Adding voltmeter to car

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.

Reply to
Dave Plowman (News)
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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.

Reply to
Dave Plowman (News)

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.

Reply to
Dave Plowman (News)

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

Reply to
Dave Plowman (News)

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

Reply to
Dave Plowman (News)

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

Reply to
chuck

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

Reply to
Keith
[snip]

Can you say that again in English?

Reply to
Steve Firth

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

Reply to
chuck

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

Reply to
Gary Schafer

A standard wet cell battery will exhibit approximately the following voltages at various states of charge at 70 degrees F: Courtesy of William Darden's Battery faqs.

100% 12.643

75% 12.443

50% 12.273

25% 12.053

0% 11.883

Maintenance free batteries will be approximately the following:

100% 12.793 75% 12.593 50% 12.393

25% 11.993

0% 11.793

Regards Gary

Reply to
Gary Schafer

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

Reply to
chuck

A few hints for the E2Ler:

"Depends" =

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"rest area" ~

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"highway" =
formatting link

Reply to
Keith

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.

Reply to
Dave Plowman (News)

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...

Reply to
PC Paul

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.

Reply to
Dave Plowman (News)

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.

Reply to
Michael A. Terrell

Is that a static voltage reading, or with the engine running and charging the battery? Where is your voltmeter connected into the car's wiring? How often is it 70 degrees F under your hood when you want to check the voltage? Too many variables to get a useful answer with a simple meter.

Reply to
Michael A. Terrell

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.

Reply to
PC Paul

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.

Reply to
Dave Plowman (News)

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