ETB Voltage gauge versus Voltmeter contradicitons
James - 18/5/12 at 02:14 AM
I have an ETB voltage gauge I bought 2nd hand (appears unused). The sticker on it dates it to the year 2000.
It came with a set of other gauges that are in the car and work well but I never fitted the voltage gauge.
As my gauges were 2nd hand, out of interest I connected the voltmeter (directly with 2 wires) to an old car battery tonight. It read 9v.
I then tested the battery with my Tenma voltmeter. It read 11.5
Any thoughts on the matter? Is a gauge that reads 2v below worse than nothing? 
Are the gauges serviceable? Calibrateable?
Thanks,
James
P.S. Is it even worth having a voltage gauge? I'll be taking my voltmeter on my drive to Southern France anyway in case of problems.
EDIT: for clarity
[Edited on 18/5/12 by James]
britishtrident - 18/5/12 at 06:16 AM
If your battery is only showing 11.5v you need to investigate why before you go your trip, in current UK ambient temperatures, with the
ignition off I would expect 12.5 even if the battery was partly discharged and 12.8 v if fully charge. With the engine running expect 13.4
to 14.9v
The problem with the ETB gauge could be a bad earth I would suggest removing it from the dash and testing both meters by direct connection to a known
good tintop battery.
Autosri - 18/5/12 at 07:47 AM
A poor ground connection would cause a low reading so stick the two wires on the battery and see what you get
Macbeast - 18/5/12 at 08:17 AM
Raeding the original post, I think that's what he did.
Dusty - 18/5/12 at 09:55 AM
If you are happy you had good connections when testing the gauge then return it to ETB with a note saying it is unused and reads low. Can they sort
it?
MikeRJ - 18/5/12 at 11:19 AM
If the battery was really only 11.5v using a high impedance multimeter then it's in a very discharged state as BT says. The ETB voltmeter is
almost certainly a much lower impedance than a mutlimeter so it would pull the voltage of a dead battery down even further.
The way to test this is to connect the ETB volt meter and your multimeter to the battery at the same time and compare readings.
britishtrident - 18/5/12 at 11:23 AM
As it is a 2nd hand gauge it would be cheaper to buy another than get ETB to repair it. McGill Motorsports on ebay do a nice 2"/52mm
Digital job.
However the first thing is to test it on a good battery with a decent charge, 2" gauges are generally bi-metal types have fairly low
resistance, it could be the battery it was tested on is so knackered that the internal resistance of the battery is dropping 2v
[Edited on 18/5/12 by britishtrident]
James - 18/5/12 at 12:12 PM
quote:
Originally posted by MikeRJ
If the battery was really only 11.5v using a high impedance multimeter then it's in a very discharged state as BT says. The ETB voltmeter is
almost certainly a much lower impedance than a mutlimeter so it would pull the voltage of a dead battery down even further.
The way to test this is to connect the ETB volt meter and your multimeter to the battery at the same time and compare readings.
quote:
Originally posted by britishtrident
As it is a 2nd hand gauge it would be cheaper to buy another than get ETB to repair it. McGill Motorsports on ebay do a nice 2"/52mm
Digital job.
However the first thing is to test it on a good battery with a decent charge, 2" gauges are generally bi-metal types have fairly low
resistance, it could be the battery it was tested on is so knackered that the internal resistance of the battery is dropping 2v
[Edited on 18/5/12 by britishtrident]
Doh! Hadn't dawned on me the gauge/meter would affect the battery to such differing degrees! Seems obvious now.
I will do both these things- test it on my tintop battery and test with both at the same time! Thank you gentlemen! 
Have looked at the McGill stuff on ebay and a gauge is about £20. They look nice- only problem is they wouldn't match the rest of mine!
Mailed ETB. Had excellent service from ETB in the past and they've kept up the standards! I mailed them asking about this at 11.27AM and had a
response 12mins later! 
Perfectly reasonably said I wouldn't get a warranty repair on a 12yr old gauge (I hadn't expected to!) and said it'd be just £8+vat
plus p&p to get it fixed.
So, if there is a problem (and there may not be!) then it's reasonably cheap to fix at least!
Well done them for good customer service so far!
Anyway, fingers crossed it's my foolishness at using a dud battery and this is a non-issue anyway!
Cheers,
James
pmc_3 - 18/5/12 at 12:30 PM
Sounds like the battery was pretty flat. The multimeter will have its own battery where as the voltmeter is powered by the battery