alternators don't need external controllers

[eidiohir]

alternators don\'t need external controllers

Re a post I made yesterday about Sailing Today and split charging systems.After reading a page on Adverc's web site I e-mailed Smartgauge to see what they had to say in defence of relay based split charge systems.
This is his reply which he said I can post on here if I want and I do want.
......
"Modern alternators do not need external controllers. That is an
undeniable fact. The only reason to install one on a modern alternator
is to compensate for the losses introduced by the split charge diode.
Hence the reason the ONLY people still trying to sell alternator
controllers are those who sell diodes. They go hand in hand. Without the
diodes, there is no need for the controller on modern alternators.

Even Adverc have, at last, finally realised this and despite their
bullshit (most of it is technical crap) on that web page they then go on
to introduce their own relay based split charge system? After saying
they are rubbish? And at the same time they start their web page with
"Anything for a sale".

That's about as hypocritical as it is possible to be.

The fact is they have been left behind by all their competitors who saw
this day coming years ago and moved on to other products. Adverc sat on
their laurels believing the day when external controllers and split
charge diodes became a thing of history would simply never happen.

It did happen, and it shocked them.."
.......
Pretty forceful stuff. javascript:void(0)
/forums/images/graemlins/shocked.gif Who is right?

 

[William_H]

Re: alternators don\'t need external controllers

Well bear in mind that some auto alternators were made to be used with external regulator. Though I think most modern alternators use the built is regulator which doubles as the brush holder.

I think that you would be wrong to claim the stepped voltage regulation system has no value. It was suggested that manufacturers of regulators are installing these into the alternator regulator as matter of course.

However i think you are focusing on practical boat owner situation regarding fitting of diode splitters versus VSR and whether to buy an external alternator controller /regulator.

if you use diodes you must compensate for the voltage drop by increasing the voltage of the standard regulator. This can be difficult because they are built in such that replacing the whole thing with an external controller battery sensed etc may be a viable option. Considering the better charging advantages as well as overcoming the diode volt drop problem.

I agree that for many a VSR with normal regulator will in many cases provide adequate battery charging. But if you find yourself running the engine purely to recharge batteries then a stepped charge controller would be far better.

Anyway I apologise if I have got the wrong meaning to your post. Mr Mercedes seems to have permanently parked an ad right over the first paragraph of your post. It seems no way I can get it gone. I am using Linux/ Mozilla Firefox.
olewill

 

[roly_voya]

Re: alternators don\'t need external controllers

Alternators never did need external regulators they are there to match the alternator the your battery. If I turn mine off it double the charge time. This has nothing to do with diodes/split charge reg it is because I use flooded led acid batteries that require a charge voltage of 14.8v and a float of 13.8. The compramise of 14.2 which the internal regulator provideds both slows charging and can cause overcharging if the engine is run for long periods. Yes if you use gell cels you get a faster initial charge because of the lower internal resistance but at a max charge voltage of 14.4v it still takes longer to fully charge the batteries because the charge rate dropps of dramatically for the last 15-20% they are also more prone to failure due to mistreatment plus cost 3 times as much. There are also issues about VCR's that I don't like mainly there potential to start a fire in failure mode they are also again more expensive. None of this comes from manufacturers data but from electronics theory and battery chemistry. You could ask the question why it seams that manufacturers are trying to get us to change what has been perfectly adequate technology for a new setup that does just the same job but costs very significantly more both to install and maintain - for whose benifit?

 

[rwoofer]

Re: alternators don\'t need external controllers

One of the reasons I posted on your Sailing Today thread was that I had similar advice, but cannot work out how it can do such a good job. Two issues that I can see with switching relays that I don't know the answer too:

1. If the relay charges the engine battery first and then switches to engine + service, surely the engine battery will be overcharging whilst the service batteries will be taking charge. From past experience I always found the engine battery is topped up very quickly, whereas the service battery can take hours.
2. Once the house batteries are up to charge, do modern alternators revert to float voltage and if so how is this done?

All the literature I have seen on voltage sensing relays suggests that overcharging is not a problem, but don't actually explain how.

 

[Talulah]

Re: alternators don\'t need external controllers

From what I understand the SmartGuage setup only decides on where to send the alternator output. It has no connections to the alternator. In essence when the user is draining the batteries the battery banks are seperated and when charging the batteries the battery banks are connected in parallel.
The claim that you don't need an external controller is IMHO rubbish. I say this because the output generated by the alternator is dictated by the 'sensed' voltage. If the 'sensed' voltage always comes from the engine battery and that battery is almost fully charged the alternator will not throw out much current and a discharged domestic battery would take for ever to charge. The external alternator controller should have one sensing wire for each battery bank. The external controller then 'fools' the alternator into throwing out sufficient charge for the depleted bank.
I do however dislike blocking diodes due to their voltage drop and much prefer 'electronic' alternatives. i.e Driftgate X-Split.
I have read the SmartGuage web site and it does not offer a balanced view. It's out to sell a product.

