Alternator - questions

[RobinJ]

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?

Ok pedantic mode !!!

Right BULK, my interpetation is a controller that is specifically designed to deliver a constant charge current. Older regulators may have charged at constant current (by default) because they were working to their maximum capacity, but I class these as constant voltage regulators because that is what they are designed to do!

ABSORBSION was supposed to be where at constant voltage a battery was allowed to absorb whatever current it wanted?

FLOAT was supposed to be to maintain a battery at full charge by compensating for its natural discharging characteristic (usually a fixed current at constant voltage).

Are we happy now?

[Gibbo]

Ok pedantic mode !!!

Right BULK, my interpetation is a controller that is specifically designed to deliver a constant charge current. Older regulators may have charged at constant current (by default) because they were working to their maximum capacity, but I class these as constant voltage regulators because that is what they are designed to do!

ABSORBSION was supposed to be where at constant voltage a battery was allowed to absorb whatever current it wanted?

FLOAT was supposed to be to maintain a battery at full charge by compensating for its natural discharging characteristic (usually a fixed current at constant voltage).

Are we happy now?

 

Even more pedantic....

 

It's close. Bulk applies whether or not it is because the charger is clever, or whether it simply limits the charge current or whether it is because the charger has run out of steam.

 

True constant voltage has (to a first approximation) unlimited available current in relation to the battery bank size so that no matter what condition the battery is in, when the charger is connected, the voltage rises instantly to the regulation voltage. If it doesn't do this then it is a bulk stage and the charger becomes a 2 stage charger.

 

That's the actual technical definition difference between constant voltage charging (ie no current limit) and two stage charging (ie an initial current limited stage - bulk).

 

You can clearly see that a constant voltage charger will become a 2 stage charger if the size of the battery bank is increased (and vice versa) so the term relates not just to the charger but also to the installation.

 

Gibbo

[Sir Nibble]

Ok pedantic mode !!!

Right BULK, my interpetation is a controller that is specifically designed to deliver a constant charge current. Older regulators may have charged at constant current (by default) because they were working to their maximum capacity, but I class these as constant voltage regulators because that is what they are designed to do!

ABSORBSION was supposed to be where at constant voltage a battery was allowed to absorb whatever current it wanted?

FLOAT was supposed to be to maintain a battery at full charge by compensating for its natural discharging characteristic (usually a fixed current at constant voltage).

Are we happy now?

Sorry! It might be best if we all mean the same thing when using the same words, thassall. Just when you sain "bulk charge" I assumed you meant the same thing as when anyone else says "bulk charge". Any chance of a glossary?

[PaulG]

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

 

Thanks for that Gibbo. Yes, that's pretty much what I meant by derating. But I did qualify that by saying 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." So wasn't really talking about specifying new installations, more about what it was reasonable to expect in performance from an existing unit, which may not be in its first flush of youth.

 

From what you have said above, if you drive an alternator too hard for the cooling arrangement, either the output current falls as the temperature rises, which effectively "derates" it anyway, or, if there's no temperature sensing (was this feature always incorporated into older units? I don't know), it blows up. Either way, allowing a bit of "headroom" on the alternator seems to make perfect sense to me.

[Gibbo]

Thanks for that Gibbo. Yes, that's pretty much what I meant by derating. But I did qualify that by saying 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." So wasn't really talking about specifying new installations, more about what it was reasonable to expect in performance from an existing unit, which may not be in its first flush of youth.

 

From what you have said above, if you drive an alternator too hard for the cooling arrangement, either the output current falls as the temperature rises, which effectively "derates" it anyway, or, if there's no temperature sensing (was this feature always incorporated into older units? I don't know), it blows up. Either way, allowing a bit of "headroom" on the alternator seems to make perfect sense to me.

 

Yes this feature has been there from day one of internally, electronically, regulated alternators. The patent goes back to the 60s.

 

Year before last I got called out to a boat with charging problems. Lucas A127, running reasonably warm, very unknowledgable (in electrical terms) boat owner, he could run his engine all day, yet at the end of it his batteries were flatter than when he started. He was getting by with a mains charger and small genny.

 

He'd previously had a cowboy round to "sort his charging out" and had left it worse than when he started.

 

The output of the alternator was connected directly to the engine casing. Effectively the alternator was running into a short circuit. It had been doing this for several hours a day for a few months. Rewiring it correctly got it all up and running again.

