Alternator - questions

[Gibbo]

It doesn't matter how many alternators Nick Billingham has repaired, serviced, or otherwise fiddled with, it has nothing at all to do with whether he is right or wrong.

 

You're right. It doesn't. But he is still wrong.

 

Gibbo

 

A few other points......

 

Sterling's alternator to battery charger was designed to get 3 stage, higher voltage, charging on an installation where it is not possible to fit a normal external alternator controller. This usually means a clever engine management system that throws up an error if one is fitted. This is getting more and more common on vehicles. In fact probably 75% of modern vehicles will complain if a controller is fitted.

 

It makes absolutely ZERO sense to fit one to an alternator that CAN have an external controller fitted. The alternator to battery charger will do a worse job, less efficienctly, and waste a fair amount of power.

 

The idea of "a charger should be X% of the battery capacity" is hogwash..........

 

http://smartgauge.co.uk/chargesize.html

 

Gibbo

 

I wouldn't trust the technical expertise of anyone who thinks it reasonable to charge batteries at 15.5V!

 

Me and lucas charge them at 16 volts. If you know what to look out for it's fine. But a charger just doing it without supervision is asking for trouble.

 

But what interests me is How does the controller know what current is flowing? There is I presume a shunt?

 

You can actrually get a very good idea of the maximum possible charge current from the PWM mark/space ratio. As you well know an alternator is a current amplifier. A 70 amp alternator with 50/50 mark/space on the rotor is not going to deliver more than baout 35 amps (ish).

 

Gibbo

[MoominPapa]

You can actrually get a very good idea of the maximum possible charge current from the PWM mark/space ratio.

Oh, I didn't know that alternator regulators are PWM. Makes sense, I suppose, to reduce power dissipation in the regulator. Do they have suitable circuit arrangements to allow the rotor inductance to smooth out the current waveform? If not I imagine the rotor will produce fairly high back-EMF as the current is chopped.

 

Is the whine you get from a heavily loaded alternator related to the regulator frequency? I had always assumed it was rotation speed x number of poles, but maybe not.......

 

MP.

[Sir Nibble]

Me and lucas charge them at 16 volts. If you know what to look out for it's fine. But a charger just doing it without supervision is asking for trouble.

So do I, but there is a world of difference between a bench charge supervised by a suitably qualified person and a regulator setting.

You can actually get a very good idea of the maximum possible charge current from the PWM mark/space ratio. As you well know an alternator is a current amplifier. A 70 amp alternator with 50/50 mark/space on the rotor is not going to deliver more than baout 35 amps (ish).

Now that intrigues me, the regulator would I presume have to compare the pwm wave with a measured voltage and stored performance perameters for that specific alternator. Hardly suitable for the after market I would have thought, and again, why?

Do they have suitable circuit arrangements to allow the rotor inductance to smooth out the current waveform? If not I imagine the rotor will produce fairly high back-EMF as the current is chopped.

There is a "field discharge diode" across the rotor.

Is the whine you get from a heavily loaded alternator related to the regulator frequency? I had always assumed it was rotation speed x number of poles, but maybe not.......

It's the output (stator) frequency.

[Gibbo]

Oh, I didn't know that alternator regulators are PWM. Makes sense, I suppose, to reduce power dissipation in the regulator.

 

Yes, they always have been. Linear regiulation would produce FAR too much waste heat. Even the internal ones (although they operate on a primitive "hysteretic" topology) are still switch mode. The field is either on or off. Never inbetween.

 

Do they have suitable circuit arrangements to allow the rotor inductance to smooth out the current waveform? If not I imagine the rotor will produce fairly high back-EMF as the current is chopped.

 

The field acts as the inductor to smooth out the current. Start from steady state off. The power switch (be it bipolar transistor, mosfet or whatever) switches on, the voltage across the field increases to maximum instantly, the current in the field (acting as an inductor) starts to rise, when the transistor switches off, the field tries to produce the back emf by normal inductor action (which is actually an attempt by the inductor to keep the current flowing). This back emf is clamped by a diode in the regulator which allows the current to keep flowing which then naturally ramps down. The voltage across the field is a squarewave, the current through it is a relatively smooth sawtooth waveform.

 

Is the whine you get from a heavily loaded alternator related to the regulator frequency? I had always assumed it was rotation speed x number of poles, but maybe not.......

 

Yes it's the PWM. On a normal alternator it changes in frequency and the pulse width remains fairly constant because that's how they operate. On an external regulator it is fixed frequency with variable on time.

 

Gibbo

 

It's the output (stator) frequency.

 

You're obviosly listening to a different sound. You can still hear it with the alternator not spinning but the reg switched on.

 

Now that intrigues me, the regulator would I presume have to compare the pwm wave with a measured voltage and stored performance perameters for that specific alternator. Hardly suitable for the after market I would have thought, and again, why?

