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A lesson in alternators from Classic Retrofit


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Jonny's latest Classic Retrofit tech video shares some interesting details on air-cooled Porsche alternator design and the failings accounted for in design and development of his high-output Porsche 911 upgraded alternators. It is a handy lesson for IBers - will be a big help to anyone who wonders where the alternator on their car is, for a start.

 

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Interesting topic Mr Hart. I experienced a regulator failure 200 miles from home whilst on route to a wedding in North London many years ago which was un nerving. I also was also loosely involved with a multi million pound Bosch alternator production line development in Madrid and UK. 

 

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3 minutes ago, Northy said:

@Jonny Hart Am I right in saying to run your air con on my SC I also need to run the uprated alternator?  Or is it just so the battery doesn’t get overwhelmed at idle when the air con is running? 

SC only has 75A unit.  Our ECU will limit the current to a settable amount, so you’d be looking at 60A to allow for the rest of the car to run and not drain the battery. It does this by varying the compressor speed. 
 

The compressor current requirement varies with ambient temp.   E.g. when we were at CLM sat in the town traffic, it was 35C and the compressor was using 75A.  On a 25C day it might only use 55A to achieve the same cooling. 
 

In the CLM scenario with a 75A alternator, the ECU would have slowed the compressor down to limit to 60A and the cooling would have been reduced.  

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I recently replaced my SC alternator recently with the WOSP LMA033 (https://www.amp-starters.co.uk/WOSP-LMA033---Porsche-911-Mounts-in-fan-Alternator__p-36352.aspx)

The output is only 90A but plenty enough for my car and about half the cost of the higher output replacements. So far, works fine and no issues with not being able to run everything.

Currently on offer at AMP Starter Motors (no affiliantion) for £280 with free delivery.

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