Adding voltmeter to car

[Douglas Payne]

Conor wrote:

In article <gc0u32t4gc55rpqe3pjfuvvev1rhlk4vl4@4ax.com>, Gary Schafer
says...


If I had only one instrument to connect to the car to watch the
battery it would be a voltmeter.


Spot the pillock who knows fuck all about car electrics.


A voltmeter will tell you much more
about the battery and the charging system than an ammeter.


No it won't. A completely fucked battery can show >12v but still not be
able to provide enough current to turn an engine over.

Think I'm wrong? Why are batteries tested with a drop meter?

Is a drop meter like a voltmeter for measuring voltage drop?

--
Douglas

 

[hob]

"Ed" <ed@NOSPAMmicra.org.uk> wrote in message
news:VUL%f.677$nh5.581@newsfe7-win.ntli.net...

hob wrote:
"Gary Schafer" <gaschafer@comcast.net> wrote in message
news:gc0u32t4gc55rpqe3pjfuvvev1rhlk4vl4@4ax.com...

On Thu, 13 Apr 2006 22:23:47 +0100, Andy <nomail@nomail.com> wrote:


I am in the UK and have a 1.3 litre Mazda which is over 10 years
old.

I have been reading a few web pages which made reference to the
reader's car which "may have a dashmoard voltmeter".

Is a voltmeter actually all that useful to see tjings like what
the condition the battery is in and how the battery copes and how
it is charging?

Can I permanently connect my cheap handheld digital voltmeter to
the car battery. I would then mount the meter permanently on the
dashboard.

Is there a real danger that the meter will get damaged by various
current or voltage surges? Is it good enough protection to have a
quick blow fuse in line with the test lead going to the positive
terminal?

Thanks

If I had only one instrument to connect to the car to watch the
battery it would be a voltmeter. A voltmeter will tell you much more
about the battery and the charging system than an ammeter.

A properly running alternator should raise the battery voltage to
around 14 to 14.2 volts. Some cars may run as high as 14.4 volts. Any
higher and you can suspect a problem with the regulator.
If the voltage fails to come up this high you can suspect a problem in
the alternator, shorted diode etc.n


or more usually, the connections on the dash. (like my three cars).


A voltmeter can also tell you if the alternator is capable of putting
out enough current.


Just kind turning on the fan and watching the lights dim, but the
voltmeter
is not nearly as accurate.

If you were to log voltage over time it would tell you a whole lot more
than current.

As you turn more things on, lights,

air-conditioning etc. the alternator should be capable of maintaining
the voltage at the 14 volt range.


granted, the voltmeter tells you that the computer says to raise the
field -

Computer? ignition simply being ON energises the armature field. I've
not seen any computer input needed here?

The computer controls the field of the alternaotr - think "voltage
regulator"

but it does not say if anything is being generated and/or sent to the
battery.

Wrong! It shows exactly this.

Sorry -WADR - wrong -- since a voltmeter only directly measures potential,
it CANNOT directly measure flow. And energy flow is what fills the battery,
not electrical potential.
14 volts on the line means 14 volts at the alternator, not amps flowing
into the battery or flowing out of the alternator.

A car battery will not rest at 14v.
therefore if your measuring 14v @ battery you know without any question
what so ever that the battery is being charged.


- kind of like my jeep did two weeks back, where the voltmeter said
all
was ok - and the battery had just enough to turn it over twice.

High internal resistance, you'll again see this by cranking the engine
and the battery voltage will fall extremely low, again an ammeter will
not be able to show this.

Hmm.. think of it this way..
crank the engine and watch the battery voltage fall extremely low and then
I can tell that I have a battery problem - a reason to have a voltmeter?

Hint - _I_ do not need a voltmeter to tell me my battery is bad when I can
also hear my starter drop off after a second or two of cranking.
"rrr..rr..rrr....." "look, my voltmeter is dropping fast"
"rr........rr..............rr.........
.......r.....................................". (It's not the voltmeter that
says my battery is dead.)

That is why the voltmeter is refered to as a "battery is missing" gauge.
It tells you there is a problem nearly always AFTER it is fairly obvious
there is a problem.

An ammeter,on the other hand, spikes and drops back after start, telling you
the alternator is outputting, the regulator is responding, and the battery
is accepting. The level of flow tells you the cable condition. The best
part is that unlike a voltmeter, it tells you before the battery is missing.

And next time it didn't start with 12 volts shown, so after it was
running
after a jump (voltmeter had said zero) - voltmeter went to 14.4 and then
went down to 13.5 after driving. But the ammeter said it was sending 10
amps into a battery. At the shop, the disconnected battery had all of
11
volts and wouldn't take a charge.

Again what you have said shows a tired and worn battery
(cracked/sulphated cells) and can be easily demonstrated with a load
(cranking) and a voltmeter.

Or rather than use a voltmeter and runa test, perhaps just use an ammeter
while driving?

(BTW, the battery in my example was less than 18 months old, and bad.)

Voltmeter was reading alternator output
voltage, not energy going into the battery. The battery had the capacity
of
a AAA, and tyhe voltmeter said 12 volts.

Your completely reading this wrong. The fact that the voltmeter was
working and correctly showed your system voltage showed you immediately
where the problem was (battery) Process of elimination. You see the
symptoms - battery voltage is ok, charge voltage is ok, yet not enough
current to crank = dead battery!

Or bad cable, security system lockout, or faulty starter relay, all of which
give the same symptoms -- and all only after I am dead in the water..

I put my DC power-ammeter on the battery cable of the running vehicle and
saw under 10 amps feeding the just-jumped 18 month old dead battery - THAT
was my definitive on the problem. The ammeter on a running vehicle said
bad, the voltmeter on the running vehicle said good.
If I had had an ammeter on the dash as we used to have or as I have in
my RV instead of a "battery missing" gauge I would have been in for a
charging system check well before I needed a jump.

