Starter Voltage When Cranking
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Logistics Pro
Joined: Mar 2010
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From: NC
Starter Voltage When Cranking
I am trying to see if I have a developing problem with my starter. I am seeing battery voltage when cranking at 32 degrees at minimum of 9.5V, at 40 degrees yesterday I was at 10.2. The batteries tested good and once running my 110 AMP alternator does get to 13.8-14.5 when the glow plug cycle ens. A 185 alternator is on my bucket list.
Is my starter pulling too much or is it good?
Is my starter pulling too much or is it good?
Posting Guru
Joined: Nov 2012
Posts: 2,123
Likes: 5
To me this would be a marginal system. Not really bad but not really good either.
A lot would depend on the amount of time for the system to recover. I would start draw down tests on each component individually trying to isolate the heavy draw.
Even at your ambient temps I seldom see much more than 10v drawdown with a quick recovery. Ambients do play a big part in all this so could be deceptive.
A lot would depend on the amount of time for the system to recover. I would start draw down tests on each component individually trying to isolate the heavy draw.
Even at your ambient temps I seldom see much more than 10v drawdown with a quick recovery. Ambients do play a big part in all this so could be deceptive.
Logistics Pro
Joined: Dec 2004
Posts: 4,138
Likes: 7
From: South Weber, Utah
I am trying to see if I have a developing problem with my starter. I am seeing battery voltage when cranking at 32 degrees at minimum of 9.5V, at 40 degrees yesterday I was at 10.2. The batteries tested good and once running my 110 AMP alternator does get to 13.8-14.5 when the glow plug cycle ens. A 185 alternator is on my bucket list.<br />
<br />
Is my starter pulling too much or is it good?
<br />
Is my starter pulling too much or is it good?
Were the batteries tested separately ( completely disconnected from one another) ? And how old are the batteries? It sounds like weak batteries to me. Also make sure all of the battery cable connections are clean and free of corrosion including the grounds. The lowest voltage I see while cranking is 10.6 as measured at the OBDII port, voltage at the batteries will be on the order of .2-.4 higher ( thank you Josh (Bullitt390) for this bit of info )
Laughing Gas
Joined: Oct 2012
Posts: 794
Likes: 1
From: Ontario
<br />
Were the batteries tested separately ( completely disconnected from one another) ? And how old are the batteries? It sounds like weak batteries to me. Also make sure all of the battery cable connections are clean and free of corrosion including the grounds. The lowest voltage I see while cranking is 10.6 as measured at the OBDII port, voltage at the batteries will be on the order of .2-.4 higher ( thank you Josh (Bullitt390) for this bit of info )
Were the batteries tested separately ( completely disconnected from one another) ? And how old are the batteries? It sounds like weak batteries to me. Also make sure all of the battery cable connections are clean and free of corrosion including the grounds. The lowest voltage I see while cranking is 10.6 as measured at the OBDII port, voltage at the batteries will be on the order of .2-.4 higher ( thank you Josh (Bullitt390) for this bit of info )
Lead Driver
Joined: Oct 2010
Posts: 5,420
Likes: 16
From: Ouray, CO
I feel your pain.. I'm not able to read voltage while cranking since the my digital gauges all reset when I engage the starter..
Try to reduce other un-necessary electrical loads until the GPs turn off..
* electric seat heater(s) - OFF
* HVAC - OFF
* headlights (I don't use auto headlights) - OFF
I just upgraded my alt & wires and I can no longer tell when the GPs turn off
because my voltage is 12.5 a couple of seconds after cold start and then a few seconds later goes to 14.6 to 14.8. 
I ran with a/c, electric defrosters, and headlights last night in the rain and my voltage at a stop was still 14.5 (in the past, I would see 12.3 and my low voltage alarm would go off on my digital gauge).
Try to reduce other un-necessary electrical loads until the GPs turn off..
* electric seat heater(s) - OFF
* HVAC - OFF
* headlights (I don't use auto headlights) - OFF
I just upgraded my alt & wires and I can no longer tell when the GPs turn off
because my voltage is 12.5 a couple of seconds after cold start and then a few seconds later goes to 14.6 to 14.8. I ran with a/c, electric defrosters, and headlights last night in the rain and my voltage at a stop was still 14.5 (in the past, I would see 12.3 and my low voltage alarm would go off on my digital gauge).
Postmaster
Joined: Sep 2010
Posts: 3,472
Likes: 2
From: Southern Cal
Correct me if I'm wrong but I think a more valid test would be to measure your amperage when trying to start.
The voltage shouldn't vary too much to affect the starter unless really bad, but amperage will.
The voltage shouldn't vary too much to affect the starter unless really bad, but amperage will.
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Post Fiend
Joined: Apr 2002
Posts: 19,311
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From: Waterloo, Iowa
Voltage is going to drop during cranking. Just how much is a quick and dirty way to determine battery health. The amp draw is high during start, maybe 200 amps or more. Most DIYers don't have capability to measure that much current or even a carbon pile.
It does depend on the temperature, but 9.5 volts is normally (warm weather) right at the "need new battery" voltage (during 15 second crank) basically that is the "poor man's load tester."
After several minutes open circuit voltage should bounce back to 12.6+ however, with a good battery.
As a practical matter measure cranking RPM to determine that is in spec during crank. If not, something is sucking up current that shouldn't be.
It does depend on the temperature, but 9.5 volts is normally (warm weather) right at the "need new battery" voltage (during 15 second crank) basically that is the "poor man's load tester."
After several minutes open circuit voltage should bounce back to 12.6+ however, with a good battery.
As a practical matter measure cranking RPM to determine that is in spec during crank. If not, something is sucking up current that shouldn't be.
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Logistics Pro
Joined: Mar 2010
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From: NC
My batteries were tested by the dealer 2 weeks ago, they are Motorcraft MAX 850s, about 1 year old. I actually took them out of the truck, let them sit for 36 hours then took them to the dealer and they tested them with a Motorcraft tester and they tested good.
Post Fiend
Joined: Apr 2002
Posts: 19,311
Likes: 97
From: Waterloo, Iowa
What's nice about battery tech is no special equipment is required, other than a reasonably accurate DMM and temperature compensated voltage tables. The chemistry was hashed out a hundred years ago. If the cranking RPM is below spec with adequate voltage then current is being lost in cables, or dragging armature etc.
http://jgdarden.com/batteryfaq/carfaq4.htm
http://jgdarden.com/batteryfaq/carfaq4.htm
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