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Auto Electrical Tutorial


Paulfc
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Hi,

I’m keen to improve my auto electrical know how as I want to feel confident things are safe if I undertake changes and/or electrical modifications to my Classic cars. So it’s an appreciation of the basic physics behind what I’m doing that I’m after. Can anyone recommend an easy to understand “Dummy’s” type guide to help me on my way?

Thanks.

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One of the basics. Is ability to read and understand the varied layouts of wiring diagrames!. Every manufacturer and workshop manual editor has a different approach.

Pete.

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It's very simple on our cars - power leaves one terminal of the battery and goes back to earth, either through the bodywork or the battery terminal, and is recharged by the dynamo / alternator. Every electrical item must therefore connect to both power and earth. Switches make or break the circuit, as do the fuses, so if something isn't working it means power isn't getting to it or through it. Think of each electrical component as being separate ie power to cable to switch to unit to cable to earth; this removes the complication of multiple units using the same wiring or fuse and confusing the issue. Each usually has its' own colour in the loom so a good clear circuit diagram makes it easy to follow the wiring and identify what is connected where. It really is very easy; modern cars are much more complicated but Triumphs are thankfully simple and a great place to start.

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Hi all, thanks there’s plenty for me to go at there. Here’s a specific question: 12v goes into the coil what comes out via the HT lead? And another: why are some coils 12v, some 6v and others 9v? What does a ballast resistor do, and, can someone show me the maths behind it, please?
 

Thanks

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1 minute ago, Paulfc said:

question: 12v

a coil on our cars develops around 22,000 volts for the HT circuit

ballast   is a resistive wire  ( dull white and pink)  or a ceramic resistor  near the coil that drops the 12v ign feed down to 6-8 volts at the coil

a 12v coil has a resistance of 3 ohms   a 6v ballast coil has 1.5 ohms  dont ,mix them 

a ballsted coil must not run on 12v as you double the current and up the HT to levels that wreck points condensers and rotor/caps 

a ballast system has a feed from the starter solenoid so when you crank it sends 12v to the coil to aid poor starting when the battery state is low

it only boosts while you are cranking it up.

if you run a 3 ohm coil on  balasted 6-8v system it will give a weak HT and poor spark at the plugs

if you fit electronic some run on 6 to 18v  so a ballasted coil with poor battery may be below the operational voltage and might not work well 

its common  to run a replacement 12v ign feed to operate eletronic units but not the coil

some electronic are made specifically for ballast systems 

just to make it more confusing  some  6v  ballast coils are marked as 12v being the base vehicle voltage

Pete

 

 

 

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The reason for the ballast in the first place is that the coil on a standard system puts out 12v, so you get a spark at the plugs when you turn the key. The 6v or 9v coil is designed to run at a lower voltage whilst supplying the same power at the plugs as the 12v system would. If you suddenly put 12v through it, you'll get a much better spark for starting when cold, but this will quickly burn out the system, so the full 12v is put through when the key is turned to the start position, and once started it drops back to the lower 6v or 9v system to prevent damage to the wiring. It's a simple way of boosting power to a standard system using basic electrical equipment and keeping costs down.

 

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Pete thanks for the very good summary, I must keep it for prosperity.

The old grey matter doesn't remember all nowadays, comment re lower voltage 6v coil being marginal (point No8) for some Electronic Ignitions and the fact my 6v coil on the Sprint was leaking oil and had to be replaced was the driver for me bypassing the ballast supply and operating the Sprint as a 12v system, the Spit and Vit were already 12v, no ballast.  

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Thanks all. I’m sure once I’ve digested a few things I’ll be back with more questions. I guess it’s an age thing but I increasingly find I have to understand the “why” of things rather than simply accepting what I’m told. Thanks for the patience shown.

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It helps if you can imagine that the car body is a wire. 

Something that confuses people is that some (most) circuits take positive power from the battery, through the switch, to the component and back to the battery by wire or the earth, while others (e.g. horn, wipers) feed positive power to the component then the switch, then back to the battery.  This is referred to as 'earth switched'.  In the case of the wipers, this allows for a self park mechanism to be fitted.  There must be a reason for the horn but I can't think why they chose 'earth switched'.

I second AA Book of the Car (Vitesse used as example for some parts)

C.

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Doug's guide is great as are all the others for various models. 

Tip... Don't use the garage smoke detector as a testing device. I know of some cooks who use their smoke detectors as a guide to when food is done!!

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Try as I might I cannot find any technical data on the Lucas HA12 coil. Can anybody help? I’d like to know the primary and secondary windings figures.

Thanks.

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21 hours ago, Paulfc said:

Hi,

I’m keen to improve my auto electrical know how as I want to feel confident things are safe if I undertake changes and/or electrical modifications to my Classic cars. So it’s an appreciation of the basic physics behind what I’m doing that I’m after. Can anyone recommend an easy to understand “Dummy’s” type guide to help me on my way?

Thanks.

You could try this

20210505_144407.thumb.jpg.39adc252ddc479d713e7d0faca575e0c.jpg

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19 hours ago, Paulfc said:

technical data on the Lucas HA12 coil.

Paull  found this    https://www.ebay.co.uk/itm/121795912891

Lucas 12 Volt ignition coil, with acorn fitting for HT lead.
Lucas part no.DLB100 model no.HA12. 
This can be used on most 12v vehicle 1930's on.
To connect this coil on a Positive earth system, 
connect the CB wire to the + Positive terminal and the SW wire to the -- Negative terminal.
To connect this coil on a Negative earth system, 
connect the SW wire to the + Positive terminal and the CB wire to the -- Negative terminal.
 
Not for use on ballast systems.
Not for use on electronic systems.
 
the terms CB = contact breaker       SW  switch wire  

 

Pete

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I found this blurb on an ad for a Remax coil, they claim it's to the original spec of the Lucas HA12:

Ignition coil Remax ES2 Made In England. 12V Standard coil for 12 volt systems with conventional ignition screw type HT connection applications. Oil filled coil, Acorns and split washer HT connector. No of poles 2, Primary resistance Ohm 3.455, Secondary resistance KOhm 6.8, Output voltage @25pF/1M = 9,540 Volts. Replaces Lucas DLB100, LA12, HA12 Supplied with the following: HT3 Long Acorn, HT1 Split Washer, HT14A Old style coil boot, 2x M5 terminal nuts & washers, 2x Double male spade terminals and Mounting Bracket. 

The lettering refers to the type: LA is standard, HA is higher spec, SA is sports; so if a coil is LA12 it's a standard 12v coil, if it's LA6 it's a 6v, and so on. I remember from somewhere that BA means ballast but can't confirm that.

You can aparrently ask the experts here: https://www.lucasignition.com/product/12-volt-coil-screw-in-lead/

Found some more info on an MG site:

(Coils) Will be dated by WWYY, Marked SA12 = Model (Sports, 12V), ribbed red insulator, slightly larger OD than stock HA12, which has smooth black insulator. Coils for Morris etc are LA12 - 20Kv, "high performance" cars like MG are HA12 - 30Kv, Sports are SA12 - 40Kv. 

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Thanks Pete and Colin. I’m starting garner the the information I’m after. I am surprised at the lack of original technical data literature available on Lucas components. I’ve ordered a copy of the book Mathew mentioned and started to develop my technical/practical skills.

Thanks again.

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Hi Roger,

I have, thanks, and picked up some very useful info. It’s an excellent resource which I’m proud to say I’ve contributed to as well.

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