 

[halcyon]

Re: alternators don\'t need external controllers

The advice I have given for over 30 years since I started designing and suppling split charge relay systems is,

If you do not have a problem do nothing, if you have blocking diodes and a battery sensed alt change the sense lead to service battery, if not a relay will improve the situation, if you still have a problem fit a smart regulator as well.

Why does the engine battery not get overcharged ? simplyfied answer

First the voltage you see is generated by the battery internal resistance, it is not a fixed alternator output voltage.
Secondly the battery resistance increases with charge rate, a flat battery on charge is 13 volt, a full battery is around 15 volt.
The alternator starts charging the engine battery, the battery voltage rises, 13.8 / 14 volt the relay cuts in, and the batteries are now in parallel. The service batteries are now at a lower charge level, so is the internal resistance. The output current takes the least line of resistance, the service battery, so this takes the output currant, and the terminal voltage falls to say 13.4 volt. This low voltage is to low to put any charge into the engine battery, the internal resitance is to high, so all the alternator output goes to the service battery. this carries taking charge till the battery voltage comes close to the engine required voltage, at this point it starts taking a charge again, and the system becomes one large bank.

In real life things are more complicated, but that is the basic theory.

Your second question, the alternator uses the same type of micro system that the smart regulators use to set up a charge cycle.


Brian

 

[Guest]

Re: alternators don\'t need external controllers

In essence they are saying: have a fixed higher voltage regulator and a relay crossover system.

Now remove the thought of the engine. Just think of it as a source of power.

Why is it that if the electrons come from the mains we use stepped chargers and if the electrons come from a local diesel engine we do not need them! Why do we want to go back to the equivalent of 1970 mains chargers with their voltage controlled relays? Obviously alternators produce more friendly electrons.

My view is that the yachting industries attraction for laughable product marketing is becoming the norm.

Second point is that with bigger and bigger boats the distances to the batteries is increasing. It is not like we can move the alternator, like we can a mains charger, to be nearer the batteries.

Everyone has seen those little demonstrations panels at boat shows. Total width is smaller than the width of my engine never mind the width or length of my boat. Anything that small will always work at high currents. Just like the front of a car.

So the biggest problem with alternators is the disparity between the resistance in the wires to one bank compared to another.

We can compensate for resistances with voltage sensing. But most alternator regulators can not sense properly over long distances. Whatever we sense the charging source can compensate for it. But if the 2 banks are on different cables then it can not be right for both banks.

The ONLY real solution is to have ONE charging source per bank.

Any crossovers are just there to allow you to continue in fault or unusual conditions.

So leave that poor alternator alone. It was designed to charge a local starting battery and maintain power to a vehicle systems. It certainly was not designed to charge huge banks that have been drained by someone's life requirements for a day. Would you DIY fit a turbo to your engine to get more power? So why do it to an alternator?

If you want a big house bank then fit the appropriate additional alternator and fit a regulator that can compensate for the wire distances.

Anything else and you are just queuing up to empty your wallet. But I suppose that is a traditional part of modern day yachting.

 

[halcyon]

Re: alternators don\'t need external controllers

[ QUOTE ]
So the biggest problem with alternators is the disparity between the resistance in the wires to one bank compared to another.

[/ QUOTE ]

No that's just bad system design.

Brian

 

[rwoofer]

Re: alternators don\'t need external controllers

Thank you for the best explanation I have heard and one that makes sense to me as well.

 

[Guest]

Re: alternators don\'t need external controllers

[ QUOTE ]
Secondly the battery resistance increases with charge rate, a flat battery on charge is 13 volt, a full battery is around 15 volt.


[/ QUOTE ]

That is not how my batteries work. The internal resistance is basically constant. The internal voltage is what changes. The current is determined by the voltage DIFFERENCE and the resistance. I.e the difference between the internal voltage and the charger voltage. That is why the current falls off rapidly to zero if you only charge at 13.8v.

In fact the internal resistance falls with charge state. Take the extremes. A flat battery has a low specific gravity readings therefore it is nearly pure water. So the resistance is higher when it is flat.