If the voltage drops well below that

range you can look for problems.



Just like a low battery does - turn the key and get a click, but the
voltmeter is not as accurate

Yes it is!

both tell you it is dead - how can one be more accurate? - it is dead, not
slightly dead.

After the car has been shut down for a period of time you can read the
battery voltage to tell you the approximate charge on the battery by
the resting voltage.

You can also watch how far the voltage drops when turning on
headlights etc. with the engine not running. If the voltage drops way
off you may have a battery that is developing a high resistance,
battery is dying.


Of course, turning the key after that test also tells you you need a tow
and
a battery.
An indication which helps a lot when you are driving - that is also
indicated by the car not starting.

If you do this test and then you are unable to start, like Gary said the
battery is dying. Clearly if you felt this was such a risk you would not
make this test unless you had another way to start the car. There are
thousands of cars on the road with batteries that have nearly no reserve
capacity, you need surprisingly little to be able to start a car, but
you only really notice after you have left your lights on for a few mins
only to discover you cannot start again!

You can also watch how far the voltage drops when starting the car.
This is another indication of battery condition.

None of these things can be done with an ammeter.


And nor does one want to - and unlike voltmeters that tell you voltage
level
rather than energy transfer, ammeters only check the battery input and
output running and motor off, and the charging circuit, the starting
circuit, alternator output, and cable/connection/belt condition running.
You
know, the energy the vehicle actually uses.

No offence I think your blinded by your own ignorance.

No offense taken, but you should know that besides having hobbied for 40
years in racing and auto restoration, and having worked on everything from
V-12 Ferarris to flathead Fords, Austins to 300Zs; having worked hands on
from 120,000 volts at 60 amps to 1 volt analogs; repaired and certified test
equipment from scopes to rf meters; as one who consulted on those
early/mid-eighties-vehicle analog computers post 80s; and as a PE, degreed
in electrical and mechanical, I do have some hands-on as well as theoretical
knowledge of measuring and automotive circuits.

And I should note that we need to keep in mind that an ammeter is just a
voltmeter measuring load across a fixed known resistance.

An in-dash voltmeter merely uses unknown loads to get qualitative
measurements of energy capacity and implied flow, while an ammeter gets
quantitative realtive measurents of amount and direction of energy flow at a
known common point, using a fixed resistance.

Everything you

say there can be shown better with a volt meter. You say that an ammeter
shows the "cable/connection/belt condition running" ok so what exactly
should the current be when its all correct? I can tell you a voltage
that I know would be right but since once the car has started and the
battery has regained its lost charge (not long under usual conditions)
how an ammeter between the battery and anything else would show nothing
useful at all, apart from a varying and often small charge. (which again
can be shown much better with a voltmeter showing around 14v)

Lets assume you connect it in series with the alternator. An instant
disadvantage is the fact that you now have introduced more resistance to
the circuit, so you slightly loose efficiency (fact of physics and is
how all ammeter works)

a .01 ohm shunt at 12 volts is far less a loss than the corrosion in the
battery cable terminals or lamp sockets. 1/8 watt loss is a red herring.

You could be running in daylight conditions

lights off and little load, you could be running at night in the rain
lights on heaters on fans on etc etc and again you see load. Great. So
are you actually going to be able to see what current is right or wrong
as fast as I can read a voltmeter and go PROBLEM or not?!

First - While voltmeter readers need to have the actual value of the
measurement to make a decision - ammeter readers only need direction and any
quantity to make a decision.

In other words, you are mistaken to believe I need a value to determine
the existance of a problem using an auto ammeter- the determinates for the
auto ammeter are "in or out", "quantity or no quantity", "large amount or
not". The specific value of flow is actually immaterial.
(and since the definitive amount of flow varies with environment and
accessories anyway, an exact amount is meaningless except to the few more
knowledgeable, and then in context.)

second - in your example, difference is -
1) I see no spike several seconds after start on an ammeter, that time just
after starting being the time when I and most people check all the gauges -
and I check the problem out before I am stuck somewhere -
- but with a voltmeter, with a good battery but alternator putting out 14
v and way-low current, it says 14 volts and my once good battery soon
becomes a 20 amp-hour-capacity-left no-reserve battery, and I am dead and
towed.

2) My ammeter says outflow five seconds after I start the car and it stays
there - time to get to garage -
same condition - my voltmeter says "OK" and I drain the battery as I drive
away on my sunny day, and after twenty miles heading to the woods the needle
is down enough to notice I have low voltage- and out twenty miles, I will
shut down on fault before I can get back to a garage.

An ammeter will only tell you if the battery is being charged or
discharged at a particular time. If the battery has a high resistance
or is fully charged you can not tell the difference with an ammeter.


Sorry, yes you can. Same symptoms as with the voltmeter.

Nope not so. A battery with high internal resistance with an ammeter all
you would see is a charged battery, that assumption made by the fact
that there will be little charge current.

A battery with a high resistance will give you a running-vehicle voltmeter
reading of 14 volts (had it happen several times), while an ammeter will
give you no flow into the battery -
(there is always flow into the battery for 30 seconds after start)

You know, there's a reason so many expereinced people in
alt.engineering.elect jumped on the thread to roundly condemn voltmeters
as
next to worthless-

Using other peoples posts to back up your own is pretty pointless.

(BTW, the reason ammeters were removed was to save weight to get fleet
mileage up - an ammeter takes a ballast resistor and heavy cables and
connectors. A voltmeter takes an inch of circuitboard foil. And,
anything a
voltmeter does is also sensed by the diagnostics and flagged, on my
vehicles)

The main reason they were removed as they are not needed as people
wouldn't know what's right or wrong, and alternators have simply removed
the need. Where as voltage meters are much more common, because that
actually shows you something useful.

