Hi,

Having problems with my generator. Measured it yesterday as Haynes suggested at my voltmeter gave 0 volts . The brushes are new, cleaned it, communator/armature seems ok to me and bearings ok.
I also polarized the generator by fitting a cable from battery + to the 51 terminal in the generator. It started to spindle but the wrong way(compared to engine rotation?

Couple of questions:

1. How do I measure the resistances and which ones?
2. Where do the generator get the ground? I painted the body, can it cause failure.

Like to be 100% of the working before ordering a new one etc..

I would be glad if someone could answer and expain the process :worship:

Jake,

Go to this link for help in checking your generator out.

http://nls.net/mp/volks/htm/gen.htm

John

and here for some technically thingies, you know, numbers, graphs and stuff ...

https://www.fiatforum.com/500-classic/304719-generator-question-500n-1958-59-a.html

Chris

Aaaargh.. Fitted new generator and electronic regulator. The light is still on whole the time?? What, and with the original regulator it goes off at ~1500 rpm. What is going on now, just dont understand. Can the battery be a problem. Shouldnt the regulator work with this genererator.
The generator works well, measured from battery.

Help!

Hi Jake,

I've just put a document together for The Hobbler to try and help him fix his ignition light problem. However he has got a 500L with a 126 Alternator engine so what I've done won't apply, however if it's worth it I can write one for a Dynamo (Generator) equipped car.
I notice on your posting you say you've painted the engine. This can have a major impact on the Dynamo as the current return is through the metal body of the Dynamo in contact with the earthed engine body. The two terminals on the Dynamo are the positive output (Terminal 51) and the field winding connection (to magnetise the armature) on terminal 67. The Ignition light is basically connected between the Dynamo output (Terminal 51) and the battery positive and comes on when the voltage difference is higher than about 6V. When you turn the ignition key before you start the motor you get 13V from the battery on one side of the ignition light, and a near earth (there is the field coil resistance in series) on the other side so the bulb is fairly bright. Once you fire the engine up, the output from the dynamo is basically the same as the battery (if the regulator is doing its job) so the bulb goes out.
Hope this helps
If you do need a deeper explanation I can put the document together.
I don't have a Fiat 500, my son has (MATTGIBSON) so if I'm talking tosh let me know
Richard

<p>thanks richard. The engine covlings are only painted. Not blocks. Noticed that the generator body is painted black. Should i remove paint somewhere?</p>

Hi Jake;
I can assure you that 'Mattsdad' is NOT talking tosh--the advice sheet that he gave me, along with some input from one of my ex work-mates (who is a more than competant auto-electrician) seems to have sorted the problem. I am going to give the car a bit of a run tomorrow; I will do a progress report after the run.

Hi Jake,

the problem I have is that I don't own a Fiat 500 (mines an MGB) and Matthews is an alternator 650 engine, so I have no physical experience of the Dynamo earthing arrangement and the Haynes manual that matthew gave me to help sort his electrical problems out isn't clear on how it's bolted to the engine so Im flying blind.
Put your test meter on its lowest resistance range (200 ohms ?)
Put the neg test lead on the Dynamo armature nut that retains the pulley - this is nearly always earthed to the dynamo body through the bearings.
Put the pos test lead on a nice clean bare metal part of the engine (mounting bolt, spark plug body etc)
The resistance should be less than 1 ohm - if higher you need to ensure that metal to metal contact between dynamo and engine is clean.
If Tom thinks I'm not talking tosh I'll write up the document but for a Dynamo. It'll be tomorrow at the earliest though.
Richard

Ok,
Thanks guys! Ill visit the garage today, lets see. Keep you up with this.

MATTSDAD said:

If Tom thinks I'm not talking tosh I'll write up the document but for a Dynamo. It'll be tomorrow at the earliest though.
Richard

Click to expand...

Richard,

If you don't mind and have the time, I for one would like to see your analysis of both the generator and alternator.

I found the windscreen wiper diagrams very useful - much better than my rather amateurish scratchings and given that we are dealing with Italian cars that are renowned for electrical gremlins, your tutorials will be very valuable.

In my experience, most of the problems are due to inadequate earth connections. The Italians seem to think that paint and rust are conductive

Cheers,
Chris

Hi,

Got the dynamo measured. Measured the dynamo like haynes says. At idle speed maybe 1000-1100 voltmeter gave 0.9V. Abit more revs 1500rpm it gave 6-8 volts. Should give 15 like haynes says?
So the generator which should be re-conditioned is not working right?
With all wires connected I measured from the battery and idle speed 12.3v and maybe at 2000-2200rpm the volts starts rising(this point the generator light goes off) and from this it goes right to 14.5V when I accelerate.
One question. Where does the generator get earth? Through the body or??
Or can this cause this, I cant figure anything else. All other wires are right.

JakeF said:

One question. Where does the generator get earth? Through the body or??

Click to expand...