If you do not believe me try: http://batteryuniversity.com/partone-22.htm (bottom of page)

As for a battery at 15v being charged. Actually a battery can not be at 15v. A charger can be at 15v but the battery will be gassing. The actual battery will still be at 13.8v approx and the rest, 1.2v and its associated current is making heat and gas. It is like connecting a compressor to a cylinder with a big relief valve, using a small pipe. The only reason the compressor reads high pressure is the resistance of the air flow through the pipe.

However, if you can cope with the water loss or the battery is capable of recombination (gels) you can push them past their internal charged voltage to decrease the charging time. But it must be time and voltage limited especially for gels. There is only so much spare water or recombination capacity in a battery.

 

[Guest]

Re: alternators don\'t need external controllers

you only have to read blurb of various threads / articles etc. - and you realise that much of it could be true.

Standard Split Diode systems - I have a Sterling unit screwed tto engine bulkhead - but disconnected - reduces charge voltage by at least 0.7V ... making it useless. So answer is to battery sense ... yeh well - show me the connector !! Secondthoughts don't bother.
So instead of Diode - go VSR ... tried and tested ... no V drop and no need to change sensing of alternator.

Right now we get to a point that I have mentioned befgore and some think is not good .... cheating the alternator senser ... Alistair Garrod in his excellent book shows you can connect a diode across the alternator regulator .... please check his book - don't take my words here as which contacts ... the diode effectively drops the alt. senseing 0.7V and so regulator steps up to compensate ... so a diode system can be used and no need for expensive boost items ...

Me I use a Maplins split chage unit with mains charger ... and rely on ME to sort from engine ... conventionally

 

[dubois]

Re: alternators don\'t need external controllers

Halcyon, Your explanation is very clear. Thankyou. Instead of using a voltage sensitive relay I was told it would be better to use a lo-loss battery splitter. I am told they use mosfet transistors (whatever they may be) and are supplied by a number of suppliers such as Driftgate, Studer, Vetus and give almost no voltage loss. They look the same and are about the same size as standard diode splitters. My question: Are these a better alternative to the much maligned VSR's and above all are they reliable?

 

[Guest]

Re: alternators don\'t need external controllers

[ QUOTE ]
No that's just bad system design.

Brian



[/ QUOTE ]

No, it is the reality of boat design not system design. There are few boats that have their engine battery and all the house banks in one place.

It is something to do with the fact that boats float, and generally people do not put the batteries in the hot engine compartment. Instead they are under the bunks near the centre of the boat (for example Bavarias)

My experience covers small boats that have small under bunk areas, to 400kg of batteries I installed on a 70 ft yacht over the keel and up to the 1400kg of batteries we installed on a super yacht. All have equal problems with layout and wire resistances. It is only the scale of the components used that changes.

Charging is dependant on 0.2 to 1v differences. Take a 35mm2 cable with a 5m distance (3m away but it has to be routed through a boat). Resistance is approx 1mV/A/m. So at 10m round trip at 50Amps that is 0.5v. Use 25mm2 and you add on ~30% more. So distance counts with both diode and relay crossover systems.

If you want to see for your self http://www.almac.co.uk/proven/FILES/cabdrop02a.xls

 

[halcyon]

Re: alternators don\'t need external controllers

A hard question to answer, looked at MOSFETs back in the mid 90's, and still do, also I uase them to control the relays.
Why do I not use them,
They have a flywheel diode across them, this provides a reverse path across the MOSFET from output to input, so you get back feed, I am not happy with is.
A relay is no more component cost than the required multiple MOSFET to give the level of security I want.
A relay is more flexiable, using the same relay we can charge a service battery from the engine, the engine battery from a solar panel on the service battery, and use the same relay to allow you to start the engine from the service bank, plus they are more fleiable, I can use one contoller to run 1,2,3, or 4 relay system.

Would I use MOSFET's, I have designs on the board that I am playing with, with luck I will have a test unit to fit on our yacht for testing next spring, time will tell.

Do I think MOSFET splitters are any good, as with a lot of things sold in the marine trade, no comment.

Brian

 

[Guest]

Re: alternators don\'t need external controllers

Poor Halcyon .... you only are asking him to report badly on his VSR's ...

Personally if I was re-vamping my engine charge system - Halcyon many moons ago gave me all sorts of info ... yes his systems - but whats best ? Talk about others ? It all made sense ... forgive the pun ! and appeared simple to fit ... with NO loss of V in the split.

I have no cennection to KDDPower / Halcyon other than he was kind enough to help me out ...

 

[dubois]

Re: alternators don\'t need external controllers

<<Poor Halcyon>> Don't understand the comment.

