Have a 99 cougar, V6 loaded............... battery will go down when car
sits for 4-5 days
purchased new battery. old one was original. had same problem with old
battery, all terminals are clean. Alternator is charging to correct
voltage.Belts are good, not slipping
Any know problems with this car for this ?
Question how much battery drain is normal , And how do you check it with
I reckon there should be practicaly none (or less than 10 mA/one hundret amp
of a drain).Watch out for your altarnator rectifer going faulty (often
causes the warning lamp to glow slightly). Also check your boot (trunk )
lights .Could be anything. I knew a guy with a Fiat with this problem & it
turned out that he had a rear wiper motor that was seized. The average car
battery is about 48 Ah so anything (including a small lamp will discharge it
in a few days)
would you like to generate an explination for that remark?
you think the battery knows what it is driving? It sees a big resistor.
when everything is off.. the resistance should be very high if it is not
then there IS a problem.
i think you should get a clue.
I went to school for this i have a clue. Not to mention all the hands on
Sure, my remark may have been a little harsh but in a nutshell your method
will not work on most modern vehicles. There are too many modules that
control things like suspension, lights, powertrain, etc. that draw a fair
amount of current untill they go into a sleep mode. Some of them like the
Lincoln air suspensions for instance stay active for quite a while. The
right way to check for a battery draw is to put an amp meter in series
between the battery and cable. It's common to see 6 to 8 amps when it's
first connected (key off, doors closed) but should come down to 50ma or less
before too long.
Try it on your own car if it's less than 20 years old. I think you'll be
I admit your method would work well on a Model T, how old are you?
Thanks for the reply... I now understand better what you were trying to have
the guy do... I told him to try a simple test... thats disconnect the
battery and prove it is one or the other...by leaving the battery sit open
with no load and see if it drains.. if it does then its the battery. I
would think the 8A is a spike and not a long lasting current draw...
Ive had to reconnect my battery at night time and the arc did not seem like
8 amps.. maybe at most 2 or 3, but thats just guessing.. i never had the
energy to put an ammeter in series with my cars battery, especially since my
ammeter has a max of 10 amps.. and to do a full test i would have to have
the car running and the starter draws quite a bit more then 10Amps.
So if what you are saying is true based on ohms law this guy should read
(12V/8A) = 1.5 ohms... i have a very bad feeling that what he reads wil
be a lot more then that.
Digital circuits draw very little current and have a huge input impedence.
So the car's cpu dont count. The car radio draws a little for memory and
presets.. i have not experienced any actuators in cars that activate when
the battery is first connected. I would assume that the actuators will
activate when the car is running, therefore they are also out of the
question. With this being said, i would think the input resistace is a
In any case... i had my way of doing it, you had yours.. yours would
always work, mine would work with most cars. I perhaps broke down the
problem too simple, and looked at a power source and a load... not
thinking this can be a varible load.
i later suggested that the guy disconnect his battery and let it sit not
hooked up for 6 days.. see if that mattered.. if it did not then he has car
problems .. otherwise its the battery and a weak cell.
Oh yes... and im 23 years of age.
you cant measure resistance on a live circuit
Disconnect the battery and mneasure resistance from black lead to red lead
on car.... but forget that test... your better of with the other one
where you disconnect the battery for 6 days and see the condition
Come on guys, get real. You can't measure the 'open circuit' resistance of
a vehicle because
1. there are very often small current circuits working all the time, such as
2. There are forward bias semiconductors that will ONLY conduct when the
forward voltages more that the forward bias volt drops of the connected
ALSO, you can't guess the current jumping a gap!
ALSO a car radio commonly has large decoupling capacitors permanently
connected to the 12 volt battery, and these cause the flashy sparks that you
see when you reconnect the battery.
So, to really find out what is going on, disconnect one of the battery leads
and put a DVM set on AMPS mode in series with the battery lead. So the
meter should go between terminal post of the battery and the lead that has
just been removed. ALSO put the meter in the 10 amps mode otherwise the
spark that we have just discussed may blow the internal fuse in the meter.
