Alternator/Battery split master switch

[David5326]

Just a quick question about the split alternator/battery master switch

If you turn off the battery switch, the alternator is turned off as well
If you turn off the alternator switch, the battery remains running.

Why doesn't the split switch allow the alternator to run without the battery running?

Thanks
Dave

[BoeingMEL]

Unlike a dynamo (DC generator) which will generate current simply by being turned (it has permanent magnets) an alternator needs current in its field-windings to generate current. battery off = no current flowing through field-windings. IIRC! Cheers bm