Adding voltmeter to car

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
--

The voltmeter web pages include:
http://www.carbuyingtips.com/jumpstart.htm
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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.

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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.

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wrote:

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.

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

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

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

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wrote:

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
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wrote:

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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)

Yes, agreed

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

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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 snipped-for-privacy@davenoise.co.uk London SW
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Andy wrote:

Don't bother with a voltmeter. A far better investment is a set of jumper cables.
Chuck
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On Thu, 13 Apr 2006 22:17:49 +0000, chuck wrote:

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

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Keith wrote:
[snip]

Can you say that again in English?
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On Sun, 23 Apr 2006 12:11:09 +0100, Steve Firth wrote:

A few hints for the E2Ler:
"Depends" = (http://www.depend.com /)
"rest area" ~ (http://www.ronsaari.com/stockImages/roadsideAttractions/nebraskaRestArea.php )
"highway" = http://www.schweich.com/imagehtml/1340_3152_4275_47sm.html
--
Keith


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Keith wrote:

Nothing of the sort, really. If one is curious about battery charging and discharging principles, then a voltmeter, ammeter, thermometer, hydrometer, a lot of time, and a text book will prove rewarding.
But if the concern is to obtain early warning of an impending battery/alternator/regulator/belt failure so as to avoid being caught on the road without an electrical system, then most of us would benefit far more from the jumper cable. ;-)
If the voltmeter would "prevent" such a breakdown by giving advance warning of sufficiently high certainty to result in an immediate trip to a competent repair technician, then it would be a good thing. Unfortunately, even if the meter did so indicate, immediately and unambiguously, one might be on the road far from any repair facilities at the time of the indication, in which case jumper cables would be most useful.
I wonder how many of us have looked at a voltmeter, concluded that something was wrong, replaced the battery, and found that the world was good again. Compare that number to those of us who, upon noticing a strange reading of the meter, made a mental note to keep an eye on the meter, and then eventually found ourselves with a dead battery. From the postings, it seems not all of us would be able to interpret various meter indications even if we had them before us.
Unlike the rest area "fix", a voltmeter will not "ward off" a leaking battery failure. ;-)
Chuck
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We might just as well throw out the fuel gauge then too. Just looking at it will not keep us from running out of fuel. Might be better to just carry a spare can of with us.
Like the voltmeter, if one doesn't know how to interpret the fuel gauge properly it does no good to have it aboard. Admittedly the voltmeter is a little more complicated to interpret than the fuel gauge but it can also be a valuable instrument.
Regards Gary
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Gary Schafer wrote:

Hello Gary,
Sorry, but I think the gas gauge analogy is pretty weak. Voltmeter readings are much more difficult to interpret. Can you imagine a thread like this one on interpreting gas gauge readings? ;-)
Many autos have been sold without voltmeters and many have been sold without fuel gages (VW for many years). My car has both an idiot light and a gauge for fuel (for volts as well, actually) but I pay much closer attention to the fuel gauge idiot light.
Many automotive voltmeters lack sufficient precision to be useful (mine has a number at each end of the scale and one in the middle, with the needle width approximately equal to the difference between 50% and full charge! When bored on long trips I tend to ponder whether the scale is actually linear. I find this activity even more boring and quickly take a renewed interest in traffic.).
I do think it is very difficult for a typical driver to extract more useful information from a typical voltmeter than from an idiot light.
Chuck
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What good is a jumper cable if your alternator/regulator/fanbelt has failed on the road? You'd need a breakdown service to fix it and they all carry starter batteries.
--
*Avoid clichs like the plague. (They're old hat.) *

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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Dave Plowman (News) wrote:

Once you've started with a jump either a battery OR an alternator+regulator will get you home.
Unless you found out about the problem because it wasn't charging and now it's run out...
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So you carry spares for these as well as jump leads?

Yes. With no charge, jumping starting the car (because the battery is flat) won't leave it running for long.
I do carry jump leads and a spare fan belt on the old car, though.
--
*It's o.k. to laugh during sex..just don't point!

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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"Dave Plowman (News)" wrote:

I used to have a spare alternator on my 1966 GTO. I blew the front bearing out so often that I got the bracket for that Pontiac 389 CID engine with an AC compressor, which required the Alternator to moved to the other side of the engine. Over rev the alternator, stop, remove the fan belt and plug from the bad alternator, plug it into the spare and install the fan belt on that side. A one minute or less repair on the side of the road. I also used #1 AWG welding cable on the main battery to reduce the voltage drop.
On other vehicles I've had a dual charging system and a pair of the biggest batteries that would fit under the hood. Need a jump? Flip a switch to tie the two batteries together with a starter solenoid and start the engine.
--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
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Dave Plowman (News) wrote:

So how did I get 100 miles in a 3.0 Supra with *no battery at all* in it then?
An alternator is quite capable of giving enough current to keep the systems going. Probably not on full beam, heated windows etc., but for daytime running it was fine.
Don't stall it though.

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The alternator was working. I was talking about when the charging system or fan belt fails. Jump leads won't help you then.

The voltage from an unterminated alternator can go sky high and fry the electronics. Not recommended.

--
*When you've seen one shopping centre you've seen a mall*

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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