Technical Control Box

[fiat500]

There's not much on this Forum that discusses issues with the control box and maybe that's because:
1. They are very reliable.
2. Many people have changed to an alternator.
3. They are old technology and seem quite daunting.
As mine is allowing 17+ volts from the dynamo at the moment, I had to do something. I have ordered a shiny new electronic one, which is less than £20
so I have nothing to lose by messing with the old one.
I have read that these things do actually require maintenance whereas I previously thought they were "plug and play", "fit and forget".
This one didn't even come off the car during the restoration and must have sat there untouched for 47 years; so pretty reliable.
MAL_7487 by Peter Thompson, on Flickr
The securing and terminal screws came out easily and under the cover it looks like new.
MAL_7483 by Peter Thompson, on Flickr
I have cleaned all the points contacting surfaces using very fine abrasive paper.
It seems that in order to increase or decrease the maximum voltage output of the dynamo I need to bend the metal support on the left hand regulator mechanism such that it increases or decreases the tension on the leaf-spring bearing on the moving contact.
MAL_7482 by Peter Thompson, on Flickr
It seems simultaneously, a very crude but very clever method which I will try once I have checked if simply cleaning the points has helped.

 

[g8rpi]

There's not much on this Forum that discusses issues with the control box and maybe that's because:
1. They are very reliable.
2. Many people have changed to an alternator.
3. They are old technology and seem quite daunting.
As mine is allowing 17+ volts from the dynamo at the moment, I had to do something. I have ordered a shiny new electronic one, which is less than £20
so I have nothing to lose by messing with the old one.
I have read that these things do actually require maintenance whereas I previously thought they were "plug and play", "fit and forget".
This one didn't even come off the car during the restoration and must have sat there untouched for 47 years; so pretty reliable.




MAL_7487 by Peter Thompson, on Flickr
The securing and terminal screws came out easily and under the cover it looks like new.
MAL_7483 by Peter Thompson, on Flickr
I have cleaned all the points contacting surfaces using very fine abrasive paper.
It seems that in order to increase or decrease the maximum voltage output of the dynamo I need to bend the metal support on the left hand regulator mechanism such that it increases or decreases the tension on the leaf-spring bearing on the moving contact.
MAL_7482 by Peter Thompson, on Flickr
It seems simultaneously, a very crude but very clever method which I will try once I have checked if simply cleaning the points has helped.

Hi,
Cleaning the contacts may well fix the issue. That one looks like it's not intended to be maintained. Some have adjustable contact gaps or spring tension, but the only means on that one is bending bits which can be a bit hit and miss. They are a very cleaver bit of electromechanical engineering. I have fitted electronic replacements into old cases in the past to maintain the original appearance.


Robert G8RPI.

 

[fiat500]

Hi,
Cleaning the contacts may well fix the issue.
I have fitted electronic replacements into old cases in the past to maintain the original appearance.
.

Thanks Robert. I hope the cleaning will work.
They are meant to be adjustable but given the palava involved, including pre-heating in an oven for thirty minutes...and then you have to quickly install it in the car! I think it would be as vague an outcome as you say.
If I end up using the electronic one, and as it looks like it fits the same studs, I'll just replace it without disguise. I'm known for liking my old bits as found, but I don't preclude honest replacement with non-original parts when it is done for reasons of practicality and reliability which leads to my continued "stretching" of the car's ability.

 

[Bambino]

When I rebuilt my engine, I replaced the dynamo with an alternator and used the old control box as a connector. Like you Peter, I removed the cover to find a near pristine innards which I carefully removed and stored.

To my knowledge it was still performing as intended when I gutted it.

Chris

 

[fiat500]

The status quo has been restored.
I don't have crocodile -clips for my electrical tester which makes it awkward to do all the "book" tests now the cleaned control box is back in place. But with my now increased, but still minimal understanding of the thing I did what I could.
The bottom line is that the output at the cut-out terminal doesn't fluctuate when it's all connected up to a fully charged battery. It's at 12.36v and the same at the coil.
The actual output at the dynamo is running slightly above 15v, but taking into account the special conditions of temperature for the official test procedure that may be OK.
I need to get the car nice and hot and have a good read of the Haynes book and then do some more precise testing now the main panic is over.

 

[jjacob]

Peter,
With a fully charged battery, and the engine running at 2000 rpm you should see 13.5 volts at the battery. If you only have 12.4 then you are not charging the battery. With a drained battery the voltage should not exceed 14.4. So depending on the state of charge of the battery you should see 13.5 to 14.4 volts.
Output at the generator is OK. Purpose of the voltage regulator is to control the voltage supplied to the battery and the rest of the vehicle. This is why you never run an engine without the voltage regulator connected. Output from a generator or alternator can go very high unregulated.
John

 

[fiat500]

Doh!

 

[g8rpi]

If you have 15V at the Dynamo and 12.xx at battery either the current or cut-out contacts are not making (or you have a bad connction). Check the contacts on the two "relays" with the thick wire.

