Hi

Successfully flashed my dynamo a couple of years back, but wondered if the same thing can be done with a Land Rover Series 3 Alternator.

The alternator looks new(ish), but is not putting out a charge.

Kind regards

Pat

email (option): sacombsashtrees@hotmail.com

Short answer, no. Alternator has no residual magnetism relying on the battery voltage flowing to earth though the windings when the ignition is switched on. If the alternator has a external regulator then you might find that easy to change, if not then it could be a diode fault or the internal regulator. Does the ignition light come on, if bulb has blown the alternator will not charge. Some alternators will self induce a charge "Lucas for instance" if engine is revved to about 4000 rpm.

email (option): iandot clare1at virgin dotnet

Hi Pat,

This cannot be done as dynamo's are DC and only push out either positive or negative voltage. Alternators push out both and alternate between positive and negative as it rotates the diode pack at the end of the alternator takes out either the positive or negative side of the current. This diode pack may be faulty on your alternator.
If you think about motorcycles with alternators they had a rectifiyer under the seat this changed the output of the alternator to either + or - and dumped the unwanted side to earth. On latter higher output alternators the motorcycle was fitted with a alloy finned divice fitted uder the bottom yoke this is a diode thet will dump to earth any high unwanted voltage. So dynamo's are DC only (direct current) and alternators are AC (alternating current). So don't try to flash it just change the diode pack.
Hope this helps
Tim Walker

email (option): t.j.walker@btinternet.com

email (option): t.j.walker@btinternet.com

Yes alternator failures are quite often the diode at fault in my experience which is an easy cheap fix.
but this question & the answers have confused me a bit as I used to always use the term "Flashing" when setting a positive earth dynamo to be used on a negative earth vehicle (& vice versa) back in the 1960's/ 70's when some cars were positive earth & some negative.
ie.. changing the polarity.
I've never used flashing as a method of rejuvenation on a non working unit. can't see how that would work as a dynamo is either serviceable or not. ??

Sometimes a dynamo that has not been used for a considerable length of time will lose its residual magnetism rendering it non functioning. A quick flash will remagnetise the field core and effect a cure. In normal use this will not be neccessary, only after an extended period of years of inactivity

My M20 dynamo wasn't working as it had been laid up for a few years. I flashed it about 2 years ago and it has worked ever since.

email (option): sacombsashtrees@hotmail.com

Hi Ian

The bulb has blown (I have checked the circuit to the bulb - a steady 12v is present)!

Seems odd that a 2.2w bulb or lack of it would stop the alternator working, but as they are only £2.00 for a pair from Halfords I will definately give it a go.

Thanks to everyone who responded.

Kind regards

Pat

email (option): sacombsashtrees@hotmail.com

Thanks Ian. Couldn't get (be bothered to go and get) a bulb, so connected the two wires on the "charge light". Alternator now belting out 14.5V.

I wonder how many people have replaced Alternators in the past only to find this little light had blown?

Kind regards

Pat

email (option): sacombsashtrees@hotmail.com

You're welcome
I have to add it has to be flashed for the correct polarity, pos or neg frame earth, otherwise it still won't work!

As an aside to the problem now solved. I had a problem with charging on my B33 changing the dynamo didn't help. Reason was a slack clutch on the large fibre wheel inside the end case on a mag-dyno unit, the dynamo charged ok with the lights off but no charge with the lights on, the extra load caused the clutch to slip so no drive or charge. Worth checking if all else fails. ALTERNATOR Don't leave the two wires connected you will end up with a flat battery, the battery will discharge through the windings if you are leaving the bye pass. Make it ignition fed and with a bulb or resistor in series with the windings.

email (option): iandot clare1at virgin dotnet

If you reverse the driven direction of a generator you must swap the field wires over. Flashing afterwards.

Landrovers do tend to knacker alternators up fairly regularly, especially if used in off-road conditions a lot. The alternator fitted to these is usually the Lucas a127, you can get a full kit for refurbing it yourself from ebay for £16, see item http://www.ebay.co.uk/itm/231103009499