 

No if you think about it putting full voltage on the field (thereby resulting in maximum field current) will produce full current output at any particular RPM. The alternator acts as a current (not voltage) amplifier with the extra energy coming from the rotation. So if you halve the field current, you will halve the output current. If the unit is spinning at decent revs, you cay be quite confident that a 75/25 mark space ratio on the field will produce *about* 75% output current.

 

It's not bob on, but it's within about 15 to 20% or so which is close enough to be able to put some sort of current limit on it without actually measuring the output current.

 

Gibbo

[RobinJ]

Conventional wisdom seems to suggest 14.8V as typical for a wet lead/acid battery. Can you explain this a bit more?

I emphasise typical of wet lead acid. A mains charger (4-6A) will charge a battery to 100% at C/20 at about 14.2V, increasing the charge rate through C/15 (about 14.8V) to C/10 (about 15.5V) is important where larger banks are installed (lower current per battery, longer charge times), but leads to gassing especially when the temperature is high.

The Kestrel was desgned to work with standard non sealed non gel batteries to achieve full charge as quickly as possible and equalise large battery banks. Most of these batteries should be able to accept high charge rates (deep cycle, leisure or starter), but is a compromise between optimum performance, high maintenance and short life span. It was marketed before the improvements in alternator control design to introduce a 'bulk' stage to the charging cycle, once complete the internal controller finishes the absorbsion and float stages, so the high charge rate should not continue for long periods? Most of the faults found on these units are connected with alternator failure (chicken and egg situation), the real underlying cause being the batteries repeatedly too heavily discharged, I have not come across a premature battery failure, but it would not surprise me.

Batteries on boats are often kept at a lower temperature than vehicles (but not always), you should generally check the electrolyte level reasonably often, and if necessary you can adjust the (Kestrel) cut out voltage.

Technology has moved on (pulse chargers are more efficient), there are better products out there for use with high consumption multi charge systems and other battery types, if your consumption is too high, your battery bank too large, your battery type different - upgrade.

Edited April 17, 2008 by RobinJ

[PaulG]

if your consumption is too high, your battery bank too large, your battery type different - upgrade.

 

Thanks for the explanation Robin. Luckily, at the moment, my consumption is parsimonious, battery bank puny, and battery type ok, and I've turned down both the charge current and the charge voltage, so it can probably last a couple of months longer.

[MoominPapa]

Yes, they always have been. Linear regiulation would produce FAR too much waste heat. Even the internal ones (although they operate on a primitive "hysteretic" topology) are still switch mode. The field is either on or off. Never inbetween.

 

Thinking more, I should have known that it was possible. In the past I have owned several 70s era Fiats which had Magnetti Marelli alternators with external "vibrating contact" regulators. Electrical, rather than electronic, PWM!

 

MP.

[Sir Nibble]

You're obviosly listening to a different sound. You can still hear it with the alternator not spinning but the reg switched on.

 

 

 

 

Gibbo

Definately, the sound I am referring to rises in frequency with revs, and in amplitude with load. I suspect that is what Moomin is hearing too.

In fact probably 75% of modern vehicles will complain if a controller is fitted.

You can actrually get a very good idea of the maximum possible charge current from the PWM mark/space ratio. As you well know an alternator is a current amplifier. A 70 amp alternator with 50/50 mark/space on the rotor is not going to deliver more than baout 35 amps (ish).

Aha! Modern engine management systems do in fact monitor the regulator on/off ratio, and in later systems can intervene to modify the alternator output, makes perfect sense.

Thanks Gibbo, you have a knack of explaining things clearly and concisely.

Bit of a laugh really, we seem to spend endless pages dealing with "How can I get national grid type outputs from boat alternators" so discussing how to chop back the output is a bit of a novelty. Still, I don't care, I have to try and keep up to date with new developments and having prof Gibbo do it for me and then present it with ladybird book clarity is most useful!

[PaulG]

You're right. It doesn't. But he is still wrong.

 

Well I disagree.

 

And, while I'm at it, I'd like to add some general comments.

 

I've been jumped on for saying "Alternators are usually derated because they are badly cooled" and I accept that I did not word that statement very clearly.

However, I did go on to explain what I meant:

 

"Most alternators would get a bit toasty if run at much more than 70% of their rated output for any length of time. This is a generalisation, but it is sensible to de-rate them" I stand by that statement. They will run hot. Will they overheat? Possibly. In a closed engine bay, or having picked up dust and general crud over a few years of use.

 

I also said that "If you've got one of the modern, high output alternators, then it may well be cooled sufficiently to run at it's rated output for long periods."

 

I've tried to explain what I meant, and the reasons for it, so if you are going to disagree with me, then please do me the courtesy of explaining yourself properly as well.