Further if current meters are such a good way of knowing the status of
charge of a battery or condition of a system then intelligent battery
chargers would measure and monitor battery charge by current - which
they don't. Virtually every type of charger stops when a certain voltage
is met, and has no concern with current other than the fact to limit it
to prevent damage to cells.

Totally different condition - the parameter in a vehicle is condition of the
charging and battery system and its controls in a two direction system-
the parameter in a battery charger is to control rate of charge and
prevent overcharge in a one direction system.

 

[hob]

"Gary Schafer" <gaschafer@comcast.net> wrote in message
news:fkgv32hadmm7s85ehgp864md13fojtdlmg@4ax.com...

On Fri, 14 Apr 2006 12:15:42 +0100, Conor <conor.turton@gmail.com
wrote:

In article <gc0u32t4gc55rpqe3pjfuvvev1rhlk4vl4@4ax.com>, Gary Schafer
says...

If I had only one instrument to connect to the car to watch the
battery it would be a voltmeter.

Spot the pillock who knows fuck all about car electrics.

A voltmeter will tell you much more
about the battery and the charging system than an ammeter.

No it won't. A completely fucked battery can show >12v but still not be
able to provide enough current to turn an engine over.

Think I'm wrong? Why are batteries tested with a drop meter?


Actually if a battery only shows "12 volts" it is near dead!

Which makes a voltmeter next to worthless for determining the amount of
energy in a battery. 50 amp hours worth of charge on a sulphated battery
reads 12 volts, and 800 amp hours worth of charge reads 12 volts.
But one take a lot of current, and the other takes hardly any.

If you will take note, when a battery is tested with a "drop meter" it
actually has a voltmeter in the instrument! Simple ones have ONLY a
voltmeter! More sophisticated ones have a voltmeter and an ammeter.

I think you are confused as to what an ammeter actually is... the drop test
uses an ammeter (a shunt and a voltmeter) to check battery condition.

An ammeter is just a voltmeter reading across a known resistance (i.e.,
voltage drop across a shunt carrying the current).

(And technically, all voltmeters use current passed through a known
resistance, the series resistor, to get a voltage indication. )


In the drop test, a known resistance is placed across the poles of the
battery, and in actuality, it is the voltage across that known resistance
that is measured to determine current flow.

In other words, and in comparison -

The "drop test" measures the amount of current drawn by the battery
through a known resistance (amps through the resistance), the amount of
current then indicated by the voltage across the known resistance. The meter
reads in volts, and the reading drops off as the current in the shunt drops
off.

An ammeter measures the amount of current drawn through a known resistance
(amps through resistance), the amount of current then indicated by the
voltage across the known resistance, The meter reads in amps, and the
reading drops off as the current in the shunt drops off (or increases as the
current increases)

In BOTH cases, a KNOWN resistance is used.

The idea of the test is to see how well the VOLTAGE holds up on the
battery with a given load placed on it. With the simple testers it is
a given amount of resistance placed on the battery for a certain
length of time while monitoring the battery voltage.

If the resting voltage of lthe battery, no load, shows 12.6 to 12.8
volts that is an indication of a fully charged battery. If that voltage
drops significantly with the load test then the battery probably has a
high internal resistance. If the resting voltage is near 12 volts the
battery is in need of charging.

With the better units which contain an adjustable load, ammeter and
voltmeter the load is adjusted to see how much current the battery can
supply before the voltage drops to a certain level. Without knowing
the voltage the rest of the test is pretty much meaningless.

If you read my first post again, carefully, you will see where I
explain (with the engine off) how to watch the voltmeter in the car
while turning on accessory items and watching how far the voltage
drops to give you an indication of battery health. Also how much the
voltage drops when starting.
This does essentially the test that is done with a load tester.

One important point about use of the voltmeter, it needs to come
directly from the battery terminals and not be connected into wiring
that also serves other things like lights etc. Otherwise you will not
get a true reading of battery voltage when turning those other things
on as it will also read the voltage drop in the wiring and not the
true battery voltage.

Also note that some factory installed voltmeters are wired as noted
above and some are also very poor quality meters.

All factory voltmeters that I know get their voltage from the circuit board
of the dash indicators.

You can have all the instruments you can manage to gather but if you
don't know how to interpret them they do little good.

Regards
Gary

 

[Andy]

"Andy" <nomail@nomail.com> wrote :

I am in the UK and have a 1.3 litre Mazda which is over 10
years old.

I have been reading a few web pages which made reference to the
reader's car which "may have a dashmoard voltmeter".

Is a voltmeter actually all that useful to see tjings like what
the condition the battery is in and how the battery copes and
how it is charging?

Auto voltmeter - also known as the "somebody stole your battery"
gauge. Because other than a missing battery, it basically tells
you, too late, what you already know - weak lights, poor start,
bad battery, etc.

On 13 Apr 2006, hob<dehoberg@comcast.net> wrote:

An in-dash ammeter, on the other hand, tells you before you are
stranded if you are charging or discharging the battery and how
much is going in or out, and the amps are if steady or
fluctuating , all of which can be used as an indicator for the
condition of the alternator and battery, the connections, and
switch-off draining.

Don't waste your time putting in a voltmeter.

Hob,

It seems to me that I can just connect a voltmeter across the
battery terminals and (as someone in this thread mention) include
an fuse inline with the hot wire near the battery as a safety
precaution.

I'm not familiar with current shunts (which you mention
elsewhere).

Where can I get a suitable current shunt from for my car and very
roughly what do they cost?

Do I simply install the shunt across the battery terminals and
then place a voltmeter (sic) across the two terminals of the
shunt?

Would I need to calibrate my multimeter to the shunt in order to
measure current values correctly?

Thank you.

Can I permanently connect my cheap handheld digital voltmeter
to the car battery. I would then mount the meter permanently
on the dashboard.

