Dynamo and (Lack of) Control Box

[silloyd]

So here's the situation:

• I have a Dynamo with a Control Box - Dynamo is refurbed and Control Box is new
• Dynamo has been checked and is fine
• Control Box has been set up using instructions in the MM Owner's Manual and checked against an old 'Lucas Generator and Control Box Tests' document that I found on t'Inter-web
• When I start the engine the needle on the Ammeter shows a small charging effect of approx. +3 to 5A (Battery is relatively new, in good condition and well charged, so wouldn't expect much additonal charge anyway). Rev the engine slightly and charge level fluctuates upwards, as you would expect
• But shortly after I start driving the charging ceases (Ammeter falls to '0' or just below depending on the load) and won't start again until I stop and restart the engine - not sure exactly when it fails, as my eyes are firmly on the road/surroundings

I've re-checked the Dynamo and Contol Box several times and all seems to be as per the book, therefore I'm flummoxed as to what is going wrong here.

Before I give up in despair and switch to an alternator set up, has anyone got any sensible thoughts on what might be going wrong / tests I can carry out / how I can fix it please?

[bmcecosse]

The battery is charged! What happens if you switch on the headlamps - does it hold the 'zero' position ok ?

[silloyd]

Thanks for the response.

Turning on electrical devices (that take a reasonable current), such as the headlights or indicators, causes the Ammeter to drop below zero whilst they're on, indicating a discharge. I can also see the Ammeter flick south of zero each time the fuel pump ticks.

Once the charge current has dropped to zero, it never heads north again until I stop and then restart the engine.

[bmcecosse]

Well - I think you just need to adjust up the charge rate slightly. At a fast idle it should run the battery at ~ 13.8 volts. -and then with headlights on - it should not drop much at all. Are the A and A1 terminals connected correctly? ie Brown to A and Brown/Blue to A1.

[silloyd]

Thanks for the response and apologies for my delay in replying.

Cables are conencted correctly.

When it was charging the voltage was fine, the problem is that it would then drop out completely.

I've sinced adjusted the cut out threshold (away from the conditions for the static test in the manual) and it seems to be cutting in/out with engine speed and hold the current flow, even with load.

Looks like I may have been following the instructions a bit too literally, rather than compensating for the real world but will keep a good eye on it until I feel more confident that it's sorted.

[bmcecosse]

Good result!