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Author Topic: Wire Size for Alternator??  (Read 7234 times)
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« Reply #15 on: January 31, 2008, 11:12:48 AM »


I would say you are correct, the voltage at the battery does prove you are getting the correct voltage out of the alt.  For your installation, that is.  Your alt may be adjusted to make more V than normal so it compensates for your configuration losses.  I would still relocate the Sense line to the bat because as your system changes, the alt will always get the bats what they need.

You can evaluate your "line loss" very easily.  Put one terminal of a volt meter on the battery + terminal and the other on the device you are powering at its input + terminal.  The voltage measured is your loss.  With a high current item like a inverter powering a AC you would expect to see a volt loss.  If you are not registering a loss of more than a volt you can't improve things much by installing bigger wire.  Also, measure the voltage across the device and make sure that you are getting the full bat/alt voltage...~14.1 with the engine revving.  Do the voltmeter thing from the neg terminal of the bat to the ground stud of the device and this will reveal the line loss in your grounding circuit.  Don't make these measurements from connectors like the battery clamp or the connector attached to the device....get on the bat term and  on the device frame or +stud.  You should intuit that if you verify all this and still have low output from the inverter you have a bad inverter circuit or the internal connections are bad.

Your bat isolator should drop .7 volts but the rest of the wire going from your alt to your bat should NOT be dropping more than a volt for you to be getting the max output of the alt.

To do this properly I should be giving you a diagram for each measurement with "connect VOM + to X and  Y.....".  Low voltage DC can be very tough to diagnose....sometimes.  The voltage you see on the washer may not be the same as the voltage you see on the stud or nut or the wire going into the connector....it gets that basic.....when nothing seems to work or make sense.  I once resolved a problem with a neighbor's Suzuki that would power up his instruments but wouldn't start.  Not even grunt.  He worked on it for a week after work and Sat without success.  He had taken that rotary engine out of the frame for some reason so he had been into almost everything.  He was meticulous and a very good DIY mechanic.  The problem I found was that he had put LockTite on the bolt that screws into the engine block and connects the bat ground.  You couldn't see any blue on the terminal and to all the world it looked like a bolt to ground....how could that be bad?  I found it by striking a 14 gauge wire from the bat+ to the bat neg...spark.  Bat to neg cable,,,spark.  bat to other end of ground cable....spark.   Bat to engine block...no spark.  Then a wondering look on everybody's face.  My question was " did you put anything on that terminal before you tightened that bolt?  Answer:  No!  Aw crap!  That F***ing LockTite.  If you think this is me bragging....you missed the point.

Listen to the Force, Luke.   And, put silicone dielectric grease on every connection always if it is low voltage DC.

Hope this helps you improve the "quality" of your connections and circuit.


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