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while this generator look
monks in a museum you might have one
like it in your classic British car and
if that's the case we have two issues
the first one is that these do
occasionally fail like any other
mechanical part of your classic car and
number two unfortunately the people who
know how to test these are gradually
going the way of the dodo however you
can test your generator yourself you can
do it in your car without a test bench
today we're going to do two tests to
show you how much you can learn with
little or no official test equipment now
to avoid the noise and better show you
what I'm doing I'm going to work without
the car I'll be simulating what you will
do with the generator installed in your
car now to begin your generator has to
be installed so if its installed of
course it's going to have a belt on it
so I'm going to put a belt there's
always a lead going to the determined on
the generator we're going to put that on
there and it's usually going on over to
the F terminal and that's on there so
this is the way it would be is moult
it's bolted to your engine so she has
ground she has a belt which drives it
she's got a lead going to the D terminal
she's got a lead going to the F terminal
now if you haven't done so it'd be good
I did a polarizer generator only takes
about 30 seconds and then everything is
ready to go so now let's have some fun
let's see if we can test this using an
old-school method and then we'll test it
again using a method it isn't quite so
old-school so the first test let's
imagine we're Fred Flinstones neighbor
okay I have no voltmeter I have no ohm
meter I have no ant meter I don't even
have a test light all I have is a
question does my generator work let's
find out first thing first turn the
engine off we're going to remove the
belt from our generator so she's free to
do what she wants also on the back of
the generator the two wires the one for
the field terminal and the one for the D
term one of them and get them out of the
way I personally like to bend them back
and put some tape on them so they can't
possibly get into any trouble now then
we need is a small jumper we're going to
use two jumpers to do this test today
one lead I'm going to connect on to the
field terminal and the other lead the
other end of the same jumper on to the D
terminal now that it's connected to my
car so because it's bolted to my card
has ground I don't have a car here so
I'm going to give this a groan but you
won't have to do this when you do the
test yourself because being both of the
engine again we'll have it and the last
thing we need is another jumper lead
this jumper lead needs current now
you're saying well where are we going to
get the current I'm coming off of the
battery here because again I'm not
working in your automobile but in your
automobile you want the other end of
this lead to go to the brown wire that
feeds your voltage regulator so here I
am I've got power because I'm connected
to the brown wire I've got my jumper
here there's no belt and all I have to
do is touch one of these and watch up
here can you see that the generator is
functioning is an electric motor it
works what does that tell us well that
tells us that the connections in here
between these terminals and where they
have to go are obviously working it's
telling us that the connection between
the leads and the field are good the
commutator and the Bush over here are
good this all works if this did not work
if this were dead it wouldn't work in
your car if it does work however it
brings another question up somebody
might say okay I see that it's working
but how well is it working or does it
work well enough in other words can we
quantify how well this is going to
function and for that we'd have to take
a jump ahead in time let's go for
example to the time of the Wright
brothers I'll say I one of the Wright
brothers neighbors and I say well you
know what I I don't have an ammeter I
don't have an only to run over test
light but I've got a voltmeter that's
all you'll need with a voltmeter we can
make this happen so let's go ahead and
run a test now this is going to be newer
school with a voltmeter to find out not
only if it works because we know it does
but how well does it work we're going to
quantify how well it works do that we
need to put the belt on the generator so
the belt is on the generator connected
so that when the motor spins this is
going to spin we will have taken the two
wires off the back again just like we
did the first time and get them safely
out of the way so they can't get into
any trouble we're going to get our
little jumper lead again just like we
did before connect the field terminal to
the D terminal just like we did then and
now we have to connect the voltmeter and
frankly this confuses some of us it
confuses me so let's see if we can
understand how volt meter's tend to have
two leads one's black and ones red
usually the red is positive usually the
black is negative so let's pretend that
we're testing a car which is negative
ground okay negative ground negative
black black goes to
ground so I'm going to connect to here
you can connect it to your block you get
into any other part of this engine where
you're going to get a ground I don't
even have to worry about the other one
because it's the only one left and I'm
going to connect it right here to 101
where leads are I'm done but how about
if somebody says but my car is positive
ground and that confuses me okay let's
take the leads off let's assume we have
a positive ground car positive ground
red is positive red goes to ground that
leads us which is one we're going to
connect it on there now then we're going
to go and we're going to set our volt
meter some of them have automatic
settings you just put it to volt and it
will adjust itself some of the older
ones you had to turn them to a preset
setting and if you've got one like that
you want to set it from zero to twenty
degrees twenty volts excuse me zero to
twenty volts that's all you're going to
do we want to set our voltage or excuse
me our idle speed in our car up so that
she aisles it around 859 maybe a
thousand revolutions per minute no more
than that and this is important let me
explain why there's going to be a bit of
residual magnetism in the field in here
so when the armature begins to spin the
little bit of magnetism make a little
bit of electricity and it's going to
come out through here loop around and go
into the field and come back in here
again when it does the field will be
stronger when she's stronger this will
become stronger stronger comes out comes
around this gets stronger still and you
can see what this is going to go it's
going to spool up and up and up and up
and out of control this 12 volt
generator will get to 40 perhaps 50
volts if you let it that's really
exciting but it will destroy this pretty
quickly we don't want to go up there so
by setting the idle speed so she's only
going to be like in the high eight nine
maybe a thousand revolutions per minute
that's fine our volt meter is here we
start our car the motor settles out at a
little speed and all we have to do is
look at your voltmeter okay if we're
getting 14 volts maybe a little more
than that this is working great we've
not only proved that it works it works
well we're done but keep an eye on the
voltmeter because if the voltage begins
to climb 16 17 18 19 20 volts 18 20
volts and open there it's time to stop
the experiment we've already proven it
works you don't have to go any further
so what have we learned today
we've learned that if we have taken this
generator out of our car and taking it
to a shop and
said please put this on your test bench
for me the guy in the shop would test it
and he would say something like it's
dead you're going to have to be the
service it or replace it fine thank you
or you might say this runs ok this tests
just fine qualifies just fine but then
you might say that's not true because my
car isn't charging but the test bench
just proved that it does charge the
professional just proved it so now
you're gonna have to look at your wiring
or perhaps your voltage regulator you've
done the same thing yourself you've
tested your own generator right in your
own car and you've proved that it's good
and if it's good you can go ahead and
leave it alone it doesn't even new work
and start looking for something else so
that's how we can bench test our own
generator right in our own car
