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Alternator Paralleler Circuit


chris w

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We have in fact two working circuits after 29 pages ...the tripple diode one and the one using a single diode and two Bosch RE 55 regulators which gives the advantage of a boosted voltage to the house bank

 

There is some sence in what you say semelly about inductive voltages damaging diodes which is why I said to leave the jump lead in place to give the current time to drop . Unfortunatly I hate technocrap on the internet as it soon spreads and becomes fact

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....if the alternator output suddenly drops from say 80 A to 10 when you pulloff the jump lead you can get a voltage spike that can damage the diodes ...this is what hapopens on many alternators and the field diodes are buggered ...even a small relay on the IND terminal will bugger the field if you are unlucky ...same as disconnecting the battery at high alternator loads

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Sorry, I still can't see where this inductive load is. Nor can I see any real risk of the alternator becoming disconnected. What motor?

 

I'm assuming they're talking about the starter motor. It's the only inductive load I can think of.

 

T.

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[Get into the real world Gibbo ....The fitting of split charge relays on the ind terminal of an alternator has caused thousands of field diode failures on Land Rovers and if your alternator output sudenly drops from a high level when a wire comes off the voltage spike will bugger diodes ...why do you think they fitted surge diodes on some alternators ( 35v DZnner )

 

you have your two circuits for parallel alternators so why not go invent something else ?

 

I will rejoin you at page 58 ha ha

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[Get into the real world Gibbo ....The fitting of split charge relays on the ind terminal of an alternator has caused thousands of field diode failures on Land Rovers and if your alternator output sudenly drops from a high level when a wire comes off the voltage spike will bugger diodes ...why do you think they fitted surge diodes on some alternators ( 35v DZnner )

 

you have your two circuits for parallel alternators so why not go invent something else ?

 

I will rejoin you at page 58 ha ha

Well I have to say I have never noticed relays damaging alternators, land rovers included and I would have thought that the quench diode fitted in the regulator between + and -ve brush would have dealt with it. I will not however deny your experience and just wonder what's different about your installations. Disconnecting alternators on load, I have done this a million times and never had damage result. I really think this load dump phenomenon is greatly over stated. An alternator stator is not in itself highly inductive and anyway a drop from 80A to 10A is called "Releasing the winch button."

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when the current in the stator drops it induces a voltage spike in the coils ..that buggers the diodes ...the stator coils have inductance as you know ...I think you are taking the piss but your funnel is too small....

Yes, I am familiar with the theory, but I repeat, I have disconnected alternators on load many many times without damage. And yes, any winding will be inductive but you know how you can get a belt if you are holding both sides of a relay coil when it de-energises? Well you don't with an alternator stator.

There have always been dire warnings about disconnecting alternators on load, the fact that experience tells me I can do it is at odds with recieved wisdom and I would like to know why. I'm afraid the size of funnel does not translate and I have no idea what you mean.

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Yes, I am familiar with the theory, but I repeat, I have disconnected alternators on load many many times without damage. And yes, any winding will be inductive but you know how you can get a belt if you are holding both sides of a relay coil when it de-energises? Well you don't with an alternator stator.

There have always been dire warnings about disconnecting alternators on load, the fact that experience tells me I can do it is at odds with recieved wisdom and I would like to know why. I'm afraid the size of funnel does not translate and I have no idea what you mean.

 

Chris often has trouble explaining himself.

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Quite clearly someone here does not understand the mechanism involved.

 

If a hard working alternator has its load suddently disconnected the output voltage will start to rise (very quickly). This is due to two parts:-

 

Firstly the stator is inductive. One of the actions of inductance is that the current cannot change immediately. If the load is made smaller, then the stator, by inductive action will try to maintain the current at the same level. The only way it can do this is by increasing the output voltage (in the opposite direction - hence back EMF when an inductor is suddenly disconnected from a voltage source). This is extremely basic electrical theory. It isn't a guess. It is fact. When the output goes very high, it isn't the voltage across the forward biased diodes that causes the problem. That cannot cause a problem because it is clamped by the diodes at their forward conduction voltage. Somewhere between 0.6 and 1.2 volts depending upon the current. The problem is the reverse voltage across the reverse biased diodes. If there is nothing to clamp the alternator output (say a battery) this can exceed their peak inverse rating (PIV). THAT is what causes the problem.

 

This is why, when a hard working alternator is suddenly disconnected, the output can rocket to extremely high levels thus damaging the diodes.

 

However, in this circuit, our Ozzie friend has stated that removing the jump lead can cause this to happen. He is wrong. Quite simply, when the jump lead is removed, the stator will try to do the same thing as above, but it can't because the output of the alternator is still limited to the battery voltage plus the drop across the newly introduced split charge diode. So that idea is completely out of the window.

