Maker Pro
Maker Pro

Auto battery question

Q

quietguy

Jan 1, 1970
0
While I do not know a lot about this issue, I thought it pertinent to
mention that some late model vehicles warn strongly against using jumper
leads that do not have full spike protection built in - apparently the
computer modules are very easily damaged by spikes

David
 
Q

quietguy

Jan 1, 1970
0
So, if he inserts the multimeter in one of the battery leads, and then
tries to start the car, he will surely need a new multimeter!

Not that I am disagreeing with you Bob, but rather the idea of putting a
meter in one of the battery leads worries me greatly. Even if the
starter current is avoided, I have an idea that late model alternaters
can put out 80 odd amps or so, and not many multimeters (or their test
leads) can handle that

Only safe way to measure the charge current to my mind is a proper meter,
or a shunt/voltage arrangement

David
 
K

Kitchen Man

Jan 1, 1970
0
That may be true, but it's crappy design, and borderline
incredible.

It isn't crappy design. The auto electrical system is designed to
operate with a BATTERY INSTALLED. If you take the battery out, you've
buggered the design. Would you saw a load-bearing member from your
home, then blame the architect when the ceiling fell in?
It's easy to design a shunt which detects
an open circuit condition.

Reckon the hard part is convincing the budgeting department to pay for
a bunch of fail-safe circuitry, meant to protect the machinery in the
event the user removes critical parts, willy-nilly.
 
K

Kitchen Man

Jan 1, 1970
0
A few days ago, my car wouldn't start. The dashboard
electronics were all working, so I figured it's a
dying battery...

Not a bad assumption.
This morning, the battery was totally dead. No electric
power. I asked a neighbor for a jump start, we hooked
it up, and again the starter wouldn't respond. However,
the electronics were operating, so it's not the regulator or anything.

The regulator hasn't had time to figure in the problem; the regulator
doesn't factor until your auto is turning rpms. The regulator
regulates alternator output to a set voltage in conjunction with the
battery, the battery regulates the whole system in conjunction with
the output current of the alternator/regulator.
I thought, oh oh, problem! Starting motor burned out,
or frozen engine. Then I thought: what else could it
be?

Could be a dead battery.
Maybe the battery is shorting out the circuitry,
is that possible? That means when we tried the jump
start, the battery drew all the current, leaving
nothing for the starter.

This is possible, but unlikely if the starter is not giving any
indication at all that it is trying to turn. If it is at least
wheezing and groaning, then the most likely culprit is the battery.

If you get nothing, I mean absolutely nothing, then you might have
some loose or detached wiring in the starter circuit. If you get loud
clicking then the starter relay is bad and must be replaced. Seized
engine is a bit unlikely. If you get a whirring sound from the
starter but no engine movement, then the starter is bad. In any case,
the battery is probably fried from its misuse these past few days and
should also be replaced.
So I unhooked the battery, and asked another neighbor
for a jump, directly to the cables. But he refused!
He said, without the battery, his alternator could
blow out. I.e. my battery 'protects' his charger.

Could he be right? It doesn't make sense to me.

He's right, as has been pointed out. The battery is an essential
component for the proper operation of the auto electrical system. It
functions as both a filter and a regulator, and its size in amp-hours
is chosen to fit the requirements of the auto electrical system.

Using your good-Samaritan neighbor's battery alone is a really bad
idea for two reasons: first, its functionality will be impaired by
being used to run two autos instead of just one. Second, once you
start your vehicle, the two autos are now merged like Siamese twins.
You take the jumper cable off in this configuration, and watch the
fireworks start!
Any suggestions appreciated -

Kindly remember that you said that! ;-) I recommend you pursue some
web sites in search of tips for proper care of batteries and starters.
Unsaid in your post is any indication of how the battery or the
starter may have been misused in the recent and not-so-recent past.
Such information is helpful when troubleshooting.
 
K

Kitchen Man

Jan 1, 1970
0
That's what I figured. I don't see how my battery being
disconnected is a hazard.

You'd do well to get over that lack of vision.
 
K

Kitchen Man

Jan 1, 1970
0
While I do not know a lot about this issue, I thought it pertinent to
mention that some late model vehicles warn strongly against using jumper
leads that do not have full spike protection built in - apparently the
computer modules are very easily damaged by spikes

A couple of three points on your excellent point - yes, modern auto
electronics can be destroyed by voltage spikes; voltage spikes can and
do appear when placing a charged battery in parallel with a discharged
battery; the more deeply the low battery is discharged, the more
potentially destructive the voltage spikes.
 
