Lowest Battery Voltage

Submitted: Tuesday, Mar 01, 2005 at 10:23
ThreadID: 20874 Views:1638 Replies:6 FollowUps:1
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Hi,
Just wondering what the lowest voltage that would be required to start a standard 4cycl engine?

Also if you buy a Voltmetre from say DSE, what else would be required to hook it up to your battery so as you have some indication of the power leftin it?

I have a multimetre that I use to check on the volts coming out of the power adapter I put in the back of the van and it usually reads about 12.48 volts +- a couple.

Cheers
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Reply By: TheUndertaker - Tuesday, Mar 01, 2005 at 10:50

Tuesday, Mar 01, 2005 at 10:50
A very difficult question to answer ,far to many variables involved to give a "correct " answer, motor size, compression ,state of tune ,spark resistance ect ect ect,,,however populist theory dictates that you should not discharge any battery lower than 50% of its capacity to increase its longevity and servicability ,,50% of charge is generaly 12.06 volts [rested batt].
Try www.windsun.com
AnswerID: 100655

Reply By: Member - Sand Man (SA) - Tuesday, Mar 01, 2005 at 11:32

Tuesday, Mar 01, 2005 at 11:32
Craig,

It's not the voltage you need to concern yourself with, but the Cold Cranking Amps available from the battery that will determine if the donk can be turned over.

The only way I know of to determine cranking capacity is to perform a load test on the battery. Any Battery Reseller outlet can do this for you. (free of charge)

To check the health of the battery cells, you can use a hydrometer, if the battery is not a sealed type. This will soon tell you if one or more cells are caputsky.
Bill


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AnswerID: 100662

Reply By: B0XER - Tuesday, Mar 01, 2005 at 16:42

Tuesday, Mar 01, 2005 at 16:42
SandMAn is on the money,

Power is the result of current and voltage, therefore to try and give a definitive answer on what voltage is minimum for a starter motor to operate is difficult. It will also depend on the batteries ability to provide the required current.

However it is not only current either - as a 6volt battery supplying 800CCA will still not turn over your engine - it is the interaction of both.

A good rule of thumb is to leave at least 11.5 - 11.7v in the battery under load (in good condition) to start your engine. This is provided you have the correct capacity battery installed in your vehicle
AnswerID: 100693

Reply By: old-plodder - Tuesday, Mar 01, 2005 at 18:11

Tuesday, Mar 01, 2005 at 18:11
Above has covered it pretty well using the starter motor.

You can get a digital voltmeter combined into the battery terminal from Jaycar.

Absolute minimum voltage is about 10.5 volts for a clutch start.

Anything less and there may not be enough voltage for the coil and to allow the alternator to charge.
Yes, I did get caught once where I couldn't even clutch start it. :-)
I had the police there to verify it. :-(
AnswerID: 100704

Reply By: Member - Craig M (NSW) - Wednesday, Mar 02, 2005 at 08:59

Wednesday, Mar 02, 2005 at 08:59
Thanks for the replys guys. I guess I had better just keep an eye on what we run off the 12v.

Cheers
AnswerID: 100763

Follow Up By: Member - Camper (SA) - Wednesday, Mar 02, 2005 at 14:05

Wednesday, Mar 02, 2005 at 14:05
You can buy a low voltage warning kit from Jaycar which when you have built it you can set. I set mine at 11 volts and turn it on if I am in camp & if I am giving the battery a hammering. Does it save your bacon? I don't know I have the biggest exide I could fit in the cradle and it has never sounded a warning as yet. Maybe in time I will know.
Camper
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FollowupID: 358925

Reply By: pixiemops - Friday, Mar 04, 2005 at 23:57

Friday, Mar 04, 2005 at 23:57
State of Charge 12 Volt battery Volts per Cell
100% 12.7 2.12
90% 12.5 2.08
80% 12.42 2.07
70% 12.32 2.05
60% 12.20 2.03
50% 12.06 2.01
40% 11.9 1.98
30% 11.75 1.96
20% 11.58 1.93
10% 11.31 1.89
0 10.5 1.75

this is for no load
AnswerID: 101186

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