Discharge Light

[jjaayyb]

Hello to all. For those of you who helped out on my last problem HID's in 93 ls400 I would like to thank you very much and to say that you guys are the best would be an understatement.

Here is the new mission if you choose to accept. (picture mission imp theme playing)

I have 93 ls400 with 202k miles and two nights ago my discharge light came on (the one that looks like a battery). My battery is less than a year old and I dont have a sound system or anything of that nature. I started the car and took the negative battery cable off to check the alternator and the car continued to run without a problem(so with that I've ruled out the alternator as the problem). The owners book says the first thing to check is the drive belt ( dont know if drive belt and timing belt is one in the same and for that matter where to locate it on the car). The only belt I see when the hood is up is the belt that sits behind the radiator fan( if thats the drive belt /timing belt it is on there good and tight and has on cracks from what i can see. I have driven the car since then and the light comes on after driving for about a half mile or so. If you guys and gals could please give me your advice and cost estimates it would be very helpful.To say I'm short on money is an understatement($250-$400max) as I've just graduated college (GO GEORGIA SOUTHERN EAGELS) and well you guys are familar with the economy (so far 1335 resumes sent out and a whole lot of nothing in response)

Thanks in advance

[curiousB]

Removing the negative battery with the engine running is a bad idea. The battery acts like a large capacitor in the circuit since the alternator puts out a rectified 3 phase AC signal. The battery is needed to smooth out the waveform to DC. The battery also protects you from voltage surges caused by load dumping when large electrical loads are switched off.

It also is a meaningless test to determine if the alternator is healthy or not. All you’ve determined is the alternator can generate enough current to satisfy a few ECUs running in the car. Pretty much a trivial current load compared to what it has to deliver worst case. The true test of an alternator is to see if it can hold the battery voltage at 13.8VDC or so with the engine idling and every electrical item you can switch on turned on (high beams, blower motor hi, AC on, rear window defrost, wipers, audio, seat heat, …). If battery voltage is maintained with all those items on then you can feel more assured your alternator is OK.

In addition to this test I would be sure the battery leads are torqued down tightly. Better still take them off, clean up with a wire brush then reinstall and torque the nuts. If you can move/turn the connector by hand on the battery post it is too loose.

[SRK]

I'll second curiousB and state that the battery must NEVER be disconnected with the engine running. Hopefully the alternator has worn brushes and was unable to produce enough current to blow a diode or two when you did that little trick. If not, the alternator will now require a complete overhaul or replacement, rather than a simple brush replacement.

If your power steering pump is leaking, or has leaked, the ATF softens the carbon brushes, and that's the root cause of the trouble.

In the future check output voltage with a VOM as a means to determine if the alternator is charging.

[RDM]

The timing belt and drive belt are not the same thing. Nowhere near it. The drive belt runs the accessories, that's the one you see.

The alternator can be rebuilt very easily, and locally I use C&S Auto Electric in Mableton, they'll do it for no more than $125 usually. I'd bet also that's the problem, the charge light comes on for a reason and the cable test doesn't prove anything, the proper way would be to remove the charging lead and test voltage at the post, the voltage will either be low or vary heavily, dropping when under a load.

Get it fixed before you're stranded.

[SRK]

The timing belt and drive belt are not the same thing. Nowhere near it. The drive belt runs the accessories, that's the one you see.

The alternator can be rebuilt very easily, and locally I use C&S Auto Electric in Mableton, they'll do it for no more than $125 usually. I'd bet also that's the problem, the charge light comes on for a reason and the cable test doesn't prove anything, the proper way would be to remove the charging lead and test voltage at the post, the voltage will either be low or vary heavily, dropping when under a load.

Get it fixed before you're stranded.

What "charging lead" are you talking about? What "post"? Voltage can be confirmed without disconnecting anything. With the right equipment, so can current.

[curiousB]

This isn't too difficult. Just measure voltage of battery at the battery + and - posts. It should be around 13.8VDC with engine running. Start switching on as many loads as possible. If the alternator is working properly the voltage will remain fairly steady +/- 0.3VDC or so. If it drops significantly that means the alternator cannot deliver the required current. This may be a loose belt, loose connections on alternator or battery, worn out brushes, or maybe a malfunctioning voltage regulator (although the previous ones are far more likely the culprit than volt reg).

