So what does the Ammeter tell me?

[MilesA]

Took my 20 year old daughter out in the 3A for the first time yesterday and she was intrigued by all the dials and switches on the instrument panel - such a change to her Fiesta. So I explained the purpose of them all. However, when I got the ammeter I stumbled a bit and realised I didn't really know what it was telling me. As those here who have kindly answered by electrical queries will know, things electrical are a bit of a blind spot for me.

 

I quick look through the original Instruction Book tells me that the ammeter "Indicates the flow of current into or out of the battery". I understand that, but so what? Does the ammeter help indicate a problem or some action required from me? Does it provide some sort of warning function?

 

My car is negative earth and the only non-standard electrical additions are a Facet fuel pump, a Kenlowe fan and a 12v output socket. It has an alternator although I do not know what ampage.

 

Generally, the needle sits at zero or slightly +ive (right hand side). If I switch on the fan I goes up to about the first white line on the +ive side. If I then switch on the lights, it moves further up the +ive scale. Self evident that in those circumstances I will be using more current but I wouldn't have thought I needed an ammeter to tell me that. It is in the instrument panel for a purpose so what I am I missing from what it is telling me?

 

PS. My daughter thought the 3A was the 'coolest' car ever and immediately started an argument with her younger sister about who was going to inherit it! A somewhat premature discussion I thought...

 

PPS. Also if anyone knows of a book from which I could get a better understanding of how the electrical systems on these cars and the purpose of all those component such as control boxes, solenoids, etc., work , I promise to read it!

 

Miles

[Norman D]

I think you need to reverse the connections on the back of your meter,it should go to the left when a discharge is taking place and to the right when charging. .Norman.

[Kiwifrog]

Miles

 

If your car is standard it has

a battry to store electricity

a dynamo to create electricity

And all sorts of electrical bits and bobs that use electricity, lights etc

 

To make electricity the dynamo has to turn, it is turned by belt from the engine so if the engine is not turning the dynamo can not make electricity. To start to engine you need electricity which is why you have a battry that stores electricity which is used primarally to start the engine.

 

A secondary purpose of the battry is to provide a temporary top up for times when the car is using more electricity than the dynamo can make, this can not go on for ever as you will drain the battry of electricity.

 

The ammeter tells you what state your battry and electricity generating is in. If you switch on the ignition without starting the car and then switch on the lights the Ammeter should register about 5-10 amps negative indicating that your are taking more electricity from the battry than the dynamo is making (in this case thedynamo is not making any electricity as the engine is not turning).

 

When you start the car the dynamo will start to turn and with the lights off it should start to replace the electricity in the battry ie charge the battry meaning that the ammeter should show a posative charge untill the battry is "full" ie the ammeter will indicate 0 when the battry is fully charged

 

To make sure you do not put too much electricity into the battry (this is a bad thing as the battry will boil and can be damaged) there is a device called a regulator which is on the firewall in the engine bay. This acts as kind of a switch that once the battry is fully charged switches off the battry charging output from the dynamo.

 

If you need more electricity than the battry can provide, ie if you switch on the lights the regulator will switch on the charging mechanism to the battry and you should see the ammeter once again move to the posative side.

 

 

This is a very simplified 'resume' of the charging circuit but gives a broad idea of what it is about

 

Cheers

 

Alan

 

p.s. I agree with Norman if you have a standard charging circuit then your ammeter is wired backward, not anything to worry about it will not damage anything it will just read opposite ie it will indicate that the battry is charging when it is discharging and indicate discharge when charging.

Edited October 21, 2012 by Kiwifrog

[AlanT]

The basic problem is that a dynamo system can only provide enough current to run the headlights when the engine speed is reasonably high.

 

We discussed this at length on the TR4 forum recently and its thought that you may need as much as 2500RPM to meet the current taken if you have the lights, the fan and thw wipers all on at once.

 

So the instrument is there, in a prominent position, to warn you that you are gradually running out of stored power that you may need to restart the engine.

 

Another problem is that if you have a battery that is a bit flat then these simple electro-mechanical systems are not clever enough to prevent the dynamo pushing too much current into the battery. Ideally you dont want a charge rate above about 4A. This overheats the battery plates and shortens their life.

 

So if you were getting too much charging then you put the lights ON. This is so counter intuitive, battery is flat, so put the lights on, that I doubt many people ever did this.

 

With experience you got used to the time it would take for the battery voltage to rise and therefore the charge-rate to fall back following a cold-start. This would give advance warning of a battery coming to the end if its life.

 

All this goes back to a time when we had "motorists" rather than "drivers".

 

Al.

[ianhoward]

Miles

 

A pretty reasonable book that explains things in a relatively simple fashion is: -

 

'Classic Car Electrics' by Martin Thaddeus published by Veloce Books; ISBN 1-903706-64-5

 

Cheers

Ian

[BrianC]

The ammeter connections should have been reversed when your car was converted from positive to negative earth.