H

Herman Family

Jan 1, 1970
0
kell said:
get a new one and drive

You can check the car for current draw easily if you have a multimeter.
Set the multimeter to measure current; put it on the highest setting.
Disconnect one of the battery cables and use the multimeter's leads to
complete the circuit you have just broken. The meter will tell you
exactly how much current is drawing.
You can check for a bad diode in the alternator. With the car off,
disconnect the heavy wire from the alternator and do the same
multimeter test.

Don't do this without checking your multimeter ranges. Some of them which
aren't made for automotive use tend to do poorly above about half an amp.

Michael
 
M

Martin Underwood

Jan 1, 1970
0
Kitchen Man said:
On 8 Sep 2005 13:16:00 -0700, "Sam the Bam" <[email protected]>
wrote:

Kindly remember that you said that! ;-) I recommend you pursue some
web sites in search of tips for proper care of batteries and starters.
Unsaid in your post is any indication of how the battery or the
starter may have been misused in the recent and not-so-recent past.
Such information is helpful when troubleshooting.

Batteries can go dead for no apparent reason. I check the electrolyte on my
battery every few weeks (it's very rare that the level is ever below normal)
and I don't leave the starter motor whining away if the car won't start - if
it hasn't started within a couple of seconds, it's not going to: let the
engine rest for a few moments and try again. And being a diesel it starts
first time every time (*) so it's rare to need a burst of more than a second
or so on the starter motor.

Even with these sensible precautions, I had a perfectly good battery go bad
on me the other year. I'd given my girlfriend a lift to the dentist and sat
and waited for ages for her to come out. I didn't have any electrics (radio,
blower, lights etc) turned on. The battery had started the car fine that
morning - and every previous morning. But when I came to set off again, the
battery was absolutely dead: it would barely light the ignition light, let
alone turn the engine over. In an older car, I'd have push-started the car
(the advantage of having a manual gearbox!) but that's strongly discouraged
in cars with fuel injection and/or catalytic converters. What made it even
more frustrating was that I was parked right outside a car-spares shop, but
She Who Must Be Obeyed told me that I was an idiot to simply replace the
battery without first of all calling out the RAC (breakdown recovery). The
RAC man took a long time to get there, by which time SWMBO was getting very
irate and telling me how late I was going to make her for work. When the RAC
man did arrive, he did a few tests and quickly established what I've
suspected all along and was prepared to take a chance on - the battery was
buggered. Two minutes later I'd bought a new battery, already fully charged,
the man had fitted it and I was on my way. I resisted the urge to say "I
told you so" - but I'm afraid I did think it!



(*) Except when the fuel pump fails - as it did on Wednesday. Engine turning
over at full speed but absolutely nothing from the engine - not a splutter
or a cough. £200 that's going to cost me in parts and the technician's time
to diagnose the fault. Grrr! Still, it happened only about 200 yards from
home so I was close enough to go home to wait for the garage man to arrive.
And as luck would have it, all except one of the customers that I was due to
visit were within walking or cycling distance of home: not often that things
work out that well for me!
 
BobG said:
Don't ever disconnect that battery once the engine is running, because
the alternator, which was happily charging the battery when it was
connected, will suddenly see the charging current drop, and shoot the
charging voltage up to 60V. This is called a 'load dump' and makes for
lots of fried 12V electronics.

Over the last 30 years, I've had 3 batteries go open circuit while
still being connnected. Apparently an internal jumper breaks. In all
cases, there was not enough power to run more than the dome light, and
all were jumped and driven to a battery store. 2 of the 3 had computers
running fuel injectors and ignition systems and none of the cars had
electronics failures. The one 30 years ago was driven 20 miles to get a
new battery. I'm sure I listened to the radio on the way. Are you sure
those weren't old mechanical (relays and such) regulators?
GG
 
J

Jasen Betts

Jan 1, 1970
0
So I unhooked the battery, and asked another neighbor
for a jump, directly to the cables. But he refused!
He said, without the battery, his alternator could
blow out. I.e. my battery 'protects' his charger.

