Parasidic drain=ohms in s10
p...@got.some.net
amount of parasidic drain on my 95 s10. Took it in to the shop after
the battery took a dump. The tech said it was just a dead battery and
replaced same. I think it's something more. If I look read across the
terminal leads (battery out) with an ohm meter I get a resistence of
8000 ohms constant. I don't think this is merely typical load with all
things off. (took the lamp out under the hood) Please post here as
return path invalid. THANKS in advance. P.
George Jefferson
:replaced same. I think it's something more. If I look read across the
:terminal leads (battery out) with an ohm meter I get a resistence of
:8000 ohms constant. I don't think this is merely typical load with all
you cant really look at the resistance like that because
much of the load is not resistive. Hook up one battery terminal
and measure current between the other terminal and the loose
wire. Make sure your meter is capable of fairly high currents,
start on 10amp range and work down.
p...@got.some.net
wrote:
What reading should I get? P. S. thank you for the prompt getpack!
p...@got.some.net
Should read ; thanks for the prompt getBack!
Werehatrack [Russ Ault]
Even if that 8K ohm reading is correct, that's a trivial drain; under
two milliamps, a rate of delivery which the battery could maintain for
a very long time without any effect. The only way to really find out
if you have a significant parasitic drain is with an ammeter. Start
by disconnecting the ground cable from the post and hooking a test
light from the post to the cable; if it doesn't glow at all, your
drain (if any) is well under one amp, which gives you a clue as to
where to start with your ammeter readings. You'll most likely need an
ammeter that goes down into the 100mA range to find the drain in that
case, and don't be too shocked if all you see is the ECU and radio
memory maintenance drains, which should be in the area of a few
milliamps at most. In my experience, the real battery killers tend to
be aftermarket accessories like alarms and auxiliary stereo
amplifiers. I used to see at least three or four cars a week with
batteries that went dead over a weekend due to miswired audio amps.
Car alarms whose key-off drain had taken a sudden jump were the number
two cause of overnight dead battery syndrome.
--
My email address is spamblocked. Remove YOURCLOTHES to reply
BOB URZ
the high amp +12 volt lead) and a switching lead. The amplifier turns on
when the switching lead
has +12 volts on it. This normally goes to the power antenna drive output
from the car stereo. This means, the amp is only on when the head unit is
on. If you wire the switch wire directly to the 12 volt along with the high
current lead, the amp will stay powered up all the time. Granted, with
modern switching power supplies it won't draw mega amps with no signal, but
over a period of time it could draw the battery down.
BOB
Larry Smith
" George Jefferson " <gj...@one.net> wrote in message
news:tetdaeb...@corp.supernews.com...
> you cant really look at the resistance like that because
> much of the load is not resistive. >
What other type of impedance can you talk about in DC circuits,
George?
George Jefferson
:> much of the load is not resistive. >
:
:What other type of impedance can you talk about in DC circuits,
:George?
electronic devices (computer, radio) don't obey ohms law. You really
need to show them the proper voltage and measure the current.
Brendan Welch
In addition to other answers given here:
First I would look for the "obvious" light staying on in the trunk.
Then, with an ammeter on the battery circuit, you can start popping
fuses to see if removing any particular one causes a sudden unexpected
drop in current.
Also, partly in agreement with the person who said to disconnect the
negative cable from the battery: I once did that and found that I still
was reading 12 volts between the chassis ground and some point. It was
due to a trail of conductive corrosion from the negative terminal, down
the side of the battery, to the metallic battery holder (maybe plastic
nowadays).
But, as was also argued, that path was able to sustain a connection
under very low (almost static) current conditions. Like so many
problems, it could be counted on to CAUSE a problem, but never relied on
to CURE one.
--
Brendan Welch, Univ. of Massachusetts - Lowell, W1LPG
Brendan Welch
JeB
Mr. Ohm's Law sez: I=E/R = 12/8000 = .0015 amps
Hopefully your battery can take that kind of load between starts.
billk...@snotmail.com
I'm not an expert on this, but I think you should be more concerned with
actual current draw.
