Morris Minor Owners Club

Alec: I'm still not sure what you're saying here.

Let's take two reasonably likely cases:

1. The engine is running. The total electrical load (ignition, lights, accessories) is 15A, and the battery is being charged at 10A. The alternator must be putting out 25A. Yes? What does the ammeter read?

2. You now stop the engine. The load drops to 12A, and, as the alternator isn't turning, it's putting out nothing, so it's all coming from the battery. What does the ammeter now read?

Where would the ammeter be wired to produce whatever readings you say it would show?

Kevin

Hello Kevin,

all I'm saying is that when the manufacturer(s) fitted an ammeter it was connected such that some of the load is connected so that the meter is carrying battery charge current plus whatever other components are being used at the time. From the couple of manuals I have it is the battery fuse supply and whatever components are fed from that. In other words, the meter may not only just measure battery charge. It was only a minor point which has got out of hand. My main point, which I repeat, was merely advice to ensure that the ammeter is not under sized, particularly as the alternator size was not specified, or indeed how the meter is connected?

Alec

Alec- that's just not so - the ammeter is ALWAYS connected simply on the feed TOO and FROM the battery...... That's ALL it ever shows. By all means show me a wiring diagram that differs from that - I think you will struggle.......

Hello BMCE,

I have them, you are welcome to come and look at them. Please give me the credit to know what I am talking about.

Alec

Seriously Alec - the ammeter only ever carries what goes IN and OUT of the battery, It just doesn't make sense to have anything bypassing the ammeter - which is what you are suggesting?

Kevin,

1. +10A Assuming that the alternator has a maximum output of at least 25A, it will be putting out 25A (15A + 10A), but 15A will be going directly to satisfy the load from the lights and accessories. This 15A will not show on the ammeter, as the load is connected to the same side of it as the feed from the alternator. The balance of 10A, which the alternator control circuit has determined to be needed to charge the battery, all flows through the ammeter, so this is the reading (+ve) it will show.

2. -12A Nothing coming from the alternator, so all the load is passing through the ammeter from the battery.

I think theres been a bit of confusion here..... I think what most are saying is that the ammeter is fed direct from the battery but that you can then take all other feeds EXCEPT the starter from the otherside of the ammeter,Thats how my triumph 200 manual shows the wiring,everything, lights ,ignition,horn etc,is fed either directly or indirectly via a relay or fusebox from the ammeter,The battery lead goes to the starter and from the same terminal to the ammeter.

Hello BMCE,

quite the reverse, the only thing that bypasses the ammeter is the starter motor current.
May I remind you of my original statement, which you have taken exception to and made a song and dance about.

"That would be fine if that's all the load the ammeter carries but it does more than just that. I would agree that most of the time it will be fine but still worth checking."

From my manuals, the battery fed fuse is connected to the battery side of the ammeter and the ignition supply and lights from the generator side of the ammeter, so in a charge situation any use of battery fuse circuits will be shown in addition to charging current and in discharge situation then all the meter shows is running load except for any battery fuse load.

Alec

Alec- manual for what car ? A correctly connected ammeter carries ALL the battery current out to the car's systems (and back from the generator) - it must be a very strange car that has circuits by-passing the ammeter - which is what you are saying! Can you show us such a system on the internet - or from a scan ?

Well that's a relief: Richard and I agree on my hypothetical cases. I'm fairly sure Roy does too.

So this little discussion boils down to whether some cars have a "battery fed fuse ... connected to the battery side of the ammeter"

I'm not aware of any: Alec is. Fine.

I'd recommend anyone still wanting, despite this thread, to fit an ammeter to a Minor, to fit it so that shows just charging/discharging current. But wherever you connect it, it will read what it's carrying, so there's no risk of passing 40A through a 30-0-30 ammeter without it being very obvious from the bent needle.

Some people on a pre-war car messageboard I follow recommend small digital voltmeters plugged into the original inspection lamp sockets, but that's more to stop them damaging their batteries with non-voltage-controlled dynamos.

Kevin

Hello BMCE,

you seem to be contradicting yourself, you said the ammeter only shows battery charging current did you not? Therefore the current for the ignition side and the lights must be fed before the meter and this current will not be added to the charge current; discharge is different, then that load is reflected in the meter indication.
See what I mean with this schematic, you may like to copy and enlarge it for a clearer picture..

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Alec

Yes Alec -the ammeter only shows charging/discharging currents - too/from the battery. Everything else connects on the car system side of the ammeter and therefore does NOT show on the ammeter - unless of course the generator is not supplying..... I have certainly not contradicted myself! It's perfectly clear to me. I'll have a go at that diagram later when I have more time - thanks for posting it.
Ok - looked at it - and that is the strangest layout I have ever seen - it's certainly not a standard layout. What car is that from? It is NOT the correct way to connect an ammeter! The whole essence of an ammeter is to show what's going IN or OUT of the battery......But I can see where you have been led astray by that strange diagram..........

