Battery Dead AGAIN!!!

R

Richard

Member
1977 SSII with 345 2bbl, headers, 727tf, trutracs front and rear.

Another question, what is the easiest way to test the 10s alternator for possible drain on battery? Is there a shade tree testing method? Not to be a stick in the mud, but I thought that I had "fixed" this problem a couple of years ago (apparently not). It is a basic setup, no aftermarket stuff or wiring. Battery is drained. Charging is good, around 14-14.5 when engine is running. Battery test show about 1/2 volt drop at battery posts when engine is running. Have checked all bh connectors, all good and clean. I am thinking that something is draining the battery, but can't narrow it down.

Any help would be appreciated.
 
Just so I understand your test. With the engine running you place one vom lead on the battery + post and one on the alternator b+ lead?
If not could you be more specific about how you determine 1/2 volt drop. I understand ir drop but need to know how you are measuring it.
Thanks

to test for an alternator that maybe draining the battery, disconnect the b+ and the 2 pole plug from your 10si. Charge the battery fully. With the key off and all electrical accessories off. Place your vom on current range 10 amp preferable and the test leads in the proper locations on the vom. It is normal to have to swap the red lead from volts/ohms to amps
test #1
plug the 2 pole plug in as usual and connect one vom lead to the b+ alternator stud (careful not to ground the lead) and the other vom lead to the free b+ wire ring terminal. The meter should read 0.0 amps of current flow. If so that test passed. If not replace the alternator. A few milli amps is totally normal as all diodes and transistors have some reverse current leakage. But no more then .02 mills.

Test #2
replace the b+ wire back to it's b+ stud. Using the vom in the same manner as you did for the b+ wire accept for selecting a lower current setting on the vom, test each of the wires in the 2 pole plug. You should remove the the wire to be tested from the plug housing and test them with the other wire connected normally. Again you should see no current flow on a properly functioning. A few milli amps is totally normal as all diodes and transistors have some reverse current leakage. But no more then .02 mills.
 
Last edited:
Well, darn good question!

I was testing with vm leads to + and - of battery. Didn't think to do it your way.
 
richard said:
well, darn good question!

I was testing with vm leads to + and - of battery. Didn't think to do it your way.
Click to expand...

So you are reading the battery voltage with the engine running. What is the 1/2 volt drop in referance to? Running you see 14.0- 14.5. Depenging on rpm that is perfect. At idle and with a load like a heater blower of lights switched on you will see a small drop if idling.
 
Thank you for the information, just so I understand this,

I am testing for current between the large threaded post on back of the alternator to each of the two wires of the plug ( test each one unplugged with the other connected, right?) and there should be no current at all between these, right?
 
B+ is the stud.

Remove the wire on the stud. The check for an amp draw between the the stud and wire you removed.

You can also remove one battery cable, set you meter to the 10a setting, and connect it between the battery cable you removed and the stud you removed it from. Make sure your key is off and doors are closed... Dome light.
 
richard said:
thank you for the information, just so I understand this,

I am testing for current between the large threaded post on back of the alternator to each of the two wires of the plug ( test each one unplugged with the other connected, right?) and there should be no current at all between these, right?
Click to expand...

Oh no. :eek6:
test each wire/connector to it's mating location on the alternator.

B+ wire to large b+ stud.
2 pole wires, wire 1 to terminal 1
wire 2 to terminal 2

and after the pinpoint tests on the alternator you can proceed to Scout-it-out's recommendations to find a system drain by going to the + battery post and checking for current flow when all things electric are off.
 
You must log in or register to reply here.
Back
Top