Using an ohm meter on solid state devices (ECU for example) may give
erroneous readings. You may have capacitors, diodes etc. involved.
Hook an ammeter in series with the battery with all electrical loads
turned off. Start with your highest meter range first!
John Ings
wrote:
>:> you cant really look at the resistance like that because
>:> much of the load is not resistive. >
>:
>:What other type of impedance can you talk about in DC circuits,
>:George?
>
>electronic devices (computer, radio) don't obey ohms law.
Well they do actually, but not linearly!
>You really
>need to show them the proper voltage and measure the current.
Exactly. A common ohmeter is up against "diode threshold" and will
show a high resistance to its single battery power source, which is
only a volt or so. Best method is to measure the actual drain on the
real 12 volt source, your battery.
George Jefferson
I measure ~200 ma (fluctuating) for ~20 seconds, then it
settles to a steady 9.3ma. The 'resistance' measures 9k ohm.
Off by a factor of 10 if you tried to use ohms law.
In article <5rrvetsn27gpfep5c...@4ax.com>,
John Ings <ji...@ottawa.com> wrote:
:On Tue, 01 May 2001 14:13:48 -0000, gj...@one.net ( George Jefferson )
:
Don Stauffer
may NOT be directly proportional to applied voltage.
Larry Smith wrote:
>
>
> > you cant really look at the resistance like that because
> > much of the load is not resistive. >
>
> What other type of impedance can you talk about in DC circuits,
> George?
--
Don Stauffer in Minnesota
stau...@usfamily.net
webpage- http://www.usfamily.net/web/stauffer
John Ings
wrote:
>just for fun, I happened to have my batt unhooked for another reason
>I measure ~200 ma (fluctuating) for ~20 seconds, then it
>settles to a steady 9.3ma. The 'resistance' measures 9k ohm.
>Off by a factor of 10 if you tried to use ohms law.
Not if you used ohm's law on a reading from an ohmeter intended for
use with semiconductors. The ECU has a non-linear resistance. If you
apply a low voltage from an ordinary ohmeter, it can't overcome the
semiconductor threshold. It's analagous to the overcenter spring on a
clutch pedal. Once the intitial resistance is overcome, you don't have
to push so hard. So if your ohmeter has a single D cell in it, you
will measure 9K, but if your ohmeter has a 3 volt battery you would
get closer to the actual value.
I agree though that a current measurement is the most accurate method.
## An ohm is an Englishman's ouse!
Larry Smith
Ohms law is still at play since you have DC. As a previous poster mentioned
some of the semiconductor devices are not linear at all with respect to
applied
voltage.
You would normally take your readings with the radio off. You can't easily
turn
the automobile computer off, unless you disconnect the cable. And, you
might well
have to do that on rare occasions.
Usually the cause of battery discharge is not in the nonlinear DC circuits
though.
I had one that nearly drove me to the edge. It turned out that a seat belt
retractor relay
would activate occasionally during the night. The battery would be flat the
next day.
In between intermittent relay applications, everything was as expected.
Even when the
relay decided to activate, Ohm was there in spirit.
Larry Smith
"Don Stauffer" <stau...@usfamily.net> wrote in message
news:3AF0BD93...@usfamily.net...
Doesn't have to be linear, Don. An understanding of nonlinear circuits IS
however
necessary in these rare occasions when confusion reigns supreme.
George Jefferson
:use with semiconductors.
well yea, if you apply 12v, measure the current, back out an
apparent 'resistance' as R=V/I, then that "resistance" will natuallly
satisfy V=IR so long as V=12. (wow).
I have to respectfully disagree with everyone saying it obeys
"ohms law" even if the system is nonlinear. This is self contradictory.
John Ings
wrote:
>Usually the cause of battery discharge is not in the nonlinear DC circuits
>though.
>
>I had one that nearly drove me to the edge. It turned out that a seat belt
>retractor relay would activate occasionally during the night. The battery would be flat the
>next day. In between intermittent relay applications, everything was as expected.