Is there a real danger that the meter will get damaged by
various current or voltage surges? Is it good enough
protection to have a quick blow fuse in line with the test lead
going to the positive terminal?

Thanks

 

[Conor]

In article <PKM%f.44330$g76.34878@newsfe2-gui.ntli.net>, Ed says...

Conor wrote:
In article <443f6aaa$0$32103$5a62ac22@per-qv1-newsreader-
01.iinet.net.au>, Rheilly Phoull says...


Each to their own IMHO I like both but if had to choose would go the
voltmeter.


walks away shaking head

What?

Ok so you have a car come in with a charging problem.

Do you:

1, pick up your ammeter and proceed to test with this.

or

2, pick up a volt meter and proceed to test with this.

Does your voltmeter tell you the condition of the battery? No.

--
Conor,

Same shit, different day.

 

[Conor]

In article <fkgv32hadmm7s85ehgp864md13fojtdlmg@4ax.com>, Gary Schafer
says...

Actually if a battery only shows "12 volts" it is near dead!

Priceless....

--
Conor,

Same shit, different day.

 

[Conor]

In article <4aa0j6Frig3gU1@individual.net>, Douglas Payne says...

Conor wrote:
In article <gc0u32t4gc55rpqe3pjfuvvev1rhlk4vl4@4ax.com>, Gary Schafer
says...


If I had only one instrument to connect to the car to watch the
battery it would be a voltmeter.


Spot the pillock who knows fuck all about car electrics.


A voltmeter will tell you much more
about the battery and the charging system than an ammeter.


No it won't. A completely fucked battery can show >12v but still not be
able to provide enough current to turn an engine over.

Think I'm wrong? Why are batteries tested with a drop meter?

Is a drop meter like a voltmeter for measuring voltage drop?

It places an extremely high current drain on the battery.

--
Conor,

Same shit, different day.

 

[Boris Mohar]

On Fri, 14 Apr 2006 10:31:58 -0700, Jamie
<jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote:

Boris Mohar wrote:

On Thu, 13 Apr 2006 22:23:47 +0100, Andy <nomail@nomail.com> wrote:


I am in the UK and have a 1.3 litre Mazda which is over 10 years
old.

I have been reading a few web pages which made reference to the
reader's car which "may have a dashboard voltmeter".



I added a wide range 270° battery voltmeter in my first Volvo. It would
read from 8 to 18 volts. One time on a long trip through Colorado I noticed
that it was reading over 16Volts. It was a very hot day and battery voltage
coefficient being negative, the reading should have been around 13V. It
turned out that the regulator had shorted out and was dumping the generator
to the battery. I turned on every electrical load and drove in the highest
gear over to the dealer.



Regards,

Boris Mohar

Got Knock? - see:
Viatrack Printed Circuit Designs (among other things) http://www.viatrack.ca

void _-void-_ in the obvious place


did you happen to smell a strange odor under the hood ? just don't
light up while looking under the hood! )

Yes. Smell of sulfur like the devil himself was on fire. BTW when I was
very young and ignorant I lit a match to look at the electrolyte level of a
charging car battery. Suffice to say that I am very glad that I was wearing
glasses. Earplugs would have helped too.

--

Boris Mohar

 

[Gary Schafer]

On Fri, 14 Apr 2006 13:12:08 -0500, "hob" <dehoberg@comcast.net>
wrote:

"Gary Schafer" <gaschafer@comcast.net> wrote in message
news:fkgv32hadmm7s85ehgp864md13fojtdlmg@4ax.com...
On Fri, 14 Apr 2006 12:15:42 +0100, Conor <conor.turton@gmail.com
wrote:

In article <gc0u32t4gc55rpqe3pjfuvvev1rhlk4vl4@4ax.com>, Gary Schafer
says...

If I had only one instrument to connect to the car to watch the
battery it would be a voltmeter.

Spot the pillock who knows fuck all about car electrics.

A voltmeter will tell you much more
about the battery and the charging system than an ammeter.

No it won't. A completely fucked battery can show >12v but still not be
able to provide enough current to turn an engine over.

Think I'm wrong? Why are batteries tested with a drop meter?


Actually if a battery only shows "12 volts" it is near dead!

Which makes a voltmeter next to worthless for determining the amount of
energy in a battery. 50 amp hours worth of charge on a sulphated battery
reads 12 volts, and 800 amp hours worth of charge reads 12 volts.
But one take a lot of current, and the other takes hardly any.

I see you like to pick things out of contexts to try and bolster your
point. If you read further about the point I make of loading the
battery, the voltmeter will easily tell you if you have a sulphated
battery. The ammeter willl not. The ammeter may tell you that there is
no or little charge going to the battery but you don't know if it is a
charging system problem, a battery problem or no problem at all.

If you will take note, when a battery is tested with a "drop meter" it
actually has a voltmeter in the instrument! Simple ones have ONLY a
voltmeter! More sophisticated ones have a voltmeter and an ammeter.


I think you are confused as to what an ammeter actually is... the drop test
uses an ammeter (a shunt and a voltmeter) to check battery condition.

I am not sure exactly what you call a "drop test" on your side of the
pond. Over here we call it a "load test" and it is done with equipment
as I described. Maybe you don't understand how a load test works?

A simple tester has just a voltmeter, used as a voltmeter not as an
ammeter, and a fixed load resistor to see how long it takes for the
battery voltage to drop to a certian voltage when the load is applied.

The better units use both a voltmeter and ammeter along with an
adjustable load resistor to accomplish the test. Again, as I
described.

An ammeter is just a voltmeter reading across a known resistance (i.e.,
voltage drop across a shunt carrying the current).

We could also turn that around and say that "all voltmeters are just
ammeters with known series resistors" if we want to try and further
confuse the issue of whether we are measuring battery voltage or
current.