 

[dubois]

Re: alternators don\'t need external controllers

<<Why do I not use them,
They have a flywheel diode across them, this provides a reverse path across the MOSFET from output to input, so you get back feed, I am not happy with is.>>

What does this mean and why is it a bad thing?

As I understood it, low voltage loss splitters are not that new. Vetus tells me they have been selling them for years without any returns?

 

[halcyon]

Re: alternators don\'t need external controllers

I am not going tell you why you should buy one, or why not, it's other firms products, you must make up your own mind.

Yes they are not new, I was looking at them over 12 years ago, and we built one for test, and yes I am still playing with them.


Brian

 

[Guest]

Re: alternators don\'t need external controllers

[ QUOTE ]
They have a flywheel diode across them

[/ QUOTE ]

[ QUOTE ]
What does this mean and why is it a bad thing?


[/ QUOTE ]

The equivalent circuit of a MOSFET (Silicon device for switching currents used in solid sate relays) is a voltage controlled switch with a diode connected across it. It is called the BULK diode. It obviously points in the opposite direction to the intended switched current flow.

It is an inherent part of the manufacture of the MOSFET.

It can be used in freewheel applications in inductive circuits but its characteristics are not ideal.

If 2 were used instead of a diode splitter from an alternator then when the alternator was not used it would be still powered by the path back through the diode from the batteries.

If used in a bank combiner circuit the Diode would mean that one direction would be always connected through the diode and only the other would be switchable.

This shows a basic isolated MOSFET solid state relay with the diode shown.

http://www.teledynerelays.com/pdf/industrial/S75DC150.pdf

This shows an example of a back to back pair that would work for battery combining.

http://en.wikipedia.org/wiki/Solid_state_relay


MOSFET have been around since I was small but integrated packages with isolation and built in self drive circuits are a lot younger.

1. When on, a Diode has a voltage drop of 0.6 to 0.9v and an internal resistance. At 50A you can see over 1v of drop.
2. When a MOSFET is on, it has just an internal resistance (2.25mOhms) So at 50A that would be 0.1v
3. When a relay is on, it has its contact resistance (say a 30A relay would be about 50mOhms, a solenoid would be around 0.8mOhms)

 

[William_H]

Re: alternators don\'t need external controllers

to Roly-Voya re external regulators. You obviously have fixed in your mind that this means a Smart charge regulator as in Stirling or similar. I was simply referring to normal regulators either solid state or relay type that are not mounted on the alternator (common in the 1960/70s. So that is just a languagee problem.

Anyway reading through the posts there is just a modicum of garbage here.....

Firstly resistance in the charging wire. This is not as serious as you describe. The reason is that (eg) if your battery is being charged at 14.4 volts at 50 amps Then you add another .1 ohm resistance (quite lot) you do not drop 5 volts so get no charge.
What happens is that in trying to drop the 5 volts the voltage falls to the threshold of the battery inherent voltage where upon current ceases so there is no voltage drop. You have full voltage so full charge. Well obviously it doesn't oscillate between full current and no current. My point is that the current and voltage drop settle to a point where enough current flows but not enough to reduce the voltage below that threshhold.
In other words resistance in the wiring will reduce the current but not by anywhere near as much as you might calculate. And as the charge state of the battery increases so current falls the resistance matters even less. It is not as critical as for a mast head light where the current is essentially constant falling only a little with volt drop so volt drop is significant to the voltage supplied to the lamp. The power lost is due to both current and voltage drop.

Now that is no reason to skimp on wire size however in practice a resistance in the charge line can even be useful to reduce huge initial charge rates while for most of the charge time not reduce current very much.

I think it has been explained why an engine battery doesn't get overcharged when a VSR connects a discharged service battery. Let me try in simplle terms.
The connection between the 2 batteries is solid metal. Wire plus relay contacts. The charge voltage must be equal to the voltage at the terminals of both batteries. If the engine battery has an inherent voltage of 13.75 (from its charge state. It is connected in paralell with a service battery whose inherent voltage is only 12 then the current will flow from engine to service battery. At the same time the alternator is trying to get the system up to its regulated voltage 14 volts so in fact moire current will flow into the service battery and very little into the engine battery. it all balances itself out without overcharge of the engine battery.

I reckon that the humble VSR is both foolproof and has no voltage drop. Yes diodes are Ok if you can compensate for the diode voltage loss. Butr why go to that trouble if you don't have too. I can't imagine how anyone could describe a VSR as a fire hazard. Is it any more danger than the solenoid on your engines starter.
finally if anyone wants to make their own VSR I can give design (quite cheap) but you need a bit of electronics savy and of course it is difficult to build to the same robustness and corrosion resistance as a commercial one. olewill