I'm trying to get more information about how the current banking system is working.
The cash cycle is somewhat easy to figure out. Merchants bring huge quantities of cash to their bank so their are credited on their account. Banks put that cash in their ATM so when you retrieve money, it is charged on your account.
The only remaining question is what if a bank has too much cash and the other not enough. Is there a market for cash? Or is everything regulated by the central bank?
Yes, its the federal funds market, and its rates are heavily influenced by the central bank. Only the banks of the Federal Reserve system and certain institutions (like Freddie and Fannie) can access this market.
Right now Bernanke has the federal fund rate at almost zero (between 0 and 0.25%). You can check their daily value here:
http://www.newyorkfed.org/markets/omo/dmm/fedfundsdata.cfm Short term the central bank uses repos to correct slight deviations of this rates, but if that is not enough it has to raise the rate or do open market operations to inject more money. Right now we are in a special situation because the banks are loaded with money (check the excess reserves) and they have no need for borrowing from the federal fund market for their operations. Right now most of the action comes from the other institutions that lend the banks the money they have around without use overnight to earn some (minimal) interest. Why do the banks borrow this money? Because they can deposit it as excess reserves and earn a 0.25% that the Federal Reserve pays them. So while this situation goes on, the federal fund rate wont go over the excess reserve interest rate that the Fed is paying the banks. Note that this is a way for the Fed to give "free money" to the banks.
But now about the bank themselves. The money on your account is only a virtual value in some computer. When you pay someone from the same bank, nothing really happens except an addition and a soustraction in an internal database. In theory, if 10 people have an account with 1000€ in a bank, this bank has 10,000€ (we will ignore loans and debts for now).
Now, what does happen when you send money to an account which is not in the same bank?
Different countries work in different ways, but usually the banks settle their balances once a day.
It looks like an ACH is used. From what I understand, an ACH is mainly a bank for bank. So each bank should have an account to an ACH.
Is that right?
Who is controlling the ACH?
How can a transfer between two ACH happens?
How could it be controlled that the bank have well the money they pretend to have?
I'm a complete n00b in that field and I'm really interested to know the answers.
Sorry, Im not from the USA and I can not give you specifics on how exactly the banking clearing system of the USA works, but there is the wikipedia page that might help you get started:
http://en.wikipedia.org/wiki/Automated_Clearing_House (according to the wikipedia is regulated, which is not a surprise at all).
Btw, there were free market clearing houses that restrained member banks from expanding the money supply. See the Suffolk bank in the USA druing the XIX century.