Engine / alternator speed to charge batteries

[Peregrine]

 

What sort of batts, sealed AGMs, sealed for life 'wet' leisures?

 

See my opening post for an outline of the system. They're sealed wet Numax.

[Peregrine]

 

We recently covered this in a similar thread.

 

To the OP: there is a pinned piece about this at the start of one of the sub forums.

 

I read through the two pinned threads on Power Generation and Alternator Paralleling before making my original post. Always learning!

 

The clamp type ammeters all work by measuring the magnetic field around the cable so if another cable or more likely that dirty great electromagnet called an alternator is close by the reading is likely to be highly inaccurate. If you can move well away from the alternator & starter, pull the cables apart as far as possible and then measure the current flowing.

 

I recognise the need to reduce magnetic interference. The cables are hefty, of course, and restrained because you don't want loose cables around an engine! I'll need to go back in the daylight and see whether I can find a spot well away from the alternator, where I'm not also battling other cables.

[Sir Nibble]

 

This is correct. But it doesn't seem to me to explain how the "domestic" alternator could have 7 amps in its +ve cable, but 26 amps in its -ve earth cable!

Domestic 7A, Engine 19A, common return 26A. Perfectly logical.

[Tony Brooks]

I know its true because it happens on my setup even to the point of the free-wheeling alternator's warning light coming on - it completely shuts down. Now I don't have an A to B but do have DAR's on each of the alternators. Gibbo explained this situation to me many years ago.

 

The fact that an A to B is used with paralleled alternators is not directly relevant to this issue. At some point towards the end of the charge cycle the alternators own regulators will come into play. One or other will attempt to limit charge voltage first due to tiny discrepancies in the actual regulated voltage. If it can't then field current will be reduced to minimum. Depending on design it may shut down altogether as with mine. Note that as soon as battery line volts drop slightly it chimes in again though.

 

Please do not extrapolate from the DAR operation. The DAR is fitted in parallel with the alternator's regulator while the A to B is fitted in the main charging leads. This means that when a DAR shuts down the alternator's own regulator takes over. If a DAR goes wrong it is either likely to cause uncontrolled output or revert to the inbuilt regulator. Your assertions about the DAR are absolutely correct but can not be applied to the A to B.

 

The A to B is far more complex and as it sits in the alternator's main charging leads if it goes wrong all sorts of odd things can happen.

 

Now Charles Sterling seems very coy about how the thing works but they have said that it keeps the alternator running at maximum output. Now at this point what you believe depends upon your detailed understanding of the workings of alternators and some on here will not be able to understand because they do not accept the conventional description of what is going on in an alternator running at and close to maximum load.

 

The only way you can keep an alternator running at maximum output is to present a load of a low enough resistance so it appears to be a well discharged battery. If you do this you can connect two alternators in parallel and as both will be producing their maximum output and thus a VOLTAGE WELL BELOW THE REGULATED VOLTAGE neither will shut down.

 

Exactly what is going on inside the A to B is not known but I suspect the alternator output is converted to AC in a low resistance/inductance load and then switched mode techniques produce the charging current at an appropriate but varying over time voltage in much the same way a mains battery charger does it.

 

 

It may be that eventually the input load is reduced so the voltage can rise and if so at that point the alternator's own regulator will take over and then things will act as you suggest UNLESS the A to B has two inputs. However I have found nothing to suggest that the A to B does reduce the input load so until someone can come up with a definitive description of how it all works we can not go extrapolation from one product to another.

 

We also must be aware that a faulty A to B is far more likely to lead to undercharged batteries than a faulty DAR/Adverc & Co.

[nicknorman]

Please do not extrapolate from the DAR operation. The DAR is fitted in parallel with the alternator's regulator while the A to B is fitted in the main charging leads. This means that when a DAR shuts down the alternator's own regulator takes over. If a DAR goes wrong it is either likely to cause uncontrolled output or revert to the inbuilt regulator. Your assertions about the DAR are absolutely correct but can not be applied to the A to B.

 

The A to B is far more complex and as it sits in the alternator's main charging leads if it goes wrong all sorts of odd things can happen.

 

Now Charles Sterling seems very coy about how the thing works but they have said that it keeps the alternator running at maximum output. Now at this point what you believe depends upon your detailed understanding of the workings of alternators and some on here will not be able to understand because they do not accept the conventional description of what is going on in an alternator running at and close to maximum load.

 

The only way you can keep an alternator running at maximum output is to present a load of a low enough resistance so it appears to be a well discharged battery. If you do this you can connect two alternators in parallel and as both will be producing their maximum output and thus a VOLTAGE WELL BELOW THE REGULATED VOLTAGE neither will shut down.

 

Exactly what is going on inside the A to B is not known but I suspect the alternator output is converted to AC in a low resistance/inductance load and then switched mode techniques produce the charging current at an appropriate but varying over time voltage in much the same way a mains battery charger does it.