 

I have to say that the arrogant attitude of some of the contributors to this thread is a shame. Especially when some of the self-proclaimed experts seem have actually learned something from others.

 

Finally, I should point out that I am a notoriously obstinate old bastard and I refuse to be browbeaten or otherwise bullied, so don't even bother trying!

Edited April 17, 2008 by PaulG

[Sir Nibble]

No browbeating Paul, there are few things more irritating than trying to dispute with someone who simply states "I'm right" and assumes that trumps any amount of reasoned debate. But look at it this way. Gibbo is known as one of the countries foremost authorities in the field of battery charging, he disagrees; I'm just a 'umble technician riding through life on my mere city and guilds and 30 years of being up to my elbows in vehicle and marine electrical systems, and I disagree.. How do you think we feel when someone tells us we are wrong? OK, so you've read a book, how can we argue with that? I shall just have to respond in the same way as I do to every customer with a copy of "practical boat owner" under his arm. "Whatever you say sir" and go back to fitting the correct parts specified by the manufacturer to each unit, the same parts specified for the alternator's vehicle based brother, 'cos there is NO DIFFERENCE except a coat of paint.

 

Edited to say:

Oh, and I am not a "self proclaimed expert" I am a qualified and experience technician in this particular field.

Two aeroplane engines, one being worked on by a bloke with 30 years of experience behind him, the other by a bloke with a haynes manual in front of him. Which one would you prefer to fly with?

Edited April 17, 2008 by snibble

[RobinJ]

Thanks for the explanation Robin ... I've turned down both the charge current and the charge voltage, so it can probably last a couple of months longer.

With your present 40A alternator you can probably safely go to a maximum current of about 25A which will work well with banks upto about 300Ah. The voltage will need to be set above 14.4V (otherwise it snot doing anything), but there is no real reason to drop it below 14.8V

If you fitted a new 70A alternator, chances are it may include a newer controller which has a bulk phase, so your Kestrel could be removed, if not you could wind it up to as much as 45A which would handle up to about 500Ah

[Timleech]

Thinking more, I should have known that it was possible. In the past I have owned several 70s era Fiats which had Magnetti Marelli alternators with external "vibrating contact" regulators. Electrical, rather than electronic, PWM!

 

MP.

 

 

ISTR that some of the older Bosch regulators were electromechanical, not unlike dynamo regs.

 

Tim

[Sir Nibble]

some of the self-proclaimed experts seem have actually learned something from others.

Gonna do it again now!

If you fitted a new 70A alternator, chances are it may include a newer controller which has a bulk phase

Robin, my understanding of these terms....

 

Bulk, The charge delivered when the source is flat out in a constant current charge en route to it's regulated voltage.

 

Absorbtion, The charge delivered when the source has reached it's regulated voltage and delivers a constant voltage charge with declining current.

 

Float, The rare luxury of deliberately lowering the voltage applied to a fully charged battery in order to prevent overcharge.

 

If I am correct (and I believe I am, but feel free to correct me) How is it possible to have a charge without a bulk phase?

[Keeping Up]

... increasing the charge rate through C/15 (about 14.8V) to C/10 (about 15.5V) is important where larger banks are installed (lower current per battery, longer charge times), but leads to gassing especially when the temperature is high.

And can also lead to the premature (and sometimes instantaneous) death of much of the 12v equipment inside the boat

[Sir Nibble]

And can also lead to the premature (and sometimes instantaneous) death of much of the 12v equipment inside the boat

And at first sight, where raising the voltage for a lower current per battery, it migh offend Mr Ohm as well.

[Keeping Up]

And at first sight, where raising the voltage for a lower current per battery, it migh offend Mr Ohm as well.

Ah yes, there's no place like Ohm

[Sir Nibble]

Ah yes, there's no place like Ohm

HELP! POLICE!

[Bullfrog]

HELP! POLICE!

 

Which service do you require, Police, Ambulance, Fire Brigade, Coastguard - or is it the Ohm Service?

 

Edited to say - or possibly the Ohm Guard

Edited April 17, 2008 by Bullfrog

[RLWP]

Which service do you require, Police, Ambulance, Fire Brigade, Coastguard - or is the Ohm Service?

 

Edited to say - or possibly the Ohm Guard

 

 

Watts goin' on 'ere then?

 

Edited to say - Sorry, I couldn't think of any good Wheatstone or Kirchoff jokes

 

 

Richard

Edited April 17, 2008 by RLWP

[alan_fincher]

HELP! POLICE!

What do you want him charged with, then ?

 

Assault on battery ?

 

I've already got my coat

[Keeping Up]

Watts goin' on 'ere then?

 

Edited to say - Sorry, I couldn't think of any good Wheatstone or Kirchoff jokes

You'll just have to cross that bridge when you come to it.

