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MG MGB Technical - Voltage Spikes

I just installed a voltmeter, which I calibrated with my multitester, and it's showing that my system occasionally jumps in voltageup to 16 and above. Doesn't seem to be hurting anything.

Will this cause damage?

Why is it happening?

How can it be corrected?
Dan Hiltz

If you have a generator it is likely the regulator, the same goes for an alternator but they are less prone to this due to the regulator being electronic in all but the first year or two. An occasional short jump to 16 volts will not hurt anything but prolonged running at 16 volts will boil water out of the battery and may shorten the life of other electrical components.
John H

How much above? 16v is above the maximum for both dynamo (15.5v) and alternator (about 14.7v). If the voltmeter just flicks up then the actual voltage spike could be much higher, which would be more damaging than if the voltage goes up to 16v, steadies, and comes down again. Normally the battery damps any spikes, and indeed it is only the battery that holds the alternator voltage down. Without a battery connected, even with an internal voltage regulator, the alternator can go up to many tens of volts and blow all the bulbs. This is why a car must never be run with the *battery* disconnected. So if you are seeing a spike on the voltmeter either the battery is momentariliy disconnecting, either eternally or internally, or the alternator output is going very high and exceeding the damping capacity of the battery. If it is the battery or its connections this could reasonably be expected to also occur during cranking, making the alternator the likely suspect. But it could also depend on where the voltmeter is connected.
Paul Hunt 2

This thread was discussed between 05/09/2006 and 06/09/2006

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