Ford 655 not charging until revved up.

[dannyidp]

I have a new alternator on my Ford and I noticed the alternator will not start charging unless I rev it really high after that it will charge at low idle. Tachometer also will not work unless I rev it high but once I rev it all is good even at idle. What could possibly be the issue here?

 

[Jim.ME]

I have a new alternator on my Ford and I noticed the alternator will not start charging unless I rev it really high after that it will charge at low idle. Tachometer also will not work unless I rev it high but once I rev it all is good even at idle. What could possibly be the issue here?

What is it for an alternator? how is the tach driven? My first two thoughts are: it sounds like a Delco type, one wire that doesn't have a low rpm excitation system, or your fan belt is loose and is slipping. More details may lead to a different thought/answer.

 

[sms]

As Jim said, some alternators require high rpms for excitement voltage. They are not a good choice for slow running engines. With more information some here may be able to help.

 

[Bob Bancroft]

I have a new alternator on my Ford and I noticed the alternator will not start charging unless I rev it really high after that it will charge at low idle. Tachometer also will not work unless I rev it high but once I rev it all is good even at idle. What could possibly be the issue here?

My 655A has the original Ford type alternator with the regulator mounted in the battery box. The tach is mechanical. You must have a newer suffix machine?

 

[Mobuck]

This is due to the internals of the alternator. Don't worry about it too much. Allow the machine to warm up a bit before running the RPMs up.
My old FORD 8N has been converted to 12V w/alternator. The alternator pulley is a bit large and doesn't spin up fast enough to initiate charging until the engine hits about 75% of full RPM. After kicking in, the alternator will charge at all RPMs until the engine is shut off.

 

[BarnyardEngineering]

Having to rev the engine is common with self-exciting alternators. Does the new alternator have all the same wiring connections as the old? A self-exciting alternator only has one connection. If the alternator has multiple connections, something is not connected correctly.

I vaguely recall that these machines get the signal for the tachometer off the alternator. Did you transfer the pulley from the original alternator to the new one?