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BrApple 10-14-2012 09:28 AM

battery voltage required for starting
 
so this morning was the second time that I had a no start condition with my car. The first time it happened the car would just crank. I realized it fairly quickly and stopped it, then it started right up.

This morning it happened again. However I tried 5 or 6 times to start the car and it wouldn't start. All the lights, and everything came up and was working. Engine would just crank but not start. So I went into test mode and saw that the battery voltage was either 11.3 or 11.6. I check ed the voltage at the battery and it was 12.3. I ended up having to jump the car to get it started. Even then it took a few tries to get it started, and I could really hear it in the idle of the other car.

That was about an hour ago, I went out and had no trouble starting the car. Checked test mode and the battery voltage was 12.3, and it was 12.6 at the battery.


What I think caused this was I moved the car twice yesterday, so it ran for about 4 minutes. NOw I can't see how it would have made a difference this morning, but the auto headlights turned on and the defroster was on. But all of those, I know the headlights do, turn off when the car cranks.

So is this from just not running it long enough yesterday? Could it also be from the temperature being ~33 degrees over the previous night? This morning was closer to ~50 degrees out.

I take it the high compression engine needs alot of power to crank over and start. Seems like for what ever reason my battery was on the edge this morning?

Thinking that I will take it into the dealer this week and have it checked out just in case. In the mean time I am charging the battery.

Daytona Coupe 10-14-2012 11:30 AM

Voltage at rest won't tell you much about the battery's state of charge, it needs to be checked under load. Have someone measure voltage at the battery while you are cranking it - it should stay above 11v while cranking. Even over 10 will probably still allow it to start. If voltage stays high while cranking, your problem is likely somewhere else.

Get the battery fully charged and the have it load tested - this will tell you if the battery is bad or not. If the battery tests ok, then load test the alternator. If both check ok, you may have some other electronic issue that will probably require a trip to the dealer

BrApple 10-14-2012 08:09 PM

Yes a load test is a good idea.

However, you are partly saying what I was getting at. Would a voltage lower then 12.5~12.6, which is normal for a good 12 volt battery effect the ability of the car to start. Again everything else worked correctly. The engine did crank over, it just didn't start. That is why I am wondering if starting it twice and only letting it run for maybe 5 minutes total would ahve caused a lower then normal charge on the battery and therefore a starting problem.

I checked the voltage across the battery while running and it was 15 volts. So the alternator is charging correctly. Also it hasn't had an issue starting at all for the rest of today.

BrApple 10-15-2012 06:53 AM

my observation from this morning is that when I tried to start the car yesterday the engine did not turn over as fast as it normally does. It turned over much quicker this morning.

So to me it seems like the voltage as just alittle low to start the car, but was more then enough to crank the engine and run all of the electronics.

TboneZX3 10-15-2012 08:34 AM

Quote:

Originally Posted by BrApple (Post 4405119)
Would a voltage lower then 12.5~12.6, which is normal for a good 12 volt battery effect the ability of the car to start.

Not necessarily, no. As already stated, open-circuit (unloaded) voltage alone is not a good indicator of the battery's charge status.


Quote:

Originally Posted by BrApple (Post 4405119)
That is why I am wondering if starting it twice and only letting it run for maybe 5 minutes total would ahve caused a lower then normal charge on the battery and therefore a starting problem.

"Lower than normal"? Yes, probably, but if the battery is good, that type of use wouldn't reduce the charge enough to cause a no-start condition. I could do that 5 times in a row with a good battery and it would still start.

Daytona Coupe 10-15-2012 12:31 PM

If you have enough power to crank the engine at a reasonable speed (sounds like you do) - then you have enough voltage for the ignition & computer to work. Voltage is not your problem.

BrApple 10-15-2012 03:22 PM

Quote:

Originally Posted by Daytona Coupe (Post 4406293)
If you have enough power to crank the engine at a reasonable speed (sounds like you do) - then you have enough voltage for the ignition & computer to work. Voltage is not your problem.

That is the thing, when it didn't start it didn't crank as fast as it normally does. However everything electronic worked.

I do feel there maybe something else going on here, I'm going to do some testing of my own on the battery and then take it to the dealer.

Daytona Coupe 10-15-2012 10:07 PM

Voltage would probably have to drop below 10 to prevent the ignition from working properly and if that was happening it would crank much slower - not just a little slower.

BrApple 10-16-2012 06:35 AM

Quote:

Originally Posted by Daytona Coupe (Post 4407347)
Voltage would probably have to drop below 10 to prevent the ignition from working properly and if that was happening it would crank much slower - not just a little slower.

compareed to normaly it was pretty slow. I'll have to try to get it on video next time it happens if it does. Best I can discribe the difference is a normal start is sounds like it turns over 4 or 5 time in about 5 seconds. When it didn't want to start it sounded like it was turning over once maybe every 5 or 10 seconds. Times are not exact, but hopefully help explain the difference between how the car normally cranks over and what it was doing.

Anyway the test mode was very useful. I used it to check the voltage while starting and it got into the mid 10s for a moment when cranking. I also loaded up the car as much as possible, defroster, headlights and high beams, fan on high and at idle and ~2 krpm the voltage was solid at 14 volts. Checking at the battery yeilded similar results for for starting and when I checked the voltage when loaded.

TboneZX3 10-16-2012 02:22 PM

Quote:

Originally Posted by BrApple (Post 4407804)
Anyway the test mode was very useful. I used it to check the voltage while starting and it got into the mid 10s for a moment when cranking.

If you're only dropping to 10 while cranking, I would suspect something other than the battery. 10 volts is good voltage for a cranking load.


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