How low of idle will a alternator charge

[junkyardjeff]

I was looking in my 1958 motors manual for the tune up info for the 57 235 I have in my 37 Chevy p/u and it says 425 RPMs which seems very low,I have a alternator on it and will it charge at a idle that low.  I never put a tach on it to set the idle before and just set it where it seemed to be ok but was wondering if a alternator would charge at that idle speed.

[enjenjo]

Yes it will.

[junkyardjeff]

After I install the larger jet in the carb I will try to set it at that speed,I have been driving I for 11 years with the idle too high and the timing too advanced. Trying to get it dialed in and running right but still need to get a heat kit to heat up the intake since it has Fenton headers.

[Harry]

Is that 425 rpm engine speed?
The alternator would be turning many times that.

[junkyardjeff]

My motors manual said 425 RPMs for the idle.

[jaybee]

If it helps put your mind at ease one of the benefits of an alternator over a generator is that they charge better at low rpm.

[junkyardjeff]

I know alternators charge at slower speeds then a generator but 425 is alot lower then what modern cars idle.

[Crosley.In.AZ]

Also depends on the design of the alternator... some of the higher amp alts will charge slightly less at low RPM than others.

I had a 100 amp chrome alt from Summit, the voltage gauge would dip down below 12 volts at idle, in gear. If the cooling fan was running it would drop to 11 volts.  Soon as the RPM came up 100 or 200 rpm, the voltage was right back up.  It was a near stock small chevy v-8

[junkyardjeff]

I am going to put a meter on it to see how much its charging at that low idle.

[38HAULR]

Obviously a manual vehicle with that idle speed?.

Frank.

[junkyardjeff]

Yes.