Alternator not charging at higher R P M ?

[FrankenPine]

Hi guys, Judging from the ignition light, which goes on when the key is turned on, off when the engine starts, then when the engine reaches about 2100-2400 R P M the light comes on again. I've got a Hitachi alt, neg ground Series V that was rewired with an aftermarket wire kit by the P O . The car seems to have developed this problem after sitting for about a month, as it ran fine before Any suggestions on where/how to go about checking this out ? I've not had any rodent helpers in the garage !
I've checked the belt, seems good with about 1/2" deflection.
Thanks, Fred

 

[Tom H]

Fred, Do you have any way to tell if the alternator is actually charging the battery? Do you have an ammeter installed? Do you have a voltmeter available? Take a voltmeter and measure the voltage at the battery. It should be about 12-13 volts without the motor running. With the motor (and alternator) running, the voltage should increase to about 14-14.5 volts indicating it is getting charged. As you rev it up, that voltage should stay at 14-14.5 volts and maybe even a little more. But if it drops when the light comes back on, then you have a problem with the alternator. If the light comes on but the voltage stays up, then there is only a problem with the indicator, and not the actual charging.

Tom H

 

[nickraymond]

this sounds ridiculous, but i thought i'd blown all of my relays when actually it was just the two white wires off of the bottom of the alt relay...

so check all your wires are on properly.

for a easy test to do, wait till it gets dark and pull your alpine up to a wall/garage door, take her to 2100 just when the ign warn light comes on, then rev her up to the highest point before the light goes off.

that will tell you if shes charging in that band as the lights should get a bit brighter..

(this is if you haven't access to a voltmeter) Tom's suggestion will be far more accurate if you do.

Nick

 

[am99ey]

Fred, this sounds very much like worn brushes of the commutator. Don't now about hitachi's, but you should be able to remove the brush holder without removing the alternator. They usually wear down until they are to short to reach the copper commutator. Visually detectable by increased 'brush-fire', the blue sparks generated at high rpm. That also means no (or little) voltage/power supply for the rotor. Check on that before you disassemble your SV.

Don't forget to disconnect the battery before any work done.
Andy

 

[Wombat]

Fred

Can't say for certain about the Hitachi alternator, but for the symptom

"Warning light normal at low speed, goes out at cut in speed then glows progressively brighter as speed increases"

the manuals I have for the Australian assembled Hillman Hunter (Lucas alternator) and for the Australian Ford Falcon (Bosch alternator) both say a likely cause is an open circuit positive output diode. I have not personally experienced this problem, so can only offer what the books say. Maybe the Hitachi works the same.

Good Luck