Why are they dead?

[nb Innisfree]

I sincerely hope that all of us get far more than 13 volts, especially with a modern alternator (i.e. one with a built in regulator). During the initial charging period the voltage will be somewhat depressed but if you are keeping to the 50% discharge I would expect something around the 13.5 volts or a bit higher. This should gradually rise to something between 14.0 and 14.5 volts as charging goes on. The exact voltage depends upon the regulator fitted but sticking my neck out rather a long way expect anything designed before (say) 1995 to charge at between 14.0 and 14.2 volts and anything later to charge at 14.4 or even 14.5 volts.

 

If at the end of a long charging period you have less than (say) 13.5 volts as the above suggests then you have either a phase or a diode in the alternator playing up.

 

A "smart" system might decide to reduce the charging voltage to about 13.8 volts once it decided the batteries are fully charged but in an inland boat without auxiliary charging this stage is not likely to be reached very often. Such systems are also likely to raise the charging voltage during the second phase of charging to 14.4 volts or above.

 

Using a meter to assess the batteries state of charge or even get an accurate measurement of the charging voltage, both of which require resolving the voltage down to (ideally) less than 0.1 volt is what demands an accurate meter. A meter with 10% accuracy could be reading up to 0.12 to 0.14 volts out so a battery voltage of 12.2 volts (as flat as you should ever let them go) could read 12.32V.

 

Perhaps I am mistaken but I was under the impression that older alternators charged at approx 13.8v i.e. a float charge? + a smart system would surely be unable to reduce a 14+v alternator to 13.8v or was you referring to a charger other than the alternator?

[casper ghost]

My batterys run flat almost every night. I then run the engine the next day for approx 2 hours which lasts another night and so on. My alternator is small and old, like the engine . Gibbo has already said I need to remove my diode splitter for a relay. I'm changing the engine soon and have a bigger alternator to fit, hope to get the setup a bit better this time.

[blodger]

My batterys run flat almost every night. I then run the engine the next day for approx 2 hours which lasts another night and so on. My alternator is small and old, like the engine . Gibbo has already said I need to remove my diode splitter for a relay. I'm changing the engine soon and have a bigger alternator to fit, hope to get the setup a bit better this time.

In the interim, you could still fit a couple of diodes in the 'sensing' line to uplift the voltage and get more charging. The Smartguage site tells how to. I have tried it (using diodes from an extinct alternator) and it works.

[Tony Brooks]

Perhaps I am mistaken but I was under the impression that older alternators charged at approx 13.8v i.e. a float charge? + a smart system would surely be unable to reduce a 14+v alternator to 13.8v or was you referring to a charger other than the alternator?

 

 

I suspect the Sterling alternator to battery charger will be able to do it because it just dumps the alternator's charge through a coil/coils and then uses the magnetic field to make more electricity at values they choose.

[mikevye]

I sincerely hope that all of us get far more than 13 volts, especially with a modern alternator (i.e. one with a built in regulator). During the initial charging period the voltage will be somewhat depressed but if you are keeping to the 50% discharge I would expect something around the 13.5 volts or a bit higher. This should gradually rise to something between 14.0 and 14.5 volts as charging goes on. The exact voltage depends upon the regulator fitted but sticking my neck out rather a long way expect anything designed before (say) 1995 to charge at between 14.0 and 14.2 volts and anything later to charge at 14.4 or even 14.5 volts.

 

If at the end of a long charging period you have less than (say) 13.5 volts as the above suggests then you have either a phase or a diode in the alternator playing up.

 

A "smart" system might decide to reduce the charging voltage to about 13.8 volts once it decided the batteries are fully charged but in an inland boat without auxiliary charging this stage is not likely to be reached very often. Such systems are also likely to raise the charging voltage during the second phase of charging to 14.4 volts or above.

 

Using a meter to assess the batteries state of charge or even get an accurate measurement of the charging voltage, both of which require resolving the voltage down to (ideally) less than 0.1 volt is what demands an accurate meter. A meter with 10% accuracy could be reading up to 0.12 to 0.14 volts out so a battery voltage of 12.2 volts (as flat as you should ever let them go) could read 12.32V.

