Volvo MD2020 alternator failure?

[Ric]

The alternator on my 2001/1700hour VP MD2020 seems to have failed - when I start the engine there is no change on battery voltage and no charging current (as measured by my NASA battery monitor) whereas normally it would be showing 13.8v and a positive charge. The alternator alarm starts after a few seconds but if I increase revs to around 1800rpm it is silenced (even though there is no change in battery voltage and still no charging). My inkling is that it the alternator is dead but before I go down that route is there anything else I should check?

I do have a Sterling regulator fitted but when I disconnected the white wire (which disconnects the Sterling and reverts to the alternators own regulator) there was no change in the symptoms.

 

[pvb]

Do you have a diode splitter?

 

[Ric]

Yes - well I think so in that I have two separate battery banks (engine/domestic) that are charged by the same alternator.

 

[VicS]

Yes - well I think so in that I have two separate battery banks (engine/domestic) that are charged by the same alternator.

You could have a diode splitter or a VSR

13.8 volts is very low especially with a Sterling regulator ... It suggests you do have a diode splitter and that the battery sensing feature of the Sterling regulator may not be correctly connected to boost the volts to compensate for the diode splitter.

However that aside I think I would check the alternator brushes and then perhaps get it checked by an automotive electrician

 

[pvb]

Yes - well I think so in that I have two separate battery banks (engine/domestic) that are charged by the same alternator.

If one leg of the diode splitter has failed, the battery which is monitored by your Nasa monitor may not be receiving charge. It's impossible to diagnose without knowing exactly what your set-up is, but this may help you to start to resolve it.

 

[VicS]

If one leg of the diode splitter has failed, the battery which is monitored by your Nasa monitor may not be receiving charge. It's impossible to diagnose without knowing exactly what your set-up is, but this may help you to start to resolve it.

But would that explain the alternator alarm ?

 

[pvb]

But would that explain the alternator alarm ?

How would you explain the fact that the alarm goes off?

 

[Birdseye]

I spent ages a couple of years ago chasing this problem on a 2030 also fitted with a Sterling gadget. The original alternator diodes gave out but replacing the alternator soon gave exactly the same problem. To cut a long story short it turned out with the replace alternator that the problem was with the solder used in China. Apparently they dont use silver solder but the normal soft stuff and the effect of the Sterling charge regulator is to raise the alternator temperature by making it work harder. This caused the solder to half melt creating intermittent dry joints. The dure was to buy an alternator made in Europe, something that wasnt too easy to do. I also ditched the Sterling charger and fitted a fan to the engine box.

 

[VicS]

How would you explain the fact that the alarm goes off?

The warning light will go off and the alarm will be silenced as the volts out from the field diodes approaches the battery volts

 

[PaulRainbow]

The warning light will go off and the alarm will be silenced as the volts out from the field diodes approaches the battery volts

So even if the alternator is not charging, the charge light still goes out ?

New one on me.

 

[Daydream believer]

I had the same problem with my MD2020. I traced it to a loose connec tion at the control panel by the rev counte. I suggest that you take the back cover off( if there is one) & work every connection by hand. I did this & the problem was solved,

 

[Ric]

DDB - thank you - you may be on to something because I recently had to replace the engine start button after control panel failures...

 

[VicS]

So even if the alternator is not charging, the charge light still goes out ?

New one on me.

What I describe is the condition which results in the light going out.
Normally the regulator will increase the filed current until its set voltage is reached ( 14 volts or so ) and the alternator will charge the battery. If that does not happen ( faulty regulator perhaps) the alternator will not be charging.

The OP's problem could be an alternator fault or could be a bad connection in the warning light circuit, although I believe a MD2020 from 2001 also has an initial excitation circuit via an excitation resistor. If so a bad connection in its circuit could be the cause.

 

[PaulRainbow]

What I describe is the condition which results in the light going out.
Normally the regulator will increase the filed current until its set voltage is reached ( 14 volts or so ) and the alternator will charge the battery. If that does not happen ( faulty regulator perhaps) the alternator will not be charging.

The OP's problem could be an alternator fault or could be a bad connection in the warning light circuit, although I believe a MD2020 from 2001 also has an initial excitation circuit via an excitation resistor. If so a bad connection in its circuit could be the cause.

The OP tells us that the light goes out and the buzzer stops, but the battery voltage, as reported by the battery monitor, does not change.

In post #9 "The warning light will go off and the alarm will be silenced as the volts out from the field diodes approaches the battery volts" But the battery monitor shows no such increase in voltage.