Jake,

There is a large braided earth strap that connects the generator casing to the body of the car - this is the earth return for both the generator and the engine itself. The front and rear engine mounts effectively electrically isolate the engine/transmission and a low resistance connection is required.

The generator and engine should also be in good electrical contact through the (unpainted) generator casing and the (unpainted) mounting bracket on the side of the engine itself. As Richard has written, the resistance from generator to engine to car body should be very low - likely a fraction of an ohm.

Chris

Chris and others what do you say about this:

Measured the dynamo like haynes says. At idle speed maybe 1000-1100 voltmeter gave 0.9V. Abit more revs 1500rpm it gave 6-8 volts.

Click to expand...

Is this the problem?

Jake,

According to the information that I have the cut-in speed (the rpm at which the generator is producing 12V) is about 1800rpm. Below that speed it is not going to produce much voltage.

The standard output curves are load curves and map rpm against current produced at constant voltage and variable load. That is, at each speed you adjust the load using a variable resistor wired between the generator out (51) and ground (the casing) until the voltage reads 12V and then measure the current produced. I've never seen a voltage vs rpm curve and I think that there may be too many variables in your experiments to get an accurate voltage reading, though I may be wrong. Richard will know.

My own experience with generators is that they either produce enough voltage or none at all. When none, they are usually have very worn brushes or are badly damaged or burned out etc.

Chris

Hi Jeff,
I was going to say that your problem could be down to 2 problems
Armarure not magnetised
High resistance between Dynamo body and ground.

I then noticed in your first statement you say that you polarised the dynamo by connecting terminal 51 to the battery. I've just got hold of a Fiat handbook (my own car is an MGB) and it shows Terminal 51 is the output coil - that's why it has a thick wire.
Terminal 67 is the Field coil (thisd is a thinner wire) which goes around the armature. It is this that should be "Flashed" to +12 Volts.
When you "flash" the field winding (the coils that spin round on the armarure) it produces a DC current which magnetises the Ferromagnetic armature core, whch because of it's ferromagnetic properties retains a magnetic field (magnetic remnance).
When the Car is first started, it is this residual magnetic field whiich kick starts the dynamo into generating a DC output.
I believe you need to "flash" terminal 67 although you might want to check with a Fiat 500 expert on the forum.
Disconnect terminal 67 (leave 51 on the Dynamo).
Connect a jumper lead to terminal 67.
Now touch this momentarily against the live feed to the starter solenoid (warning - always connect the "dead" side of a wire first otherwise you're holding a "live" wire in your hand and if this touches the body work - BANG !).
When you take the lead away from the live feedafter "flashing" the terminal there should be a small blue flash (the back emf produced when the armature magnetic field collapses).

Now reconnect terminal 67 and give her another go at starting.
If there's still a problem we'll look at the earth return path.
Take care when working on live unfused circuits (Battery/Starter/Fuse Feeds etc).
The other thing is when you take measurements always take them from a good earth point. The only "true" earth is the battery negative post but if this is not handy then the engine block.

Good Luck
Richard

Hi Jake,
sorry but I need to clarify what I said in my reply above.
Because I've worked on Alternator cars so long, I've put the Magnetic field being generated in the rotor (which it is in an alternator) - and its the fixed stator that produces the output voltage.
With a dynamo its the reverse, the spinning armature generates the output voltage via the brushes on the commutator segments and the energising Field windings are on the Stator. Otherwise what I said is OK re enegising the Field coils. Next time I'll read it before I post the reply
Sorry to cause confusion.
Richard

Jake,

I dug out my old generator mounted it in my vice, attached the impeller and wired it up according to the diagram below to test it as a DC motor.

With a 12V supply and under the load imposed by the impeller, it drew 5.46A which is within the tolerances quoted (5.0A +/- 0.5A) though I'm unsure of the rotational speed.
The voltage under load was 11.8V - close enough to 12V to give valid results.

This is the simplest test that you can do and does give you valuable information.

Chris

PS: I restored this generator with new bearings, new brushes, a thorough check over and clean, so I know it's OK.

Thanks chris!
I dont know if I have tools for this and understanding about the connections, dont even know what is a impeller? I have never understanded very well any electrical stuff.

But, I would be more than grateful if someone with a dynamo(230W) equipped 500 could take the readings straight from the dynamo terminals at idlespeed and at ~1500rpm. The voltmeter red to the dynamo +terminal and voltmeter - to earth.
I got 0,6-0,7 at idle speed and 1V 1500rpm. Just worried about these ones, sound so low.

Jake

Sorry Jake - I didn't mean to confuse or annoy you.

The setup is quite simple but in light of your comment, maybe a trip to the local friendly autoelectrician is in order.

Chris

Hi,

No worries chris you are only helping!
I am still strugling with bloody generator!
If someone could measure the volts from the generator i would be grateful.
One question, does the dynamo charge the battery at idle speed(or low speeds)? I have been told that in the regulator place 30 controls the charging, an on/off switch and switches the generator off at low speeds?
And how does the light work if it is not charging? Dont understand?