Re: Amp gauge

[Bob Farrell <farrell@icdh16.dseg.ti.com>]

> 
> i know this is a dumb Question  but this just has not been my week so ill ask
> this Question so i dont Screw up something. Anyone know where the + wire goes
> from the amp guage??? obviously it is not to the + on the battery or for that
> matter anyswitch that goes directly to the Battery . 

But it does. The problem is what to do with the - on the Amp meter. To install
an amp meter you must effectively cut the wire going between the battery and
the load. One wire on the amp meter goes to one of the ends created by cutting
and the other amp meter wire goes to the other end. 

Normal auto amp meters do NOT measure current to the starter. The current is
just too large. If that is what you are really interested in then you will
need to get something like a 500 amp/50mv shunt and a suitable meter. 
(Electric autos use such meters, and suppliers of parts to people building
such vehicles would be a good source.)

If the question you are trying to answer relates to starting I would suggest
using a voltmeter. (Which coincidentally would be connected up in the manner 
you seemed to be describing for the amp meter.) Watching a voltmeter while 
cranking the engine would tell a lot. If the voltage drops to less than, say
8 volts, then the starter isn't turning over as fast as it was designed to and
the ignition spark is significantly less too. (Unless the coil had not been
saturating at 800rpm cranking speed at 12V, thus allowing proportionally 
greater current cranking at 400rpm. This is pretty unlikely because it would
mean only 1/10 the spark at 8000rpm when you are running.)  If you really are
having difficulty starting due to tight engine, high compression, heavy oil,
cold temperatures, etc, then the dual battery trick might work for you. 
In general, a small e.g. motorcycle battery is used to power the ignition 
while the main battery powers the starter motor. If due to heavy draw the 
main battery falls to 8 volts, it will not affect the voltage going to the 
ignition which will still be at 12V. The problem is how to charge the two 
batteries. Some system of dual regulators, diodes etc. must be employed 
so each is properly charged. For guidence on this look at charging systems for 
large boats which often have dual systems: one for running accessories when 
the engine is off and one for starting the engine. (If you leave the lights
on and run down the battery you can still start the engine using the other
battery.)

Bob Farrell



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