"

 

[VicS]

The OP tells us that the light goes out and the buzzer stops, but the battery voltage, as reported by the battery monitor, does not change.

In post #9 "The warning light will go off and the alarm will be silenced as the volts out from the field diodes approaches the battery volts" But the battery monitor shows no such increase in voltage.

That's right. The monitor is showing the battery voltage. It wont increase if there is no output from the alternato, or if it does not increase above the battery volts.

 

[PaulRainbow]

That's right. The monitor is showing the battery voltage. It wont increase if there is no output from the alternato, or if it does not increase above the battery volts.

You are not making any sense. If there is no output from the alternator the warning light will not go out and the buzzer will not stop. The OP reports the light going out and the buzzer stopping.

This surely suggests that the alternator is charging but the charge is not reaching the battery that the monitor is connected to, or the monitor is faulty in some way.

PVBs suggestion is therefore valid and worth checking with an independent volt meter/multimeter.

 

[VicS]

You are not making any sense. If there is no output from the alternator the warning light will not go out and the buzzer will not stop. The OP reports the light going out and the buzzer stopping.

This surely suggests that the alternator is charging but the charge is not reaching the battery that the monitor is connected to, or the monitor is faulty in some way.

PVBs suggestio is therefor valid and worth checking with an independent volt meter/multimeter.

The warning light and buzzer circuit is connected between the battery , via the so called ignition switch, and the 61/D+ connection between the field diodes and the regulator.
Initially current flows from the battery through the warning light, the regulator and the field coil . When the volts output from the field diodes becomes equal to the battery volts there will be no voltage difference across the warning light and alarm circuit. The light will therefore be extinguished and the alarm silenced.

PVB suggests that one leg of the diode splitter could be could have failed. This would explain the reading on the monitor (if it only monitors the battery connected to the failed leg) but it does not explain the behavior of the warning light and alarm. With no other fault they would behave normally.

 

[PaulRainbow]

The warning light and buzzer circuit is connected between the battery , via the so called ignition switch, and the 61/D+ connection between the field diodes and the regulator.
Initially current flows from the battery through the warning light, the regulator and the field coil . When the volts output from the field diodes becomes equal to the battery volts there will be no voltage difference across the warning light and alarm circuit. The light will therefore be extinguished and the alarm silenced.

PVB suggests that one leg of the diode splitter could be could have failed. This would explain the reading on the monitor (if it only monitors the battery connected to the failed leg) but it does not explain the behavior of the warning light and alarm. With no other fault they would behave normally.

I know how a charge warning lamp is wired, i've been doing this in the real World for some time, i'm not sitting here Goggling the answers.

If the light goes out, the alternator is charging, at least something, but nothing is showing on the battery monitor. I've seen cases where the alternator puts the warning light out, but doesn't put any meaningful charge into the battery, i've seen failed diodes that do exactly what PVB suggests as a possibility, there are of course other possibilities. The OP would do well to make some checks with a multimeter, starting with checking the voltage at the alternator, with the engine running.

 

[VicS]

I know how a charge warning lamp is wired, i've been doing this in the real World for some time, i'm not sitting here Goggling the answers.

If the light goes out, the alternator is charging, at least something, but nothing is showing on the battery monitor. I've seen cases where the alternator puts the warning light out, but doesn't put any meaningful charge into the battery, i've seen failed diodes that do exactly what PVB suggests as a possibility, there are of course other possibilities. The OP would do well to make some checks with a multimeter, starting with checking the voltage at the alternator, with the engine running.

Quite possible.

However the point I was making before you intervened was that the behavior of the warning light , as reported in #1, does not support pvb's suggestion that one half of a diode splitter may have failed. That would result in one battery not being charged, but the waring light and alarm would operate normally.

( If the Sterling battery sensing was correctly connected it might result in the other battery being overcharged but it seems from the low voltage the OP regards as normal that the battery sensing is not connected correctly.)

 

[PaulRainbow]

Quite possible.

However the point I was making before you intervened

Intervened ?

It's an open internet forum, where the poster asked a question.

was that the behavior of the warning light , as reported in #1, does not support pvb's suggestion that one half of a diode splitter may have failed. That would result in one battery not being charged, but the waring light and alarm would operate normally.

( If the Sterling battery sensing was correctly connected it might result in the other battery being overcharged but it seems from the low voltage the OP regards as normal that the battery sensing is not connected correctly.)

One again, i don't need you smug, condescending comments explaining to me how things work. I post from real World knowledge and experience, i don't sit here Googling my answers or downloading endless schematics and manuals to be able to answer questions.

What is your real World experience and qualifications regarding boat electrical systems ?