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[crumbly65]

I've always been a complete dud with electrics. 

I fail utterly to understand things like the difference between volts, amps and ohms.  I know current flows (in a similar way to water in some ways), and that there are live, neutral and earth terminals, but that's about it.

The problem stems from the fact that I am colour-blind, so I've always struggled to differentiate wiring, even if I can follow a rudimentary wiring diagram.  So I've always just shut my mind to electrics, and had to find and trust those who are electrical experts.  And that's been ok.

But I still would like to know for example, the difference between an ammeter and a volt meter.  I think a volt meter displays the charging voltage going to the battery, whereas an ammeter......?

As an aside, and from another thread, it's a testament to the friendliness of this forum that I'm happy to admit my ignorance so publicly.   

[Gareth]

This.

[martinthefirst]

The usual analogy is a hosepipe, the speed of the water through the pipe is the "volts", and the volume of water (diameter of pipe) is the "amps". Ammeter shows charging or discharging, volt meter shows battery condition.

[22900013A]

Ohms is the resistance of a conductor . Lower ohms would allow more amps to flow for a given voltage. Voltage is the pressure of the electron flow, amps is the "amount" of electricity.

[Herald1360]

The usual analogy is a hosepipe, the speed of the water through the pipe is the "volts", and the volume of water (diameter of pipe) is the "amps". Ammeter shows charging or discharging, volt meter shows battery condition.

Hosepipe may be the analogy for a conductor but there your descriptions fail.

Pressure difference between ends of pipe (Volts) causes a rate of flow of the water (Amps). The resistance to flow (Ohms) ties the other two together and determines the rate of flow at a given pressure difference.

The weird cartoon is a pretty good illustration!

The ammeter (in a vehicle at any rate) shows the amount and direction of flow of electricity in/out of the battery. The voltmeter shows the electrical pressure between the battery terminals determined either by the battery itself on discharge or the charging source (engine driven electrical generator) on charge. This either lets electricity into the battery if the charging source (engine driven electrical generator) produces a voltage higher than that of the battery or out if it doesn't. In simple terms at least.

[andrewR]

Pressure difference between ends of pipe (Volts) causes a rate of flow of the water (Amps). The resistance to flow (Ohms) ties the other two together and determines the rate of flow at a given pressure difference.

This is bang on. I used to use this at University to teach undergrad students (well, they were MechEng students being forced to take an EEE module, so every analogy helps!)

If you want to take it a bit further:

Hose:
Flow Rate in m^3/s = Pressure in N/m^2 (i.e. Pascals) / Resistance in (some odd units)      in a hose

Electricity:
Current in Amps = Voltage in Volts / Resistance in Ohms   
commonly known as I = V/R
or you can reorder as the even more well-know V=IR

Its not uncommon in media reports to hear of things like "11000 Volts of current" which is of course completely nonsensical.

[w3526602]

Hi,

If you are working on a Landie (or virtually any other modernish car) it will be 12 volts (6 two-volt cells ... I think cells are always nominally 2 volts, but don't know why. Should I ask that French bloke ... LeClanche? (sp?).

Amps are the things you see on your ammeter, to show you are either charging or discharging, preferably the former.

One of my tests is to watch the battery acid while somebody else pushes the starter button (perhaps goggles should be worn?). If the elecrolyte bubbles, that cell is toast. Six cells equal 12 volts (nominally), but maybe not all of it reaches the starter motor. One dud cell means you have (nominally) only 10 volts ... your truck will probably start on the handle, but unlikely on the starter motor. If desperate, fit a 6 volt coil ... it will probably run for quite a while, but not long, on the full 12 volts. Hmmm! A BALLASTED coils is designed to run on (I think) 9 volts, and probably easier to buy locally, than the 6 volt version. But it will destroy the CB points very quickly.

Ahem, I once borrowed a 6 volt battery (one of two) from Dad's Austin 10, to start my Austin 7. Dad wanted to use his car, found what I had done. Oops! He knew where I was, so wired the car on the one remaining battery, hand cranked it to start, and came to get his other battery. I do not know what damage a 12 volt dynamo could have caused to a 6 volt battery (or vice versa). 

Does a "Tyro" really need to know any more than that?

This was one of the things I missed by being "up-flighted" six weeks at RAF Trade Training. (13 week course) Anything else I missed, I had a working (eg: hobby), knowledge of anyway. I managed to avoid the later 6-month "Fitters" course, by going straight for the 3 days of exams. (Taking my own NEW files and hacksaw blades (Courtesy of Ford's Body Plant Tool Room ...  )

602

PS. Has any body tried a BALLASTED coil on a Series that is reluctant to start. If it does start, perhaps it would be a solution to wire the car "properly" for ballasted ignition? In the meantime, I'll go and get the mouthwash.

[Exile]

On my early coilsprung LR's I have voltmeters.

None seem to work. They are either always stuck at extreme right, or don't move much from extreme left.

At least the ammeters on my Series go up and down and give the appearance of doing something!