Too much voltage

[subzali]

Here's the problem: before Cruise Moab this last spring, I checked my battery voltage and realized that the alt. was putting out way too many volts with the engine running - on the order of 17-18 at highway rpm.

10/76 FJ40 (pretty much stock)

I've been trying to do everything I can to fix this problem - I'm not sure when it started or how long it's been going on, but here's what I've done:

1) did a cursory review of the wiring in the immediate vicinity of the alternator and voltage regulator to check for bad connections/corroded wiring (of which there were a few that I had to fix).

2) replaced the voltage regulator with a new one from Toyota - this one does not appear to be adjustable; there are two tabs that are folded and soldered to the side of the housing that would prevent me from opening it up to adjust the contacts and reduce the voltage.

3) replaced the battery (one of the cells died this summer and left me roll-starting it a little bit - I think it was related to having way too much voltage going down the road.

4) replaced the alternator - this also had gone bad at some point, for some reason.

So I'm running (what seems to me) good wiring, good battery, good alternator, and good voltage regulator and I'm still getting around 15.8V going down the highway, down to around 14V at idle. It's better than it was, but still higher than it should be and I'm trying to figure out what to do.

I would think if I had any more bad wiring/bad grounds it would REDUCE the voltage off the alt., not INCREASE it.

I do not have an OEM alt. belt, I have a narrower NAPA belt, maybe I should replace that, it would reduce the rpms of the alt. and maybe lower the voltage

 

[1979fj40]

belt wont lower voltage. I asume your checking with a digital meter?

 

[mudnyreye]

I have had the same problem with my '76. I replaced the voltage Reg. several times (OEM Toyota), but continued to have the problem. I solved my issue by running a FJ60 Alt. with solid state voltage reg. The factory '76 volt regs are just plain CR*P!

 

[dgangle]

I suspect the voltage regulator. I'd suggest taking it to someone more knowledgeable on automotive electronics and and have them diagnose before you cook another battery. The narrower belt has nothing to do with this.

 

[mudnyreye]

Check the post by bsevans below. He has a easier fix than the 60 Alt.

 

[alkarich]

Here is the link mudnyreye was talking about:

https://forum.ih8mud.com/40-55-series-tech/95862-solid-state-replacement-mech-voltage-regulator.html

 

[grant5127]

Check all grounds, including the regulator..... next inspect the wiring harness between the alt & reg. ohm it out, each wire individually and the plug terminals for integrity........

 

[spotcruiser]

I suppose it's possible that a poor connection to the regulator sensing input could cause it to have a high output. It just makes sense: if the regulator sees low system voltage, it applies field to raise the system voltage. Bad connections (high resistance connections) equal voltage drops when there is current flow.

I think you'll have a black/yellow sensing wire at the regulator. Ground, of course, is the other side of the sensing circuit. The black/yellow wire is from your ignition circuit (ignition switch and fuse block/engine fuse). You might want to clean all connections in that circuit really well (battery disconnected, of course), as well as the white/blue wire connections from the alternator to the ignition switch. Additionally, you might want to make sure your regulator and alternator have good grounds (as well as the chassis, block, and tub; just GP).

You could independently wire sensing and ground to the regulator, just to test the theory, if needed.

Good Luck with it.

 

[subzali]

I'm using a digital meter on the battery but also using my Ham radio when I'm cruising down the highway - it's wired straight to the battery (and fused) and shows the voltage when you first turn it on.

spotcruiser - when you explain it that way it makes sense, so I bet I have more bad wiring.

My approach is that Toyota intended the system to work the way they have it set up, the solid state regulator *may* band-aid the problem, but to me it's not a real fix. There's something else going on that is throwing things off. I'll start chasing some more wires to see if I can find the problem.

 

[Pin_Head]

I suppose it's possible that a poor connection to the regulator sensing input could cause it to have a high output. It just makes sense: if the regulator sees low system voltage, it applies field to raise the system voltage. Bad connections (high resistance connections) equal voltage drops when there is current flow.

.

X2

What is the voltage at the regulator? If it is lower than that at the battery, there is a bad connection somewhere.

 

[subzali]

It appears I have won.

I disassembled the new OEM voltage regulator, which had bent over tabs that were soldered in place, and as soon as I got the cap off it was apparent to me that the adjuster was bent up too high. So I took it out to the truck and fiddled with it, bending it to the right spot, and now at higher rpm (I would really like to get a tach on this truck) the charging system is sitting at 14.0-14.1 V, so I'm happy. Put it back together, bent the tabs back in place etc. and I'm good to go. I was just surprised I guess that I had to mess with the unit that came stock from Toyota, but no big deal.

I will probably take a closer look at the wiring to make sure I don't have a bad connection that is artificially lowering the voltage at the regulator, or on the way back to the alternator, but for now, since it's cold out most of the time, I'm going to leave it, because as long as the battery isn't seeing too much voltage I wouldn't think that would be a problem with the rest of the system.