How to measure battery CCA?

[KUN YU]

I have a small multimeter and I wonder if I can measure the Cold
Cranking Amperage of my car battery. If yes, how? Is it safe to the
meter or to me? How large a CCA is good for a 4 cynlinder engine?
Thanks for any hints.

ky...@lehigh.edu

[Harry L. Simmons]

I believe that a small multimeter is only capable of measuring fractions of
an amp. A good battery is capable of CCA of 600 amps and above. If I a
right about that, you and your meter are in danger of coming out of
the experience looking like a fried chicken that took its multimeter with
it into the frying pan.
--

[Wes Fujii]

KUN YU (ky...@CS1.CC.Lehigh.EDU) wrote:
: I have a small multimeter and I wonder if I can measure the Cold

: Cranking Amperage of my car battery.

You can get a calibrated bussbar which you can put in line with your
starter cable. Then, by measuring the voltage drop across the bussbar,
you can calculate the amount of current flowing to your starter. It
will tell you how much current the starter is drawing, rather than
how much your battery can deliver. To check the ultimate capacity of
the battery, you'll have to hook it up to something that demands a
higher load than what the battery can deliver. Then you'll find out.

The other method is to borrow someone else's inductive pickup current
meter. My father gave me one about 15 years ago so I know they exist.
I've used it several times to troubleshoot battery/starter problems.

Don't just hook your multimeter across the leads of the battery when
it is selected to amps. You'll instantly cook your meter unless it
is fuse protected.

Wes Fujii
________________________________________________________________
___ ___ ___
/ / / // /
/ /__/ // / A real motor is an Oldsmobile Rocket 455
/ HURST // / "This is NOT the new generation of Olds"
/ / / // /_______
/__/ /__// // ___ \
/ // / \ \ Wes "BANZAI" Fujii
/ // /OLDS/ / Boise, Idaho
/ / \ \___/ / we...@hpdmd48.boi.hp.com
/__/ \_______/

[Dennis Lou]

In article <31d30m$7...@usenet.INS.CWRU.Edu> cy...@cleveland.Freenet.Edu (Harry L. Simmons) writes:
>In a previous article, ky...@CS1.CC.Lehigh.EDU (KUN YU) says:
>>I have a small multimeter and I wonder if I can measure the Cold
>>Cranking Amperage of my car battery. If yes, how? Is it safe to the
>>

>I believe that a small multimeter is only capable of measuring fractions of
>an amp. A good battery is capable of CCA of 600 amps and above. If I a
>right about that, you and your meter are in danger of coming out of
>the experience looking like a fried chicken that took its multimeter with
>it into the frying pan.

Almost all small multimeters are fuse protected. You and your small
multi-meter will not look like a fried chicken who took its multimeter

with it into the frying pan.

However, the rest of Harry's post is right. You'd need an inductive
ammeter capable of measuring up to 1000 amps to measure how many cold
cranking amps your battery is putting out for your starter. If you
want to measure it's maximum capacity, you'd probably need in
addition:

1> wiring capable of 1000 amps
2> a current draw of 1000 amps (lesse, at 14 volts that could be a
.014 ohm resistor rated for 14000 watts)
3> a way to dissipate 14000 watts of power (usually in the form of
heat)
4> containment for the battery and associated gases it may put out

BTW, the 1000 amp figure includes the safety margin. Most good
car batteries don't put out much more than 700 CCA.

Dennis Lou || "But Yossarian, what if everyone thought that way?"
dl...@ucsd.edu || "Then I'd be crazy to think any other way!"
[backbone]!ucsd!dlou |+====================================================
dl...@ucsd.BITNET |Steve Jobs and Steve Wozniak went to my high school.

[Clifton Koch]

dl...@worf.ucsd.edu (Dennis Lou) writes:

Measuring CCA of a battery would not be a trivial task. CCA is a measurment
of how much current a battery can deliver while maintaining a specified
voltage at a specified temperature. I don't have the correct specifications
to say exactly what those numbers are. You would need a test rig capable of
being temperature controlled, measuring the voltage, and varying the amount
of current draw (a very large current) to get down to the test voltage.

If you just want to measure starter current draw, all you need is an
inductive pickup ammeter as has been mentioned. I've never found these to be
terribly accurate, but it would be close enough. Just clamp it around the
battery cable and have someone read it while cranking the car.

Cliff
--
-----------------------------------------------------------------------------
Cliff Koch
Motorola Cellular Infrastructure Division
ko...@meerkat.cig.mot.com