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Alternator voltage Low ?


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Defender 200 tdi 1993

I've had battery/alternator issues recently. After a night drive of ever diminishing headlights I had to jump start her the next day. After a long drive the battery was reading 12.8v but the alternator was only giving out 13.4 volts, a good volt or more short ?

I acquired a brand new 70 amp STC234 from Barry 4x4. After fitting it's only giving me 13.9 volts under slight revs.

Wonder if I should be expecting 14.5 volts and if so, ruling out the actual alternator what could be causing the drop ?

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Is the charge lamp working in the dashboard?

Does it illuminate before engine start and fully extinguish when the vehicle has started and is running?

It provides a series resistance to the altenator commutator to excite the commutator (basically provide a voltage plus current to energise it)

Check that it extinguishes under dim light (ie confirm it's gone out)

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Commutator should rear rotor (stood here with manual in hand in garage). Regulator controlled voltage says 13.6-14.4v

Manual says start engine and gradually increase speed at about 775 rpm the lamp should be extinguished

Hold speed at about 3000 rpm (6000. Alternator rpm) the voltmeter should read 13.6-14.4v. The reading should be steady

Let us know what you find

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I dont get the warning light at all at low revs. I think I got this occasionally with the old one but only recently when it wasn't delivering the volts !

We noticed yesterday that the wipers are now like normal wipers, before they dragged themselves lazily across the screen. Will try to get out tonight to test lights / heater all together.

I'm going to get me a voltmeter in keeping with the fuel and temp gauges on the dash. Any suggestions what to get and how to wire it so it's only on with ignition welcome.

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