 

 

Hi Tony within this detailed analysis is there an optimum engine revs? On the Barrus gauge panel 14+ volts are displayed from 1000 RPM upwards. I tend to run the engine at 1200 RPM during the charging cycle as it limits the visible emissions and doesn't appear to race the engine in neutral

[Tony Brooks]

Hi Tony within this detailed analysis is there an optimum engine revs? On the Barrus gauge panel 14+ volts are displayed from 1000 RPM upwards. I tend to run the engine at 1200 RPM during the charging cycle as it limits the visible emissions and doesn't appear to race the engine in neutral

 

 

As far as charging VOLTAGE is concerned once you reach a steady voltage reading (be it 13.8 up to 14.4+) there is nothing rev related about it. It would probably maintain that voltage at idle. HOWEVER that is an exceptionally long way from saying there is no optimum engine revs because the optimum revs for charging is related to current (AMPS PRODUCED).

 

I am sure you have read the threads that state that most marine alternators are never riven fast enough to reach maximum output. I may take a less definite view but it has an awful lot of truth in it.

 

It's easy to set the optimum charging revs if you have an ammeter. Just gradually increase the engine revs until the ammeter stops rising. Over time the ammeter will fall so you reduce the revs but still maintain the maximum current flow possible.

 

On my boat the optimum charging revs start off at about 1500, about 10 minutes later they drop to about 1300 and over the next three or four hours can be reduced to idle.

 

If you do not have an ammeter indicating alternator output I fear you have no way of knowing the optimum revs throughout the charging period. A £25 Durite clamp on meter can be great help here.

[alan_fincher]

Hi Tony within this detailed analysis is there an optimum engine revs? On the Barrus gauge panel 14+ volts are displayed from 1000 RPM upwards. I tend to run the engine at 1200 RPM during the charging cycle as it limits the visible emissions and doesn't appear to race the engine in neutral

Mike,

 

It is not possible to give a general answer about optimum engine revs for battery charging.

 

For a start different alternators have different characteristics for the speed at which THEY have to be rotated to give a good output.

 

But more significantly, there is a typically two to three times multiplier in how fast your alternator turns versus how fast your engine is turning, determined by the ratio of the pulley size on the engine crankshaft to that on the alternator.

 

Typically an engine that has been marinised with pulleys with only (say) a 2:1 one ratio will need to be run a lot faster to get the same output from the same alternator as one that has a (say) 3:1 ratio.

 

Curiously older engines are often better in respect. Our old BMC is pullied at 3:1, so gives a respectable charge even when at idle speed (650 RPM with an A127 Alternator). However it seems many modern marinisations run one (or more) of their alternators on a lower step up ratio, so will not give a lot of charge until engine speed is advanced well beyond idle.

 

If you say what alternator you have, and the diameter of your crankshaft and alternator pulleys, one of the experts will probably be able to give you a better idea, but IMO the best thing is to have an ammeter fitted, and actually see what charge you achieve at different engine RPM.

 

EDIT:

 

Ah! Tony got there first! Hopefully although we have said things differently, I have not said anything not in agreement with what he has. We both think an ammeter makes sense, at least!

Edited November 24, 2009 by alan_fincher

[FORTUNATA]

I can't quite recall the specifics of float and bulk charge but, as you know, there is a certain requirement during the bulk charge phase to overcome plate internal resistance. That's why, as you said, voltage needs to go somewhat beyond 13 volts to overcome said resistance. That is, if you want to get a decent charge.

I think I recall measuring my terminal voltages some months ago and I got 13. point something volts although the alternator had only just kicked in after engine start. Mine is a basic Lucas alternator on an old Lister SR2.

These days, charging systems go far beyond what you'd find on my old seventies boat. There is temperature sensing (so the alternator isn't fooled into voltage reduction due to plate surface temperature increase, for example. Even back in the early nineties, they had cycle charging via a chip in an external "smart" regulator. That, as some people know, accommodates the phases of bulk, absorption, float and equalisation.

Correct me if I'm wrong but I seem to recall it's the float charge that is sort of neutral and poses no threat at all to overcharging cells (somewhere around 13 point something volts.

