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1300 FWD Control box rating


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Can you advise me?

I bought a new control box for my 1969 1300 TC. It is in my car now and performing well.
However. By mistake, I bought a 25Amp model instead of a 22Amp.
Will this overheat the commutator on the dynamo at high rev's?

Thank you!

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I reckon it'll be fine. I think the control box rating is the maximum dynamo output that the control box can handle. It can't drive the dynamo any harder than the dynamo will take. It might spend more time with the dynamo at full output but that's not going to damage anything with a 15% increase. And if it did overheat then it wouldn't be the commutator anyway - it would be the field coil, probably.

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well the control box should be matched to the dynamo as 25A is the maximum current that it will allow the dynamo to produce so if thats more than the rating of the dynamo it could overheat.

Its unlikely that your system is going to draw that much current except if the battery has become heavily discharged on starting then, as the engine revs increase, the dynamo will supply current up to the control box limit and until the battery voltage reaches the control setting.

Of course if its a problem the current setting of the control box is adjustable although I dont know over what range. In the manual it looks quite simple to do although would need a suitable ammeter...

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With just a 15% increase, and only in the danger zone with high demands, it should be OK then.
A high current at low revs can happen as well. I never thought of that.
I was just wondering if the charging limit is a setting that can be adjusted or that it is the current regulator bobbin having 2 windings less.
Maybe adjusting the cam could level out the 15% difference.
But for now, Ill keep it as it is. And keep an eye on it.

Thank you for your help.

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Yes I think you should get away with it.

The manual says to do the maximum current setting with the engine at 3300rpm so being able to produce this amount of power obviously depends on sufficient dynamo speed and field current. The procedure does sound a bit hairy as you have turn all the lights on while shorting the voltage regulating contacts so the system volts will rise to whatever they want. It also says in capital letters not to turn on any other lights during the procedure as it may blow their bulbs! 

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