Not charging, then overcharging

[marlinh]

I brought home a new to me tercel a few months ago and started working on i t recently. I drove it home with no apparent concerns with the charging system. Light not on. I have moved it a few times. Yesterday, I started it and the light stayed on. I checked the voltage at the battery and it was 11.3 V. So, I replaced the alternator with a known good one and now it is charging at 18.5 V. This vehicle does not have an external regulator. Any ideas? The FSM is unclear in it's repair schematic. The vehicle is an 86. The charge fuse is good. No obvious damage to visible wiring that I see so far.

[larry mcgrath]

Is the battery fluid at the corect level ? how wellcharged is the bat sounds like it hasnt been driven much?

[marlinh]

The battery is fine. I have checked continuity on all the wires from the alternator to the battery and fuse panel. With the car running, the 7.5 amp charging fuse does not have battery voltage to it. On another vehicle I compared it to it does, and only when running. Has anyone traced the wiring from the ignition fuse to this fuse?

[Petros]

that might be normal, seems a bit high but the batt will not charge unless the voltage is between about 14.5 and 15.5v. It there a spect for charging volatage in the FSM? Nominal voltage of fully charged battery is 13.2 (six cells x 2.2 volts each), so you have to recharge well over that voltage or the electrons will not know which way to go.

[marlinh]

18.5 volts is too much. That will boil a battery dry. Any idea why the charge fuse is not getting power? The alternator I removed that was no longer charging smelled like burnt wires.

[marlinh]

I checked wiring from the fuse to the dash and couldn't find any problems. I finally tried another alternator and everything seems to be ok. It is charging now in the normal range.