If you decide to switch your ammeter connections to show the correct charge/discharge reading, be very careful to ensure that the battery is disconnected and that the wires are very securely re-attached to the ammeter. This is especially important if your car has an early ammeter with screw terminals. If one comes loose and touches earth (e.g. anything metal behind the dash) you will see the famous Lucas smoke - possibly followed by flames

[Menno van Rij]

The ammeter connections should have been reversed when your car was converted from positive to negative earth.

If you decide to switch your ammeter connections to show the correct charge/discharge reading, be very careful to ensure that the battery is disconnected and that the wires are very securely re-attached to the ammeter. This is especially important if your car has an early ammeter with screw terminals. If one comes loose and touches earth (e.g. anything metal behind the dash) you will see the famous Lucas smoke - possibly followed by flames

 

 

and since your car has an alternator, you could also convert to an Voltmeter.

 

I had an 'under dash fire' back in the 90s with my Spitfire. Something I never want to experience again!

When restoring my TR, Stuart pointed me towards a period correct voltmeter (from a Scimitar I think).

 

Menno

[RogerH]

With an alternator fitted it is quite possible for the ammeter to be connected correctly and yet show an increased charge on the ammeter..

 

With the engine not running and the lights on you should see a discharge. If this is so then the meter is correctly wired.

With the increased charge indication, when running, it shows that the take off for the lights/services and alternator wiring are not quite right.

 

If the system is wired correctly you should only see the charging current or the discharge current if the enigne is not running.

 

As I've stated before it would be handy to have the ammeter thick brown wires in a steel tube so that if they decide to let the smoke out they don't set fire to the car.

 

Roger

[tthomson]

Hi Miles,

 

The Ammeter shows the current flow into or out of the battery.

 

I know that sounds a bit generic, but it is correct.

On a classic car, electricity is used for three things:

Igniting fuel

Headlights and other external lights

Auxiliaries (like the gauges and dash lights and everything else)

 

The electricity to these circuits is supplied by the battery. If there was no charging system, the battery would soon run out of juice.

There is a charging circuit that consists of a dynamo or Alternator that provides electrical energy to the battery.

 

When you have an alternator the ammeter is less important since the current flow is not normally a problem, but when you have a dynamo, the rate at which the battery charges depends on the speed at which the dynamo rotor is spinning. To monitor the charge condition between the battery and the dynamo, an ammeter is used in the charging circuit.

 

The ammeter is there to show whether the battery is gaining or losing charge.

Others have commented about the polarity of the ammeter and all you need to know is when the battery is charging it should show +ve and when the battery is discharging it shows -ve.

When there is a problem, either the battery is overcharging and therefore likely to fail early, or it is undercharging in which case the battery will keep running flat.

 

With an Alternator, a voltmeter is more useful and can be connected between the ignition circuit and ground.

 

I hope this has helped

 

TT

[MilesA]

Thanks everyone - fantastic response and that all now seems pretty clear to me.

 

As ever with a TR, some extra work to do! Some testing and potentially some remedial work.

 

Roger - can I just clarify the steel tubes suggestion? If I have understood the idea, it is to encase the ammeter wires in such tubes (to address the risk Brian identifies) from the back of the ammeter but how far along their length (or have I misunderstood completely)?

 

Ian - thanks for the book recommendation. Just ordered from Amazon - the postage at £2.80 cost more than the book!

 

Regards to all - Miles

[AlanT]

The problem with the "thick brown wires" is that they go straight to the battery without passing through a fuse.

 

If the insulation ever wears through so that they touch the chassis then the battery will make them

red-hot before they burn-out.

 

Roger suggests that if they were in a tube the heat produced would not set fire to the whole car.

 

There would be a lot of work required to get this done.

 

Simpler thing would be to have a battery switch. This is a good idea on any car that does get used every day.

And its not to hard to fit. There is a proper period Lucas part, but modern ones are easy to get.

 

http://www.vehicle-w...me/homepage.php

 

Al.

Edited October 24, 2012 by alanjohnturner

[RogerH]

Hi Miles,

my tubes idea is more whimsical that reality. It would reduce fire risk but as Al stated could be a pain to implement.

Putting spir-wrap sleeving over the brown wires would give them extra chaffing protection.

 

Roger

[MilesA]

Al and Roger - thanks for saving me from whimsy! Battery isolator switch already fitted but I might make a modest investment in some spiral wrap. Think I will also draw up a diagram of the wiring in my car to complement the original version for a 3A which I have.

 

Thanks also again to Ian for the book recommendation - now delivered and read. I would thoroughly recommend the book to anyone who like me needs a basic grounding in the electrical systems and key components of cars of this period. It even provoked some VERY dim recollections of messing around with wires, pins, paper clips, cotton reels and magnets as a child...

