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Old 31 January 2012, 10:17   #11
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It sounds to me as if the insulation of the alternator coil is breaking down under load.

Does the voltage also fall if you increase the engine speed under no load?

Take it up to, say, 4000 rpm and measure the voltage.
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Old 31 January 2012, 10:32   #12
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also put the meter on to the AC setting and see if there is any AC voltage there.
if there is then the regulator is not working. ( rectifer breaking down)
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Old 31 January 2012, 11:37   #13
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Other one to check is the main isolator. Considering what they do and what relies on them to work, they have to be the least waterproof switches ever designed.....

I now carry a short jump cable and have two spare nuts on the switch terminals after having two failures.
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Old 31 January 2012, 14:54   #14
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Originally Posted by jezza2011 View Post
also put the meter on to the AC setting and see if there is any AC voltage there.
if there is then the regulator is not working. ( rectifer breaking down)
+1
Start at the alternator itself before the rectifier and voltage regulator (which are often one epoxy potted unit anyway). I don't think this is a cabling issue. But basically I would start:
1) AC voltage across alternator output
2) AC amps at regulator output
3) DC voltage across rectifier-regulator output
4) DC amps at regulator output
5) DC voltage at battery posts
6) DC amps at positive battery terminal
7) Then DC amps at return points to alternator again.

The amps are small enough you should be able to check both the voltage and then disconnect the positive cable and check the amps at each point. But check that your meter can handle the load. Clamp the meter leads to the disconnect lead with pliers. If your meter can't handle the amps you can get one of the wrap around types to check amperage.

I would have all the other loads turned off for this demo.
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Old 31 January 2012, 15:28   #15
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Based on the assumption that all connections are clean and performing well can I ask what method was used to test the battery? If this was not a high rate discharge test your time was wasted (assuming it is a lead acid battery and not GEL filled) if not this is you first action.

At low rpm high alt output is normal and as the rpm increase it can drop off but never below nominal battery voltage. In essence you either have a battery which has a open circuit (internal fault) or an alternator fault.
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Old 31 January 2012, 17:46   #16
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Fellows Swabs

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I wonder is this the culprit !!!!!

Was about to start stripping out cables to check condition and found this

Will fit new connectors and see what happens ,fingers crossed cheap fix hopefully

Will post results

Many thanks for all reply's

Ken

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Old 31 January 2012, 18:38   #17
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On the face of it, it doesn't look too bad, but the join between the copper and the connector has to be tiptop. I had a day out ruined by an old crimped connector with a seal on it. It looked and felt fine, but the join was poor and reduced the current to the point where the starter wouldn't turn. After that I started packing spares and a bolt for joining cables
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Old 01 February 2012, 11:32   #18
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Other one to check is the main isolator
Battery switch? Never had a problem with mine (though to be fair, it's in a fairly dry location.)

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Old 01 February 2012, 11:44   #19
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Ken
get a new pair of connectors the difference will be marked. You have to have good surface contact.
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Old 01 February 2012, 12:37   #20
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Attachment 65311

Attachment 65312

I wonder is this the culprit !!!!!

Was about to start stripping out cables to check condition and found this

Will fit new connectors and see what happens ,fingers crossed cheap fix hopefully

Will post results

Many thanks for all reply's


Ken

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Solder the cable in as opposed to crimp!
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