I am fully aware of how an ammeter and voltmeter work and how they are
used.

And technically, all ammeters are not necessarily voltmeters. As a
matter of fact most all of the older automotive ammeters were not
voltmeters inside them. They worked on the principle of directly
measuring the magnetic field produced by the wire passing through
them. No voltage drop across any resistance required.

(And technically, all voltmeters use current passed through a known
resistance, the series resistor, to get a voltage indication. )


In the drop test, a known resistance is placed across the poles of the
battery, and in actuality, it is the voltage across that known resistance
that is measured to determine current flow.

In other words, and in comparison -

The "drop test" measures the amount of current drawn by the battery
through a known resistance (amps through the resistance), the amount of
current then indicated by the voltage across the known resistance. The meter
reads in volts, and the reading drops off as the current in the shunt drops
off.

Is "your" "drop test" measuring battery voltage or current supplied?
In other words, what is the meter calibrated in?

An ammeter measures the amount of current drawn through a known resistance
(amps through resistance), the amount of current then indicated by the
voltage across the known resistance, The meter reads in amps, and the
reading drops off as the current in the shunt drops off (or increases as the
current increases)

In BOTH cases, a KNOWN resistance is used.

The idea of the test is to see how well the VOLTAGE holds up on the
battery with a given load placed on it. With the simple testers it is
a given amount of resistance placed on the battery for a certain
length of time while monitoring the battery voltage.

If the resting voltage of lthe battery, no load, shows 12.6 to 12.8
volts that is an indication of a fully charged battery. If that voltage
drops significantly with the load test then the battery probably has a
high internal resistance. If the resting voltage is near 12 volts the
battery is in need of charging.

With the better units which contain an adjustable load, ammeter and
voltmeter the load is adjusted to see how much current the battery can
supply before the voltage drops to a certain level. Without knowing
the voltage the rest of the test is pretty much meaningless.

If you read my first post again, carefully, you will see where I
explain (with the engine off) how to watch the voltmeter in the car
while turning on accessory items and watching how far the voltage
drops to give you an indication of battery health. Also how much the
voltage drops when starting.
This does essentially the test that is done with a load tester.

One important point about use of the voltmeter, it needs to come
directly from the battery terminals and not be connected into wiring
that also serves other things like lights etc. Otherwise you will not
get a true reading of battery voltage when turning those other things
on as it will also read the voltage drop in the wiring and not the
true battery voltage.

Also note that some factory installed voltmeters are wired as noted
above and some are also very poor quality meters.


All factory voltmeters that I know get their voltage from the circuit board
of the dash indicators.

You can have all the instruments you can manage to gather but if you
don't know how to interpret them they do little good.

Regards
Gary

 

[hob]

"Andy" <nomail@nomail.com> wrote in message
news:Xns97A5C73F32FA474C1H4@127.0.0.1...

"Andy" <nomail@nomail.com> wrote :

I am in the UK and have a 1.3 litre Mazda which is over 10
years old.

I have been reading a few web pages which made reference to the
reader's car which "may have a dashmoard voltmeter".

Is a voltmeter actually all that useful to see tjings like what
the condition the battery is in and how the battery copes and
how it is charging?

Auto voltmeter - also known as the "somebody stole your battery"
gauge. Because other than a missing battery, it basically tells
you, too late, what you already know - weak lights, poor start,
bad battery, etc.


On 13 Apr 2006, hob<dehoberg@comcast.net> wrote:

An in-dash ammeter, on the other hand, tells you before you are
stranded if you are charging or discharging the battery and how
much is going in or out, and the amps are if steady or
fluctuating , all of which can be used as an indicator for the
condition of the alternator and battery, the connections, and
switch-off draining.

Don't waste your time putting in a voltmeter.


Hob,

It seems to me that I can just connect a voltmeter across the
battery terminals and (as someone in this thread mention) include
an fuse inline with the hot wire near the battery as a safety
precaution.

I'm not familiar with current shunts (which you mention
elsewhere).

Most external ones that I have seen are mounted on the firewall. The cases
were about two-three inches long. They are more used on vehicles with big
alternators.
Connection: Remove cable between alternator post and battery and run to
post on the shunt case which is bolted on the firewall; Alternator post
cabled to the other post on shunt case. Small leads off the two case posts
go to dash meter movement.

Dash mounted ammeters (one in my hand) have internal shunts inside the case
that fits in the dash, and there are posts on the back of the case to
connect heavy wire eyes. That would be the easy way to go for a smaller
vehicle.
Connection: Alternator post cable goes to dash gauge post, other dash gauge
post goes back to battery post. About number six wire, I think.

(Note that some European vehicles used to run the starter lead to the
alternator post and then on to the battery, unlike American cars that ran
separate leads from the battery to starter and alternator - the former had a
lot of problems in the US in cold climates/corrosion since some of the
hundred plus starting amps naturally went through the alternator rather than
all through the starter cables, smoking alternator parts as cars aged. Note
that If you put a regular auto ammeter in line with a starter, you may smoke
the ammeter)

Again - an ammeter is connected in series with the alternator-battery
cable so it reads the smaller charge-discharge amps of the alternator, and
it is not connected so it reads the large starting current.

Where can I get a suitable current shunt from for my car and very
roughly what do they cost?

The ammeter gauge I last bought was about $10 US. Truck repair places
probably have internals on hand (and probably also external)

For a while, they made dual gauges - top part an ammeter and the bottom part
a voltmeter (or vice versa). Haven't seen those in a while, though

background on the shunts in ammeters-

The shunt is in parallel with a meter movement (a voltmeter, bascially)
having an amp scale on its face, and the "voltmeter" reads the voltage drop
across the shunt. Since the shunt is an accurate resistance, the amps is
interpolated internally for the amps of the "ammeter" face (from ohms law).

