Starter Voltage while cranking

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moparmade43

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Hey guys, 75 duster with a 416 stroker and new mini starter from 440 source. The car has 1300 miles since new engine and starter, and the starter started randomly clicking at times (pulled it out and contacts were bad). The starter/alternator "Guru" in our area said this could have been caused by a low voltage situation to the starter. It has since been rebuilt with good known contacts and plunger (probably originally was made in china i'm sure). Now, before I put it in, I checked the battery for giggles to make sure there is no low voltage issues, turns out it was 12.6 volts with the car sitting for about a week. I checked the end of the big starter lug positive cable, same voltage, 12.6, and the small lug wire when key is turned to start, 12.2 volts. So after I installed the starter, I checked it again. While cranking engine, the big lug at the starter showed 10 volts and the small lug showed 8 volts under load. Nothing else was using electricity except my msd ignition box. The car cranked fine, not like it was struggling or anything. So, my question to anyone who knows is, are these voltages under load what I should see at the starter, or are they in fact too low and could have been the culprit for my new starter's contacts failing? Also, the car has been totally rewired, so I don't have any crappy old wiring I'm dealing with. The main thing is I just wanna make sure that the starter is getting the appropriate amount of voltage under load so that it lasts this time. Thanks in advance
 
Battery is a year old, shows 12.6 volts after sitting all week. Also have a brand new starter relay
 
I have always used 10 volts as the lower limit under load. Some of the newer cars shut down the computer if the voltage drops to 8 volts.
 
If you have a trunk mount battery, power it runs up the body, thru the ground strap between the engine and body. In general, I would have 2 gauge wire for high amp connections (juicing the starter). I would have a 2 gauge wire to a shiny clean heavy thick part of the frame unibody bolted with a clean sanded bolt (or engine block if batt under hood), lead batt terminals and post clean, connection between neg cable and batt terminal done right and sanded shiny. Then move to positive wire, run a 2 gauge from batt to the starter relay and a 2 gauge from the relay to the starter, again all clean wire brushed connections in mint condition. Voltage drop is just resistance in the power wire or in the connections. The larger the conductor and the better the connections, the less voltage drop. Fine stranded copper works better with DC. With a large enough conductors (2 or 0 gauge) and pristine the connections, you should see very little voltage drop. Here is something to check: volts at battery during start (cranking), then volts at starter motor during cranking, theres the voltage drop. My last remote battery had 2 gauge for positive and negative battery leads. Neg went to frame in trunk. Then from frame in engine compartment to block (2 gauge as well). All connections points were sanded bare, connected tight, then a coat of anti-sieze over them for oxidation prevention. Frigging engine had 10.25 to 1 and spun like 300 rpms on the starter.. With this arrangement you should see about 1.15 - 1.22 volts drop from battery terminals to starter motor assuming 200 amp starter load during cranking. Your system has some loss in wiring and connectors currently.. Or the dang battery is shot (volts at battery during cranking are like 10 or drop to 10 or 9 quickly) Start testing by charging battery fully and having it tested at Autozone or with another load based method.. My two cents.
 
Battery Testing can be done in more than one way. The most accurate method is measurement of specific gravity and battery voltage. To measure specific gravity buy a temperature compensating hydrometer, to measure voltage use a digital D.C. Voltmeter. A quality load tester may be a good purchase if you need to test sealed batteries.

For any of these methods, you must first fully charge the battery and then remove the surface charge. If the battery has been sitting at least several hours (I prefer at least 12 hours) you may begin testing. To remove surface charge the battery must be discharged for several minutes. Using a headlight (high beam) will do the trick. After turning off the light you are ready to test the battery.

State of Charge Specific Gravity Voltage
12V 6V
100% 1.265 12.7 6.3
*75% 1.225 12.4 6.2
50% 1.190 12.2 6.1
25% 1.155 12.0 6.0
Discharged 1.120 11.9 6.0

taken from http://www.batterystuff.com/tutorial_battery.html
 
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