 

Removing the jump lead will do absolutely no damage whatsoever.

 

Secondly, the output can rise because when the reg senses the rising higher voltage on the B+ terminal it will instantly switch the field current off to prevent any further rise. However the field has a quench diode across it to prevent its back EMF from damaging the reg. And by exactly the same inductive action the field will try to maintain the same current in it by conducting its previous current through the quench diode. This maintains the magnetic field at the same level even though the regulator has switched off the field current. This current will only reduce as a result of the resistive (and other) losses in the field. This can take up to 500mS or so. This is the second reason that the output voltage of the stator goes very high when the load is removed.

 

But again, the output is limited to the battery voltage plus the diode drop of the new diode splitter. So, again, removing the jump lead can do no harm.

 

I repeat. I am not guessing at this (which clearly Mr Oz is).

 

The idea of a small split charge relay connected to D+ damaging the field diodes is yet more rubbish. The only way any damage could result to the field diodes would be as a result of a relay coil pulling far too much current (and that would be a bl**dy big relay coil) or a high positive voltage spike on the D+ terminal thus reverse biasing the field diodes. Any form of inductive action, whether from the relay coil or from the stator can only result in a negative voltage spike on the field diodes. Thus, again, no damage can result.

 

Now, the reason this damage to alternators when suddenly disconnected doesn't happen as often as some people's logic implies it should do is because the real (ie full) inductance of the stator (which is very high) isn't what causes the voltage spike. The real inductance is magnetically linked back to the field as in a transformer and the rotor can clamp a huge part of the voltage spike. It is only the leakage inductance of the stator that can cause the high voltage spike. And in modern, well engineered, alternators the leakage inductance is extremely small.

 

I know Sir Nibble will agree with the above (because it's all fact as opposed to supposition). And if me and Snib both say the same thing, what are the chances of Mr Oz being right and us being wrong?

 

Gibbo

 

Right Mr loudmouth Ozzie. You now explain with your broken electronics "knowledge" how this alternator can be damaged by removing the jump lead and I'll then waste another 15 minutes of my life explaining to you why your idea is wrong, where your error lies, which parts of electronics you do not understand (that could take some time) and how flawed your logic is.

Edited by Gibbo
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Now I don't want to be party an any arguments right?

Yes, I agree with nearly all of what Gibbo says. The rest of it is new information to me and nicely tops off my understanding of the phenomenon.

Interestingly, many modern alternators now use high power zener diodes in the rectifier which should finally lay the subject to rest.

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This is why, when a hard working alternator is suddenly disconnected, the output can rocket to extremely high levels thus damaging the diodes.

 

 

Good we agree

 

I was just trying to make the point for the less electrically knowlegable that it is not a good idea to disconnect anything on a charging system while it is in use ...not all boat alternators are modern.

Edited by pistnbroke
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So... Sir Nib was right, my concerns seem to have some foundation however the engineering means that they're inconsequential...

 

Love

 

The less electrically knowledegable who thinks this whole business is a really good idea

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True cannot be disconnected but could be seriously reduced if the start battery was being giving a high charge current ,,,,

 

Any way why not get your heads out your asses and say ...we have two good practical circuits for paralleling alternators one which which allows an increased voltge easily switchable ...

 

If I was the moderator I would reduce this to a few relavent posts with the approved circuits and delete all the irrelavent techno crap which confused those who just want to KISS....then lock the post .....

 

bye .....got better things to do and other problems to sort for more appreciative people ....

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True cannot be disconnected but could be seriously reduced if the start battery was being giving a high charge current ,,,,

 

Which can do no harm. You said it could blow the diodes. It can't.

 

If I was the moderator...............

 

If you were a moderator there would be no members left.

 

Look, you obviously have some knowledge of the subject, just not as much as you think you do. Why not stick around, sort your attitude out, realise there are people here who know more, learn from them and also introduce your own ideas. Everyone can have good ideas. That way we can all get along nicely.

 

Gibbo

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Look, you obviously have some knowledge of the subject, just not as much as you think you do. Why not stick around, sort your attitude out, realise there are people here who know more, learn from them and also introduce your own ideas. Everyone can have good ideas. That way we can all get along nicely.

 

Gibbo

Worked for me! I have learned more from this forum by picking others brains and studying issues raised for myself than anywhere else since I left college.

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Worked for me! I have learned more from this forum by picking others brains and studying issues raised for myself than anywhere else since I left college.

 

Me too, I learn something new every day from this forum.

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If I was the moderator I would reduce this to a few relavent posts with the approved circuits and delete all the irrelavent techno crap which confused those who just want to KISS....then lock the post .....

 

I mainly read the forum for the 'techno crap'.

 

I don't want to keep it simple, I like it complicated (but not too complex), thanks.

 

PC

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