The particular shunt and particular ammeter movement are coordinated -
electrical supply houses sell shunts, and you are looking an ammeter with an
external shunt around ,around .001 ohm/ 60-100 amps.

http://www.deltecco.com/resources.htm

Do I simply install the shunt across the battery terminals and
then place a voltmeter (sic) across the two terminals of the
shunt?

NOT across the terminals. That would short out the battery.

Basically, it is connected in line with one battery cable, with the meter
movement reading ONLY across the shunt.
It is the shunt voltage drop that the meter movement is "calibrated to" so
as to give accurate amp readings

Would I need to calibrate my multimeter to the shunt in order to
measure current values correctly?

Yes - but, again - in-dash ammeters are all set up - internally shunted -
just connect them in-line.

Thank you.


Can I permanently connect my cheap handheld digital voltmeter
to the car battery. I would then mount the meter permanently
on the dashboard.

Is there a real danger that the meter will get damaged by
various current or voltage surges? Is it good enough
protection to have a quick blow fuse in line with the test lead
going to the positive terminal?

Thanks

 

[Gary Schafer]

On Fri, 14 Apr 2006 23:50:21 -0500, "hob" <dehoberg@comcast.net>
wrote:

"Andy" <nomail@nomail.com> wrote in message
news:Xns97A5C73F32FA474C1H4@127.0.0.1...
"Andy" <nomail@nomail.com> wrote :

I am in the UK and have a 1.3 litre Mazda which is over 10
years old.

I have been reading a few web pages which made reference to the
reader's car which "may have a dashmoard voltmeter".

Is a voltmeter actually all that useful to see tjings like what
the condition the battery is in and how the battery copes and
how it is charging?

Auto voltmeter - also known as the "somebody stole your battery"
gauge. Because other than a missing battery, it basically tells
you, too late, what you already know - weak lights, poor start,
bad battery, etc.


On 13 Apr 2006, hob<dehoberg@comcast.net> wrote:

An in-dash ammeter, on the other hand, tells you before you are
stranded if you are charging or discharging the battery and how
much is going in or out, and the amps are if steady or
fluctuating , all of which can be used as an indicator for the
condition of the alternator and battery, the connections, and
switch-off draining.

Don't waste your time putting in a voltmeter.


Hob,

It seems to me that I can just connect a voltmeter across the
battery terminals and (as someone in this thread mention) include
an fuse inline with the hot wire near the battery as a safety
precaution.

I'm not familiar with current shunts (which you mention
elsewhere).

Most external ones that I have seen are mounted on the firewall. The cases
were about two-three inches long. They are more used on vehicles with big
alternators.
Connection: Remove cable between alternator post and battery and run to
post on the shunt case which is bolted on the firewall; Alternator post
cabled to the other post on shunt case. Small leads off the two case posts
go to dash meter movement.

Dash mounted ammeters (one in my hand) have internal shunts inside the case
that fits in the dash, and there are posts on the back of the case to
connect heavy wire eyes. That would be the easy way to go for a smaller
vehicle.
Connection: Alternator post cable goes to dash gauge post, other dash gauge
post goes back to battery post. About number six wire, I think.

(Note that some European vehicles used to run the starter lead to the
alternator post and then on to the battery, unlike American cars that ran
separate leads from the battery to starter and alternator - the former had a
lot of problems in the US in cold climates/corrosion since some of the
hundred plus starting amps naturally went through the alternator rather than
all through the starter cables, smoking alternator parts as cars aged. Note
that If you put a regular auto ammeter in line with a starter, you may smoke
the ammeter)

Again - an ammeter is connected in series with the alternator-battery
cable so it reads the smaller charge-discharge amps of the alternator, and
it is not connected so it reads the large starting current.


Where can I get a suitable current shunt from for my car and very
roughly what do they cost?

The ammeter gauge I last bought was about $10 US. Truck repair places
probably have internals on hand (and probably also external)

For a while, they made dual gauges - top part an ammeter and the bottom part
a voltmeter (or vice versa). Haven't seen those in a while, though

background on the shunts in ammeters-

The shunt is in parallel with a meter movement (a voltmeter, bascially)
having an amp scale on its face, and the "voltmeter" reads the voltage drop
across the shunt. Since the shunt is an accurate resistance, the amps is
interpolated internally for the amps of the "ammeter" face (from ohms law).

The particular shunt and particular ammeter movement are coordinated -
electrical supply houses sell shunts, and you are looking an ammeter with an
external shunt around ,around .001 ohm/ 60-100 amps.

http://www.deltecco.com/resources.htm


Do I simply install the shunt across the battery terminals and
then place a voltmeter (sic) across the two terminals of the
shunt?


NOT across the terminals. That would short out the battery.

Basically, it is connected in line with one battery cable, with the meter
movement reading ONLY across the shunt.
It is the shunt voltage drop that the meter movement is "calibrated to" so
as to give accurate amp readings


Would I need to calibrate my multimeter to the shunt in order to
measure current values correctly?


Yes - but, again - in-dash ammeters are all set up - internally shunted -
just connect them in-line.



Thank you.


Can I permanently connect my cheap handheld digital voltmeter
to the car battery. I would then mount the meter permanently
on the dashboard.

Is there a real danger that the meter will get damaged by
various current or voltage surges? Is it good enough
protection to have a quick blow fuse in line with the test lead
going to the positive terminal?

Thanks

Hob,

The way you are explaining to hook up the ammeter will only give
indication of charge output from the alternator. It will not show any
discharge from load on the battery.

The ammeter needs to be in the alternator lead but between the point
where the supply to the car's electrical system is taken from and the
battery. In other words, the lead to the cars electrical system will
be on the alternator side of the lead that connects to one side of the
ammeter. The other side of the ammeter would go to the battery.

