Dominator alternators

Its an early (old!) one. The stators seem to last well ,the rotors can seperate from the center tube ,but the early ones do seem to hold together better than some later ones. My 1959 one is still fine. If the magnetism in the rotor will hold its own weight it will usually work. You can test for shorts in the coils but its unlikely. Colours sound right to me .Check an early Diagram.

Previously peter_gibson wrote:

Hi

does anyone know if there is a way of checking an alternator without the engine running I'm restoring a 99 and want to keep the 6 Volt alternator but would like to know if its ok

secondly the three wires on the alternator are different colours to those on diagram in manual

the colours on mine are green/ yellow, light green, and dark green

and wonder if anyone can help identify

Hello its time for a up date you Need RM21 two wire and rotor to fit Norton crankshafts and one Solid state rectifier there are only 4 wire to hook up one red to frame one blue to ammeter one yellow too lighting switch the other goes to battery negative side jobs a good one new 12v bulbs and bingo you better light all round yours zranna3

A 3 phase alternator (which is what you have) can be connected any way round - all the green/yellow cables that go to your regulator/rectifier can be connected in any order.

The important ones are the +ve and -ve that come out of the other side of your regulator/rectifier.

This age bike is usually +ve to the frame (so opposite to a modern car)

Contrary to Anna's advice, I would be more inclined to stick with a three phase alternator. You will get more charge at lower RPMs compared to a 2 wire stator which gives you more at a higher rev range. A three phase stator is much better suited to poodling about and with stop/go traffic.

Treat yourself, and replace the rotor - these lose their efficiency over time plus as Robert pointed out, there was a time when the centre and rotor parted company. They go with a bang and can leave a horrendous mess in your primary case, or even worse!!!

I don't think this is a 3 phase alternator just a very early 2 phase 6 volt with the switch controled charging. These were 3 wire. And you will find (if that is the case )that new rotors are not availiable ,New rotors are made to a different diameter.Old 3 wire stators have the coil wiring exposed ,later ones are encapsulated. The old type rotors possibly last longer because they have reduced magnetism and give the center an easier time!. A photo would help .

Three phase have 9 poles on the inside of the stator and single phase 6 poles.

Basic testing of alternators and the 70mm/74mm information can be found on my web site. (This information is on my web site AOSERVICES.co.uk) as opposed to in the Roadholder to save Editors interfering with the words). 3 phase has 9 pole pieces Single phase has 6 pole pieces. The colours are a bit non standard, it is not very crucial their connection, if it is wrong no harm is done but you will have reduced output. Retain your 6 V if you like, but a modern encapsulated rectifier might be a good idea.

The observation with regard to encapsulated later but open wiring on earlier is not true, but might be a general guide. but be aware your case is specific. You do not have 2 phase, you have single phase.

Al Osborn

My Ruse worked!.I knew if I waffled on a bit with slightly wonky information Al would chime in .Now I need him to tell me what to do with my iffy 1930's bth mag.I'm beginning to think a coil ign conversion has to be the best way forward. Has anyone used the mag points to trigger a points assist unit and fire a small low consumption coil?.

What's wrong with the mag?

Hi Richard. Its a 36/39 mag , it loses the spark on full retard, Its possible that it has the pre-Alnico type magnets which are not good at retaining the is'm . It probably needs a new condenser. Even if I find a good magman how long will it last? For minimal expense I could convert to a coil as long as the dynamo keeps going and I could fit a spare battery as a get home failsafe. Don't intend to ride at night.What do you think?.

The guide below applies to the old style Lucas alternators with the Low output and High output 3 wire system...it is not so useful for the 3 phase as generally the 3 pairs of coils are wired in a delta format and they all measure the same....so

Imade this little guide up...it can sometimes come in handy when you are testing an old alternator or substituting one with different coloured wires.

ALTERNATOR LEADS.jpg (16.54 KiB) Viewed 239 times

ALTERNATOR LEAD INDENTITY AND BASIC TESTA quick way to identify each wire especially if the colour has faded and to test the coils is as follows.Looking at the diagram above:The UPPER common wire is...........................COMMON WIRE..............AThe single coil wire is the ...............................LOWER O/P COIL............BThe two coils parallel up are the..................... HIGHER O/P COILS.........C With a sensitive multi-meter with an OHMETER resistance range, first short the test-leads together and note the reading. This is not always zero as it takes into account the test-lead resistance or simply poor alignment set up. The noted reading needs to be subtracted from all the other readings, but if very low it can be ignored. Code each wire differently with a label or different colour tape for easy identification..Then measure at wire ends ABC (3 pairs)You should get 3x different readings and these readings should work out as follows IN THE SAME PROPORTION.The LOW reading should be HALF the MIDDLE reading.The HIGH reading should be the SUM of the LOW and MIDDLE reading.So using typical figures we would get:0.8 Ohms.....1.6 Ohms........2.4 Ohms....if you get this sort of difference all is OK as long as none of the lead out wires short to the alternator framework....test with the meter.Now we need to know which wire is which.You can use this diagram below...Just arrange the wires to the same positions from the resistance tests (Large Black Dots). By superimposing this layout on your 3x tested wires you will have identified what lead is what....shown by the A B C IN RED.

Even if I find a good magman how long will it last?

The magneto on my Dominator was overhauled about 35 years ago and is still going strong many, many miles later.