REFLECTOR: Bus, Battery & Electrical Instrumentation

[michalk]

Yes, it matters, but the difference is probably not measurable.

Along the cable, current is always constant.  However, the cable has 
resistance, and the resistance along the cable causes a voltage drop. 
The more current(more loads), the higher the voltage drop.

Jim Sower wrote:
> Ooops - forgot my other question:  Does it matter if I measure right at 
> the B+ post on the alternator or at the Alt Relay on the firewall near 
> the battery?  I would think not, but then, closer to the battery might 
> damp out some of the ripple.  I don't know ... Jim S.
> 
> Wayne wrote:
> 
>>> Does anyone know of a simple way to detect out of bounds Alt ripple? 
>>> ... Jim S.
>>>
>> Now that you have reminded me  I used this technique for a quick and 
>> dirty power supply check on the equipment I used to troubleshoot.
>>
>> measure the output voltage of the alternator with a decent digital 
>> meter set to AC volts. The ripple should be  fairly low. The DC 
>> component will be ignored by the meter due to the AC coupling to the 
>> meter.
>>
>> Record in your logbook the value when your system was new and in good 
>> operating order under various load conditions. You should have a good 
>> clue because the ripple will jump up several hundred millivolts  (for 
>> a 12 volt system)  when a diode craps out.
>>
>> Wayne
>>
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