Dangers of alternator conversion?

[Paudman]

I’ve recently been warned that there are problems with the old traditional method of dynamo to alternator conversion which has been written about for years now, where the wires are connected together bypassing the control box.
The exact wording of the warning is as follows:

“All alternators are not the same. There are 2 main types of regulator used, Machine sense, and Battery sense , and also integrated and external although external ones are not common.

if you have a Battery sense alternator and wire it as you describe you will disable the regulator causing it to over charge the battery.

if you have a machine sense one then it will work but the wiring you are running through is only safe up to 30A and modern alternators are capable of 60A or more.

The fuse system in small chassis Triumphs is not capable of protecting the wiring under fault conditions and  there is no fuse in the supply side of the alternator.”

As I’m not intending to use a modern alternator I assumed the older version fitted to 70s Triumphs or the equivalent replacement sold by Triumph Parts Suppliers would have been suitable? I’m also running a 55 amp alternator on my Mk1 GT6 for many years with no problems with the original wiring loom.
The information above is new to me - can any electrical guru comment?

[Clive]

No idea about the sensing side of things.
The current bit is easy though. The original dynamo gave 20 odd amps, and the main wire was appropriately thick. For any upgrade over 30amps or so just run an extra (thick) cable from the alternator  to the battery positive.

[Richard_M]

Sensing does need to be considered and wired appropriately, but if you're using a Lucas 17/18ACR etc then just separate the brown/yellow wire and put that on the sensing connector, and the rest firmly connected together on the main output. If you look at almost all Triumph wiring diagrams there are multiple brown wires - that all go one way or another to the battery terminal.

Another point. Although Triumph/classic car wiring gets a bad reputation, and Lucas particularly, these old cars are SERIOUSLY overwired. The wires, thin and thick, are VERY over-spec'd and can take far more current than the spec says. Modern wiring in cars is tiny in comparison - even for large loads. I imagine wiring in the 60s was over spec'd to allow for the apparently inevitable short circuits and shorts to earth that tended to occur, but this is usual down to bad insulation (through bulkheads/grommets etc) or wandering wires touching the chassis etc - both issues that modern cars tend not to have, through better design and a proper circuit-by-circuit fuse box.

Press on!

[Rallyspit]

Modern wiring is invariably "thinwall" insulated. Although the wiring may look lot thinner it is still capable of carrying heavier loads. As modern cars tend to use relays (lots of - my Volvo had over 20) there's no problem in using thinner wire for the relay switching circuit, but the main feed to the relays and onwards to the high current item, eg lights, horn, radiator fan, sound system, etc. is invariably made of chunkier stuff. My Volvo used starter type cable as the feed to the battery - but it did kick out 100 amps. The thicker the cable, the less resistive loss - which is particularly good for lighting!

Vehicle Wiring Products have a website catalogue with a guide to typical current useage and the correct cable to use.

Better to over-engineer and build in lots of fuses! I've seen quite a few fried Spitfire looms.

[DougBGT6]

both issues that modern cars tend not to have

Unless you've got a Peugeot!  ;D Blown number plate bulb stops brake lights working?!  ??) Connector 6 inches above the road full of water, (who'd have thought that would happen?  :-/ ) killed the radiator fans.  Broken wire in door loom stops central locking. Many more but, not for this forum.

My Son-in-Law recently blew up my GT6 ACR16 alternator by reverse charging my battery. My fault for letting him help. Hey Ho. Ordered new rectifier and regulator. New regulator had 2 wires, old one 4. Phoned supplier, "Ah yes, Battery sensing just connect the wires you've got" Sent it back got a 4 wire one. I would be very interested to know what these sensing things do/are for.

[Richard B]

The type of alternator that only has two wires senses the voltage via the ignition warning light.

All is good, unless the bulb blows, then the alternator does not know what voltage to supply.

Battery sensed has a separate feed to the regulator that is not dependant on the bulb.





Willing to be shotdown if I have this wrong....   :B

[DougBGT6]

Ah! I'm glad I was cautious and got the original 4 wire one then.  :)  So, that's the 2 wire and the 4 wire, what's the 3 wire one do?  ;D

[partsaver]

With the three wire alternator as found on  most 70s cars  one wire goes to battery. One to ignition and other to ign warning  light.

[Steve P]

Richard_B wrote:

The type of alternator that only has two wires senses the voltage via the ignition warning light.

All is good, unless the bulb blows, then the alternator does not know what voltage to supply.

Battery sensed has a separate feed to the regulator that is not dependant on the bulb.





Willing to be shotdown if I have this wrong....   :B

Thats interesting as i have an alternator and a 10mm red LED for the ignition light.Only difference i notice is that it takes about 3k revs to make it go out on startup.

I will measure the charging voltage.
S

[DougBGT6]

Just found this:

http://www.rowand.net/Shop/Tech/AlternatorGeneratorTheory.htm

4 wires good, 2 wires bad.

Animal Farm!  ;D ;D ;D

[piman]

Hello Steve,

" 10mm red LED"

The LED doesn't draw enough current to start the alternator charging, fit a normal incandescent lamp.

Alec