Alternator puzzle

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Graham_Wright

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I have a beefy (130A) Motorola/Prestolite/Leece-Neville) alternator for which I have found a useful amount of information. It has a built-in regulator and appears straightforward.

However, the three stator windings are brought out to terminals.

I can ignore them but what are they for?

I suppose if they developed a fault, the individual winding integrity could be checked by measuring the ac volts out of each but is there a better reason?
 
Is the rectifier inside or does it require an external one.

Must admit though i have seen (In fact do own) one with an external regulator but not external rectifier.
 
It would need to be a very special transformer to go from output voltage to the voltage you require, 220/110volts and stand very a high frequency, a lot of heat would be generated so cooling would be designed in . Somewhere in this world a company builds such a beast. My advice to you would be to contact them via the link in my last post and ask them for details of equipment that can be connected or where it can be obtained.
 
Alternator 3 phase connections

Most alternators are star connected with the centre point being brought out for auxilliary uses. Typically for Tacho drive. (I had a Ford long ago that used this 6v AC output to feed a carb heater to release the auto choke.)
Anyway with a delta connection there is no centre connection so you could use one of the phase outputs for the same purpose.
I vaguely remember an article in some magazine where the alternator was used for an arc welder. But I think that was using star connected alternator and then I can't imagine how you fed one electrode.


So all very mysterious good luck olewilll
 
Could be used for lighting or heating without rectification. Because the alternator is regulated the voltage at those terminals is also regulated.
 
Alternator

Hello Alex you mentioned you are confused. I wonder if you understand what star and delta connection means?
It relates to 3 phase AC and how it is connected. Star connection is drawn with the 3 windings each connected together in the centre and radiating at 120 degrees. The centre becomes the neutral and if we are talking 250V AC systems then you get 250V RMS from any of the 3 outside points when measured to neutral.
Now delta connected is drawn as an equilateral triangle here the 250V AC is developed between each point of the triangle. The neutral is a point in the middle which can only have any significance if we measure the voltage to the neutral from all three outer points at once.
With star connection the voltage between each phase will be less than that between the legs and neutral so if there is 240V between each leg one to another then the voltage between the legs one to another will be more than 240V. (i can get confused here)
This means that a 3 phase AC motor can be started and run on delta connection then changed to star connection for more power. (my appologies if is the other way around)

The concepts and advantages of 3 phase are a bit hard to grasp for a DC orientated mind. It is best understood by drawing graphs of the 3 different AC waves each 120 degrees spaced. In both star and delta connection the current in the neutral wire is balanced to zero so the wire can be omitted. Further the current in the 3 phase leg wires cancels one another out to a degree so that total current in the wire is reduced. (less copper needed while the system still carries the full total power.

3 phase is a cost saving for Alternators for cars and boats in that current in the coil wire can be less than the DC output so saving on heating and wire thickness.

I would suggest if anyone wants to know more about the maths of 3 phase they consult a good text book.
Just remmeber it is all about saving cost of wire conductor. Especially if you are shifting many megawatts across 100s of miles where the combination of high voltage (so lower current and 3 phase makes it all possible.) olewill
 
Olewill, It is not the Star/Delta concept that confuses me, fifty years in the trade on land and sea gives me an incling! Thanks for the reply anyway.
I am not sure how he has an internally connected delta winding with three extra wires brought out. I would have to see the installation to give a clear answer.
I did originally think that the three phases were brought out to the diodes and the other three tails, in question, brought out to facilitate an extrenal Delta or Star connection.
Hope you can follow that.
By the way as a "Nuetral Scot" Can I ask how your ashes are?
 
Alex_Blackwood said:
Olewill, It is not the Star/Delta concept that confuses me, fifty years in the trade on land and sea gives me an incling! Thanks for the reply anyway.
I am not sure how he has an internally connected delta winding with three extra wires brought out. I would have to see the installation to give a clear answer.
I did originally think that the three phases were brought out to the diodes and the other three tails, in question, brought out to facilitate an extrenal Delta or Star connection.
Hope you can follow that.
By the way as a "Nuetral Scot" Can I ask how your ashes are?
Click to expand...
The delta apex connections are made internally to diodes (only one bank) but also brought out to the external terminals. The regulator is built in (thus no need for two lots of diodes in series).The response from Prestolite was;-
The 3 phase terminals are used for auxiliary equipment, normally a rev (sic)counted. Any one of the three terminals can be used for rev counted connections.
It could also be used to devise a (sic) warming light system via relays.

It seems a bit over the top to me!
 
Last edited:
TheAshes

Hello Alex. It is no good asking me about the ashes or any professional sport. Sailing (racing participation) is my sport. However despite being a fifth generation Ozzie (my ancestors came from Wick and also Cambridgeshire) I do feel a little sorry for the Brits being beaten so often in the sports promoted by the media. So actually I am happy to see England ahead in the ashes but please don't tell anyonne on this side. olewill
 
Dont worry Will. The idea of England winning even one game of cricket is as much of a surprise to us as it is to you. I'm sure we will revert to normal before the series is over so you wont have to go searching round the attic to find the ashes.
 
OK. All makes sense, think I may have confused the issue, and myself! with the curved ball about the star/Delta connection.
Most alternators just bring out one phase and call it "W" for stuff like rev counters etc.
 
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