Alternator Warning Lamps etc.

[G4ILN]

In order for an alternator to produce any output its armature or rotating
winding must be rotated inside a magnetic field. This magnetic field is
produced by applying a voltage to the stationary or field windings causing
an excitation current to flow through them. When the ignition is turned on
initial excitation current is supplied from the vehicle's battery. Once the
engine is started the alternator starts to produce an an output voltage
which as well as charging the battery is applied to the field windings. The
alternator is now said to be self exciting and the initial excitation
current can be removed.

The initial excitation current can be supplied via a resistor, but it is
more usual to supply it via a bulb. This is the charge warning lamp.
Sometimes a bulb and resistor are used in parallel. This has the advantage
that if the bulb blows the alternator will still receive initial excitation.
The higher the wattage of the bulb the greater the initial excitation
current. If the bulb wattage is too low the alternator will not generate
any output, will never self excite and even with the engine running flat out
it will not charge the battery at all. For a 12 Volt system a 2 Watt bulb
is normally used.

When the ignition is turned on 12 volts is applied to one side of the bulb,
the other side being earthed via the field windings. Hence the bulb lights
showing no charge. Once the alternator self excites and starts charging the
battery, the bulb has 12 volts on both sides. It goes out indicating that
the battery is being charged.

It is fairly easy to test the charge warning lamp circuit:-

1. When the ignition is turned on the lamp should illuminate.

2. If the wire is now removed from the WL or IND terminal on the alternator
the lamp should go out.

3. If the wire previously removed is connected to earth the lamp should
illuminate.

4. With everything reconnected and the engine running the lamp should go
out.

Alternators can be rotated at higher speeds than alternators, so the
alternator pulley is generally smaller than that fitted to a dynamo. Hence
an alternator will produce a useful output at low engine speeds, which a
dynamo will not.

Some posters have said that wires from their alternators are connected to
the fuse box. I would not connect any wires from the alternator to the fuse
box. The large terminals on the alternator provide the output voltage and
should be connected to the battery via the large terminal on the solenoid.
The small terminal on the alternator is for initial excitation and should be
connected to the charge indication lamp. This is the small wire previously
connected to the D or WL terminal of the control box when a dynamo was
installed.

The only reason I can think of for connecting an alternator via the fuse box
is so that the ammeter can be retained rather than replacing it with a
battery condition indicator, which is in fact a voltmeter. If you want to
retain the ammeter you should change the 30 Amp ammeter for a 50 Amp version
and increase the size of the cables to it. The ammeter must be connected
between the battery and the load, ie in series with the wire connected to
the large tag on the solenoid. The large terminals of the alternator can
then be connected to the NON-BATTERY side of the ammeter. All these
connections can generally be made at the fusebox. In this way the ammeter
will indicate both charge and discharge currents.

I hope these notes are of use to someone.

Graham.

[nygroup]

Graham,
Very comprehensive and helpful explanation. In my car, my ign
warning light is 2.2w. I don't think the Denso alternator is wired
the way you indicate. This alt has 3 wires. One large wire for
supplying power to the car (as per Dave Bean instructions...wired to
the old control box, which is then wired to the battery on the
solenoid), one wire to the fuse box, from terminal labeled L for
load on the alt, and the third is the one you are talking about
which is from alt terminal labeled I for ign, connected to the ign
light circuit. I do have an orig Smiths 30amp ammeter in the car,
but, during troubleshooting I bypassed the ammeter as a test, and
still have the same problem. I also bypassed the old control box as
a test, but no joy there either. At this point, Dave Bean
Engineering is sending a replacement volt regulator for this
alternator. So, I'll try that and see what happens. It's probably
the problem. If not, then I'll push to get a different alternator
since this Denso is also for racing applications, and perhaps it
will not put out much power at low revs, even though it's fitted
with a small pulley.

thanks,
steve



--- In ***@***.***, "Graham" <G4ILN@B...> wrote:

[nygroup]

Well, tried installing new volt regulator in the Denso alternator
from Dave Bean, but no luck. Still have problems generating
sufficient power to power lights, radio, elec cooling fan at rpm
below 1500. I've checked everything I can think of, so at this point,
I'm thinking this alternator is not really for street application and
is more appropriate for racing (minimum accessories and therefore low
power demand at idle, but ability to rev high). I'll contact Dave
Bean and request a substitute suitable for the street.

steve

--- In ***@***.***, "nygroup" <Nygroup@a...> wrote:

[jopalm]

Steve-

Sorry, I can't offer any suggestions as to why you have low output at lower RPMs, but
maybe I can offer one more data point to consider. I've had the Bean conversion in
my car for 2-3 years and have always had more than enough output available. I tried
(unsuccessfully) to use a mirror to read the model number, etc. from the plate on the
underside of the unit. If it truly becomes an issue, over the next couple of days, I
could dismount the alternator and capture that information for you.

Regards,
-John
'69 Lotus Elan S4 DHC 45/8290
'74 1/2 Jensen Healey #18918

[saarhus]

Steve,

There are a couple of things you can do to verify the performance of the alternator. First, if possible, get a clamp-on ammeter to directly measure the alternator's output in amps. I'm going to guess that your alternator israted for 40 or so amps, a typical "compact" alternator rating. If your output, at off idle engine speed, is less than this, and you have changed the regulator, there are still a couple of things to look at. To be on the safe side, it might be wise to take the alternator to an auto electric shop or a parts store such as O'Rielly's and have the rotor and stator tested for continuity. At the same time, you will be able to verify the output. Ifthe output is within specs, you need to check the grounds on the car.

Make sure that the braided ground strap past the engine mount is in place and intact. Another area that is very vulnerable is (on the S3 and up, and I'm guessing, the S1 & S2 as well) the interface between the two rearmost chassis/body connecitons. One of these two bolts is also used as the attachpoint for the battery ground. Between the body and the frame at that location, I found a spacer of aluminium that was very heavily corroded. This whole area is very prone to corrosion and thus, a high resistance path to ground. HTH

Stan

----- Original Message -----
From: John Palmer
To: ***@***.***
Sent: Monday, May 10, 2004 11:55 PM
Subject: Re: [LotusElan.net] Re: Alternator Warning Lamps etc.



Steve-

Sorry, I can't offer any suggestions as to why you have low output at lower RPMs, but
maybe I can offer one more data point to consider. I've had the Bean conversion in
my car for 2-3 years and have always had more than enough output available. I tried
(unsuccessfully) to use a mirror to read the model number, etc. from the plate on the
underside of the unit. If it truly becomes an issue, over the next couple of days, I
could dismount the alternator and capture that information for you.

Regards,
-John
'69 Lotus Elan S4 DHC 45/8290
'74 1/2 Jensen Healey #18918