Date:         Mon, 03 Apr 1995 14:49:00 +0600
Sender:       Vanagon Mailing List <vanagon@vanagon.com>
From:         anon869@vt.edu (Christopher Bridge)
Subject:      Re: Big Battery = Destroy Starter

>Derek Drew writes:
>> 
>> I was reading in the Bosch Technical Instruction booklet about Electric
>> Starting Motors and it says, "Blah, blah, blah... Starting systems are
>> designed to take into account a given voltage drop in the system. Therefore,
>> in order to avoid mechanical overload or overheating of the starting mtor, a
>> storage battery with more than the specified ampere-hour capacity must not
>> be used."
>> 
>> This raises the question of how to wire our auxiliary batteries. If you wire
>> two 12 volt batteries together, or allow them to connect together during
>> starting only as I have done, then it would seem you risk frying your 
starter. 
>> Hummm...
>
>Interesting... now that you mention it, I have noticed that voltage at the
>starter drops to 10 (or even 8) volts while the motor is cranking on my
>bus.  I thought this was not normal.  Still, if the starter is rated 12V
>then it should stand up to 12V.
>
>-David
The VW has a series wound DC starter motor.  This will draw around 160~205 
amps _while_  cranking your engine.  The reason the voltage drop is that the 
battery has a very small resistance which gives a substantial I^2*R voltage 
drop.  This article is total BS.  The amount of time your starter is on and 
cranking is so short, the starter should have no time to heat up.  How then, 
can you melt through some windings?  I might also add that the elevator in 
your local high rise also is most probably driven by a series wound DC 
motor.  Oh, BTW, the EE types also run locked rotor tests on these motors, 
like draw run up to 300 amps at 6 volts.  They don't burn up there either.  Ha!
  

  Chris Bridge
  
  ''71 Westy (Sportsmobile?)
  Favorite quotes:
  "Virginia Tech- yea, the best 5, or maybe even 6 years of your life."
  "They even throw in the stomach ulcers for free." 
  E-mail cbridge@vt.edu