there is a higher voltage, the house batteries will not charge or will charge very little.

Rich Stidger · Nov 17, 2013

OK, Brian, your alternator probably has an internal regulator and will taper off quick quickly. For deep cycle house batteries this is not a good feature, but the taper is not the cause of your net deficit after running your engine. The alternator should always supply all of the load power and still add charge back into the batteries.

If you have a relay, it is probably located in the engine compartment. You should be able to trace the heavy red wire from the alternator to two places. It should be connected to the starting battery and also to the combining relay or solenoid.

See the picture below. This is a picture of my combining relay. If you have something that looks like this it is probably the unit.

Ron20324 · Nov 17, 2013

Rich Stidger said:
...You should be able to trace the heavy red wire from the alternator to two places. It should be connected to the starting battery and also to the combining relay or solenoid.....

Uummm.... maybe I misunderstood all the posts I've been reading, but isn't it preferred that the alternator be wired to the HOUSE bank?

Rich Stidger · Nov 18, 2013

Yes, Ron, you are correct. However, most owners seem to have the alternator connected to the starting battery by the factory. Thus my comment as to what Brian is likely to find.

Thinking about this more later last night, there has to be either a combiner or a solenoid that connects the house and starting banks together for charging. If Brian is sure that he doesn't have a combiner, then I think he must have a solenoid located somewhere.

A wiring diagram of his sailboat would show the existence, but not the location.

The only other possibility that I can think of is that he has a dual-output alternator. however, these are not that common and he said that the alternator was factory stock.

I only mentioned the solenoid as a possible failure item because my solenoid failed and I had the same result in that I could not charge the house bank.

Additional T/S would involve measuring the charging voltage at the alternator, starting battery, and at the house bank. Those measurements would tell a lot.

Rich Stidger · Nov 18, 2013

BWagner said:
Rich,

Okay, it appears I have said solenoid somewhere - haven't found it yet, it's not in my engine space and I suspect it is under the nav station near where the battery switches are located.

It shows up in the diagram in my owners manual. One stupid question: What does it do? Recently I have noticed that my start battery is using a LOT of water. Could that possibly be related to this as well. As for testing, the boat is on the hard for a few more days, hope to have it back in the water on Wednesday.

Thanks for all your help.

Sorry I can't help with the solenoid location, but it will have heavy wires and will be connected between the house bank and the starting battery.

In the absence of any other problem, I would suggest that if your start battery is using a lot of water, it is probably defective. But you are apparently getting too much charge into the start battery (high water usage) and too little charge into the house bank (AH deficit). I'm not a big believer in coincidences, so I expect these two observations are related.

I think your problem could still be the solenoid, but it could also be a bad start battery. Ponder this- If the start battery has a shorted cell, it would absorb most of the charge from the alternator resulting in high water usage. In this case, all of the cells in the start battery except the shorted one would use a lot of water. However if the solenoid were bad, (high resistance), most of the charging current would be directed to the starting battery and all cells would use a lot of water. Which condition do you have?

At this point, I would do a couple of things. First I would pull out the starting battery and get it load tested. This test will rule out or confirm the health of the starting battery.

Second, after your boat is back in the water, run the engine at 1500 rpm or so with all your normal loads on and make the following voltage measurements:

Output voltage of the alternator
Charging voltage across the start battery
Charging voltage across the house bank
Voltage drop across the connecting solenoid

Desired results:
The alternator output voltage should be a minimum of 13.6V
The start battery voltage should be the same as the alternator output
The house bank voltage should be very close to the alternator output
The voltage drop across the solenoid should be less than 200mv

If you have a clamp-on current meter, turn off all house loads and:

Measure the current out of the alternator
Current into the start battery
Current into the house bank (this might be negative based upon your problem)

The alternator output current should be the total of the start battery charge current and the house bank charge current.

If the currents don't total correctly, you must have another load somewhere drawing power.

Post your results and we will think about the next step. You could have a bad connection to your house bank from the alternator charging circuit. The above measurements will help to sort it out.

Maine Sail · Nov 19, 2013

BWagner said:
Hello,

I have noticed recently that when under power we are operating at a net deficit with respect to power. What I mean is that according to my Link Pro after running with the engine for eight solid hours we are actually down amps from when we started. Not a lot, say maybe ten to twenty amps down but still I would expect to have full batteries after an eight hour day. Instead I need to run our generator to top off the batteries.

The alternator is new. It is a 90 amp unit the same as the old one. I have checked and initially the thing is putting out somewhere in the area of 50 amps according to the link pro. At some point though the alternator reduces the power it is putting into the battery bank which makes me think maybe something is up with the regulator? Or is this normal? Our draws are only our instruments and normal house loads such as refrigeration while underway. Is there some way to change the way the regulator is working?

Any insight would be appreciated. Thanks.

Sounds like your battery monitor may simply be out of calibration... When was the last time it was manually synced?

Batteries only accept what they can accept at a given SOC & voltage.

When your bank is accepting less than 2% of the rated Ah capacity, eg: 2A @ 14.4V, then you can manually resynchronize the BM.. It also may not be programmed or wired correctly..

Need to know:

Absorption voltage set point of alt
How shunt is wired
How BM is programmed

Personally I never rely on the BM's auto-synch feature and only rely on "known full" manual re-sets. Your bank is full enough for a re-set when you meet less than 2% acceptance at 14.4V....

If your alt output flows through a start battery first this in not the best approach. For optimum performance the alt should be fed to house first with the start pulling off an ACR or Echo type charger.

It is important that you are seeing a bare min of 14.2V AT THE BATTERY TERMINALS when in absorption mode. Voltages lower than this can result in drastically extended charge times.. At say 13.6 you may need 15 - 20 hours to hit full but at 14.4V you may be able to do it in 6 - 8 hours... Charging terminal voltage is the PRESSURE that determines how much CURRENT the battery bank will accept...

Alternator Question

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