 

Alternaotrs are inherently self current limiting. They are TOUGH.

 

Gibbo

[PaulG]

Yes this feature has been there from day one of internally, electronically, regulated alternators. The patent goes back to the 60s.

 

Year before last I got called out to a boat with charging problems. Lucas A127, running reasonably warm, very unknowledgable (in electrical terms) boat owner, he could run his engine all day, yet at the end of it his batteries were flatter than when he started. He was getting by with a mains charger and small genny.

 

He'd previously had a cowboy round to "sort his charging out" and had left it worse than when he started.

 

The output of the alternator was connected directly to the engine casing. Effectively the alternator was running into a short circuit. It had been doing this for several hours a day for a few months. Rewiring it correctly got it all up and running again.

 

Alternaotrs are inherently self current limiting. They are TOUGH.

 

Gibbo

 

I bet his engine warmed up quickly!

[Sir Nibble]

Alternaotrs are inherently self current limiting. They are TOUGH.

 

Gibbo

I entirely agree with that, except the spelling.

Different makes of alternator fail for different reasons. For instance paris rhone alternators have brushes made deliberately so hard that they go into the slip ring like lathe tools and limit the replacement life of the unit. diode failures are Very rare. Hitachi's have everlasting brushes and blow diodes. Nippon densos wear out their brushes. A127s are reliant on a good flow of cool air over the diodes which are THEIR partucular weak point. Bosch are built like stukas!

[Keeping Up]

Either way, allowing a bit of "headroom" on the alternator seems to make perfect sense to me.

I'm still puzzling over how to allow such headroom.

 

As I posted above, I have a 70 Amp alternator. When the batteries are low it delivers 55 amps on its own, or 60 amps courtesy of the Adverc controller.

 

The alternator is deciding its own headroom.

 

Incidentally Snibble, what is the most common cause of failure on Motorola units (not counting the "dog-hairs blocking all the air-flow" failure that I had 2 years ago)

[Sir Nibble]

I thought.... Oh never mind.

[RobinJ]

Sorry! It might be best if we all mean the same thing when using the same words, thassall.

Any chance of a glossary?

Well things are often interpreted differently so it might be a good idea, (these are not my definitions and there does seem to be variation in voltages)! Figures in brackets refer to 24V systems. Any more required?

 

BULK: Constant current charge until the voltage has risen to 14.4V (28.8V) at 20C.

ABSORPTION: Constant voltage charge at 14.4V (28.8V) until current falls to 17% of full charge current.

FLOAT: Constant voltage charge at 13.7V (27.4V) while the current remains below 17% of full charge current.

EQUALISATION: Constant voltage charge at 15.4V (30.8V) for a period of up to two hours to bring weaker cells up to full charge.

[Sir Nibble]

I thought.... Oh never mind.

Sorry, had a "senior moment", wrote out along reply and then posted it into oblivion.

There is motorola europe, and motorola usa. If your alternator is one of the european models then the weak link is a very cheap brushgear with small, short, hard brushes and sliprings pressed from sheet copper.

The American ones use the same O ring type setup to retain the slip ring end bearing as the old acr alternators, and just like the acr, sometimes it lets go and the bearing spins in its housing and eats the bracket. Rotor meets stator and goodnight Vienna.

 

Well things are often interpreted differently so it might be a good idea, (these are not my definitions and there does seem to be variation in voltages)! Figures in brackets refer to 24V systems. Any more required?

 

BULK: Constant current charge until the voltage has risen to 14.4V (28.8V) at 20C.

ABSORPTION: Constant voltage charge at 14.4V (28.8V) until current falls to 17% of full charge current.

FLOAT: Constant voltage charge at 13.7V (27.4V) while the current remains below 17% of full charge current.

EQUALISATION: Constant voltage charge at 15.4V (30.8V) for a period of up to two hours to bring weaker cells up to full charge.

Righto!

[Gibbo]

Well things are often interpreted differently so it might be a good idea, (these are not my definitions and there does seem to be variation in voltages)! Figures in brackets refer to 24V systems. Any more required?

 

BULK: Constant current charge until the voltage has risen to 14.4V (28.8V) at 20C.

ABSORPTION: Constant voltage charge at 14.4V (28.8V) until current falls to 17% of full charge current.

