Dynamo conversion to alternator wiring

[englishmaninwales]

1966 S3 Coupe.
I know this had probably been done to death on here, but I'm just checking through some of the wiring and connections as one of the over winter jobs on my newly aquired car.Electrics are not at the top of my skills!

The car has been converted previously to alternator, with the control box disconnected.The charging system and electrics all work but the are some nasty nasty looking connections that I'm replacing but also I have some queries:
There are 3 wires connected to the alternator.
1. Feed from the alternator to the battery (at the solenoid) - what rating should this be? looks like 30A wire, but I guess the max output from the alternator could be higher so what would be safe?
2. Feed which is spliced into a brown/yellow in the loom - I suspect this is the IGN warning light?
3. Feed which is joined to two brown/blue in the loom - I suspect this is the alternator field ? Does this have to be connected to both? What rating should this wire be?
Thanks!
Malcolm

[billwill]

This is the usual wiring diagram of an alternator.


Please read topics
lotus-electrical-f38/ignition-light-not-t28756.html?hilit=alternator%20diagram
and
lotus-electrical-f38/dynamator-conversion-t28679.html?hilit=alternator%20diagram

Full current output from the alternator will be rare, so you might get away with wire with a nominal rating less than the max output of the alternator. But it is up to you.

[PeterK]

Is it a new main alternator fed wire - the modern thin wall wires are capable of far higher current for the same outside diameter as older wire, so all may be fine.

In terms of alternator output, they can vary from around 35 upto 75A, most typically 45 or so, so you need to know the output before determining wire suitability. A quick check with an ammeter and a half discharged battery would be informative.

Brown /yellow is ignition warning light feed.

Brown /blue - there were 2 running to the control box, so it is normal to just join them. If you are re-wiring, then you don't need two, and with some alternators, you don't need any as the alternator has been wired with an internal link.

For my car I went with a cable capable of full alternator output, as I don't like the idea of hot wires in a fiberglass car.

Peter

[englishmaninwales]

Bill and Peter
Thank you for your most informative posts, links and diagrams. Peter, the alternator feed is not modern thin wall wire and is old and has been there some time as the insulation has hardened with age and heat so I think replacement is due regardless of the rating. A quick check in Halfords show they only stock 27A max - what / where is a good UK source of automotive wire and terminals?

Just to confirm - the two brown / blue that are joined are the stator feed (presuming a non internal link) ?

Finally, to determine the alternator output with the ammeter, where is the safest place to place the terminals?

Sorry for all the questions, but I'm better at the mechanical bits than all things electrical!!
Malcolm

[oldelanman]

A quick check in Halfords show they only stock 27A max - what / where is a good UK source of automotive wire and terminals?

Here's a couple.....
http://www.autoelectricsupplies.co.uk/category/10
http://www.vehicle-wiring-products.eu/V ... mepage.php

[PeterK]

Malcolm
Another vote for Vehicle Wiring Products - got most of my wiring and connectors from them.

To test alternator output with an ammeter, my preference is a non-intrusive ammeter, placed near to the starter solenoid. Failing that, remove the wire (from the alternator) where it joins the starter solenoid, making sure that the ammeter has a large enough range and keeping all live terminals away from everything else.

Peter

[billwill]

You probably won't get full current out of the alternator unless you have a near flat battery, in which case how would you start the engine?

It is not safe to disconnect the battery while the alternator is running, it will probably shoot up to a high voltage and damage its diodes or regulator.

Just get its max output from its specification, from its type number.

[PeterK]

Thanks Bill, a useful clarification, where I said remove the wire ....., I didn't mean while the engine was running !

Disconnecting the main output wire whilst running would likely see 80volts, just before the alternator expired.

Don't you just love communication - it was completely safe and clear to me as/when I wrote it, but I can see a completely different interpretation now.
Peter

[billwill]

Thanks Bill, a useful clarification, where I said remove the wire ....., I didn't mean while the engine was running !

Disconnecting the main output wire whilst running would likely see 80volts, just before the alternator expired.

Don't you just love communication - it was completely safe and clear to me as/when I wrote it, but I can see a completely different interpretation now.
Peter

Ah, same be true for me...

Wot I meant was you can't start engine with a good battery then remove it and substitute flat battery to see how many amps emerge from alternator, because alternator will probably die during changeover.

[PeterK]

How about putting a flat battery in the car and a jump start from another ?

That said, can't be completely flat, or it won't take full charge initially
Peter

[billwill]

How about putting a flat battery in the car and a jump start from another ?

That said, can't be completely flat, or it won't take full charge initially
Peter

When you connect the full battery accross the flat battery to jump start, it will charge it up.. So it won't then be flat.

[ricarbo]

I think you should consider putting a fuse in the alternator output circuit. It must be better to lose an alternator with an overvoltage condition than set fire to your fibreglass car. This raises the question of what rating should the fuse be, given that they have several ratings, e.g. instant, continuous, etc.. Not an easy answer. My view is that you should look for an alternator with a lowish maximum output. That will also lessen the load on the drive belt and therefore the load on the water pump, then choose a fuse that won't burn your wiring and decide which alternator on the basis of your fuse.
Not as simple as it may first appear.
regards
Richard

[billwill]

If you can't get a thick wire that you desire, you can always lay 2 or 3 wires in parallel well joined at the ends.

If you use 3 you can do a pretty plait of the 3 wires.


Lucas ACR 17 is the usual alternator, which seems to be rated at about 36 or 38 amps.

Here is a page I found about wire thicknesses.

http://www.seoc.co.uk/alternator.htm

[prezoom]

When trying to figure out the correct wire size for the maximum load, I have found britishwiring.com to have a handy chart. Click on their Legacy Pages, then Component Catalog, and then Bulk Wire. Their chart will tell the number of strands and the maximum load those strands will carry.

Rob Walker
26-4889