Of course, to be honest, I don't rely on my alternator as I don't cruise as much as I ought to (for lack of time) and have an inverter/battery charger. The inverter keeps my batteries up to snuff but I think when cruising it may not be so easy. My boat has already been wired up by the former owner but, for some reason, he connected the 12 volt cabin lights to A.C. via a transformer so the system is power hungry. I have had instances of the inverter flattening my batteries and really need to separate the starter battery from the house via a relay.

 

 

I sincerely hope that all of us get far more than 13 volts, especially with a modern alternator (i.e. one with a built in regulator). During the initial charging period the voltage will be somewhat depressed but if you are keeping to the 50% discharge I would expect something around the 13.5 volts or a bit higher. This should gradually rise to something between 14.0 and 14.5 volts as charging goes on. The exact voltage depends upon the regulator fitted but sticking my neck out rather a long way expect anything designed before (say) 1995 to charge at between 14.0 and 14.2 volts and anything later to charge at 14.4 or even 14.5 volts.

 

If at the end of a long charging period you have less than (say) 13.5 volts as the above suggests then you have either a phase or a diode in the alternator playing up.

 

A "smart" system might decide to reduce the charging voltage to about 13.8 volts once it decided the batteries are fully charged but in an inland boat without auxiliary charging this stage is not likely to be reached very often. Such systems are also likely to raise the charging voltage during the second phase of charging to 14.4 volts or above.

 

Using a meter to assess the batteries state of charge or even get an accurate measurement of the charging voltage, both of which require resolving the voltage down to (ideally) less than 0.1 volt is what demands an accurate meter. A meter with 10% accuracy could be reading up to 0.12 to 0.14 volts out so a battery voltage of 12.2 volts (as flat as you should ever let them go) could read 12.32V.

 

 

I often wonder how many wasted watts I produce in vain when cycling to work and back (45 minutes each way usually). Anyone who's into cycling might be surprised Lance Armstrong produces about 500 watts when climbing mountain stages in the Tour De France. Seeing as alternators are really more sophisticated dynamos, using coils and then rectifying the alternating current, it didn't surprise me to hear scientists are now experimenting with human energy to produce electrical output.

I've heard of gymnasium that are kitting out treadmills and bikes to generators, thereby producing electrics for the entire building!

Now, my electric fire on the boat is merely 300 watts and produces a reasonable amount of heat but who knows... Maybe one day we'll be doing a workout indoors on the boat while charging up our batteries in the process.

 

 

Mike,

 

It is not possible to give a general answer about optimum engine revs for battery charging.

 

For a start different alternators have different characteristics for the speed at which THEY have to be rotated to give a good output.

 

But more significantly, there is a typically two to three times multiplier in how fast your alternator turns versus how fast your engine is turning, determined by the ratio of the pulley size on the engine crankshaft to that on the alternator.

 

Typically an engine that has been marinised with pulleys with only (say) a 2:1 one ratio will need to be run a lot faster to get the same output from the same alternator as one that has a (say) 3:1 ratio.

 

Curiously older engines are often better in respect. Our old BMC is pullied at 3:1, so gives a respectable charge even when at idle speed (650 RPM with an A127 Alternator). However it seems many modern marinisations run one (or more) of their alternators on a lower step up ratio, so will not give a lot of charge until engine speed is advanced well beyond idle.

 

If you say what alternator you have, and the diameter of your crankshaft and alternator pulleys, one of the experts will probably be able to give you a better idea, but IMO the best thing is to have an ammeter fitted, and actually see what charge you achieve at different engine RPM.

 

EDIT:

 

Ah! Tony got there first! Hopefully although we have said things differently, I have not said anything not in agreement with what he has. We both think an ammeter makes sense, at least!

[blodger]

Mine is a basic Lucas alternator on an old Lister SR2.

Correct me if I'm wrong but I seem to recall it's the float charge that is sort of neutral and poses no threat at all to overcharging cells (somewhere around 13 point something volts.

Of course, to be honest, I don't rely on my alternator as I don't cruise as much as I ought to (for lack of time) and have an inverter/battery charger. The inverter keeps my batteries up to snuff but I think when cruising it may not be so easy. My boat has already been wired up by the former owner but, for some reason, he connected the 12 volt cabin lights to A.C. via a transformer so the system is power hungry. I have had instances of the inverter flattening my batteries and really need to separate the starter battery from the house via a relay.

Basic Lucas alternators are easier to modify than others it seems.