Could he be right? It doesn't make sense to me.

having a battery in the circuit helps the regulator in the altenator do its
job, you're unlikely to damage his altenator. but running your car with no
battery is a bad idea.
Any suggestions appreciated -

give the starter motor a good hard whack on the side (prod it vigorously with the jack
handle etc... the case is 1/4" steel or thicker - you're unlikely to damage it)
then try the starter again, (repeat upto 10 times before giving up)

If that works your the cause of the failure may have been worn brushes in the
starter - time to rebuild it (or exchange it for a rebuilt one)

Bye.
Jasen
 
Q

quietguy

Jan 1, 1970
0
The symptoms are also suggestive of a poor connection to one or both of
the battery terminals - high resistance connection allows the dashboard
stuff to work, but not the starter etc. - could also be a bad connection
of the earth or starter cables at either end

Worth checking just in case

David
 
K

Kitchen Man

Jan 1, 1970
0
The symptoms are also suggestive of a poor connection to one or both of
the battery terminals - high resistance connection allows the dashboard
stuff to work, but not the starter etc. - could also be a bad connection
of the earth or starter cables at either end

Worth checking just in case

True. Starters do not operate in the cleanest of environments, it
would do to check the connections.
 
G

Guest

Jan 1, 1970
0
If a battery is low on electrolyte, it can appear to be nearly a dead short.
Check the electrolyte
FIRST, and top up with distilled water, if needed.

Clean the battery posts and terminals. Both tend to oxidize badly over time
and present an
unacceptably high resistance in the circuit. (Some multiple battery cables
(particularly GM types)
may corrode underneath the terminal insulation. They may look good but in
reality be defective.
These too can be cleaned but it is a bit more of a chore.)

Invest in a cheap 6-8 amp battery charger. You can get one for about $20,
and your neighbor won't
have to risk his alternator and battery. ( Yes, if you don't really watch
what you are doing, you can
blow the diodes in an alternator and, in some cases, cause the battery to
explode.) Charge your
battery overnight and have a go.

If your battery is getting over a couple of years old, it may be bad. Lot
of cheap crap in the market.
(Lots of expensive crap too.) Other things that can discharge a battery
include drive belts (can be
burnished with use and may slip) and courtesy lights which are staying on.
 
J

Jasen Betts

Jan 1, 1970
0
So, if he inserts the multimeter in one of the battery leads, and then
tries to start the car, he will surely need a new multimeter!

:) I've never lost one to over current (burned out a few fuses that way
though) I did manage to bend the needle round the stop once by giving it
600V while on the 10V range, I burned out some resistors hat time too.
Not that I am disagreeing with you Bob, but rather the idea of putting a
meter in one of the battery leads worries me greatly. Even if the
starter current is avoided, I have an idea that late model alternaters
can put out 80 odd amps or so, and not many multimeters (or their test
leads) can handle that

easiest way is to use a clamp meter. cheapest is to mesaure the voltage
drop acrosss a portion of the earth strap. while draweing a known current, and
extrapolate forom there.

Bye.
Jasen
 
J

Jasen Betts

Jan 1, 1970
0
["Followup-To:" header set to sci.electronics.basics.]
Why not? As I understand it, the alternator runs everything
after start up. Is there an interlock, which shuts down the
system if it detects an open circuit condition?


the freewheeling diode in the regulator means that whebn the regulator
senses the over voltage all it can do is stop boosting the current it the
altenator's field windings (which behave like a large inductor), it can't
kill the current and while the current is decaying the altenator is
producing an over voltage.

If the altenator was charging at maximum power when the battery was
disconnected nasty things can happen.

if you get jump started had have an open circuited battery the voltage in
the system is initially limited by the other car's battery and with the
other car's engine running the regulator won't see a low voltage and wont
turn the altenator on at full power...
Any service garage can check for this?

pretty much, the first test is to hook a voltmeter across the battery
terminals and rev the engine a little (2000-3000 rpm is enough) if the
needle stays below 13V the altenator isn't working if it's stays below
14V there's probably somethign wrong.

most DIY service manuals (eg Haines, Gregorys, etc) cover this in the chapter
dealing with the electrics, check the local library.

the cause could be a loose cable, worn brushes, a dead regulator, a diode failure,
or other more catastrophic (ie expensive) altenator failure.
How to do this? There are no gauges on the dashboard.

measure the voltage across two points on the earth cable (but not the ends
in case the terminals on the cable are loose) do it firrst with some small
load turned on (eg dome light) and then with it turned off (the reading
shoud be significantly less (all that should be running is the clock, alarm,
etc... )
 
Top