Dynamo not charging.

99% of the time it's the brushes, I'd bet they are fairly cheap to replace. Personally, unless the dynamo is a nightmare to change, I'd just stick some brushes in and see how you go. Spin the dynamo up with a drill and check you get some volts out of it before fitting it perhaps?

If you want to test it, test between each strip in the commutator and earth (the spindle). You shouldn't get any connection. Testing for open coils is trickyer because you need to know how it's wired and I forget how.

p.s. I knew I had the wrong word for the commutator hence the brackets, its really annoying when the word you want just slips out of your head.

Actually, you had it right. In a DC generator (dynamo) it's called an armature. In an AC generator (alternator) it's a commutator.

Fit some brushes and put it back on. If it charges, it works

One point however... dynamo will only charge when the F terminal is taken live (+ in a -ve earth system) and the points in the control box switch this live. Was the charging lamp illuminated on the dash when you were testing for output?

Are you sure? I reckon they both have an armature - the bit with the thick power producing wiring (stationary on an alternator) but if it doesn't have a commutator it has slip rings.

Sorry, Scary, but I'm quite sure that calamity is right.

The armature is the power producing coil. In a dynamo the spinny thing (rotor), in an alternator the static thing (stator).

The field is the thing that excites the machine - it provides the magnetic field which actually produces the electricity when the machine is moving. Controlled by the regulator: less field current = less power output.

The commutator is the segmented switch attached to the armature (aka rotor) in a dymano - the brass bit that the brushes run on. It commutates the windings - ie it switches between the various wires to produce a DC output.

Slip rings are the AC analogue of the commutator. Provides the field current in an alternator.

Paul - one test of a dynamo that crops up in several sources (Haynes, Rootes workshop manuals, Crypton test meter instructions) is to:

1) Disconnect the dynamo from the car's wiring, and connect the F terminal to the D terminal. 2) Connect a voltmeter from D to ground.
3) Start the engine BUT DO NOT REV IT (it might be best to start with a warm engine, so you don't have the fast idle of a cold engine).
4) Gradually increase the revs - if the voltage rises quickly then the dynamo is good. Don't let the voltage rise above 20V - the insulation of the windings won't take much more before it breaks down.

If the voltage doesn't increase rapidly, then it's the dynamo at fault - either the feild or armature windings could be open or short circuit, the brushes too worn (likely from your description), or possibly shorted or dirty commutator segments.

The commutator can be cleaned with fine abrasives, and some can be re-faced by a machine shop if the segments are deeply grooved.

If the voltage does increase, then the regulator is probably at fault.

A 2 bobbin regulator has 2 tasks. The first is disconnecting the dynamo from the battery when the current starts to flow in the wrong direction. This is the cut-out. It will have bigger contacts and thick wiring on the bobbin. The dash light is connected across these contacts, so will illuminate whenever the dynamo isn't charging.

The other job is to regulate the voltage - this is performed by the smaller set of contacts, which act like a voltage-sensitive relay: When the voltage is too high, the contacts are pulled open, turning off the dynamo. The voltage then drops, and the contacts close again. This cycle will repeat quite quickly when the voltage reaches the set point - you might hear it on a a radio as a buzzing. The bobbin will be mostly small wire, but it may have a few turns of thick stuff.

How about taking the opportunity to swap it out for a modern alternator? I did that a while ago so I could run some extra electrics and don't have to worry about the battery not charging now. And it meant I could junk my mechanical regulator.

Measure up the mounting points as best you can (tricky while it's still on the car, I know) and scour the breakers or ebay for something close and cheap. Diahatsu Matiz alternators are pretty compact and often come with a vee pulley.