Why am I needing frequently to tighten my alternator belt?

[nicknorman]

19 minutes ago, Theo said:

But at safe voltages you can only put so much current into the battery bank.  At 80% charge and 14.4V my nominal  810AH (very old) battery bank is only accepting in the region of 18A.  This will, of course be due to surface charge, but can such chemistry be overcome by lots of electronics?  I am using an Adverc, and very excellent it is too, but I can't see how I would manage to keep my alternator working flat out any more than it is now.

 

 

Well something is wrong there, maybe the batteries are knackered or your estimation of SoC is incorrect. 2% of 810Ah is 16.2A which many people consider to be 100% SoC.

 

But other factors such as thin alternator and battery interconnect wiring designed for a 50A alternator, voltage lost in battery isolators etc may be at play. Is the 14.4v actually at the battery terminals, or somewhere else along the way?

[Theo]

"It’s to do with the regulation curve of an alternator’s rather basic regulator. The current supplied by an alternator is related (inversely) to the terminal voltage. So if we presume for example that the regulated voltage is 14.4v, at 14.4v it is producing no current. At 14.39v it is producing  maybe 1% of its output. At 14.3 maybe 10%. At 14.2v maybe 25% You have to get right down to perhaps 13.7v before it is producing 100% of its output. (Figures made up, but the principle is right)."

 

I have quoted the bit from nicknorman's post that I can't get me head around.

 

Lets forget that we are using an alternator for a moment.  If we were to use a true constant voltage source where the voltage is entirely independent of the current drawn, then the current delivered at, say 14.4V, would be entirely dependent upon what the battery bank would accept.

 

Now take the case of nicknorman's alternator.  The battery bank is at 14.4V so the current delivered is zero as controlled by the alternator electronics.  Now let's say that some charge is drawn from the bank so that its voltage drops to 14.39.  In the case stated by nn the alternator immediately delivers its 1% which, with a 70A alternator is 0.7A or a 140A alternator is 1.4A.  If we take the load drawn out of the equation by assuming that it is switched off the moment that the voltage drops to 14.39V then the alternator will continue to charge the battery until the voltage reaches 14.40V and then stops.  Ah! It is becoming clear what nn is saying even as I am typing the reply.  What he means (and says clearly) is that, assuming the same alternator controller characteristics, a 140A alternator will charge the battery more quickly even at the low tail currents.

 

My old alternator is a Bosch to which I fitted an adjustable controller.  I originally found that it would charge reasonably rapidly at the beginning of the day's cruising but the current would drop off far to early.  I got around this with an Adverc which made a huge difference...

 

Thanks, nicknorman.  I believe that I now understand but will not be fitting a bigger alternator because of the issues of fitting new pulleys etc.  I will live with what I have.  (And keep the belt tensioned properly.)

 

 

Edited October 18, 2021 by Theo
Lots of little mistakes in typing

[nicknorman]

10 minutes ago, Theo said:

"It’s to do with the regulation curve of an alternator’s rather basic regulator. The current supplied by an alternator is related (inversely) to the terminal voltage. So if we presume for example that the regulated voltage is 14.4v, at 14.4v it is producing no current. At 14.39v it is producing  maybe 1% of its output. At 14.3 maybe 10%. At 14.2v maybe 25% You have to get right down to perhaps 13.7v before it is producing 100% of its output. (Figures made up, but the principle is right)."

 

I have quoted the bit from nicknorman's post that I can't get me head around.

 

Lets forget that we are using an alternator for a moment.  If we were to use a true constant voltage source where the voltage is entirely independent of the current drawn, then the current delivered at, say 14.4V, would be entirely dependent upon what the battery bank would accept.

 

Now take the case of nicknorman's alternator.  The battery bank is at 14.4V so the current delivered is zero as controlled by the alternator electronics.  Now let's say that some charge is drawn from the bank so that its voltage drops to 14.39.  In the case stated by nn the alternator immediately delivers its 1% which, with a 70A alternator is 0.7A or a 140A alternator is 1.4A.  If we take the load drawn out of the equation by assuming that it is switched off the moment that the voltage drops to 14.39V then the alternator will continue to charge the battery until the voltage reaches 14.40V and then stops.  Ah! It is becoming clear what nn is saying even as I am typing the reply.  What he means (and says clearly) is that, assuming the same alternator controller characteristics, a 140A alternator will charge the battery more quickly even at the low tail currents.

 

My old alternator is a Bosch to which I fitted an adjustable controller.  I originally found that it would charge reasonably rapidly at the beginning of the day's cruising but the current would drop off far to early.  I got around this with an Adverc which made a huge difference...

