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Old 13-03-2020, 20:40   #1
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Alternator voltage high D1-20f

My 3 year old Dufour 310 with volvo penta d1-20f which has the 115amp alternator is not regulating.

Alarm is coming on and when checking the battery is over 15V

Checking with a multimeter is showing 16v which does not change with revs.

I replaced the battery but no help. 70A lead acid

I imagine it is the regulator in the alternator.

My problem is that it is impossible to get at and i may have to move the motor forward to remove the alternator.

It is producing current okay. There is no Solar or other inputs.

Is it possible to fit an external regulator ? Hopefully, without having to do anything to the existing alternator.?

Also anyone else had this problem on a relatively new motor.
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Old 13-03-2020, 20:56   #2
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Re: Alternator voltage high D1-20f

Yes, other people have had relatively new alternator regulators fail. It happens.

Yes you CAN fit an external regulator, BUT... There is no way to retrofit an external regulator to an internally regulated alternator without having the alternator in hand and opening it up to access the internal wiring.

This is vital to fix. It is COOKING your batteries, dangerously so.

It is a shame that your boat was designed with so little thought that the alternator can't be removed without moving the engine, but if that's what you need to do to fix it, then that's what you need to do!
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Old 13-03-2020, 21:16   #3
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Re: Alternator voltage high D1-20f

The Volvo’s often have voltage sense wires going from a alt post to the battery. If this was lose or disconnected it would cause your havoc.
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Old 13-03-2020, 22:28   #4
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Re: Alternator voltage high D1-20f

The stock Mitsubishi alternator uses a separate voltage sense wire as smac999 says. It is a small ~14 AWG wire, yellow in the default harness, that runs from the back of the alternator to the starter post. If that connection gets loose or corroded it can cause your symptoms.

As a quick test you can disconnect the yellow wire (make sure to insulate the end, it will be hot when the engine is running) and try running without it. If there is zero voltage on the sense terminal the regulator defaults to sensing from the main battery connection.

Also check the negative battery cable connection to the engine block and the alternator mounting. Resistance/corrosion at these locations can lead to bad voltage sensing.
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Old 14-03-2020, 08:30   #5
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Re: Alternator voltage high D1-20f

As previously stated the first thing to check is the sense wire. Most likely it is either a loose connection or corrosion at the battery. It is possible for the wire to be broken internally. Since you can't get at the alternator end try using an ohmmeter with one lead at the battery in with it disconnected from the battery and the other Probe on both the the positive and ground output wires from the alternator to the battery. Shake the wire while you're doing this. Also run the same test with the ohmmeter meter probes reversed. The next easiest thing to try is placing a DC power supply or several Flashlight batteries in series and raise a sense wire voltage up to 16 or 17 volt if output voltage does not come down then the sense circuit most likely has malfunction. The next backup is to Place several diodes in series with the voltage output going to the battery. use some fairly large diodes at least 100 amps. For starting point assume the Silicon voltage drop will be about seven tenths of a volt. There are other ways to compensate but they're probably more complicated than you want to attempt yourself.
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Old 14-03-2020, 10:26   #6
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Re: Alternator voltage high D1-20f

Quote:
Originally Posted by ben373 View Post
My 3 year old Dufour 310 with volvo penta d1-20f which has the 115amp alternator is not regulating.

Alarm is coming on and when checking the battery is over 15V

Checking with a multimeter is showing 16v which does not change with revs.

I replaced the battery but no help. 70A lead acid

I imagine it is the regulator in the alternator.

My problem is that it is impossible to get at and i may have to move the motor forward to remove the alternator.

It is producing current okay. There is no Solar or other inputs.

Is it possible to fit an external regulator ? Hopefully, without having to do anything to the existing alternator.?

Also anyone else had this problem on a relatively new motor.
I would recommend adding an External Regulator (such as the Balmar MC-614-H) and having your present Alternator serviced at an electrical shop to remove its internal regulation. This should remove the problem and give you total control of charging.

I commiserate with you on the difficulty getting to various engine parts, most of us suffer as well. However, I would be very surprised to learn that there is absolutely no way to remove the alternator without moving the engine, it just doesn't make sense. Perhaps you can contact a dealer or other maintenance shop to learn their "secret".

Good Luck.

~ ~ _/) ~ ~ MJH
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Old 14-03-2020, 13:36   #7
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Re: Alternator voltage high D1-20f

Solved

Thanks for your help everyone.

It was the sense wire. It came up to a battery combiner, diode type.

The sense wire was on the house battery but the diode in the combiner appears to be open circuit. So the house battery was not charging and the sense wire staying low.

So the start battery kept going up. The motor alarm came on at 15v. All makes sense now, well the lack of it!!

It was your advice though that put me on the right track. Thanks so much.

Now to find a new combiner.

It is a sure power model 1202

Strangely, some power goes to the house through this?

Once the motor is stopped the combiner isolates power back to the alternator. This is used to control relays for bilge fan and windlass it seems.


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Old 14-03-2020, 14:04   #8
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Re: Alternator voltage high D1-20f

look at the victron argo fet model.

you don't want another diode combiner. they are old junk.
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Old 14-03-2020, 17:26   #9
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Re: Alternator voltage high D1-20f

I recommend, whatever you do with the diode pack, to add a Nordkyn VRC-200 controller. This does not require modifying the alternator. Instead it uses the yellow voltage sense wire to "trick" the internal regulator into following an appropriate multi-stage charging profile. It is simple to install and keeps the internal regulator's thermal protections in place.

The bleeding edge crowd love to put down older technologies - try to put that into perspective. Diode isolators are inexpensive and work well; the loss of energy is small and rarely has any effect. The main downside is that the starting battery is going to stay at acceptance charge voltage longer than ideal. It is quite acceptable to just replace with another diode pack, but do be certain that it is rated for that 115A alternator.

That said, I have come to think that it is preferable to hard-wire the house bank to the alternator, with a separate DC-DC battery charger connected to the start battery (which only turns on when the alternator is working). This arrangement allows the alternator to properly, and reliably, charge the house bank. The separate DC-DC charger can then maintain the starting battery without overcharging. A smart battery combiner is another possibility, which I bought but haven't installed yet; it is not quite as good of a solution for caring for the starting battery. There are long threads that discuss these options more fully so search a bit before proceeding.

Greg
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Old 14-03-2020, 17:42   #10
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Re: Alternator voltage high D1-20f

I agree with CarinaPDX that the VRC-200 is a great piece of kit for these alternators, if a bit spendy.

One caution about trying to remove the internal regulator to go some other direction (Balmar external, whatever) - the stock Mistubishi alternators on the Volvo's are N-type (negative field), most aftermarket regulators are P-type (positive field). It's not a big job to make the switch, but it adds a minor bit of complication if you want to go down that road.

If you go back to a diode (or even an FET) isolator, the best practice (opinion, of course) is to wire the alternator output/direct connection to the same battery as the sense wire and the isolated output to the other battery. This does mean that if you had the exact same problem again your engine battery would not get charged, but you shouldn't over-volt your house bank. And you should get an alarm from your engine panel if the start battery isn't charging.
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