Are both my alternators shot?

[Nick_H]

Set off yesterday on a longish cruise, two hours at 800 rpm, no issues, then 2,000 RPM for 30 mins, then back to 800 RPM. Some time after this I noticed the battery warning light on port EVC. Start battery volts looked a bit low but OK, so carried on with no problem for a few hours, then back to 2,000 RPM for an hour during which time the start battery volts slowly dropped. I had the genny running the whole time, so the mains charger was also running.

Anchored up at the other end, and with the mains charger running but no engine load, the start battery volts recovered.

This morning I tried each engine in turn at 1,000 rpm in neutral with the charger off, and measured volts at the batteries with a voltmeter. Before starting either engine - 25.4V, after starting either engine - 25.1V. When engines stopped, the volts slowly recovered back towards the 25.4V. When I then turned both engines off and the mains charger on, the volts rose steadily to 26V+.

The alternator drive belts are both OK, alternators spinning fine with no unusual noises, smells etc. Battery fluid levels are good, though start batteries are 10 years old. Engines are D-12's with early EVC, 2004 vintage.

Armed with very little knowledge of boat electrics, I've concluded that both alternators are probably not working. When engine load is low (ie. at 800 RPM), the mains charger can keep up, but at high load (2,000 RPM) the charger can't keep up, hence the warning light and dropping start battery volts. It seems unlikely that both alternators failed at the same time, so maybe one failed some time ago, but the other could manage on its own? Alternatively, is there a systematic fault that has fried both alternators?

Before I shell out £££'s on two new alternators, does my reasoning sound good? If i'm right, is it reasonable to go to sea relying on the mains charger, as there may be better repair facilities about 30 NM away.

 

[westernman]

These alternators probably have a field wire - usually connected to a smart controller.

My bet would be the problem is that the field wire is not "excited".
This can be due to :-

1) a corroded/dodgy connection between the field wire and the smart controller

2) a fault in the smart controller

3) A corroded/dodgy 12V connection to the smart controller (no juice and it won't work)

4) The ignition switch input to the smart controller is corroded/dodgy and it is simply not turned on

I think it is unlikely there is a problem with the alternators themselves - certainly not two at the same time.

 

[volvopaul]

Hi nick .

Unless you have both engine alternator lights on then there is no reason to suggest alternators have failed.

You have a split charge system whereby each engine will charge both start and house batteries so running say on one engine will keep it all charged .
There will be a sensing wire to each alternator which tells the alt to charge the relevant batteries. There is an inline fuse at one end , if this has blown then the alt think all is well and don't sense charge is req.

I would be looking at new batteries if they are ten years old as it sounds like there failing. You have done very well out of them especially in the med.

To test them as there 24v system you need to separate them and test each one because one bad one in the pair will drag down the other. I always replace a pair on a 24 v system to ensure longevity.

Is there a bad egg gas smell in the boat , are they getting warm ?
Is the gyro unit anything g to do with the system ? I think it's 240 volt from memory, but check.

Cheers

 

[Nick_H]

Thanks Michael and VP.

No bad smell or warm batteries. I'll try splitting the pairs and checking each battery. I'll also try and check the sensing wire and fuse, is it fairly obvious what I'm looking for?

Gyro is 240V. Control is 24v, but is on the domestic side anyway.

 

[MapisM]

I had the genny running the whole time, so the mains charger was also running.

Just another thought: IF your charger recharges (as most do) both the domestic and the engines batteries, are you sure that there isn't some sort of conflict when running both together? I mean, both the charger and the alternator of course, not both engines.
I'm asking because I've seen several boats requiring to NOT run the charger together with the alternator(s).
...though I guess that if this would be the problem, you should have had it also in the past...
Anyway, just a thought, as I said.

 

[boatingdave]

I have tamd71b's. They don't like it if the charger is on at the same time the engines are running. The alternator light comes on (and is designed to) when the voltage is above the alternator voltage. Although it does sound as if you have a problem having the charger on whilst running may give you some funny indications.

 

[Nick_H]

OK, so I seperated the four start batteries, and each of them slowly dropped from around 13.2 to around 12.7V over the course of four hours. I've checked all the wiring from the alternators to the 24V panel to the batteries, and there are no obvious broken wires, no corrosion, and all the trip switches are OK.

Paul, when you said there's an inline fuse, did you mean the 70 amp breaker next to the alternator, or is there another one somewhere.

I cant find anything that is obviously a smart controller, unless it's part of the battery charger, or the small Mastervolt box next to the charger. This has a green flashing light so it must have power, but nothing else to indicate if it's working or not. In the control panel is a Kendrion mganetic battery switch/relay, is this anything to do with alternator charging? There is nothing on this to indicate if it has power or not.

Any help much appreciated because i'm stuffed at the moment, as none of the local mechanics can even come and look at it for a few days, let alone fix it. The only saving grace is that there are far worse places to be stuck than St Florent in Corsica, but if i'd wanted a land based holiday I wouldn't have bought a boat!

