Smiths battery gauge

Post by **MikeNash** » Fri Dec 23, 2005 9:57 pm

Both! Both! You can't have too many gauges! The more the merrier! Mind you, my Traveller cockpit is beginning to look like a cross between an Lancaster bomber and a nuclear power station.
I suppose , Bmceccosse, your ammeter must be one of the magic ones if it takes no power at all. Lucky man. MikeN.

Post by **Packedup** » Sat Dec 24, 2005 3:23 am

Ammeters are great and don't take much at all from the system... But when they fail it's a trifle more annoying than if a voltmeter packs in...

Plus they're just too worrying in heavy traffic at night -mWatching that little needle flickering close to discharge doesn't make me feel any calmer!

Post by **bmcecosse** » Sat Dec 24, 2005 5:44 pm

Well yes - the ammeter does take all the current going to/from the battery - but it passes it all on without actually keeping any for itself! The dodgey bit of course is that the big thick main current cables are coming into the car and there is more risk of a short developing one day. In general I avoid gauges - but this was donated by a well meaning neighbour and so it had to be fitted to show him I appreciated the gift. I have never heard of an ammeter failing!

Post by **Cam** » Sat Dec 24, 2005 5:56 pm

Well...... not strictly true as the ammeter will be drawing current through it's shunt which will be heating up slightly and showing a potential difference which is then displayed by the gauge!

Post by **Packedup** » Sun Dec 25, 2005 4:30 am

Cam wrote:Well...... not strictly true as the ammeter will be drawing current through it's shunt which will be heating up slightly and showing a potential difference which is then displayed by the gauge!

Yup - That's what I meant when saying they take very little - They obviously take some energy from somewhere to be able to move the needle, and if they didn't move the needle they'd be quite pointless! ;)

Post by **Pyoor_Kate** » Sun Dec 25, 2005 7:09 am

not move the needle... pointless... he he he

*grins*

Post by **Cam** » Thu Dec 29, 2005 12:30 am

Packedup wrote:
Cam wrote:Well...... not strictly true as the ammeter will be drawing current through it's shunt which will be heating up slightly and showing a potential difference which is then displayed by the gauge!
Yup - That's what I meant when saying they take very little - They obviously take some energy from somewhere to be able to move the needle, and if they didn't move the needle they'd be quite pointless! ;)

Yes, but the shunt effectively 'shorts out' the terminals allowing large currents to pass and a tiny current to pass through the meter itself by the way of the developed potential difference across the shunt's small resistance...

Post by **jojax64** » Tue Jan 03, 2006 2:37 pm

I recently fitted a Smiths Battery Condition gauge, and I'm glad I did.

You see, when I fitted a new fusebox last year, I also splashed out on a nice new shiny regulator box from MGM spares. The old box was fine, I just decided to fit a new one.

Anyhoo, since fitting the battery gauge the needle was WAY up in the red. My nice new shiny regulator was happily cooking my new battery.

MGM replaced the faulty (or badly adjusted) regulator, but unless I had fitted the battery gauge I would have been blissfully unaware.......

Post by **crossword** » Tue Jan 03, 2006 5:27 pm

My first post
You could further explain the function of the ammeter as a very low value resistance ( the shunt ) across whose terminals is connected a high resistance voltmeter . This combination has most of the current passing through the shunt & a very small amount through the meter . As the current increases the voltage developed across the shunt increases ( Ohms Law ) & is measured by the voltmeter .
This arrangement is used in your multimeter to measure varying maximum ( Full Scale Deflection ) current. By using a smaller resistance for the shunt, the voltage developed across it will be smaller allowing greater possible full scale reading , a larger shunt resistor will permit a smaller full scale value . ( With the same meter )
In the multimeter , the same basic meter movement could have different resistors put in series with it and be used to measure different maximum full scale voltages . Used this way the, meter & the series resistor both carry the same current. They DO form a potential divider

Post by **crossword** » Tue Jan 03, 2006 5:36 pm

Forgot to mention, I own a 1964 saloon , my younger brother a 1959 saloon , my youngest brother a saloon ( 1960 ? ) & a traveller ( 1968 ) . We are all MMOC members .