After things settle down, I wouldn't expect that no more than 10 to 20
milliamps should be consumed. But in very rough terms, you can work out
the current taken in the 'OFF' condition. The battery will have an amp-hour
figure. And assuming that the battery is in good condition and fully
charged, just divide this figure by the length of time taken to drain the
battery in hours. Easy really. I think that either the alternator bridge is
defective (but in which case the ignition light will be on either when the
engine is running, or off, as appropriate) , or a small bulb is on all the
time - a light in the trunk may be?
i did go to school for this.. the resistance should be very high.... now
looking at a car as the electrical load.. hes right there are too many
things to consider... by the way the only way to measure resistance in a
live circuit is to use a shunt resistor or measure the current and then
calulate the resistance.. I DARE you to take a resistance measurement of a
480V device while it is running.
If the car was a simple load my method would work perfectly. The car is not
a simple load.. it consists of many loads in complex circuits. At first i
was thinking of the car as a whole as a lightbulb per say... it is not..
another thing you can do to check the current insted of possibly blowing a
meter is to take a really small resistor (.01 ohms) and use it as a
shunt... measure the voltage across the resistor.. oh make sure it is 10W
or more rated or it will just puff smoke, expect it to get hot.
you know the resistance there and you measure the voltage so u can caluclate
the current. If you dont want to damage your meter... not all of us have
meters that protect themselvs with fuses.
I admit i was wrong in the beginning.. and i admitted this long before you
started asking me questions tom...
i said disconnect the battery and let it sit open circuit.. then try and
start the car.. see if it was still no good.. if it was no good then it is
obviously the battery.
Now look... i admit i was wrong.. only because i looked at the car as a
simple load... in many aspects my way would work fine.. as with an older
It would be interesting however to see what the input resistance of a car
is... i expect it is very high.
Why not simply take a voltage drop measurement of lets say the engine ground for
You put on a dance to justify your comments..........
"In any case... i had my way of doing it, you had yours.. yours would
always work, mine would work with most cars"
What are you going to do when the battery starts the car once, but fails to
start the car a second time one hour later? Your theory proves nothing. Again
I'll ask you, Would it not be better to check the OCV and SG to find if the
battery is good or
not? About 10 minuets, not 6 days.
Note, both acronyms are industry standard, you should know them.
No it would not.
You can find the calculated resistance in the engineering schematics, but that
does not take in to account for corrosion, ect. Kind of a hint.
You proved your point... I guess everybody thinks i am an idiot. I
dont really care..
I went to school for electrical engineering... not the study of
automobiles. Sure you can do an OPEN CIRCUIT VOLTAGE test (OCV) Or a
specific gravity test (SG) Big acronyms... tough to handle.
The point is early on the guy who originated the post said the battery was
at 12.5V when it was open circuit... sounds like the batttery is fairly
good to me. Based strictly on an open voltage test.. which proves nothing
in my book.. the battery may fail under load.
As for specific gravity test.. the batter may have the correct chemical
make up and a good solid OCV.. however I have seen batteries where the
plates are so distroyed that they only hold a fraction of their capacity.
OCV and SG together cant prove this case.
For the price of a battery today if the battery is in question and over 3
years old.. get a new one. they are not worth the time.
He said that after sitting with the battery connected for 6 days it would
not start the car.
If he opened the connection on the battery and let it sit for 6 days he can
test it. Im trying to provide the cheapest way possible not necessarily the
A specific gravity sucker (tecnhnical terms) may cost 18 - 24 bucks. If
the battery starts the car ok and wont after running the car for a bit..
sounds like a charging problem along with a possibly bad battery.
Would you like to explain how you measure a voltage drop of a ground on the
car? That line confused me very much.
You said "Why not simply take a voltage drop measurement of lets say the
engine ground for
one?" do you mean the drop in voltage of the wire that gets mounted to the
block? What will that prove? do you know the resistance of that wire
exactly? When you measure it, it will likely be less then half an ohm...
since wire is not calibrated it would be difficult to deduce anything from
those measurements, unless of course i mis understood what you were
If i had the problem.. i would already be back and running. some things
are better shown then explained... I beleive this may be a case.
anyway... perhaps my thoughts are better welcome at other things... like
small electrical circuits, since that was my core of study.
