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.
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
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.
Sorry Ian, posted at the same time but we mean the same thing, don't flash it!
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
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.
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
Thanks, I didn't know that & I have been messing about on bikes & cars for 40yrs... that's a bit worrying , but then again every dynamo I've had has worked after a refurb brushes & a good clean so I must have just been very lucky.
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.
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!
Its just occurred to me that the same thing will apply to a dynamo that is rotated in a direction other than its normal direction. ie take a dynamo off an m20 and fit it to a Norton 16H or visa versa(it runs in the opposite direction on the Norton) and it will have to be flashed before it will work. (to reverse the polarity of the residual magnetism)
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