tickter

A few days ago my battery light came on. I had it tested at the auto parts store and it showed the voltage was not going up to 14v. Figuring this was the alternator, I changed the alternator. After changing the alternator, the battery light was still on. I drove it around for a bit and when i pulled into a parking lot, it died.

The previous owner said that he had to charge the battery, so i figured the battery might just be dead. Before changing the battery, I had the auto parts store test the old battery with the new alternator and the results were the same as before. The machine stated "Recharge".

I put the new battery in and had them test again. The results were the same (though higher voltage because the battery wasn't drained), again the machine said "Recharge". We did the test one more time testing for battery draw. During this test, my battery light went off. The machine showed the battery as OK with a normal 13.x volts but also showed that there is a 0.9A draw.

Any ideas? I'm completely lost

tickter

Bump.

Issue seems very intermittent.

Went on a 60 mile drive without the light coming on. Pulled into the parking lot and the battery light came on.

When leaving, the light stayed on for maybe a minute while in the lot and then shut back off and hasn't come back on since then.

I tested for ohms between the battery ground cable and the ground going to the valve covers and there was 0 resistance (0.00)

Anybody know what else i could check?

Kingdom934

Hmm, might need to check to see if the car alternator is charging the battery. It should be around 13.8 and 14.2.

If you are getting 0.9a draw (900mA), that is something serious. It'll drain your battery fairly quick.

https://www.clublexus.com/forums/per...ma-steady.html

May need to check for a parasitic draw with a multi meter and then pull different circuits to see which one is causing such high draw. Anything aftermarket such as lights, stereo, alarm?

2013FSport

iTrader: (2)

^^ Well said tho 14.2 will likely boil a LAB dry. 13.8v will do.

Measure and report the following:
All lights everything off for 4hrs battery voltage: _____
Start car and idle at 2500RPM lights & accessories off: ____
Idle for 10min: _____
Engine running should be 12.75v or better or the battery is losing charge.

tickter

another update from more testing:

Battery life was off before starting
removed battery to check chassis ground
ground was fine
started the car after plugging the battery back in
battery light was on. voltage on alternator positive cable was 18v, battery was at 12v. Alternator was trying to compensate
Problem seems to be between the alternator fuse box entry and exit or the cable/connector
Checked resistance between the alternative positive cable (on fuse panel) and the connector, had anywhere between 0.00 and 20 ohms depending on where I put the lead.
Plugged battery back in and started the car. No battery light.
Voltage at alternator cable was at 14.4 while the battery was at 13.8

So I know that there is some problem between the entry point of the alternator fuse box and the battery

lexpilot

2013FSport

iTrader: (2)

An ohm test on a 4 gauge cable could yield very unpredictable results. It should read like 0.1 ohms max or its bad.

Measuring 18V off the alternator implies the voltage regulator is bad. If ran to long like that, not only does it kill your battery but likely other electronics along its path.

Get a new voltage regulator in there and don't drive it until you do. Please check your test equipment too. Measure other items around the house that offer known repeatability.

Oh Biggest tip yet; if for example you measure the alternator cable at the battery and at the alternator and it shows more than say 0.30volts (maybe 0.50), the cable is bad. Yes, I meant volts. You can measure the ground cable to from battery to engine block. It should not show any voltage drop.

tickter

tickter

bump, gonna work on it tomorrow. Any ideas?

tickter

I cleaned up a bunch of the grounds as well as the positive battery cable(s).


I'm still seeing a .4-ish volt drop between the alternator cable and the battery terminal. Not sure what to test for that

2013FSport

iTrader: (2)

Engine off; you're measuring both ends of the alternator cable from a common ground and get 0.4v drop.

Measure the cable from A to B. One probe on one end and the other probe on the other with the engine off. There should be zero drop.
Now repeat with engine on, lights on, heater on high and maybe rear defrost on. What do the two test methods show?
The Alt has an internal voltage regulator. It should never output more than say ~ 14.6v. Keep in mind it is current that charges a battery not voltage. That said your alt voltage has to be above ~12.85v to charge the battery.

What kind of meter are you using. Brand and model? That 18v number implies something is wrong.

Although yes, one would like to think NEW alternator is good, it has components in it that fail. New parts can fail. It should never output 18volts. Period.

tickter

The .4-5 voltage drop was while the engine is on. The voltage is consistent when the engine is off.

The resistance from A to B was 0.00


I agree that the alt should not charge @ 18v, however, it only does that when the battery is not charging.

Am I wrong in thinking that the alternator(really, ecu) is compensating, trying its hardest to charge the battery? I can't think of why the alt would be at 18v and battery at 12v...

I did make some kind of progress. Testing resistance from negative battery cable to alternator casing started at between 0.00 and 0.08 depending on where I put the lead on the casing. Now its 0.00 everywhere.

Kingdom934

I've never heard an alternator push that much voltage even if there is an issue with the circuit....unless the alternator was bad.

The only time I heard of the system being over charged is due to a bad alternator (voltage regular) or some kind of crazy grounding issue where the regulator doesn't know how much it's putting out (which I think is a grounding issue??)

I'm really surprised you didn't blow something out by now. I've heard batteries boiling at 16v and blowing out random lights at that voltage as well.

tickter

The thing is, the battery does not see 18v, it only sees 12v.


thinking of it more now, perhaps it is a grounding issue...

When I tested that alternator voltage, I didnt test the ground at the alternator, I tested it elsewhere.


Yesterday I cleaned a bunch of wires, including all the grounds I could get to and an extremely corroded positive battery terminal connector.

Light has not come back on yet. Will report back if/when it does

Kingdom934

I'm...thinking that would be it. If it is corroded, the previous old battery was leaking. Best to clean it up but if it was my car, I'd replace it with a OEM like or OEM battery terminal.