Im thorugh making suggestions, everybody ignore what i said, since none of
it can possibly be correct.
Happy new year to all
I guess that explains it... The electrons that -you- studied
somehow work dirrerently than the ones riding around in an
pretty much explains the sad state of affairs in todays
educational system, and why engineering services are being
sourced to countries like China and India.
Standard usenet protocol, nothing big about it.
12.5 volts in a lead cell battery is 75% charged.
Schooling leave you well rested did it?
At 75% state of charge, a load test is more than a bit premature.
Sure they can. there is no way that a battery with plate damage
can sustain a correct specific gravity unless someone had
adulterated the electrolyte. Bone up on the chemistry of a lead
And when that doesn't work? What, another guess at the problem?
Sounds like a key off draw to me, easily quantified with basic
What if he doesn't have six days to wait? Could be he was on
vacation but now he needs his vehicle up and running.
So let's suppose he does have six days to sit and wait and watch
the grass turn brown, after six days he'll still not have any
useful data as to what the cause might be. An experienced
technician can glean from the parasitic draw measurements
(milli-amps) what the offending component might be.
(I use a refractometer myself)
for a bit..
Charging problem along with a bad battery and six days wasted.
Sorry, six days to determine what can be done in less than six
-minutes- is unacceptable, even for a DIYer.
You're schooled as an EE and you don't know what a "voltage drop"
In not so scientific terms, yup, that's the one.
Whether the wire exhibits any excessive resistance under load.
That is precisely the point of doing a voltage drop on the
Ever connected a volt meter to an ohmeter?
Do you suppose that the voltage level and the amount of current
that your ohmeter is able to sustain is orders of magnitude lower
than what might be experienced given the load of an operating
What do you mean "not calibrated?" Every gauge of wire has an
ohms per foot specification. It's one of the reasons that your
house or apartment doesn't burn to the ground when you switch on
Just as it would be difficult to deduce anything from your "Input
On the other hand, feel free to use your ohmeter to measure the
resistance of (say) a typical #194 automotive bulb and tell us
what amount of current will flow thru it in a 12 volt circuit
using Ohms Law (as applied by yourself previously).
If you had a problem, you'd be riding the bus or hitch-hiking.
Yes, best to stick to ones specialty.
Sorry, no offense, but if you're what passes for an educated
professional these days, the soup kitchens are going to be
overloaded in the near future.
No they dont, but i do not know what the automobile contains as far as
circuits go. I said measure the input resistance of the automobile.. I
still do not know why this wont work for finding a shorted part or something
in a circuit somewhere thats not right. When we have a power problem on PC
boards we measure the input resistance of the power supply (and it works)
its simply a test ... maybe there is something shorted so far down the line
that it looks like a few hundred ohms... at least that will show up on the
Im not being sorced anywhere... my focus of study was on small circuits
(IC's and the such and microprocessor controls) Not on larger equipment
(alternators, generaters etc...)
Maybe the educatinal system is falwed... as a matter of fact i know it is..
i see people graduate who truly know nothing about the field they studied.
Ever hear of sarcasim?
and yet 12.66V is 100% ... interesting.. how close is the meter you are
mesureing with? Maybe its not a fluck87 maybe its a radio shack hunk o crap
and is off by 20%
So charge it some then do a load test.
On batteries where you can get to the electrolyte expect it to be altered.
Its alwas been the case with the batteries i deal with.
That was not a guess... the battery is 3 years old, it is suspect to be a
problem, get a new one to eleinate that from the picture.. you need one
Could be a shot battery. Cant it?
If he left the battery open for 6 days and it did not start the car it was a
usefull test.. he should go buy a battery.. but he already did that since
the battery was 3 years old anyway.. so if you listened to me in the first
place the problem may have already been solved.
Where do you shop?
6 minutes does not give you 100% proof of anything.. stop kidding yourself.
explain to me what tests you do in 6 minutes and ill give you flaws in those
I do but the way it was worded was incorrect... he made it sound like i
should measure the drop in the chassis. Not a real useful test.. if he
said the drop in the wire that goes from the battery to the block then it
makes more sense.
