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Minimum voltage needed to start car?

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Old 01-06-2013, 02:45 PM
Sulfuric Sulfuric is offline
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Vehicles: 1996 Honda Accord 5Speed
Location: Orlando, FL
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Minimum voltage needed to start car?

After getting into a crash on June 1st I got a new (to me) car, a 1996 Honda Accord, manual transmission.

I recently bought an Ultragauge and am very happy to finally be able to see all the details.
My main question is this:
What do you think is the minimum voltage needed to start my car?
If driving normally, it hovers around 14.2 volts, and when in FAS it drops to the mid 12 range. However, during my nighttime P&G it's been falling to as low as 11.5v toward the end of my trip. I'm just concerned that it might drop so low that I won't be able to start my car with the key.

Relevant: I have an Optima Yellow Top battery, only 6 months old, and my starter is takes an average amount of volts/amps to start the engine


Edit: this probably would be better off posted in "General" but I forgot how to delete threads so help me FSM
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Old 01-06-2013, 05:07 PM
herm herm is offline
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Re: Minimum voltage needed to start car?

No idea about the voltage but it has to be fairly low since all it has to do is provide ignition, fuel pump etc and drive the head lights.. the head lights must consume much more than all those other. You are not using the starter right?

Sorry about the crash, I hope all is well healthwise.. tell us more about the Accord.. price???
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Old 01-06-2013, 05:10 PM
herm herm is offline
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Re: Minimum voltage needed to start car?

Here in Miami all Accords are made of gold, I think they appreciate when you drive them off the lot.
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Old 01-06-2013, 08:40 PM
CPLTECH CPLTECH is offline
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Re: Minimum voltage needed to start car?

Voltage drops even in a new battery when a high current starter is energized. I think the best thing to do is to kick-start whenever possible, as Herm implies. Also, is your driveway on a slope so as to kick-start in the AM? Many do not realize the additional fuel the alt takes to run the lights or the blower since the minimum idle is computer regulated. Those of us that drove carburated cars heard the engine slow. My SG2 shows at idle a 10% increase in GPH whenever those are turned on. It seems to me that the small cars have a low amp capacity alt compared to the big engines so that it doesn’t tax the little motor so much. That may be why it can not keep up with the battery.

Be aware that batteries are made for certain purposes. A marine battery for trolling is designed to give a certain AH over a “long” period of time, but poor as a starter battery. Whereas a car battery will give lots of amps briefly to start the car, but not so good over a “long” period of time. When replacing a battery, I always opt for the largest CCA I can get in that size. Usually doesn't cost that much more.
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Old 01-07-2013, 03:56 AM
Sulfuric Sulfuric is offline
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Re: Minimum voltage needed to start car?

I'm talking about starting the engine with the starter, perhaps at a light somewhere on my drive back from work. No driveway (apt complex near college), and I don't have a marine battery, I believe that would be a "blue top". Optima makes reds for normal cars, yellow for vehicles that run a lot of accessories (big stereos and the like, I think, but also doubles great when P&G'ing a lot), and blue for marine.

Accord details:
$1400 from small time dealer (plus taxes), ~145 miles
Approx $1.2k in repairs + new tires immediately (I knew that would happen)
Rack and pinion went bad about 2 months later
Rack and pinion fixed for free like it should have been, but they *did NOT do an alignment afterwards* and I forgot
Drove 120 miles out of alignment
New front wheel bearings + alignment + something else needed ~$450
Something + alignment when I went home ~$230
Hopefully fixing chronic alignment problems tomorrow
I didn't stick up for myself when I should have and made the shop pay for my front wheel bearings, so lesson learned there hopefully
Overall very sour about car but very happy with mpg
Also the passenger inside door handle broke and the windows are slow to roll up in the front
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Last edited by Sulfuric : 01-07-2013 at 04:04 AM.
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Old 01-07-2013, 07:10 AM
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CRT1 CRT1 is offline
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Re: Minimum voltage needed to start car?

I find that I start to have problems in my FIT the 11.2-11.4 V range with a fully warm engine. It will still start if it drops that low but that is when I start to get really worried. I'll ease up on the FASing until I can get the battery topped off again.

Also, note that it is MUCH harder to crank a cold engine than a warm one, so you will need a higher V to start your engine before it is fully warmed up. I also try to use my ear and ease up when it doesn't quite sound right starting up. This is sometimes at higher Vs.

A lot of the guys around here who FAS a lot use a trickle charger at night. I don't have an outlet near my parking spot so I have been topping off my battery about once per week. Probably not good for battery longevity but its all I got.
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Old 01-07-2013, 12:30 PM
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priusCpilot priusCpilot is offline
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Re: Minimum voltage needed to start car?

What kills the battery as some of you guys know is the sulfation buildup on the plates. Im testing out a few disulfators out so once I know whick one works Ill post. They make one that you just leave on the battery and it keeps it from building sulfate. Also you can setup and solar charger so alls you do it plug it in were you park.
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Old 01-07-2013, 12:38 PM
herm herm is offline
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Re: Minimum voltage needed to start car?

Maybe one of those solar chargers on the dash?.. only way to keep the battery alive on a friend's car with only a 2-3 mile commute.
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Old 01-07-2013, 02:58 PM
WriConsult WriConsult is offline
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Re: Minimum voltage needed to start car?

Twice, on my previous car, I inadvertently let the voltage drop too far while FASing, and found myself unable to restart at a red light. In one of these instances my Jetta's battery was starting to fail, and in both instances the voltage drop came on earlier than you might expect in broad daylight because that car's DRLs are active anytime the key is in the RUN position.

Unfortunately I had not been watching the voltage prior to either of these incidents (or they wouldn't have happened) so I'm not exactly sure how low it had to go before I couldn't engage the starter.

Ever since then, I have made a point to always have the VLT gauge displayed on my SG, and I watch it carefully anytime I'm FASing in city conditions, especially at night when I have the headlights on. Basically I start to get nervous anytime the voltage drops below 11.5, though I don't know exactly how far I can safely let it drop.
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Old 01-07-2013, 03:09 PM
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some_other_dave some_other_dave is offline
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Re: Minimum voltage needed to start car?

Starting is one thing, running is another. My old 914 would die below 9V, probably because of the aftermarket electronic ignition setup I had in it. I think with points, it would have run lower than that.

On a modern car, there is probably a good bit of head-room between normal system voltage and "too dead to run the car". I'd be worried if it dropped below 10 at any point, but I think 11 is OK for the short term. Over the long term, low charge levels (e.g., below 12V) can lead to battery damage or at least it dying on you earlier than it might.

How much voltage it takes to crank the engine over depends on lots of things. How easily the engine cranks (e.g., high compression and new tight motor or low compression and old tired motor, oil thin and warm or thick and cold, etc.), how efficient the starter motor is, how much capacity and internal resistance the battery has, what sort of voltage drop there is through the power and ground paths from the battery to the starter and back, and so on. Many of those things vary from start to start even on the same car.

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