Try measuring one coil at a time and see if there is a voltage.

The coil voltages will not add unless they are "in phase". See the basic principles below.

are you using an AC voltmeter and an AC ammeter?

one important thing is that there is a difference
concerning hooking the coils together, if
your alternator

a)is a single magnetic disk arrangement, single phase (as the original otherpower 'Volvo') system with laminates
or
b) a dual disk system as the 'Hugh Piggott
style' later otherpower generators are.

----

With the single disk the magnets are alternating:
... -N-P-N-P- ...

So the coils must be hooked after
each other:
...-in-in-out-out-in-in-...

As in this picture:

I'm assuming that all your coils are laid on the
stator the same way.

---

We need to know, if you are making your alternator
the same way as the original 'Volvo' alternator
of the 'otherpower' or not.

That arrangement is easy to get working.
You simply make the coils so that they occupy
a little bigger space than the magnets. Lay the magnets so that they are alternating
... -N-P-N-P- ...
and leave such a space between them that totally
your coils and magnets make same diameter
rings.

Please see the pictures
http://www.otherpower.com/wardalt.html

---
Please NOTE:

It is best to measure the coils one by one
and hook the coils after each other measuring the
output each time assuring that the output
rises every time, when you hook one more coil.
---

Please NOTE:

That kind of a single phase system with laminates is not the most effective way to use your magnets. You will get a better output if you make your generator as a three phase.

After you understood the idea of the single phase
machine with laminates it is easy to understand the layout of three phase alternators with an otherwise similar arrangement
with one magnet disk and laminates.

Please see the excellent pages at:
http://www.windstuffnow.com

And various posts and pictures here at this discussion board by Electric Ed during many discussions concerning coil layouts.

---

Further,
many people are thinking that a dual
disk arrangement with two magnet disks without
laminates, but the coils in between the magnet disks is a better arrangement.

I don't know which one is the most effective.
They work a bit differently concerning the
way the magnetic flux is creating current in
the coils. I think that only exact measurements
could tell, how to get the best out from
your magnets.

But certainly by studying the excellent pictures by Electric Ed and the various other posts here concerning the layout and shapes of coils and hooking them together you will get your alternator working.

This I don't exactly understand.

a)
But if you have got your coils arrangement a such way that the center of each coil is in the center
of a magnet when the magnet disk (the rotor) and
the coil disk (the stator) are laid on the top
of each other, your stator is more or less OK.

b)
I got the impression that you've
got 12 coils and 12 magnets.
Is this correct?

c)
Please see the pictures of the original
'Volvo' alternator.

This is the reason the original 'Volvo'
alternator is so easy to get working.
You have no need to worry so much about
the exact dimensions to get it working.

But later when you become convinced that it
works this way, you can study the details
how to make it really good. By studying the
best shapes of the coils, making it with
three phases etc.

------------------------

Each coil produces in principle AC.
You have to use a rectifier to get
the ready alternator charging a battery.

If you put your meter to measure voltage AC
you should be able to see the difference,
when hooking together two coils compared
to the measurement of one coil only.

You should make your coils with so many turns
that you could turning fast with hand get
about 1V from one coil. In order to get
the alternator charging easily a 12V battery.

If your coils are in phase one coil produces
1V; adding the next, together they'll produce 2V, adding the third you'll get 3V etc.

If the voltage is not getting higher
by adding together more coils
then you are connecting them the wrong way.
It is that simple.

You can check the results by a snall
flashlight lamp as well. It should get brighter
and brighter the more you connect coils.  

--------

Further: if you are hooking your coils
opposite ways your alternator becomes really
hard to turn, because the coils are canceling
each other. You can realize the wrong
arrangement easily from that phenomena, too.