FLOAT: Constant voltage charge at 13.7V (27.4V) while the current remains below 17% of full charge current.

EQUALISATION: Constant voltage charge at 15.4V (30.8V) for a period of up to two hours to bring weaker cells up to full charge.

 

We'll get there eventually.........

 

1. "absorption" is also known as "acceptance".

2. The acceptance voltage varies depending upon the charger manufacturer's beliefs and the battery type.

3. The "drop down" (known under various other names) current varies enormously but 17% is WAY too high.

4. Float voltage varies drasitcally depending upon the manufacturer's beliefs and the battery type.

5. Equalisation voltage varies drastically depending upon the manufacturer's beliefs and the battery type.

6. A 2 hour equalisation charge is nowhere near long enough.

7. It is irrelvant what the float current is.

 

So it becomes...

 

BULK: Constant current charge until the voltage has risen to the acceptance voltage.

ABSORPTION/ACCEPTANCE: Constant voltage charge between 14.0 and 15.0V until current falls to some predefined level - typically 1% to 5% of the bulk current.

FLOAT: Constant voltage charge between 13.0 and 13.8V.

EQUALISATION: Constant voltage charge (but current limited for safety) between 15.0 and 16.5V for a period of up to 8 hours to bring weaker cells up to full charge, remove sulphation and stir the electrolyte up.

 

Gibbo

[Sir Nibble]

Yes this feature has been there from day one of internally, electronically, regulated alternators. The patent goes back to the 60s.

 

Year before last I got called out to a boat with charging problems. Lucas A127, running reasonably warm, very unknowledgable (in electrical terms) boat owner, he could run his engine all day, yet at the end of it his batteries were flatter than when he started. He was getting by with a mains charger and small genny.

 

He'd previously had a cowboy round to "sort his charging out" and had left it worse than when he started.

 

The output of the alternator was connected directly to the engine casing. Effectively the alternator was running into a short circuit. It had been doing this for several hours a day for a few months. Rewiring it correctly got it all up and running again.

 

Alternaotrs are inherently self current limiting. They are TOUGH.

 

Gibbo

Hang on! Thinking about it, since the +ve voltage would be clamped to the diode voltage, there will probably be no more excitation than provided through the warning lamp. Precious little more anyway, if any. That unit probably had a little holiday circulating a few amps!

[Gibbo]

Hang on! Thinking about it, since the +ve voltage would be clamped to the diode voltage, there will probably be no more excitation than provided through the warning lamp. Precious little more anyway, if any. That unit probably had a little holiday circulating a few amps!

 

Exactly, they are inherently self current limiting. This is just one of the many limiting systems.

 

You can of course go a good way to removing this particular limit by putting an external p type regulator on them!

 

Gibbo

[smileypete]

6. A 2 hour equalisation charge is nowhere near long enough.

Would a smallish constant current trickle charge equalise a battery? (...albeit eventually!)

 

cheers,

Pete.

Edited April 18, 2008 by smileypete

[RobinJ]

Would a smallish constant current trickle charge equalise a battery? (...albeit eventually!)

It must be voltage limited (depending on type), otherwise it can lead to overcharging and cell damage.

[Gibbo]

Would a smallish constant current trickle charge equalise a battery? (...albeit eventually!)

 

cheers,

Pete.

 

Yes that's how the Statpower Truecharge units do it. They just run a charge with a current limit at (IIRC) about 1/10th the charger capacity until the voltage reaches 16 volts. It basically does the same thing.

 

In fact the Heart Interface Freedoms, Trace Truck series and Mastervolt Dakars, although saying they use fixed voltage equalisation have such a small current limit on them that they amount to the same thing. The difference being that once the voltage is reached they carry on for hours at the same voltage until you reset them.

 

Gibbo

[smileypete]

Would a smallish constant current trickle charge equalise a battery? (...albeit eventually!)

Yes that's how the Statpower Truecharge units do it. They just run a charge with a current limit at (IIRC) about 1/10th the charger capacity until the voltage reaches 16 volts. It basically does the same thing.

 

In fact the Heart Interface Freedoms, Trace Truck series and Mastervolt Dakars, although saying they use fixed voltage equalisation have such a small current limit on them that they amount to the same thing. The difference being that once the voltage is reached they carry on for hours at the same voltage until you reset them.