 

 

It may be that eventually the input load is reduced so the voltage can rise and if so at that point the alternator's own regulator will take over and then things will act as you suggest UNLESS the A to B has two inputs. However I have found nothing to suggest that the A to B does reduce the input load so until someone can come up with a definitive description of how it all works we can not go extrapolation from one product to another.

 

We also must be aware that a faulty A to B is far more likely to lead to undercharged batteries than a faulty DAR/Adverc & Co.

Surely the A2B is primarily a boost switch mode power supply? The only slightly "clever" bit will be to ensure that amount of current "sucked" out of the alternator is such as to achieve max power output from the alternator (ie alternator operating at its max power output voltage). I would liken it to an MPPT solar controller except that the latter is a buck switch mode power supply whereas the former is boost mode.

[by'eck]

Thanks for the lecture Tony but you dismiss many of the subtleties of the A to B.

 

Can I suggest you read the manual particularly noting in the example with graphs how the alternators own 13.9 volt regulator cuts in, every 15 minutes and constantly during float.

[nicknorman]

Thanks for the lecture Tony but you dismiss many of the subtleties of the A to B.

 

Can I suggest you read the manual particularly noting in the example with graphs how the alternators own 13.9 volt regulator cuts in, every 15 minutes and constantly during float.

Hmm, typical sterling manual! If the 13.9v alternator regulator is adjustable, why not adjust it up to 14.5 - 14.8? I get the feeling the "rest periods are just to allow the alternator voltage to rise enough to charge the starter battery, rather than for any benefit to the domestic batteries.

[Tony Brooks]

That manual indicates that it can not be relied upon by the statement "It is designed to pull this voltage down a little in order to enable the standard alternator regulator to produce its full current". I also note that the alternator chosen as an illustration has a very low regulated voltage when compared with most others today. This again brings the veracity of the document into question. How would it compare to one of the 14.7/14.8 regulator alternators Beta have or still do fit.

 

The regulator has nothing to do with producing full current. When the alternator is doing that the voltage is depressed and the regulator is doing nothing.

 

Read what Nicknorman says about how it works, he and I are not far apart. If the device is in effect shorting itself out when those falls in output current take place then for the period of low charging current I agree that the possibility of one alternator shutting down needs consideration and care in when any reading are taken. However one of boat's the warning lamps should then flash on and off in time with the pulses - that is unless the builder/mariniser is using one warning lamp for both alternators.

 

If the device is not shorting itself out then that low resistance/inductance load must still be in place and the rise in voltage is done by the A to B, not the alternator regulator. The manual seems silent on exactly what is going on.

 

 

What I dismiss are claims for products that are made in a way that are not transparent to both people who have knowledge of the subject and the general public at large. I also tend to dismiss claims when the conditions under which "test" are carried out are either very favourable to the product or are not substantiated by independent testing or considerable field experience across a wide range of users. Hence my attitude to Axioms.

 

Will this product do any better than an Adverc "wound up" to around 14.7 volts? I rather doubt it. Its advantage in our bit of the marine field seems to be no need to mess with the alternator regulator. Of course if you believe that pulsing the charge reduces sulphation then that may be a further advantage but I have not seen any evidence that 20 minute frequencies have this effect and the although the graphs do show a higher frequency pulse I rather suspect its is caused by the electronics switching to regulate the voltage.

Edited October 29, 2014 by Tony Brooks

[dmr]

I believe that the Sterling A to B thingy was designed as a brute force method of providing the functionality of an external alternators for applications where it was not possible or desirable to make the small alternator modification that is required by Adverc and the other Sterling controllers. In now appears to have become the first choice method of raising alternator voltages in many cases, though it does have the advantage of combining the two alternators, but if you read all the documentation I am not 100% sure that it actually does this.

 

.............Dave

[Peregrine]

Domestic 7A, Engine 19A, common return 26A. Perfectly logical.

 

Yes, this was my first thought. But when I traced the earth cable from the domestic alternator, it went straight to the engine lug. As far as I can tell, another similar cable goes from the same lug to the engine alternator (though I have to check its run again). So it could only be a common earth if the lug is in fact not an earthing point.

[Sir Nibble]

perhaps it isn't. It's not uncommon for a negative bus bar to be isolated.

[by'eck]

Hmm, typical sterling manual! If the 13.9v alternator regulator is adjustable, why not adjust it up to 14.5 - 14.8? I get the feeling the "rest periods are just to allow the alternator voltage to rise enough to charge the starter battery, rather than for any benefit to the domestic batteries.

Well yes I admit to smiling when I saw the alternator chosen for the test although in fairness wouldn't any manufacturer want to highlight the performance of their product. I also agree that there seems to be a degree of killing two birds with one stone in the explanation for the rest periods especially as a diode splitter is used with attendant voltage drop. My comments still remain though.

 

Regarding the warning light issue from a free-wheeling alternator. Although it does come on with my setup its surely not a prerequisite of an alternator operating with minimum field current, but dependant on regulator design and function.