Reverse Generator Field Terminals

Some diodes may be involved....

Exciter core is made to retain some magnetism, enough to kick start the electricity production. Reversing exciter terminals will eliminate that, feedback will be negative, and electrons will stay home. S.M.

In a dc motor if you reverse field terminals,will it rotate in reverse direction?.

I would think so, unless there are come diodes in the circuit. However, the efficiency is higher in the intended direction because the brushes are offset to compensate for field distortion due to the rotor's rotation.

See:

en.wikipedia.org/wiki/Brushed_DC_electric_motor#The_commutating_plane

Depends upon the DC motor type.

Most with wound fields still turn in the same direction. I could say all but I bet there is one type with say full wave rectifiers that is not affected somewhere....

Some small motors have permanent magnets for field poles, they will reverse...

There are also DC motors without a commutator (brushless), some, if you reverse the supply, you burn out the hall effect sensors....

Could you be more explicit please?

Are you talking about a DC output generator or (as I suspect) an AC output Alternator?

I personally reserve Generator for DC and Alternator for AC, but many don't......that would help in giving back valid infos.......

I talk about AC Synchronous generator (brushless)

To add to Rixter's post, it is unlikely that a randomly chosen voltage would just be strong enough to cancel out the residual magnetism, and on many modern brushless excitation systems maintaining the proper polarity to the pilot exciter field is very important.

As Tornado pointed out, there are diodes lurking in those systems. In most cases there is a diode across the exciter field leads, sometimes it's located at the output of the excitation system, other times it's located internal to the exciter and across the leads into the field winding.

Normally it's back biased and doesn't conduct, it's purpose is to absorb the inductive kick if one of the field leads becomes disconnected. It also will conduct if the field lead polarity is reversed as OP originally postulated; that will also effectively prevent any current from the battery from reaching the actual field winding and causing any voltage buildup.

Good point, if there are snubber diodes, it would be a bad idea to reverse the polarity. If the polarity is marked, there very well may be a good reason. It's best not to experiment.

I have seen AC generators where two of the exciter field poles are permanent magnets to give enough residual volts for soft start. In this case polarity is important. But generally if applying directly to the exciter field shouldnt be a problem.

What voltage is generated with no voltage on the exciter field?