 

Thanks, nicknorman.  I believe that I now understand but will not be fitting a bigger alternator because of the issues of fitting new pulleys etc.  I will live with what I have.  (And keep the belt tensioned properly.)

 

It certainly is a “big deal” to modify an engine to take a polyvee belt and drive a 175 or 240A alternator. And you are used to what you are used to, which is fine.

 

I liken it to the Morris Minor owner who quite likes their car, provided they don’t go over 50mph and have strong arms to operate the non-power steering, the non-servo brakes and the lack of synchro on first and reverse, dim headlights, no aircon etc etc etc.

 

But for me with my Skoda Superb 280 with 280bhp, power everything, DSG gearbox, adaptive cruise control, lane holding, automatic parking, voice control etc it would be utterly horrendous to contemplate going back to a morris minor.

 

So my point is that if you are happy with your present system and it meets your needs and expectations, that is absolutely fine by me. What wouldn’t be fine is if you were to “dis” people with greater expectations who had large alternators and electrical systems with matching demands, for having pointless kit. Not that I’m suggesting you are doing that.

[TheBiscuits]

26 minutes ago, Theo said:

I have quoted the bit from nicknorman's post that I can't get me head around.

 

In fairness it startled Nick when he was developing the alternator controller - simply because it goes against the received wisdom of decades.

 

I believe him though.  Without faffing with all the canbus and lithium stuff there's probably a market for a remote switchable high charge / low charge alternator regulator.

[Theo]

I suppose that makes a happy conclusion to the didscussion.  I have, I hope, a non-slipping alternator belt, a bit more knowledge about the way that alternators work and the continued knowledge that there is seemingly endless help to be got from CWF.

 

Thanks for all the contributions.

 

Nick

Edited October 18, 2021 by Theo
more mistakes!

[cuthound]

13 hours ago, Theo said:

"It’s to do with the regulation curve of an alternator’s rather basic regulator. The current supplied by an alternator is related (inversely) to the terminal voltage. So if we presume for example that the regulated voltage is 14.4v, at 14.4v it is producing no current. At 14.39v it is producing  maybe 1% of its output. At 14.3 maybe 10%. At 14.2v maybe 25% You have to get right down to perhaps 13.7v before it is producing 100% of its output. (Figures made up, but the principle is right)."

 

I have quoted the bit from nicknorman's post that I can't get me head around.

 

Lets forget that we are using an alternator for a moment.  If we were to use a true constant voltage source where the voltage is entirely independent of the current drawn, then the current delivered at, say 14.4V, would be entirely dependent upon what the battery bank would accept.

 

Now take the case of nicknorman's alternator.  The battery bank is at 14.4V so the current delivered is zero as controlled by the alternator electronics.  Now let's say that some charge is drawn from the bank so that its voltage drops to 14.39.  In the case stated by nn the alternator immediately delivers its 1% which, with a 70A alternator is 0.7A or a 140A alternator is 1.4A.  If we take the load drawn out of the equation by assuming that it is switched off the moment that the voltage drops to 14.39V then the alternator will continue to charge the battery until the voltage reaches 14.40V and then stops.  Ah! It is becoming clear what nn is saying even as I am typing the reply.  What he means (and says clearly) is that, assuming the same alternator controller characteristics, a 140A alternator will charge the battery more quickly even at the low tail currents.

 

My old alternator is a Bosch to which I fitted an adjustable controller.  I originally found that it would charge reasonably rapidly at the beginning of the day's cruising but the current would drop off far to early.  I got around this with an Adverc which made a huge difference...

 

Thanks, nicknorman.  I believe that I now understand but will not be fitting a bigger alternator because of the issues of fitting new pulleys etc.  I will live with what I have.  (And keep the belt tensioned properly.)

 

 

 

In the early stages of charge the alternator is current limited, that it it cannot produce more than its rates current without the voltage dipping.

 

As the battery charges the alternator voltage rises because the alternator is no longer working flat out and the current drops. Eventually the voltage rises to the regulators set voltage and current virtually ceases.

[Tony Brooks]

I have been pondering what Nick says because given the ability to supply the current at any given voltage it is the battery "resistance" (I know that s not the absolute truth but will do) that determines the current flow. Alternators do not have that ability so we have a charging period where the high current flow causes the alternator output voltage to drop. Once that phase is over it would appear at first site to be a simple Ohms law (I know it is not true resistance) calculation to determine the current flow into a given battery. That would seem to suggest that Nick is not correct and knowing Nick's tendency to be a bit pedantic about electrical things that is very unlikely, so more thought is required.