I had one even an ammeter couldn't catch. It was a brand-new battery
that discharged itself over a couple of days. It had an internal
leakage somehow. If you ran the car daily it was OK, but skip a day
and it went flat even though the ammeter showed minimal drain from
the ECU etc. I finally realized it was the battery itself when I
disconnected it completely and it was flat two days later even though
it had a full charge when I left it.
John Ings
wrote:
>:Not if you used ohm's law on a reading from an ohmeter intended for
Um, well, it is and it isn't. Old man ohm is never wrong, but you've
got some variables in there that won't hold still. For instance a
zener diode in the power input line of the ECU will fiddle its
internal resistance to keep the voltage across itself constant. That
means the apparent resistance of the ECU will vary with the voltage
you apply to it when that voltage exceeds a certain value. The system
is dynamic, but ohms law still applies. It just applies dynamically.
billk...@snotmail.com
Jefferson ) wrote:
> just for fun, I happened to have my batt unhooked for another reason
> I measure ~200 ma (fluctuating) for ~20 seconds, then it
> settles to a steady 9.3ma. The 'resistance' measures 9k ohm.
> Off by a factor of 10 if you tried to use ohms law.
>
>
You probably are getting an initial current surge because you are charging
capacitors etc. Once they are "charged", the current drops to its actual
parasitic drain.
--
To email me, change snot to hot
George Jefferson
"you can always measure voltage and current and label the rato as R"
??
Robert Hancock
resistance just changes based on voltage..
--
Robert Hancock Saskatoon, SK, Canada
To email, remove "nospam" from hanc...@nospamhome.com
Home Page: http://roberthancock.netfirms.com/
" George Jefferson " <gj...@one.net> wrote in message
news:tf0qjo...@corp.supernews.com...
George Jefferson
:resistance just changes based on voltage..
yes, but it aint Ohms law.
Halliday and Resnick,
Ohms law: "the resistance of a conductor is the same no matter what applied
voltage we use to measure it" -
further,
"modern electronics depends in a fundamental way on the fact that
transistors [etc] <it>do not obey</it> Ohm's law"
Don Stauffer
explain what I meant. If there is a semi-conductor junction in the path
whose resistance you are trying to measure, the resistance you will
measure will depend on the voltage the ohmmeter uses. So, the reading
is not that valuable.
Much better is to disconnect one battery terminal. Use VOM in ammeter
mode. If it is a slight drain, almost any meter should be able to
handle current. However, to be on safe side, start, of course with
meter on highest current scale.
Incidently, here is a weird drain I had about twenty years ago on a
Datsun. Drain was high when weather was wet, and was non-linear.
Turned out to be that headlight relay had a very cheap varnished
cardboard base section that had gotten impregnated with salt during
winter (it was somewhat exposed, up on wheel well). Salt would create
conducting solution when weather was damp. Replaced relay, put new one
in plastic bag with opening on bag at top, taped around opening and
wires.
AJDalton7
>turned off. Start with your highest meter range first!
>
>
Also, for those who do not want to interrupt memory [ECU, Radio tuning,codes,
etc.] ,
You can put one lead from meter to center of bat terminal and slide the cable
eye
up the insulator on the meter lead.
No circuit interruption that way.
Other lead on the cable eye, of course.
Robert Hancock
There are lots of conductors that change resistance depending on the voltage
applied. The second is true, I suppose, but the reason is that the
resistance depends on the voltage applied.
--
Robert Hancock Saskatoon, SK, Canada
To email, remove "nospam" from hanc...@nospamhome.com
Home Page: http://roberthancock.netfirms.com/
" George Jefferson " <gj...@one.net> wrote in message
news:tf2kfq...@corp.supernews.com...
Mark Olson
As has already been pointed out, an ohmmeter reading across the battery
terminals is practically useless unless the ohmmeter forces 12V (unlikely)
into the battery terminals. There are non-linear semiconductor junctions
involved, the car does not look like a resistor to the battery.
Hope this helps.
Mark