Sounds like a job for a small solar panel (Solar panels rool! )

 

If you charge at a low rate of say C/400 would all the cells get equalised without reaching such a high voltage?

 

cheers,

Pete.

Edited April 18, 2008 by smileypete

[Gibbo]

Yes that's how the Statpower Truecharge units do it. They just run a charge with a current limit at (IIRC) about 1/10th the charger capacity until the voltage reaches 16 volts. It basically does the same thing.

 

In fact the Heart Interface Freedoms, Trace Truck series and Mastervolt Dakars, although saying they use fixed voltage equalisation have such a small current limit on them that they amount to the same thing. The difference being that once the voltage is reached they carry on for hours at the same voltage until you reset them.

 

Sounds like a job for a small solar panel (Solar panels rool! )

 

If you charge at a low rate of say C/400 would all the cells get equalised without reaching such a high voltage?

 

cheers,

Pete.

 

To a certain extent yes but (like most things) it's never that simple. The whole thing is a compromise.

 

Flatten a battery completely.....

 

11 volts will remove some sulphate.

12 volts will remove more.

13 volts will remove even more.

14 will remove yet more.

15 volts remove lots of it.

16 volts remove a whole load of it.

17 volts will remove even more.

18 volts will probably remove 99% of it.

19 will in all likelihood get rid of it all.

 

But against that you have to consider that....

 

11 volts will cause no other problems.

Neither will 12 or 13 volts.

14 volts will start to cause some plate shedding.

15 volts will cause more plate shedding.

16 volts will cause a fair bit of plate shedding.

17 will remove whole chunks to the bottom of the battery casing.

18 volts....

 

There are also problems of plate/grid corrosion due to the localised higher SG following equalisation.

 

You get the gist!

 

Gibbo

[smileypete]

To a certain extent yes but (like most things) it's never that simple. The whole thing is a compromise.

 

Flatten a battery completely.....

 

11 volts will remove some sulphate.

12 volts will remove more.

13 volts will remove even more.

14 will remove yet more.

15 volts remove lots of it.

16 volts remove a whole load of it.

17 volts will remove even more.

18 volts will probably remove 99% of it.

19 will in all likelihood get rid of it all.

 

But against that you have to consider that....

 

11 volts will cause no other problems.

Neither will 12 or 13 volts.

14 volts will start to cause some plate shedding.

15 volts will cause more plate shedding.

16 volts will cause a fair bit of plate shedding.

17 will remove whole chunks to the bottom of the battery casing.

18 volts....

 

There are also problems of plate/grid corrosion due to the localised higher SG following equalisation.

 

You get the gist!

 

I do, but charging at a low current say C/400 you won't get to 15+ volts surely?

 

I'd expect there will be a small amount of gassing which limits the voltage across the battery.

 

If the SG in all cells returns to normal levels, then the battery can be considered equalised I'd have thought.

 

cheers,

Pete.

[Gibbo]

I do, but charging at a low current say C/400 you won't get to 15+ volts surely?

 

It might, it might not. A bit hit and miss to rely on though!

 

I'd expect there will be a small amount of gassing which limits the voltage across the battery.

 

Well I do know that C/100 will get the terminal voltage to well over 20 volts eventually! Though I've never looked to see what a lower current will do. You could be right.

 

If the SG in all cells returns to normal levels, then the battery can be considered equalised I'd have thought.

 

Indeed.

 

Gibbo

[ditchcrawler]

If the SG in all cells returns to normal levels, then the battery can be considered equalised I'd have thought.

 

cheers,

Pete.

Don't remind my, in the past I have spent hours recording SG's before an equalize cycle and then hours afterwards recording them again.

 

Brian

[sueanddaren]

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.

 

 

How long does the Kestral hold the 15.5 Volts for? It is timed?

 

Daren

[Gibbo]

How long does the Kestral hold the 15.5 Volts for? It is timed?

 

Daren

 

It doesn't hold it. It switches the alternator off completely once it reaches it. The 15.5 volts is actually adjustable.

 

Gibbo

[sueanddaren]

It doesn't hold it. It switches the alternator off completely once it reaches it. The 15.5 volts is actually adjustable.

 

Gibbo

But thats only 2.58Vpc, so the batteries might not be fully charged.

 

Daren