 

(Sorry, it's not my volt)

[PaulG]

No browbeating Paul, there are few things more irritating than trying to dispute with someone who simply states "I'm right" and assumes that trumps any amount of reasoned debate.

 

Can't argue with that!

 

But look at it this way. Gibbo is known as one of the countries foremost authorities in the field of battery charging,

 

I know, and so I respect his opinion. But see above.

 

I'm just a 'umble technician riding through life on my mere city and guilds and 30 years of being up to my elbows in vehicle and marine electrical systems, and I disagree.. How do you think we feel when someone tells us we are wrong? OK, so you've read a book, how can we argue with that? I shall just have to respond in the same way as I do to every customer with a copy of "practical boat owner" under his arm. "Whatever you say sir" and go back to fitting the correct parts specified by the manufacturer to each unit, the same parts specified for the alternator's vehicle based brother, 'cos there is NO DIFFERENCE except a coat of paint.

As I said before, I am sure that you are extremely knowledgeable. I wasn't taking the p*ss, I meant it. But, as you amply demonstrated, you can still be wrong!

 

Edited to say:

Oh, and I am not a "self proclaimed expert"....

I didn't say you were. But if the cap.... Sorry. That was out of order. Puerile remark withdrawn unreservedly.

 

Anyway, thanks for responding.

 

Now, can you give me some advice on where I should mount my galvanic isolator?

 

I'll get me coat..

[Sir Nibble]

But, as you amply demonstrated, you can still be wrong!

Of course I can be wrong! Who do you think I am? Tony Blair? But I don't think I have amply demonstrated it (at least not in this thread) I have stated an opinion that I would not trust anyone to set a regulator who thinks it's ok to set it to 15V, that is a matter of fact, I wouldn't, I have driven batteries to over 17V for short bursts 'cos I think it suits my purposes and is ok if closely supervised. That's a matter of opinion. But as an alternator setting? Nah.

I have with one or two things, like current sensing enquired how, and been answered, that don't prove me wrong, but rather ignorant.

 

One interesting thing that has occurred to me tho', Chris W has twin 80A A127 alternators fitted on his boat, they aren't the same as their vehicle brethren 'cos they don't make A127s with a higher output than 72A for vehicles. Derated?

[Gibbo]

I've been jumped on for saying "Alternators are usually derated because they are badly cooled" and I accept that I did not word that statement very clearly.

However, I did go on to explain what I meant:

 

"Most alternators would get a bit toasty if run at much more than 70% of their rated output for any length of time. This is a generalisation, but it is sensible to de-rate them" I stand by that statement. They will run hot. Will they overheat? Possibly. In a closed engine bay, or having picked up dust and general crud over a few years of use.

 

Ok I took your statement as meaning something other than what you now seem to mean.

 

Internally regulated alternators have temperature sensing which backs off the output current if they get too hot.

 

This is something that chris w seems to think is a bad thing as he says the output voltage drops when they get hot. This is to stop them blowing up! It's a protection mechanism. So he recommends adding an external controller so this doesn't happen. But then recommends one with alternator temperature sensing so it ends up back as it was to start with. So what's the point? Why not just leave the internal reg alone? (assuming the voltage is high enough).

 

External alternator controllers CAN overheat alternators and they can get seriously damaged as a result. However, in all fairness, it is not a common ocurrence. I think I know of 2 instances out of probably in excess of 5000 installations with which I am familiar.

 

As for deratring them, I assumed you meant only fit a (say) 70 amp alternator in an installation that will only ever use (say) 45 amps maximum as running it at full power will ruin it. This is what I understood the author of the book to mean.

 

I repeat.....

 

He is wrong.

 

Gibbo

Edited April 17, 2008 by Gibbo

[PaulG]

Of course I can be wrong! Who do you think I am? Tony Blair?

 

Heavens above no! I'd never even think of using such a terrible insult in a public forum!

 

But I don't think I have amply demonstrated it (at least not in this thread) I have stated an opinion that I would not trust anyone to set a regulator who thinks it's ok to set it to 15V, that is a matter of fact, I wouldn't, I have driven batteries to over 17V for short bursts 'cos I think it suits my purposes and is ok if closely supervised. That's a matter of opinion. But as an alternator setting? Nah.

I have with one or two things, like current sensing enquired how, and been answered, that don't prove me wrong, but rather ignorant.

 

OK. Point taken. I hereby withdraw the use of the word "amply".

 

One interesting thing that has occurred to me tho', Chris W has twin 80A A127 alternators fitted on his boat, they aren't the same as their vehicle brethren 'cos they don't make A127s with a higher output than 72A for vehicles. Derated?

 

Now you're just teasing me, aren't you?

 

Well stop being so naughty.