Alternator wiring confusion.

[hatman]

Having finally grown tired of sitting with non-operating flashers, waiting to make a right turn, I've decided to go the alternator route.

To that end I've read the workshop manual and trawled the archives of this site and, today, acquired an alternator from a scrapped mini that, physically, is a good fit for the Elan; the fitted v-pulley even lines up with the crankshaft and water pump items AND I can mount it on the existing bracket, by using a length of threaded rod and a collection of nuts. Result!

Now to the head-scratching bit. I gather that the thick, brown, output cable gets connected to the hot side of the solenoid, the thinner (also brown) field cable attaches to the ignition switch via the fuse box and the thin, brown and yellow wire connects to the warning light. However, both of the brown wires (output and field) shared a common connector on the mini and attached to the solenoid, rather than having the field wire hooked up to the fuse box - can I copy this on the Elan (ie output and field connected to solenoid; thin wire connected to warning light?)

I'm almost sure that one of the postings in the archive referred to such a method of connection, saying that the warning lamp bulb needs to be of 2 watt rating as the alternator gets its 'charging' message from this. Have I understood this right or (as is entirely possible) am I going mad?

[wojeepster]

Wire it the same as the mini if they are both negative ground. The warning light supplies the initial voltage to get the alternator working. Without it the car will not charge. Once the alternator starts charging there is 12v on both sides of the bulb and light goes out. Does mini alternator have internal regulator?

[hatman]

Does mini alternator have internal regulator?

Yes, it does. Thanks for your clarification re the wiring-up. Just one thing puzzles me now (a world first for me) - why are other Elan alternator fitments wired up via solenoid and fusebox rather than this way?

[iain.hamlton]

Howard, I think the reason the Elan (and plus two) have two brown wires is historical; this is the way electrical systems evolved. Also the circuit going to the solenoid has the ammeter in it; the other doesn't. So the ammeter measures the incremental current charging (or discharging) the battery - hence no connection to other load like the lights. It doesn't measure the current delivered by the dynamo.

Be careful that the brown wires you are sufficient for the current the alternator can deliver. Do you how much current the ammeter is rated for? Let me know, and I can advise the size of the wire you need.

In my case I ran new, much thicker, brown wire to the solenoid eliminating the ammeter. The ammeter may not be sufficient either. I fitted a voltmoter in the ammeter's place. I am happy with the result.

Good luck - it is definitely a job worth doing.

best regards, iain

[hatman]

Hi Iain - thanks for the further enlightenment. As the Elan doesn't have the luxury (or weight!) of an ammeter matters seem to be even more straightforward, vis-a-vis connecting up the alternator than I'd realised.

As regards what the output of the alternator is, I'm afraid that I just don't know (no indications that I can find on the alternator itself) but I'm working on the basis that if it's man enough for a mini's electrical needs it'll do the job OK on an Elan - certainly more so than the output of the feeble generator with which St Colin blessed his creation. I nicked the mini's wiring together with the alternator itself, so logic tells me that that should be OK too.

Kind regards, Howard.

[iain.hamlton]

Howard, I am concerned the alternator might produce more current than is good for the Elan's wiring. Over the years, alternators of different capacities - some relatively large - were fitted to minis. If there is no other indication, suggest you compare the gauge of the mini's alternator cable with those of the Elan.

best regards, iain

[RotoFlexible]

Howard, I am concerned the alternator might produce more current than is good for the Elan's wiring.

How can an alternator (assuming it is properly regulated) produce more current than is demanded by the combined loads in the electrical system? The rating is presumably for current capacity. In theory, an alternator with excess capacity should be functionally equivalent to one with adequate capacity. Now, if the wiring to a given load is not adequate to carry the current demanded by that load, the alternator with excess capacity will burn up the wiring quicker than one with one with barely adequate capacity, but that's a different issue.

[iain.hamlton]

Good question.

A discharged (or faulty) battery will accept an awful lot of current if offered 14 volts. If a modern alternator can produce 100 amps, I'll bet a flat battery would draw at least that. Personally, i'll stick to dimensioning the cable according to the rated output of the alternator.

best regards, iain

[RotoFlexible]

Good question.

A discharged (or faulty) battery will accept an awful lot of current if offered 14 volts. If a modern alternator can produce 100 amps, I'll bet a flat battery would draw at least that. Personally, i'll stick to dimensioning the cable according to the rated output of the alternator.

best regards, iain

Good point. I have seen an installation with an 80-amp fuse in that big brown wire between the alternator and battery, and I plan to do the same.

[redskatejbf]

Question for Ian.Hamilton
I recently purchased a new Lucas A127 alternator but have not had time to fit it as yet, it has a max. output of 70 amps.. As I could not see the loading exceeding 40 amps. I was going to fit a 40 amp fuse very close to the alternator using high capacity thinwall cable rated at 39 amps. and then onto the solenoid with the same cable. I believe a blade fuse (used in todays cars) will blow at approx. double its rating. Does that installation sound sensible to you? Thanks for any observations / comments.
John.

[wojeepster]

The alternator putting out lots of amps to charge your battery and run all your lights, acc, etc is a good thing but if it exceeds the rating of the ammeter it will burn it (the ammeter) out. Lets say ammeter is 80 amps and alt puts out 110. This will not be good.

[iain.hamlton]

John, your 40 amp fuse would protect your existing wiring, but you may have to change the fuse often. I would consider this more of a nuisance than running a new bit of cable.

For a 70 amp alternator, i'd use 10mm2 cable (rated at 70 Amp) and an 80 Amp or larger fuse. I'd assume the fuse would blow just above its rated current. You can get "slo-blow" fuses for some applications; these will stand higher currents for a moment, but probably a few hundread milliseconds rather than seconds. These are only intented to survive spikes and transients, which do not heat up cables enough to damage them.

best regards, iain

[hatman]

Iain, mindful of your warnings about the dangers of overloading cables, why not use the heaviest bit of hawser you can lay your hands on, then you know for certain that you won't overload it? ie is there such a thing as having a too-heavy-duty cable?

Also, as regards alternator/dynamo substitution, I've read the manual's instructions to remove the control box and chop off lumps of wiring but can't I just leave the box where it is (for possible later reversion) and just disconnect the wires?

[iain.hamlton]

Howard,
I take your point about heavy cable. Two minuses: cost and weight - at odds with the Lotus ethos. The only other draw back of very heavy cable is it can be rigid and unwealdy to run. Other than that, it doesn't matter.

As far as the regulator is concerned, I can't see much wrong with leaving it. In my case, once I was happy the alternator was working properly, I took the old regulator off.

best regards, iain

[Frank Howard]

...if it exceeds the rating of the ammeter it will burn it (the ammeter) out. Lets say ammeter is 80 amps and alt puts out 110. This will not be good.

Not necessarily. The smallest alternator I could find puts out 35 amps. (The Lucas generator puts out 22 amps.) I got a larger alternator from a 1988 Mazda 323. Not sure what the output is, probably in the neighborhood of 40-45 amps. At the same time, I added a Smiths ammeter. You can get a 30 amp model or a 60 amp model. Not thinking, I opted for the 30 amp model. I drove the car today after sitting for 8 weeks. When the battery is really discharged and the alternator is trying to charge it back up, the ammeter pegs at 30 amps, but it has not burned out so far. This is not the first time I have started with a severely discharged battery and pegged the ammeter. I'm actually glad I opted for the 30 amp ammeter because smaller changes are easier to see then they are on the 60 amp model.