2 bobs worth
My two pennies worth ....
Those 3 brush dynamos are self regulating to a large degree .. a small amount of voltage is tapped via the 3rd brush .. Unlike the more modern 2 brush design , there normally isn't any external voltage regulator involved , in the 3rd brush system , the regulating is done by the internal inductance/reactance characteristics of the thing. They often had a high/low charge rate which was swtitched in and out depending on /winter summer conditions etc.
Some people used to remove the 3rd brush and convert them to a 2 brush system with an external regulator ... that's not a good idea because : the 2 brush design has the full nominal output voltage across the field coils .. In the 3 brush setup , only a small amount of voltage appears across the field coils .. result of the conversion is the coils carry far more current than they were designed for and they eventually break down from over heating.
Richard , check that it isn't a bodgy conversion that somebody has done on that truck ...
Mike
__________________
1940 cab 11 C8
1940 Morris-Commercial PU
1941 Morris-Commercial CS8
1940 Chev. 15cwt GS Van ( Aust.)
1942-45 Jeep salad
|