To charge or not to charge

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To charge or not to charge

Postby doc knutsen » Tue Jul 21, 2015 8:17 am

Ran into a little head-scratcher last time out with the Imps, in that mye car stopped charging, yet I cannot find anything wrong. The car is fitted with an alternator, and the wiring is very simple
as this is a race car. For two seasons, the alternator has worked perfectly, but all of a sudden... The ignition light does not light up when the ignition is switched on, so on finding a non-working bulb, I thought the problem was solved. However, a new bulb did not change things, nor did fitting a spare alternator. The alternator has three terminals, and I use the standard plug that was originally fitted: One thick cable to the pos terminal of the battery, the other to side the ignition side of the starter relay in the engine bay, and the last one (small terminal) to the ignition light.
The ignition light comes on when this terminal is connected directly to earth, but not when wired though the terminal on the alternator. Soooo...any bright ideas to light up my day?
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Re: To charge or not to charge

Postby colin rooney » Tue Jul 21, 2015 11:06 am

Best bet is contact dave lane ,noddy on the forum he is an electric wiz kid

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Re: To charge or not to charge

Postby The Nun » Tue Jul 21, 2015 11:21 am

Do you know the spare alternator is a good one?
Normally no ignition light means either the alternator isnt earthed or the diode pack has failed?
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Re: To charge or not to charge

Postby ImpManiac » Tue Jul 21, 2015 2:43 pm

Trace all the wiring through using a multimeter or equivalent. If there is no fault in any of the charging system, the likelihood is that the alternator has a defect. :idea:

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Re: To charge or not to charge

Postby Dave ' Linwood ' Lane » Tue Jul 21, 2015 3:36 pm

doc knutsen wrote: The alternator has three terminals, and I use the standard plug that was originally fitted: One thick cable to the pos terminal of the battery, the other to side the ignition side of the starter relay in the engine bay, and the last one (small terminal) to the ignition light.

This doesnt make sense , Im guessing you have a Lucas alternator , rear plug has two large fat terminals and the small one , whats confusing me is your one fat wire to the battery and one to the solenoid , the two fat terminals are in series ie. linked so you only need the one wire which normally goes to the solenoid terminal the + battery lead connects to , its not normal to connect the alternator directly to the battery .

Here's the way it works. One wire to the light is white. In our cars, all white wires are "hot" when the ignition switch is turned on. The other wire to the warning light is brown with a yellow tracer. The way this works is, with the key on but the engine off, power is fed to the light by the white wire, and the brown/yellow wire is grounded through the alternator, completing the circuit and illuminating the bulb.

When the engine is started and the alternator is working properly, the brown/yellow wire is energised, so that the bulb is receiving 12 volts from both sides. As a result, there is no ground circuit, so no completed circuit and, therefore, the bulb does not illuminate when the alternator is charging.

Suggest you trace the white wire to confirm that it is indeed hot with the ignition key on, and also have the alternator tested to confirm that, with the alternator at rest, the terminal for the brown/yellow wire is grounded, and with the alternator charging the terminal for the brown/yellow wire shows charging voltage.

Good explanation of how it all works here

http://www.carparts.com/classroom/charging.htm
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Re: To charge or not to charge

Postby doc knutsen » Wed Jul 22, 2015 8:23 am

Thanks fellers, I really appreciate your comments and suggestions! As you can tell, of all the things I am not, an automotive electrician is towards the top of the list...

To Noddy specifically, I would like to know more regarding the use the two large spade terminals at the alternator. The ignition lamp is wired from the hot side of the ignition switch and this then connects to the small (6mm) spade connector of the alternator. If I connect this to earth via an extra cable, the ignition light comes on, so that this would seem to indicate an alternator defect.
About the two big (9mm) spade connectors, am I to understand that one of them is in fact redundant, and only one needs to be connected to the + side of the battery (or the starter relay)? The loom on the car is custom made, and the wiring of the alternator is copied from a wiring diagram in an old Cars and Car Conversions magezine, dealing with converting a Mini from a generator to an alternator. This diagram shows one big spade terminal connected to the pos of the starter relay, with the other one going straight into the main battery feed. If I understand you correctly, I may use only one of the big spades on the alternator, and connect this to the live big spade terminal of the starter relay, with no direct wire to the battery? Or in other words, only two wires to connect the alternator, ie a live pos feed over the ignition switch to the small spade terminal, and then a thick cable from one of the big spade terminals to the corresponding spade terminal on the starter relay?
Incidentally, the alternator is a Lucas one, bought new from our local Mini emporium, it is the one fitted to the 1970s Minis which is identical to the one that came with the Imp when i bought it.
Assuming that the alternator is dead, could this be due to my habit of switching off the engine by using the FIA main switch (located close to the steering wheel) rather than the ignition switch itself? Somebody told me that the sudden withdrawal of power to the still-spinning alternator would cause an electrical spike or surge that will overload the diodes. I am thinking this could be what has killed the alternator after two seasons.