There are more sophisticated ways to do this but this simple voltage test at the battery will get you 98% accurate diagnosis.

Alternators are rated in power output in Watts. Watts is simply voltage multiplied by current. So to test upper end of alternator it has to deliver a large current and keep charging the battery. This is why switching on loads is important as you want to be drawing 50 Amps or so to be sure the Alternator can cut it under peak load.

[VBdenny]

you can buy a cheap vot meter at many places. I've seen them at Sears, Home Depot and Lowe's. I imagine that most auto parts stores would have a VOM you could use and there is a good chance that you can get them to check it for you. If this was my problem, I would make sure the battery terminals are clean and tight before suspecting anything else. Of course you know it won't be that but better to check. Just because they look clean, doesn't mean they are clean. Good luck with it.

[jjaayyb]

Thanks for all of you guys help. Here is the latest. Since last talking to you all, I took the car to a local parts store that used a hand-held decvice telling me I had bad alternator. I put new alternator in and discharge light still came on. Two days after that my battery died. Had battery charged up cause its only 10 months old. I put the battery in yesterday and the discharge light still comes on. The light goes out when im on the gas and once i slow down enough or at a stop the light is on. I have no clue what the issue could be

thanks in advance

[VBdenny]

Did you have the new alternator tested BEFORE you installed it? I have had so many bad NEW alternators over the years that as a routine, I always have them tested right out of the box. Sucks I know, but that is the way it is. Also, just because your battery is quite new, it doesn't mean it is good. If it were me, I would check both of these items before moving on any further. If both turn out to be good, it sounds like you are getting a big draw from something.

[curiousB]

Go buy a voltmeter. You can get one at Harbor Freight tools for $5 thats accurate enough for what we're talking here.

Tells us battery reading for following situations:

1) Car off nothing turned on _____ VDC

2) Car running, nothing turned on other than engine running ____ VDC

3) Car running, everything you can turn on turned on (High beams, blower, a/C, rear window defogger, ...) ___ VDC

All measurement made at the battery posts + and - terminals and exactly the same way for each test case.

Lets us know your readings.

[python]

you start removing electrical components while the car is running u can and will short things out like the ecu....this isnt your 1960's car with nothing but an alternator,voltage regulator and a battery

[RDM]

The timing belt and drive belt are not the same thing. Nowhere near it. The drive belt runs the accessories, that's the one you see.

The alternator can be rebuilt very easily, and locally I use C&S Auto Electric in Mableton, they'll do it for no more than $125 usually. I'd bet also that's the problem, the charge light comes on for a reason and the cable test doesn't prove anything, the proper way would be to remove the charging lead and test voltage at the post, the voltage will either be low or vary heavily, dropping when under a load.

Get it fixed before you're stranded.

What "charging lead" are you talking about? What "post"? Voltage can be confirmed without disconnecting anything. With the right equipment, so can current.

Not so. The charging lead is the large gauge wire that feeds current to the battery from the alternator. The 'post' is the terminal the charging lead bolts to. By measuring voltage with the battery still connected you're not getting an accurate measure from the alternator. With it connected you're measuring the battery voltage as well, disconnected you're only measuring the alternator's output, which is what you want.

[curiousB]

If the alternator is doing its job the battery will be at 13.8VDC +/- 0.3V If its not (supplying enough current) the battery voltage will be lower. If you are suggesting measuring alternator with battery disconnected then you are making a very bad recommendation as noted in earlier posts.

If battery is around 13.8VDC with engine running and all elecric device you can turn on turned on then the alternator is fine and doing its job. Open circuit voltage of a lead acid battery is 12VDC, 13.8VDC measn the alternaotr is supplying all downstream current and able to hold the battery in a charge state above the nominal voltage.

[jjaayyb]

Well it turns out that it was the alternator. The new one they put in didn't put out what it was supposed to. The shop put another one in and the light hasn't been back on.

Thanks to all for your help