 

Miles

[gabriele]

Hi

Is it possible if The dynamo not recharge enough that The tr3 run bad? Recently i drove arround 250 miles with out exhaust black smoke same day last 100 miles with light black smoke. I control carbs but all was ok , The only difference i remember for

Last 100 miles is that i drove with switch on lights

[Dave Larnder]

Hi Guys

 

Remember! if you have a dynamo and an overdrive engaged, the engine revs drop, so does the output from the dynamo, so if you have a charge rate problem, don´t use the overdrive. Alternators on the other hand are not affected by the overdrive.

 

Dave

[BrianC]

I'm sure this has been discussed before, but results were not conclusive (nothing new there then ). So...

 

...on a positive earth car, should the battery cutout be on the positive or negative side?

[McMuttley]

Ive have just bought the following from Amazon (but hopefully also available from many independent retailers)

 

 

Classic British Car Electrical Systems: Your Guide to Understanding, Repairing and Improving the Electrical Components and Systems That Were Typical ... Cars from 1950 to 1980 (Essential Manual) Rick Astley (Author)

 

Whether it is any good - i dont know yet, but as Rick says .... 'Never Gonna Give You Up', then he also sang 'Lights Out'.... not a good omen !

[TR Mitch]

on a positive earth car, should the battery cutout be on the positive or negative side?

 

Technically it doesn't matter as the switch will still be isolating the battery whatever side it's on. Although all your components will be "live" in that they are still connected to the "hot" side of the battery if the switch was placed on the positive terminal of a positive earth car, nothing would happen as no circuit could exist anywhere for current to pass back to the battery.

 

However, the most correct way would be to switch the "live", ie the negative terminal on a positive earth car or vv.

 

Another recommendation too for Rick Astley's book.

 

Ammeter vs voltmeter? I just swapped my ammeter for a voltmeter (TR5 with alternator). The ammeter is pretty inaccurate in the region where you need to keep an eye on things, ie slow but steady discharge of battery due lights, heater fan, rad fan etc. A voltmeter on the other hand always shows the current "health" of the battery and it is easier to spot a trend, eg slow discharge of battery by gradual reduction of volts on the gauge.

 

Edited to add that Roger would probably prefer his unfused cable runs were all done in pyro!

Edited September 25, 2013 by TR Mitch

[RogerH]

I started reading this thread and was getting all excited to throw in a response when I came upon my bit of whimsy.

Titter ye not I say.

 

Many a working loom have been removed over the years only to find a molten mass of plastic and copper.

Isolating the brown ammeter wires at the very least would be a good idea. Putting them in an insulated steel tube would be perfect - Pyro is above and beyond the call of whimsy.

 

Also just to clarify a couple of points -

1, batteries do not store electricity - they make it through a chemical reaction. Eventually the chemicals fail and the reaction stops.

 

2, on an alternator based system the charging current is limited by the battery. After start-up you may notice quite a high charge - 20amps+ - and then reduce to more normal rates after a few seconds. I think dynamo systems are regulated as the dynamo can't keep up with demand.

 

Another good book on auto electrics is the Haynes 'Automotive Electrical and electronic systems manual' .

 

Roger

[JayeM]

Just to throw in another confusing issue......

 

Depending on how the alternator conversion's been done and where the power feed for the Kenlowe and lights is taken from, it's perfectly possible to get a "charging" reading on the ammeter of 20-odd amps, even with the battery charged!

 

It took a little thinking about on the SP, which has almost the same loom as the 3A, until we realised that the very convenient feed point we'd used to power the relay bank for electric fan, horns, headlights and foglights was the original feed for the horns, which doesn't go via the ammeter - it comes straight from the battery via a fuse. So when any of these are in use, the ammeter reads the current the alternator's supplying to them rather than just the charging current to the battery. Panic over!

Incidentally, it does give a comforting confirmation that the fan is actually running!

 

I also fit a 250A Megafuse to the battery feed, as a backstop in case of a "brown wire chafe-through" - don't want all that Lucas smoke to disappear!

 

John

[Nick Webster]

Seems an opportune time to mention that although these days we all seem to be obsessed with a healthy charge (trying to avoid the word positive here) and the subsequent need for an alternator, it was not always so. Even when the TR was new which in the grand scheme of things is not that long ago, it would be expected that a night time drive would involve some discharge by the battery to supplement the dynamo. The useful ammeter would help you calculate how long you could keep this up before the battery was so low you could not expect the starter motor to turn over the following day. Most of the time all was well if you had a healthy battery. In ye olde times cars were not even fitted with voltage regulators and the ammeter would help you calculate when to swich off the dynamo to avoid over charging the battery. You would then proceed with a discharge showing on the ammeter and armed with the knowledge of the amp hour rating of your battery and a little mental arithmetic could calculate when you would need to turn the dynamo back on. Or just guess which seemed to work reasonably well. Personally, it worries me not at all that my ammeter shows a modest discharge as I cruise along at night with lights and heater in operation.