 

It seem to me that if, as is true, a high output alternator will push more current into a given battery than  a lower output one during the bulk phase then the effect of current reducing the output voltage must be less on a high current alternator than  a lower output one so at any current the voltage delivered by a high output one would be higher until the voltage regulator actually clamped the charging voltage. To me that explains what Nick was saying is correct.

 

However a higher charging current must charge the batteries faster so you get to the fully regulated voltage sooner than on a low output alternator when it is just the batteries controlling the current flow so the question must be how much shorter will this time turn out to be. There also seems to be a question about the effectiveness of charging at higher currents but I suspect the long low current charging period negates any loss resulting from the high current flow.

[nicknorman]

8 minutes ago, cuthound said:

 

In the early stages of charge the alternator is current limited, that it it cannot produce more than its rates current without the voltage dipping.

 

As the battery charges the alternator voltage rises because the alternator is no longer working flat out and the current drops. Eventually the voltage rises to the regulators set voltage and current virtually ceases.

With a large alternator with conventional regulator (and LA batteries), your first para (typically called the bulk phase) only lasts a few seconds, less than a minute anyway. The phase when the voltage is fixed and the current decreases (normally called the absorption phase) also only last a very short time. But yes in between we have a lengthy crossover period of many hours when the voltage is rising and the current is decreasing, which I think is what you’re saying. IMO this notional splitting of alternator charging into the binary phases of bulk and absorption is factually incorrect and confusing.

[Tony Brooks]

 

Which is basically what I said, a large alternator will always provide more current at a given voltage than  a lower output one until it's voltage is clamped at maximum.

[nicknorman]

11 minutes ago, Tony Brooks said:

However a higher charging current must charge the batteries faster so you get to the fully regulated voltage sooner than on a low output alternator when it is just the batteries controlling the current flow so the question must be how much shorter will this time turn out to be. There also seems to be a question about the effectiveness of charging at higher currents but I suspect the long low current charging period negates any loss resulting from the high current flow.

A conventional alternator regulator works on error feedback. In other words, if there is a difference between actual voltage and nominal regulated voltage, current is supplied in increasing amounts in rough proportion to the error. Same concept as a Diesel engine governor. Put it another way, there MUST be a difference between actual and regulated voltage in order for any current to be supplied.

 

So if you were to plot a graph of alternator voltage against current as full charge is approached, it would be a roughly asymptotic reduction to zero in current and a roughly asymptotic approach to the regulated voltage.

 

The difference with a larger alternator is the steepness of the curves, not their general shape.

 

Of course if you use a digital regulator, you can have PID (Proportional, Integral & Differential) regulation. The “Integral” bit means that you no longer need any error between actual and nominal voltage, to get current. So a decent after market regulator (or one controlled by a car’s ECU) can produce full output within a few tens of millivolts from the regulated voltage. Forum wisdom was that this doesn’t make much difference “because the battery controls the current” but now I have actually tried it, I see that this isn’t true - big time!

4 minutes ago, Tony Brooks said:

 

Which is basically what I said, a large alternator will always provide more current at a given voltage than  a lower output one until it's voltage is clamped at maximum.

Yes. I would just caution use of “clamped at maximum” because that implies that maximum voltage is reached when there is still a lot of current flowing. Which isn’t the case. With a conventional regulator, maximum voltage is only reached as the current falls to zero.

[cuthound]

39 minutes ago, nicknorman said:

With a large alternator with conventional regulator (and LA batteries), your first para (typically called the bulk phase) only lasts a few seconds, less than a minute anyway. The phase when the voltage is fixed and the current decreases (normally called the absorption phase) also only last a very short time. But yes in between we have a lengthy crossover period of many hours when the voltage is rising and the current is decreasing, which I think is what you’re saying. IMO this notional splitting of alternator charging into the binary phases of bulk and absorption is factually incorrect and confusing.

 

Indeed, the point I was trying to make is that the alternator is either in current limitation or voltage regulation.

[Theo]

On 18/10/2021 at 18:25, nicknorman said:

Well something is wrong there, maybe the batteries are knackered or your estimation of SoC is incorrect. 2% of 810Ah is 16.2A which many people consider to be 100% SoC.

 

But other factors such as thin alternator and battery interconnect wiring designed for a 50A alternator, voltage lost in battery isolators etc may be at play. Is the 14.4v actually at the battery terminals, or somewhere else along the way?

Just rereading the thread, I noticed that I had not replied to this post from nicknorman.

 

The 14.4V is read off the SmartGuage which is connected directly to the battery terminals.  I believe the batteries to be pretty well knackered.  I have had them living aboard for 3 years  and 4 years not living aboard being looked after by the solar panels but for a period they were abused at the boatyard by being left without the solar panels connected.  So they don't owe me much and I should really be thinking of replacing them.