Hello BMCE,

it's a Jaguar layout but the Triumph 2000 is the same.

I can't understand why you think it is the wrong way to connect an ammeter. How would you propose to do it?

Alec

Yes exactly the same as myTriumph 2000 layout, Jaguar and triumph must have got it wrong then ,no wonder they stopped producing these cars after .... how many million uhmm

It's a Jaguar layout but the Triumph 2000 is the same

Oh and much closer to home as well, much much closer, in fact right here on the Morris Minor as well!

When the very late Minors were fitted with the 11AC Lucas alternator, the official wiring diagram shows an optional ammeter, connected in exactly same same way as the Triumph 2000! The ignition switched loads are taken from the 'alternator side' of the ammeter, and so will show a discharge with no engine running, but the non-ignition accessories and all the lighting are taken from the 'battery side', so no discharge with no engine running, but the ammeter will show a charge to cover these even when the battery is fully charged. It's definitely not the best way the connect an ammeter, but it seems it was done quite commonly within BMC/BL?

The scan below shows the relevant wiring diagram.

58 is the optional ammeter

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Hello Islip Minor,

Do you have any schematics of what you consider the correct or desirable way to connect an ammeter.

Bear in mind that it is very difficult to separate the charging current from general running load as the whole of the wiring is interconnected? For example if you look at this forum's schematic of how to connect an alternator, you might think that it is desirable to connect it in the link from the alternator to the battery (Red line). However that also links to A and A1 which together feed the cars ignition, lighting and battery fuse. and that current will be included in the ammeter reading?

Alec

Alec,

I have used the sticky created by Louise (hope you don't mind Louise!) and adapted it to include an ammeter in a more conventional circuit than was used by some Jaguar, Truimph or Morris (and probably other BMC/BL cars of the the same era?).

As has been said earlier in this post the 'conventional wisdom' is to connect all the electrical load, except the starter motor, to the alternator side of the ammeter. That way the reading on the ammeter, with the engine running at a reasonable speed, will be what is being fed into the battery, AFTER all the other loads have been satisfied. With a well-charged battery this should be no more than a few amps 5-10 minutes after starting the engine. If the charge stays at ~10A or more for a long time, either the alternator control circuit is malfunctioning, or the battery is in a poor state (sometimes this will also result in virtually no charge going into to it as well).

A -ve reading with 2000 rpm or more, means that the alternator is not covering the applied load, and the battery is being discharged by the amount shown on the ammeter - could be either the alternator does not have enough output to cover the load, or again the control circuit is malfunctioning.

With either of the alternator circuits, the original dynamo control box plays no part in the new charging circuit - without an ammeter you can remove the brown and brown/blue wires from terminal A and A1 and join them together (solder not anything like scotch locks!), insulate the join well and tape the wires to the original harness. With an ammeter the join is made on the back of the ammeter, but the either both wires will need extending to go through the bulkhead to connect on to the ammeter, or make the join close the the old control box and solder a single larger wire to go up to the ammeter.

I would not suggest you use the original dynamo main (brown/yellow) wire to connect to the alternator, it is sized for ~19/20A, and any alternator that you are likely to fit could be twice that output or more. A new heavier cable is required - see below for sizing:

Capacity Size Area
5.75A 9/0.30mm 0.65mm2
8.75A 14/0.30mm 1.00mm2
17.5A 28/0.30mm 2.00mm2
21A 35/0.30mm 2.50mm2
27.5A 44/0.30mm 3.00mm2
35A 65/0.30mm 4.50mm2
42A 84/0.30mm 6.00mm2
50A 97/0.30mm 7.00mm2
60A 120/0.30mm 8.50mm2

Many of the common Lucas alternators have 2 35A Lucar spade connectors for the main output connection, and to keep the cabling slightly easier, and more flexible around the engine, you can use 2 smaller cables that together provide the full output capacity. As an example we use 2 x 35A cables (each is 65/0.30mm) from our 55A alternator up to the ammeter, and then a single 120/0.30mm cable from the ammeter to the battery connection.

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Hello Richard,

your diagram is the same as mine, except that the battery fuse is on the generator side. I have puzzled why this layout was used and my best guess is to do with the rather poor scale forced by the range of current that might be shown. Generally, the needle remains at centre scale most of the time with a normally running car. Use of the horn or headlamp flasher will cause the ammeter to react which may reassure the driver that the meter is functioning? I'm sure there was a sound reason for this circuit?
However, getting back to the original point again, and particularly in view of the sticky diagram, where would most people connect an ammeter, I suggest in the red generator to solenoid wire which is why I am again repeating why my advice to ensure the ammeter is adequately rated.

Alec