Robert G8RPI

 

[fiat500]

If you have 15V at the Dynamo and 12.xx at battery either the current or cut-out contacts are not making (or you have a bad connction). Check the contacts on the two "relays" with the thick wire.

Robert G8RPI

Robert, spot-on
I have just read this after returning from a cold, dark and blustery garage where I was determined to sort it out. I have a new electronic box on the way but the learning of this Dark Art is very satisfying.
The steering-wheel had perfectly obscured my view of the ignition light and it was only as I sat warming the engine that I noticed it behaving erratically. Obviously this was related to me messing with the points, and by encouraging the cut-out to close manually that part of the problem was sorted.
But now I was back to having 16 and 17 volts at the generator. I tweaked the spring post on the regulator downwards to reduce the tension. This is not easy to do, in-situ with the precision needed and I went too far and needed to gradually bend it back by extremely small amounts until finally I hit just under 14 volts which can be seen as slightly less at the battery. I think I need a little more voltage although I do a lot of runs so it may be acceptable if it stays consistent.
I am loathe to tweak any more as it really is an infinitely precise job where I can easily end up back where I was.
At least I am confident that I can get in a local journey tomorrow and on Christmas Day and most likely I will fit the new one for peace of mind and reliability when it arrives in the New Year.
Thanks to both of you for the guidance and observations.
Merry Christmas.

 

[g8rpi]

Hi,
Just under 14V should be OK for an older car with no electronics. The "old" voltage setting was 13.8V. This has risen over the years to between 14 and 14.4v for modern cars, but with temperature compensation and other refinements. They used to make special tools for adjusting these they looked like a screwdriver with a bent and slotted end or a small bicycle tyre lever. They had different angles for increasing or decreasing the setting.

Happy Holidays,
Robert G8RPI.

 

[fiat500]

The New Year's resolution was to mess about even more with Fiat cars and to post even more to the Forum. So the first job was to fit the electronic regulator which arrived yesterday.
It needed the top corners of the aluminium backing panel to be trimmed so that I could use the original rubber drip-cover, but otherwise it was a direct swap for the old one and fits perfectly but looks a bit insipid.
Annoyingly it doesn't come with new screws and washers but the old ones transferred easily.
There is a much more distinct cut-off point to the charging now and co-incidence it may be, but the car started from cold after three days in the garage with less hesitancy than usual.
At around £15 from AG it seems great value and I will hold onto the original, in careful packing and storage, so that any originalista who may come to own it in the future can always replace the old item.

 

[F123C]

Peter,
With a fully charged battery, and the engine running at 2000 rpm you should see 13.5 volts at the battery. If you only have 12.4 then you are not charging the battery. With a drained battery the voltage should not exceed 14.4. So depending on the state of charge of the battery you should see 13.5 to 14.4 volts.
Output at the generator is OK. Purpose of the voltage regulator is to control the voltage supplied to the battery and the rest of the vehicle. This is why you never run an engine without the voltage regulator connected. Output from a generator or alternator can go very high unregulated.
John

Where dynamos are concerned, IIRC, there also used to be a test for dynamo condition where the F and D (or +) wires were disconnected at the dynamo and the engine then run. If output was c. 3 volts, dynamo was considered ok. Afaik this test relied on there being residual magnetism? in the field winding pole shoes? [ Haven't done this sort of work in 40 years, so memory is a bit hazy!, I'll try to look it up next time I'm up in the loft (my library!)]. There was also a test for dynamos called a 'motor test', don't be tempted to try this with an alternator....

 

[g8rpi]

Where dynamos are concerned, IIRC, there also used to be a test for dynamo condition where the F and D (or +) wires were disconnected at the dynamo and the engine then run. If output was c. 3 volts, dynamo was considered ok. Afaik this test relied on there being residual magnetism? in the field winding pole shoes? [ Haven't done this sort of work in 40 years, so memory is a bit hazy!, I'll try to look it up next time I'm up in the loft (my library!)]. There was also a test for dynamos called a 'motor test', don't be tempted to try this with an alternator....

Hi,
That is correct. The purpose of the check was to ensure there was enough residual magnetisim to allow te dynamo to start up. It also checks that the polarity is correct. The mechanicl regulators are not polarised so you could net negative voltage if the residual magetism was wrong.
The cure for weak residual magetisim was to connect a battery directly to the dynamo field terminal with the engine stopped. This is known as "flashing the field". A dynamo will act as a motor if both the field and armature are energised but care should be taken if trying this as it can damage the motor. I'd at least put a headlamp bulb in series with the field winding.
It may be a surprise to many that many modern gas turbine engines (turboprop and helicopters) like the PT-6A still use dynamos. This is because of the motor effect. The same unit is used for both and starting and generation. Not surprisingly they are called starter generators. A typical rating is 200A at 28V. Pistion engined aircraft use car type alternators and starters, large aircraft use air powered starters and 400Hz AC generators. The very latest designs "More Electric Aircraft" use AC starter generators (variable frequency) with sophisticated electronic control.
Robert G8RPI.