 

[jfm]

OK, so I seperated the four start batteries, and each of them slowly dropped from around 13.2 to around 12.7V over the course of four hours. I've checked all the wiring from the alternators to the 24V panel to the batteries, and there are no obvious broken wires, no corrosion, and all the trip switches are OK.

Paul, when you said there's an inline fuse, did you mean the 70 amp breaker next to the alternator, or is there another one somewhere.

I cant find anything that is obviously a smart controller, unless it's part of the battery charger, or the small Mastervolt box next to the charger. This has a green flashing light so it must have power, but nothing else to indicate if it's working or not. In the control panel is a Kendrion mganetic battery switch/relay, is this anything to do with alternator charging? There is nothing on this to indicate if it has power or not.

Any help much appreciated because i'm stuffed at the moment, as none of the local mechanics can even come and look at it for a few days, let alone fix it. The only saving grace is that there are far worse places to be stuck than St Florent in Corsica, but if i'd wanted a land based holiday I wouldn't have bought a boat!

Hi Nick
Lucky you, I love St Fl! Was there week before last. Go on the flying Rib, takes off from the beach across the gulf. Pilot is a cool dude called Leo; you'll bond with him

The fuse mentioned is not the 70A breaker - that breaker is in the main charging cable. Scuse the suck eggs, but let's just cover how an alternator works (at v basic level). It generates electricity by moving a coil of wire in a magnetic field, but the clever part is how the output voltage that the alternator makes is controlled. The trick here is that the magnet is actually an electro magnet, and you'll have a voltage regulator black box somewhere that varies the voltage to that electromagnet (ie the so called excitation or field circuit). Varying the electromagnet is the trick used to control the voltage on the big 70A output wires. So, as well as the fat 70Amp wires, you must have at the alternator a couple of thin wires (or one wire)going into the alternator, for the excitation circuit, sort of 5-10 amp gauge wire. They could have a fuse or a bad connection, so check that (with "ignition" on). Also the voltage regulator black box that controls this could be busted, or something. If there is no voltage on these "excitation" wires, there is no magnetism, and the alternator will make no output. Worth checking this line of enquiry.

I doubt your 2 alternators have both died together. More than likely they both charge both engines, so one could have died ages ago (unnoticed) and the other more recently

Ref: cant find anything that is obviously a smart controller, unless it's part of the battery charger, or the small Mastervolt box next to the charger. This has a green flashing light so it must have power, but nothing else to indicate if it's working or not. In the control panel is a Kendrion mganetic battery switch/relay, is this anything to do with alternator charging? There is nothing on this to indicate if it has power or not.

...the voltage regulator will not be part of the 230v batt charger. If there is a separate mastervolt box it could be that but it will be very small, and there need to be two of them, and usually they are mounted close to the alternators, so I doubt that is it. The kendrion doesn't sound ike it. Point is, there must be TWO voltage regulators, so maybe keep looking and follow the excitation wires from the alternator because I'd doubt the regulators are more than a metre away

 

[Nick_H]

Thanks to all, and especially to Volvopaul who took time out to ring me and talk through the problem.

To confuse matters further, I just measured the voltage across the terminals of each of the alternators with the engines running and the mains charger turned off, and they're both reading about 28.7V. At the same time the start batteries are 25.2V measured with the same multimeter, but when I stop the engines they recover a bit to 25.5V. It seems the alternators are creating a charge, but for some reason it's not being transferred to the batteries, or at least to the start batteries.

I now have a "peut etre" from a mechanic for tomorrow, so fingers crossed on that one, but still happy to hear any other input or ideas in the meantime.

 

[Nick_H]

Hi Nick
Lucky you, I love St Fl! Was there week before last. Go on the flying Rib, takes off from the beach across the gulf. Pilot is a cool dude called Leo; you'll bond with him

Yep, picked up the flyer in the Capitainerie, so hopefully can arrange for tomorrow, though a bit more wind is forecast so depends if he can still fly.

As I said, far worse places to be stuck!

 

[jimmy_the_builder]

...the voltage regulator will not be part of the 230v batt charger. If there is a separate mastervolt box it could be that but it will be very small, and there need to be two of them, and usually they are mounted close to the alternators, so I doubt that is it. The kendrion doesn't sound ike it. Point is, there must be TWO voltage regulators, so maybe keep looking and follow the excitation wires from the alternator because I'd doubt the regulators are more than a metre away

The regulators may well be inside the alternator housing and not user-accessible (this is the arrangement on the Mitsubishi-manufactured alternators that are OE on the D6).

 

[Portofino]

my Internet Diagnosis ---- duff batterie(s)

Treatment = Replace batteries - assuming leads have had a good connection on all the posts

 

[Nick_H]

I finally managed to get an electrician on board today, and the problem was with the diodes directing charge to the start batteries. He has bridged them for now (he assures me this is OK for a few weeks till we get back to Antibes).

I guess one probably failed some time ago, but I didn't notice because the other alternator was still charging and I never run only one engine, but the other must have failed on the way across to Corsica.

edit: correction, he hasn't bridged the diodes, but has put both domestic and start on the domestic side of the isolators, which are still working. Isolators are a standard VP part, look like this