Voltage drops

[Setnev]

I seem to fighting a weird electrical anomaly with my car recently. I say recently because I only noticed voltage drops since I upgraded my radar detector to one that has a built in voltmeter. It's pretty accurate, I used it in my old car that suffered terribly from voltage inconsistencies (and it was a newer car). I noticed it before with the car, but only when the headlights and heater were on in the winter. At idle the lights were dimmer than normal and then when I'd take off, the lights would brighten and heater seemed to speed up.

 

When I'm driving around town now, I can monitor the voltage more closely. When I'm at a stop light for more than 30-40 seconds, the voltage drops to 11.7 or lower. When it sits like that for more than 15 seconds, the alarm on my radar detector goes off and tells me car voltage low and auto shuts off until I accelerate from the stop light and it turns on and the voltage is around 13.5+. It does not matter what I have turned on in the car.

 

The alternator is fairly new, reman date 5/2016, I just replaced all of the battery cables with brand new 4 gauge wire. I have a 4 ga wire running from the positive to the starter lead and positive to alternator lead. I also changed out the ground wire on the block to a 4 ga wire leading directly to the negative cable. I did not replace the negative to body wire yet. The battery is brand new (about a year old) and I just replaced the battery terminals with gold plated connectors. Mind you, these symptoms were present before I worked on any of this and I did not replace the battery or alternator, these were done before I got the car, but I read the dates on each of them. The battery was strong, even in the winter, cold starting the car in 30 degree weather on first try with no weakness in cranking.

 

Any ideas where to look next?

[twisty]

i saw similar with one of the alternators i had in my wagon. i looked up specs for days trying to get info on the output ranges and such, found a source on a tag in an alternator box at oreilly auto that had the output range by RPM and was surprised to see that the amp load for charge was almost nil at 600 rpm. it wasnt putting out enough to run the system and charge the battery at idle, i tested it by forcing the idle to 950ish and it would sit about 13A or so. the one i have now is from a 2005 H6 outback and puts out about 40A at idle, charges fine.

[Setnev]

I have a spare alternator from an 01 H6 Outback, I might try that, if it fits, which it sounds like it does.

[doublechaz]

Once you have the 01 in for test, try the original at a parts store tester? Sounds like it's a deal weaker than mine at idle.

[08SpecB_DE]

Sounds like a bad alternator. 13.5 to 14.2 is the sweet spot. I've seen slightly larger pulleys on aftermarket alts cause similar problems (As recently as last week). If the belt is tight and you have the correct amp alt, then she's defective.

[Setnev]

Sounds like a bad alternator. 13.5 to 14.2 is the sweet spot. I've seen slightly larger pulleys on aftermarket alts cause similar problems (As recently as last week). If the belt is tight and you have the correct amp alt, then she's defective.

 

I might take the car to my local Autozone to have them test the alternator on the car. Like I said, the only thing not replaced by me is the batter and alternator.

[08SpecB_DE]

You can pick up a voltmeter for cheap. Run your own tests so you don't have to rely on someone who may or may not know what they're doing.

[doublechaz]

I'd have to recommend buying the alternator somewhere other than autozone. I warrantied 3 of theirs. When it died again for the fourth, I just used it as the core on the other side of the parking lot. Their colors match UofM where I went to school, so it feels better anyway.

[08SpecB_DE]

I wouldn't use Autozone parts either but to each their own. I've had the best luck using Remy reman alts.

[Setnev]

You can pick up a voltmeter for cheap. Run your own tests so you don't have to rely on someone who may or may not know what they're doing.

 

I have a really good voltmeter but I was unsure if they use something else other than that. In the last few days, everything seems to be working fine. I've had no voltage drops or low voltage alarms when sitting at a light or idling for an extended period of time

[doublechaz]

Comes and goes doesn't make me think diode problem unless there is a connection problem between the diode and the socket.

[Setnev]

That's what I am thinking too. It's inconsistent. It'll go days working fine and then one day I'll be sitting at a stop light and bam, low voltage alarm.

[doublechaz]

I haven't had one of these open. Are the diodes socketed? If not then I'm thinking connector somewhere. I don't believe you would be one to run the OE grounding or I would have suggested that already.

[Setnev]

The only OE ground I didn't replace was the battery to body, the small little 10 gauge wire that runs from the battery negative to the body right above the driver side headlight. I replaced the ground going from the battery to the engine, replaced the starter to battery positive wire and ran a brand new wire from the alternator to the battery. All replaced with good 4 gauge wire. I'm probably going to order more of those battery leads I used before since they were only about $6 a piece for a 3 foot 4 gauge wire. I'm going to do body to battery and body to engine grounds next. Ran out of daylight when I did the other 3 upgrades. The old wires had corrosion inside the stranded wire under the insulation, so I was sure that that was the issue, but I'm going to rule everything out battery cable related first.

[doublechaz]

As I thought. You're already all over those wires. I've got to pull my alternator again soon to try to get an oil sender under it. Maybe I'll be able to see something about how the voltage clean and regulate works while I have it out.