Sometimes this is difficult to do as often the car's power is taken
from the battery cable where it attaches to the starter. Sometimes it
is taken at a splice / junction in the lead between the alternator and
the battery, much easier to do here.

Regards
Gary

 

[hob]

"Gary Schafer" <gaschafer@comcast.net> wrote in message
news:2f7242dl9ls9psvbhmpr13v5ee35hjd5d4@4ax.com...

On Fri, 14 Apr 2006 23:50:21 -0500, "hob" <dehoberg@comcast.net
wrote:


"Andy" <nomail@nomail.com> wrote in message
news:Xns97A5C73F32FA474C1H4@127.0.0.1...
"Andy" <nomail@nomail.com> wrote :

I am in the UK and have a 1.3 litre Mazda which is over 10
years old.

I have been reading a few web pages which made reference to the
reader's car which "may have a dashmoard voltmeter".

Is a voltmeter actually all that useful to see tjings like what
the condition the battery is in and how the battery copes and
how it is charging?

Auto voltmeter - also known as the "somebody stole your battery"
gauge. Because other than a missing battery, it basically tells
you, too late, what you already know - weak lights, poor start,
bad battery, etc.


On 13 Apr 2006, hob<dehoberg@comcast.net> wrote:

An in-dash ammeter, on the other hand, tells you before you are
stranded if you are charging or discharging the battery and how
much is going in or out, and the amps are if steady or
fluctuating , all of which can be used as an indicator for the
condition of the alternator and battery, the connections, and
switch-off draining.

Don't waste your time putting in a voltmeter.


Hob,

It seems to me that I can just connect a voltmeter across the
battery terminals and (as someone in this thread mention) include
an fuse inline with the hot wire near the battery as a safety
precaution.

I'm not familiar with current shunts (which you mention
elsewhere).

Most external ones that I have seen are mounted on the firewall. The
cases
were about two-three inches long. They are more used on vehicles with
big
alternators.
Connection: Remove cable between alternator post and battery and run to
post on the shunt case which is bolted on the firewall; Alternator post
cabled to the other post on shunt case. Small leads off the two case
posts
go to dash meter movement.

Dash mounted ammeters (one in my hand) have internal shunts inside the
case
that fits in the dash, and there are posts on the back of the case to
connect heavy wire eyes. That would be the easy way to go for a smaller
vehicle.
Connection: Alternator post cable goes to dash gauge post, other dash
gauge
post goes back to battery post. About number six wire, I think.

(Note that some European vehicles used to run the starter lead to the
alternator post and then on to the battery, unlike American cars that ran
separate leads from the battery to starter and alternator - the former
had a
lot of problems in the US in cold climates/corrosion since some of the
hundred plus starting amps naturally went through the alternator rather
than
all through the starter cables, smoking alternator parts as cars aged.
Note
that If you put a regular auto ammeter in line with a starter, you may
smoke
the ammeter)

Again - an ammeter is connected in series with the alternator-battery
cable so it reads the smaller charge-discharge amps of the alternator,
and
it is not connected so it reads the large starting current.


Where can I get a suitable current shunt from for my car and very
roughly what do they cost?

The ammeter gauge I last bought was about $10 US. Truck repair places
probably have internals on hand (and probably also external)

For a while, they made dual gauges - top part an ammeter and the bottom
part
a voltmeter (or vice versa). Haven't seen those in a while, though

background on the shunts in ammeters-

The shunt is in parallel with a meter movement (a voltmeter, bascially)
having an amp scale on its face, and the "voltmeter" reads the voltage
drop
across the shunt. Since the shunt is an accurate resistance, the amps is
interpolated internally for the amps of the "ammeter" face (from ohms
law).

The particular shunt and particular ammeter movement are coordinated -
electrical supply houses sell shunts, and you are looking an ammeter with
an
external shunt around ,around .001 ohm/ 60-100 amps.

http://www.deltecco.com/resources.htm


Do I simply install the shunt across the battery terminals and
then place a voltmeter (sic) across the two terminals of the
shunt?


NOT across the terminals. That would short out the battery.

Basically, it is connected in line with one battery cable, with the
meter
movement reading ONLY across the shunt.
It is the shunt voltage drop that the meter movement is "calibrated to"
so
as to give accurate amp readings


Would I need to calibrate my multimeter to the shunt in order to
measure current values correctly?


Yes - but, again - in-dash ammeters are all set up - internally shunted -
just connect them in-line.



Thank you.


Can I permanently connect my cheap handheld digital voltmeter
to the car battery. I would then mount the meter permanently
on the dashboard.

Is there a real danger that the meter will get damaged by
various current or voltage surges? Is it good enough
protection to have a quick blow fuse in line with the test lead
going to the positive terminal?

Thanks



Hob,

The way you are explaining to hook up the ammeter will only give
indication of charge output from the alternator. It will not show any
discharge from load on the battery.

I imagine that vehicles may differ, and perhaps I wasn't clear
- in mine, the starter gets a heavy cable off the hot post, and the
alternator gets a lighter cable off the hot post. The vehicle non-starter
power is then taken off that alternator post which feeds the battery. That
puts the ammeter between the alternator and power panel lead, and the
battery.
If there are three feeds off the hot battery post (starter, alternator,
and accessory power panels), you may well need to cut that (third) power
panel feed cable at the battery post, add a crimped on eye on the end, and
move that power panel end over to the alternator post holding the
alternator-to-battery cable.
In other words, move the panel-feed end from the battery post to the
alternator post ( it's the same point electrically)

The ammeter needs to be in the alternator lead but between the point
where the supply to the car's electrical system is taken from and the
battery. In other words, the lead to the cars electrical system will
be on the alternator side of the lead that connects to one side of the
ammeter. The other side of the ammeter would go to the battery.