And again, very many thanks for your helpful suggestions!
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Re: To charge or not to charge

Postby The Nun » Wed Jul 22, 2015 9:53 am

It'll be a Lucas 16 or 17ACR then?
Generally it does say you arent supposed to disconnect or connect an alternator whilst its running so this is maybe where your problems are coming from??
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Re: To charge or not to charge

Postby ImpManiac » Wed Jul 22, 2015 11:56 am

As above, your modus operandi of shutting the engine down using the kill switch may have taken the alternator out. They do not respond well to being disconnected whist still spinning, I've heard. :!:

The two large spade terminals on the back of the alternator are ganged together, I believe. This would be easy to check anyway using a multimeter. In my Imp, I connected both large spade terminals using 35-amp wire to the permanently live terminal on the starter solenoid, as Noddy says. The smaller spade terminal takes a feed from the switched live from the ignition switch. This circuit also contains the charge warning lamp, which is necessary as a resistor in the circuit. This switched live feed supplies current to the alternator field windings, providing the magnetic field to allow the generation of electricity by the alternator. No current in the field windings, no current from the alternator. :wink:

You say that earthing the alternator feed (the wire to the alternator small spade terminal) illuminates the lamp. That suggests to me that the switched live feed is working, so your wiring is probably good. :) However, when connected to the alternator, no current passes (bulb does not illouminate). This suggests to me that the failure is in the soldered joint inside the alternator that connects the small spade terminal to the field windings in the alternator. As Noddy will attest, this is a common failure point in Lucas alternators - he has said as much many times on this forum, I believe. :idea:

If that is the case, you could take the matter up with your alternator supplier, if the unit is sufficiently new. If not, it may be new alternator time. Or you could dismantle the alternator carefully and repair the connection between the small spade terminal and the field windings. :idea:

I hope this helps. :wink:

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Re: To charge or not to charge

Postby tim sears » Wed Jul 22, 2015 12:41 pm

One large spade terminal can't take the current output from a 45 Amp alternator.The 2 large terminal connectors which are in parallel (joined together) are needed to spread the load.The other end can go to the battery terminal or the main feed to the solenoid as these are the same point in the circuit.this end needs a ring terminal large enough to take the current.
As is with all wires taking large current the shorter the better to avoid voltage drop.

The most common failure these days ,in my opinion, is the voltage regulator in the alternator which uses tiny surface mount resistors and transistors.I have never had a diode fail but have had a few voltage regulators fail over the years.A faulty voltage regulator can show up in many ways ,no warning light,warning light staying on, warning light appearing to work OK but the battery not charging and overcharging the battery.I have a battery gauge in my everyday Imps as on a couple of occasions the warning light has behaved as it should but the battery wasn't charging.

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Re: To charge or not to charge

Postby moose » Wed Jul 22, 2015 3:27 pm

the kill switch should have a large resistor wired into the circuit to protect the alternator, if not it could be damaging the alternator, best wiring/procedure for stopping a competition car is turn off fuel pump (relieves the pressure from the needle valves on the floats which stops them bending over time and causing flooding, usually why people pay good money to have webers reset "because they have gone out of tune") after a short time period i.e. allowed fuel pressure to drop turn off ignition, any electric fans and water pumps should be wired seperatley from the ignition circuit and allowed to run to bring temperatures down in the engien to prevent heat soak, then turn off all electric equipment and then use kill switch.
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Re: To charge or not to charge

Postby Dave ' Linwood ' Lane » Wed Jul 22, 2015 4:31 pm

So some care needs to be taken to determine just which type of wiring, plug and alternator you have when making changes, even swapping alternators which take the same plug. If by looking at the two large spades on the alternator you can see they are clearly connected together, then you have a machine-sensing alternator and you can use either or both large spades for the output. But if the two are clearly insulated from one another, then you have a battery sensing alternator.
With the 3-pin type you have there seems to have been two variations of how the spades were used - on one the central large spade is the output and the other large spade is the battery sense terminal, with the normal-sized spade being the warning light terminal, this is the type where the two large terminals are insulated , and on the other both large spades are outputs where either (or both together for more current carrying capacity) can be used, and the normal-sized spade is as before the warning light terminal.
Battery sensing alternators must have the 2nd brown wire, or at least a link in the harness plug between the + and B+, to operate correctly.
IMHO one B terminal will cope fine up to 45A on a machine -sensing unit ,With a 60A unit it would be wise to run two brown wires in parallel , one from each B terminal , these can both go to the same solenoid terminal .
Go bigger than is needed but not mad ,
This malarky is why I went over to a Denso unit , much simpler :)
If you need to know the current capacity of any wire just count the strands and use this chart , the 14/025 6.0A isnt very common but a micrometer will measure a strand if your not sure , I use 97/030 50A for the alternator and permanent live fuse box feeds with no voltage drop , over-kill but very safe.
Most Imp wiring is 14/030 8.75A , Thats the lights , main loom etc , there are exceptions though so be careful out there :lol:
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Re: To charge or not to charge

Postby Dave ' Linwood ' Lane » Wed Jul 22, 2015 4:47 pm

These are much better than the now aged Lucas ACR units
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Re: To charge or not to charge

Postby Dave ' Linwood ' Lane » Wed Jul 22, 2015 4:50 pm

One final point Tim Sears has raised , It is best to fit a voltage gauge so you know for sure whats going on , over-charge is more hazardous than under-charge and you get no warning of this from the light. An unregulated but otherwise working alternator can kick out over 22Volts , not good for anything other than cooking your battery , blowing bulbs or worst
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Re: To charge or not to charge

Postby tim sears » Wed Jul 22, 2015 9:26 pm

The insides of a Lucas regulator without the surface mount transistor which had failed (gone bang)
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Re: To charge or not to charge

Postby doc knutsen » Thu Jul 23, 2015 9:28 am

Wonderful amount of knowledge on this forum, I am truly grateful for all assistance! In compensation, I shall try to goad Matt into providing links for more in-car shots from our Imps. Our next outing is at our local Rudskogen track,in three weeks time. The track was extended in 2011 and features the aptly named Angstkurve, approached downhill in top gear... The track is very hilly and puts a premium on torque, so we will have our hands full against the 1300 Minis that are homologated at 175lbs lighter weight than an Imp.
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