Why does the red "No Charge" warning
light stay on?
Dr Andy Klava (Woodcote Green 0532) from Yorkshire was
puzzled why his warning light was staying on after a cold start
and posted a query on the V8 Website bulletin board. Brian Moyse
posted a reassuring reply. (Feb 03)
posting from Andy Klava said "I have noticed from
cold starting that once the engine has started on my RV8, the red
"No Charge" light on the dashboard fails to go out unless
the engine is rev'd. Initially I attributed this to the alternator
belt but the problem still persists despite it being changed. Once
working or when warmed up, charging and alternator function is good.
Any ideas as to why this happening? Could the alternator be at fault?"
Charge" warning light is marked (7) above. (Sketch: MG Rover)
to Contents listing
On page 69 of the
Instruments section of the MG RV8 Owner's Handbook AKM7144ENG
there is a note. "NO CHARGE - The light extinguishes when the
engine is running. If it remains on, or illuminates whilst driving,
a fault is indicated. Seek qualified assistance urgently." But
there was no mention of why the light might come on in this case or
whether it might be a sign of an alternator malfunction. Fortunately
an RV8 member was on hand!
Brian Moyse (Woodcote Green 1714) from Surrey posted a response
saying "my UK specification RV8 has exactly the same characteristic
and although at this point I cannot give you a full technical explanation,
this is a feature of the operation of the electronic voltage regulator
unit built into the alternator which controls the "No Charge"
warning light and is not a problem. The alternator output voltage
has to be above a certain threshold level (programmed into the electronics)
before the warning light will extinguish. Immediately after starting
the engine, the battery/alternator output voltage is depressed as
the battery is taking additional load from the alternator to replace
the energy expended by starting from cold. By revving the engine a
little, the alternator output voltage rises above the threshold level
and the warning light extinguishes. We used to get a similar effect
in the good old days of dynamos - remember how the warning light often
came on at tick-over?"
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