The way it was worded i had to guess. How did you know it was not the
ground of the starter to the engine block mount for the ground? Maybe the
chassis has so much rust that it doesnt conduct anymore (HAH)
What will checking the voltage drop in this case prove.... the guys car
wont start after 6 days... if it would never start i would look for ground
problems.. you are going in the wrong direction.
Not when a wire is old and corroded do you have a chart for age and
enviorment as well... i think not.
although it would be interesting. And explain possibly what is going on..
maybe the guy would measure 20 ohms... what then? He was able to find the
problem very quickely.
Sorry temperature will affect it a little much
I think not... your humor as much as it seems hard thought out and applied
I agree and im sorry i atempted to help a person in need. Ill think twice
now when I see somebody stuck in fear that you will come by and bash me.
(sarcasim again in case you didnt know)
Give me a schematic of a car and I can troubleshoot with the best of them...
I know small electrical circuits.. microprocessors and control systems.
I have no fear of the soup kitchens.. I already am part of a business that
treats me well. As a matter of fact im going on the road to prove to our
customer that the problms they are having is theres and not ours. It only
takes a scope to do so.
Explain to me why the input resistance test is useless i want to know from
a professinal such as yourself.
When someone posts "I really don't care," it usually indicates
that they do.
Thanks for confirming.
Then why in the name of Gary Glaenzers grandfather would you
think to begin to offer advise?
By your own admission in another post, you've never even seen an
automobile electrical system wiring diagram.
Because it is a meaningless test that I'd be frought to find a
specification to compare to. IOWs, it's a "how many bubbles are
in a bar of soap" question.
You measure input resistance -of- a power supply and because that
works for that particular application expect that to be a valid
and equivalant test to use on an automobile, bearing in mind that
the test you recommended is 180 degerees different in what it is
you're measuring (supply vs. consumer)?
The day isn't over.
Basically, the throw away stuff, where if changing the CMOS
battery doesn't fix it, it gets shit canned.
You do realize that if the above sentence were part of your
fourth grade final exam, you'd be taking the year over, don't you?
Yes, the educational system is very very seriously flawed.
Why yes, yes I have. Too bad [yours] wasn't an example.
Went a "googleing" did ya?
How close is the meter that *I* am measuring with?
As a matter of fact, it would be a (in no particular order) Fluke
87, and a Fluke 77, and a Fluke 12B, and a Tektronics 5103 analog
oscilloscope, and a Pico scope, and a UEI 7100 DSO (Sun LS-2000),
and a MT-1560 AVR, and a MT-3000 DSO/engine analyzer. Then
Hooray!!! Someone else is talking sense. Very well done Neil, you are
absolutely correct in what you say (not that I need to tell you that as you
seem to understand PN junctions and how to cope with their vagaries) .
The problem is either the battery or the vehicle. Forget how old the
battery is, its irrelevant - have you never bought anything new that's bust?
Also, whilst 12.5 volts is a good indicator, that's all it is. You can't
tell what's going on inside the battery. I had a battery, 2 years old,
that would only hold its charge for about 2 days. Not start the car over a
weekend and forget Monday morning! yet it would start the car every
consecutive day. Change the battery and problem solved.
But the problem could be a steady drain on the battery. If you have a
clock in the car, a car alarm, etc then you will always see a small current
draw. With a trunk light with a faulty switch, a fused PN junction in any
electronic device that is permanently connected to the battery (e.g.
alternator) then a minor fault in any of these may cause a few hundred
milliamps to be drawn and therefore drain the battery in a few days. If
you have a major component failure drawing more that a few amps then a fuse
will blow or if unfused the car catches fire.
So, do the following to identify where the problem is:-
1. remove the ignition key,
2. remove the +ve lead from the battery,
3. put a meter between the battery terminal and the lead just taken off and
read the current.
If the current is more than a few tens of milliamps then there is a problem
somewhere with the vehicle and follow Neil's very sensible advise to
identify where the problem is. If the current drawn is less than about 20
milliamps then changing the battery will fixed then problem.
And don't trust any battery over 3 years old, especially in winter time, and
lets hope we all get 7 years out of a battery like a previous writer.
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