overheating control box

[MikeB]

Hi all

I am getting near to the end of my winter refurbishment and have the engine back in the car and about to attach all the components, however one thing that I kept in mind before I started the work was the fact that I had charging issues just before I put her way for the winter, I am aware of all the testing procedure for the dynamo and control box and will be going through those as I restart the engine, however the week before I laid the car up I had an issue with the control box overheating whilst the engine was stopped, I could smell burning and found the control box smoking and the wiring coming out of the dash to the control box very hot, I immediately disconnected the battery, not a quick job ! (Going to fit an isolator before starting the engine again for the new season) once everything had cooled down I checked for any loose connections and generally tightened all connections down, the next time the engine was run the ammeter was showing overcharging in conjunction with engine speed changes, I then put her away for the winter refurbishment

Two clues as to what may be going on, ; When I bought the car the ammeter gauge had obviously overheated and melted the gauge face and did not work, I replaced it and did not have a issue with the replacement, IE correct charging rate etc. however after many runs out and having no problems , I put my hand on the wiring loom coming from the dash to the control box I felt it was very warm to the touch, so I made sure all the connections were tight at the ammeter, I can't recall it getting hot again until the issue with the smoking control box

Here is my question; obviously the ammeter is connected to the battery in some way and the fact that the old one melted there was obviously a problem with the wiring, however if the car is stationary with the engine off why would the control box overheat and smoke ? and what do I need to check /replace or repair to understand what is going on, poor earthling comes to mind, however I cannot blow up the wiring diagram large enough to see were all the earth wires are supposed to be, I intend to fit fused links to the majority of the component wiring to avoid any wiring damage going forward, however I am no expert

Any body had similar issues ? and feed back would be appreciated

Mike

[GOY189]

Given the problem, the question is when was the Wiring loom installed. If it is original, It is at least 70 years old and a sensible course of action is probably to replace it. In any case
It is good practice to install fuses for the individual circuits, either in line or in a separate box.

High current draw items such as horns, Headlamps etc are probably best controlled via relays.

Hope that this helps

Mike

[David Bliss]

If you have had the regulator cutout stick this will cause the 30+ amp discharge when you turn the engine off. If you have an ammeter and have noticed that this has gone into full discharge immediately restart the engine, this should bring the discharge down to zero. If you are unlucky when you turn the engine off for the second time it may stick again, you then either have to disconnect the battery quickly or disconnect the battery with the engine running, however there can be a problem with this method as the generator can sometimes keep the ignition side alive in which case the engine won't stop and either you stall it or turn the ignition off. I am a great believer in a battery safety switch, often I don't bother to put this on the heavy duty battery cable side but fit it between the positive or negative feed side that goes to the regulator and ignition switch. This can usually be fitted to be easily accessible from the drivers seat. Many of the early cars had fuses on the dynamo circuit so, if there was a short in the charging side, it would blow. For some reason when they changed to a voltage regulator unit most cars were not fitted with this fuse. This seems to be shortsighted since if a regulator unit sticks it could be damaged beyond repair, and this might not do the dynamo a lot of good either. In my lifetime I have had two instances when fan belts have broken and the cut-out has failed to cut out, this normally doesn't cause any damage since the dynamos will motor until the battery is disconnected. When there has been a short in the dynamo while the engine is running the cut-outs will stay together, in this case the battery needs to be disconnected very quickly to avoid damage to the wiring.

Until I had a car with one of the very early electric starting and lighting setups I hadn't realized that technology had gone one step forward and two back. The early dynamo on my car is a two brush one and is self regulating, it will put out a charge up to its maximum continuous output then not climb any higher, as the battery voltage climbs the charging amperage will drop automatically. It does this without the complication of of a third brush that dynamos in the 30s often had, or the later regulator units which were fitted and did the same job as the earlier third brush dynamos. Why didn't they just keep it simple?