Yes, agreed

Sometimes this is difficult to do as often the car's power is taken
from the battery cable where it attaches to the starter.

While I have personally not seen that panel-connection coming off the
starter, I would think the moving of the panel-connection cable end over to
the alternator post would solve the problem.

Right? Input is always good - you never know...

Sometimes it

is taken at a splice / junction in the lead between the alternator and
the battery, much easier to do here.

Regards
Gary

 

[Dave Plowman (News)]

In article <Xns97A4E3D492A8F74C1H4@127.0.0.1>,
Andy <nomail@nomail.com> wrote:

Can I permanently connect my cheap handheld digital voltmeter to
the car battery. I would then mount the meter permanently on the
dashboard.

You can get small LCD voltmeters from the likes of RS components. They
have approx a 16:9 aspect ratio and are about an inch wide. One hole
fixing. I've got one on my SDI. Only two wire connection. Only trouble is
no illumination - but you might find one that has now, I haven't looked
for a few years.

--
*Make it idiot-proof and someone will make a better idiot.

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

 

[Dave Plowman (News)]

In article <yICdnfkf1sLIVaPZ4p2dnA@comcast.com>,
hob <dehoberg@comcast.net> wrote:

Auto voltmeter - also known as the "somebody stole your battery" gauge.
Because other than a missing battery, it basically tells you, too late,
what you already know - weak lights, poor start, bad battery, etc.

An in-dash ammeter, on the other hand, tells you before you are stranded
if you are charging or discharging the battery and how much is going in
or out, and the amps are if steady or fluctuating , all of which can be
used as an indicator for the condition of the alternator and battery,
the connections, and switch-off draining.

Don't waste your time putting in a voltmeter.

Err a voltmeter tells you the same things if you know how to read it. And
it will also tell you the condition of the battery when you switch on
which an ammeter can't.

--
*If a mute swears, does his mother wash his hands with soap?

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

 

[Dave Plowman (News)]

In article <MPG.1ea994bd86d1a81398c581@news.individual.net>,
Conor <conor.turton@gmail.com> wrote:

If I had only one instrument to connect to the car to watch the
battery it would be a voltmeter.

Spot the pillock who knows fuck all about car electrics.

And I agree with him. ;-)

A voltmeter will tell you much more
about the battery and the charging system than an ammeter.

No it won't. A completely fucked battery can show >12v but still not be
able to provide enough current to turn an engine over.

Simply switch on the headlights with the engine not running. If the
battery has a high impedance cell the voltage will drop like a stone. An
ammeter won't show that.

Think I'm wrong? Why are batteries tested with a drop meter?

As an instrument on the dash? Do tell. ;-)

--
*One of us is thinking about sex... OK, it's me.

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

 

[Dave Plowman (News)]

In article <443F9E39.486BB588@earthlink.net>,
Michael A. Terrell <mike.terrell@earthlink.net> wrote:

After all, a car alternator is a constant voltage charger.

They're not unless using a SLA gel battery. As some off roaders may.
You'll see about 14.4 volts if the battery is low dropping back to 13.8
when it's charged. That's looking at a recent BMW with an accurate volt
meter.

--
*Some days you're the dog, some days the hydrant.

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

 

[Dave Plowman (News)]

In article <fkgv32hadmm7s85ehgp864md13fojtdlmg@4ax.com>,
Gary Schafer <gaschafer@comcast.net> wrote:

Actually if a battery only shows "12 volts" it is near dead!

Not so. 11.5 should start the average car on an average day.

--
*Parenthetical remarks (however relevant) are (usually) unnecessary *

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

 

[Dave Plowman (News)]

In article <MPG.1eaa044421eea28098c58f@news.individual.net>,
Conor <conor.turton@gmail.com> wrote:

Does your voltmeter tell you the condition of the battery? No.

Does your ammeter tell you the condition of the battery? Bigger no.

--
*They call it PMS because Mad Cow Disease was already taken.

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

 

[chuck]

Dave Plowman (News) wrote:

In article <443F9E39.486BB588@earthlink.net>,
Michael A. Terrell <mike.terrell@earthlink.net> wrote:

After all, a car alternator is a constant voltage charger.


They're not unless using a SLA gel battery. As some off roaders may.
You'll see about 14.4 volts if the battery is low dropping back to 13.8
when it's charged. That's looking at a recent BMW with an accurate volt
meter.

Dave, I think the voltages you reported are representative, but the

voltage doesn't drop because the battery is charged (I realize you
didn't say it did, but someone might think that is what you meant). Many
cars have temperature controllers built into the charging circuit that
drop the voltage as temperatures rise (i.e., when the car has been
driven a while). It's a way of discouraging over-charging, especially on
long summer trips.

Without temperature sensing circuitry, the alternator/regulator would
supply a constant charging voltage but due to voltage drops, the voltage
at the battery terminals would actually RISE from a lower voltage to the
regulated 14.4 volt level as the battery is charged. Just the opposite
of what you reported.

FWIW

Chuck

 

[Keith]

On Thu, 13 Apr 2006 22:17:49 +0000, chuck wrote:

Andy wrote:
I am in the UK and have a 1.3 litre Mazda which is over 10 years
old.

I have been reading a few web pages which made reference to the
reader's car which "may have a dashmoard voltmeter".

Is a voltmeter actually all that useful to see tjings like what
the condition the battery is in and how the battery copes and how
it is charging?

Can I permanently connect my cheap handheld digital voltmeter to
the car battery. I would then mount the meter permanently on the
dashboard.

Is there a real danger that the meter will get damaged by various
current or voltage surges? Is it good enough protection to have a
quick blow fuse in line with the test lead going to the positive
terminal?

Thanks



Don't bother with a voltmeter. A far better investment is a set of
jumper cables.

That's kinda like suggggesting one wear Depends instead of stopping at the
a rest area on the highway.


--
Keith