Size of the terminal might be an indication too.
Like you said, the B is prbably the battery positive and should be larger than most others. The N could potentially be the Negative, it might be small and connected with the housing (check for continuity), or big like the B when you have an isolated Negative terminal. F is very likley the field coil and that's where the regulator is connected. But be carefull as there are variations: The field coill could be between this terminal and negativ or between this terminal and positive. And sometimes there could be an internal regulator. Some external regulators are internally switchable for positive or negative field supply, some are dedicated for just one type. I could help you find out with a few more tests what it is.
The E is unclear but could very likely be a stator tab that is used for RPM metering of the engine.
Not seen an alternator with with terminals labeled like you describe.
They are pretty simple devices and given you have got 5 terminals, it suggests they could be: An isolated field coil, maybe between F and A. An isolated battery charge circuit maybe between B and N, and a stator tap maybe E.
Names F and B, suggest field and battery and N maybe negative.
The field coil is relatively easy to find with a multimeter measuring resistance. It's fairly low resistance, depending on alternator size I'd expect between 3 and 20 Ohms.
So I would first check if any terminals measures anything against the case; If it is an all isolated alternator like we suspect, then you shouldn't.
Next I would try to find the field coil, measuring F against any other. Most likley other candidates are A or E.
Unless you have a meter that puts out more than 2 V, you will not be able to measure anything on the battery circuit, because you will not get over the voltage that makes the diodes conduct. This means given enough voltage you should measure conductivity in just one direction over the battery circuit.
If your meter cannot do it, you can't do any harm running a small 12V lamp from a battery through that circuit.
There may be a chance to confuse battery with a stator tap, but the terminal size should tell it all. They battery terminals are usually noticeably bigger than any other.
Once you figured out the alternator you need to check the regulator whether it is positive or negative regulating to attach the field coil correctly. If the field coil is isolated like we suspect, then any type regulator will do, but you need to connect the other end of the field coil to plus or minus alternatively. -No damage if you connect this one wrong, just no charge.
Dismantled the whole thing now. Turns out the unit does not have a regulator inside at all.
E Is connected to -, ground and to the field coil
N I connected to the side were all three stator wires meet (Strange no idea what the purpose is?!
F is positive field coil
A Seems to be D+ and connected to the positive side of the diodes
this looks pretty standard, maybe with some options to modify it.
The way you describe it, with the field coil connected to -, you will need a positive regulator or one that can do both. There are multi-stage regulators (like the Sterling) on the market, that can be switched to either way and in addition are very efficient. If you don't already have a regulator, that's what I would recommend.
You say: E is connected to minus, ground and the field coil. If these are separable, like E just going to the field coild, then you could run this alternator either way.
I guess from your description, that the minus-diodes are going directly into the casing, which means minus and ground are fixed together for good. So, probably no isolated minus possible.
The A and B+ (or D+) being the same is not entirely unusual, the smaller terminal is in that case meant to provide the power for the filed (through the regulator).
When all the three stator coils are conected to a common point, you have a star configration, as opposed to a triangle. For practical purposes this is meaningless, but explains the N standing for neutral or NULL point. If all diodes and coills are workig properly, it will settle at half the baterry voltage. The remaining AC-ripple on it, may be enough to filter out a rotation speed signal that could be used on some engines for the RPM-meter; it's cheaper than a separate sensor.
yep your further assumptions are correct. Ground, minus and the one side of the field coil cannot be seperated so it must be a fixed positive excited alternator. I just bought a Sterling Regulator and will have a go connecting the whole bunch and see what happens. If you do not see the smoking remains of our boat on CNN it worked ))).