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From: Fred on 30 Jan 2010 04:17
Hi,

I've bought a max/min multimeter as recommended by you all.

The voltage before I started the car was 12.2V

When I started the car the voltage dropped to 9.1V minimum during
staring.

Once the engine was running, the voltage was 14.5V maximum.

Am I right to be worried about the 9 volts? It seems low to me but
OTOH I am not having any problems starting the car at the moment, so
isn't that the biggest test of the battery?

I compared it to my other half's car and the voltages for that were:
12.4V before, 10.1V during, and 14.6V after starting.

By the way, the multimeter claims to have two settings to test 1.5V
and 9V batteries. The manual claims it puts a small load across the
battery and displays the voltage. Anything about 1.2V is ok for a 1.5V
battery, and anything over 7.2V is ok for a 9v battery, or so it says.
I had some flat 1.5V batteries that measured 1.25v, so they passed the
meter test but were useless in practical terms. Are these [non-car]
battery test settings a waste of time? I seem to remember that when I
was at school we were told you should test a battery by its current,
not its voltage?

TIA
From: Duncan Wood on 30 Jan 2010 04:28
On Sat, 30 Jan 2010 09:17:48 -0000, Fred <fred(a)no-email.here.invalid>
wrote:

> Hi,
>
> I've bought a max/min multimeter as recommended by you all.
>
> The voltage before I started the car was 12.2V
>
> When I started the car the voltage dropped to 9.1V minimum during
> staring.
>
> Once the engine was running, the voltage was 14.5V maximum.
>
> Am I right to be worried about the 9 volts? It seems low to me but
> OTOH I am not having any problems starting the car at the moment, so
> isn't that the biggest test of the battery?
>

That's the critical bit, the 9V just tells you that it's borderline, the
14.5V tells you the alternators working properly

> I compared it to my other half's car and the voltages for that were:
> 12.4V before, 10.1V during, and 14.6V after starting.
>
> By the way, the multimeter claims to have two settings to test 1.5V
> and 9V batteries. The manual claims it puts a small load across the
> battery and displays the voltage. Anything about 1.2V is ok for a 1.5V
> battery, and anything over 7.2V is ok for a 9v battery, or so it says.
> I had some flat 1.5V batteries that measured 1.25v, so they passed the
> meter test but were useless in practical terms. Are these [non-car]
> battery test settings a waste of time? I seem to remember that when I
> was at school we were told you should test a battery by its current,
> not its voltage?
>
> TIA

Generally they'll just tell you when it's dead flat.
From: Tim.. on 30 Jan 2010 04:59

"Fred" <fred(a)no-email.here.invalid> wrote in message
news:1nt7m55dtud40n3baguo00r660ai2nrmvs(a)4ax.com...
> Hi,
>
> I've bought a max/min multimeter as recommended by you all.
>
> The voltage before I started the car was 12.2V

If meter is accurate, and battery fully charged and healthy you should be
seeing 12.5 - 6v at rest.

dropping to 9v under cranking is somewhat low. I would say you have a dead
cell.

Tim..

From: Dave Plowman (News) on 30 Jan 2010 06:36
In article <1nt7m55dtud40n3baguo00r660ai2nrmvs(a)4ax.com>,
Fred <fred(a)no-email.here.invalid> wrote:
> I've bought a max/min multimeter as recommended by you all.

> The voltage before I started the car was 12.2V

Battery not fully charged - but not uncommon in practice. Or it could be
on the way out. Only way to be sure is a proper test with an electronic
tester. Your local battery specialist will have one as do Halfords. But of
course you have to trust the operator. ;-)

> When I started the car the voltage dropped to 9.1V minimum during
> staring.

That is distinctly borderline. Could indicate the battery is past its best
or the starter motor taking too much current. The first is far more
likely.

> Once the engine was running, the voltage was 14.5V maximum.

Again suggesting a low battery. It should be approx 13.8 when fully
charged. Either charge the battery externally or check again after a
daylight run of about 20 miles.

--
*If God dropped acid, would he see people?

Dave Plowman dave(a)davenoise.co.uk London SW
To e-mail, change noise into sound.
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