Flashing an Alternator

There should be no need to flash an alternator, a generator, yes, but an alternator, no. It is the voltage regulator that is in charge of ensuring the field is proper on an alternator.

The field circuit terminals from the AVR have to be removed and also the batteries disconnected. ( In fact two wires + and - from the existing battery, should be routed through a proper circuit breaker with rating matching with the rated field current of the generator to the field wires removed from the AVR).

Don't flash more than 5 seconds.

cheers.

What are the reasons that you feel this needed? What type of alternator is it, from a car of vehicle?

Andy,

Google:

Flashing an Alternator

I did.

Why would I need to read that, I have flashed DC Dynamos already, many times when we converted cars from positive earth to negative earth, I know what to do and how to do it!!!

I found a web site that explains the problem even better, it says at one point:-

A new alternator just out of the box may not have this residual magnetism and so may not be able to kick-start itself, in which case the ignition warning light circuit is essential. ON NO ACCOUNT should you try to generate this magnetism by 'flashing' the alternator connections across the battery like you would polarise a dynamo, you may well blow the diodes.

I was just questioning the need to flash on an alternator.......here is a good description of an automotive alternator, which describes as how the exciter is powered initially by the battery and then from its own output while running etc etc..

Alternator

So it is a mystery to me why flashing is needed and I was hoping for more detail so that I could understand the problems better....

There are permanent magnet alternators, but if they have lost their magnetism, I feel that it will need more than a flash to get the magnetism back!

The only units I know of personally that need to get flashed occasionally are DC Dynamos........but please be so kind as to complete my education in this area if I am missing something important.......

Yup... I agree completely.

Sorry,

I misinterpreted your question. I assumed that you were asking from the point of view of someone who wasn't familiar with flashing. Such as myself.

No offense intended.

LL

No offense taken, I had just hoped to learn something new......

By the way, in the UK at least, "Flashing" can also mean exposing yourself .......

Didn't the Williams sisters get flashed recently? During a doubles match?

I don't remember the country.

In the USA, we streaked.

Maybe they still do. I'm too old.

Technically "streaking" means running naked.......in the UK too.....

Flashing is really only "showing your Willie", not necessarily otherwise unclothed, nor necessarily even moving.......

Semantics!

You are right.

Funny, but when I search Google, as you suggested, it turns up nothing of use on the subject of "flashing an alternator".

.

Its not easy to find, but I did find one article that mentioned NOT to try and flash an alternator.

I posted a link (the first link) to it in my last post.

Firstly gentlemen please note that a generator set has a prime mover and an alternator. Thus Zenthil may be referring to an alternator supplying dc (at low voltage?) or ac (at higher voltage?).

I have had call to flash dc single terminal alternators. These only have one connection to the battery and of course the common neg. They rely on the residual magnetism to start up the regulator. It is important to flash the field in the same polarity as the regulator as, if it is wrong, when the regulator cuts in it counteracts the residual and results in zero output.

If the OP refers to an ac output device then he should try first to get the manufacturers manual as following the mfrs info is always the safest method. If that is not possible then OK, flash anyway.

Disconnect the AVR (noting the polarity of field)

Check the field resistance to see that you will produce a sensible current with your battery. If you have something under 1Ω then you must ask yourself if the wire will support the current. Check the winding has no connection to ground. If so then you should use an isolated battery. You should only need to flash the field for a second or so. I usually do this several times. As with the alternator above, it is important to get the polarity right if it is a brushed set. Brushless sets don't care as the rotating rectifiers take care of the job for you.

Run the set and check the residual voltage. Typical values 6 to 9V, this is usually enough to get the AVR going.

There are other methods than the above to flash a generator. Putting a charged capacitor of a suitable size and voltage rating across the output while it is running at rated speed. Be careful as it can make rated voltage immediately!

Hope this helps

Chas

It may seem like hairsplitting to you when I say here what I personally think on the subject, but here goes anyway.....I like clarity and accuracy! (and safety as many here already know!)

In a "normal" Alternator, you can have a DC and an AC part, I believe you are referring to the DC part only. Technically this is a dynamo or DC generator in my book.

I do not know where the name Alternator originated, but it always seems to refer to an AC generator, even when one actually has diodes in the output to make DC as in most car Alternators.

It appears to me that the name could most probably come from the fact that in the machine at one point AC or "Alternating" Current is produced......though this is at best an educated guess, not a fact.

You mentioned at one point "I have had call to flash dc single terminal alternators." I personally have never heard of anyone, up to now at any rate, refer to an Alternator as producing DC!! (except in the version I mentioned above for car power systems!)

So to find out if I was being just "Picky" or not I Googled "definition of Alternator", the first of many hits was at:-

...and what did it say but:-

n.

An electric generator that produces alternating current.

I then Googled "definition of Generator" and found the following:-

generator

1. A machine that converts mechanical energy into electricity to serve as a power source for other machines. Electrical generators found in power plants use water turbines, combustion engines, windmills, or other sources of mechanical energy to spin wire coils in strong magnetic fields, inducing an electric potential in the coils. A generator that provides alternating current power is called an alternator. See also induction.

I then did the same search for Dynamo and found the following:-

dynamo

n. pl. dy·na·mos 1. A generator, especially one for producing direct current.2. An extremely energetic and forceful person: a vice president who was the real dynamo of the corporation.

[Short for dynamoelectric machine.]

I think that demonstrates in a reasonable manner that an Alternator must generate AC at some point and a Generator needs to be qualified with either AC or DC to be fully accurate......

I hope my hairsplitting accuracy has brought some clarity into this shocking problem!!

Hi Andy,

no argument with that. It was just that the OP didnt specify or give any clues as to which of the two groups of machines he was refering to. He didnt even use the terms AVR or regulator which would give a clue although they are essentially the same.

Chas

YOU ARE PERFECTLY CORRECT, I could not agree more.......

I was just trying to define the terminology and make sure that nobody was flashing the AC part of an Alternator....

I personally feel that he may have got his terminology wrong......but there is no guarantee with idea that I am hasten to add!!

yes apart from what has been said about disconnecting the field disconeect the electronics before flashing.Is it not building up voltage ?

Yes, you need to disconnect all electronics; high voltage spikes may be generated while connecting & disconnecting DC source to windings. Second most important thing is connecting correct polarity. good luck!