173 amps from alternator?!?!?!?!

[my126benz]

My 80 300SD didnt start when I left work today. I got a jump starter and started it and took it to the autozone were i used to work. They tested the battery (fully charged) and he tested the alternator (173 amps!) I couldt remember what the alt. was supposed to put out. My question is, would a overcharging alternator cause the car not to start? And if so, why would a jumpstarter start it?

I would apprciate your thoughts

Thanks

[pawoSD]

I have a feeling that fellow at autozone did something wrong, or his tester isn't working right. Most of our (stock) sd's only have a 55A or 65A alternator. Some people have upgraded to 80 100 or 120, but I doubt 173, thats like comerical vehicle output.... your car is not starting probably due to a weak battery. The starters on these cars use a huge amount of power (1.2kw)

[Hatterasguy]

The alternator is bad, its probably the regulator. I'd order a good Bosch rebuild and swap them out. You may have ruined the battery as well, time will tell. The Delco alt on my moms Old's did the same thing, but it took out the battery as well.

[pawoSD]

So when an alternator goes bad it pumps out extra amps? I thought it was the other way around. On my fiance's buick the delco died and wasn't putting out squat when I checked it. No voltage at all, and it was only 2.5 months old. New one worked fine, and its been almost a year so far.

[Whiskeydan]

Did you see a lot of smoke?

I think the Autozombie needs calibrating.

[Mustang_man298]

Originally Posted by pawoSD

So when an alternator goes bad it pumps out extra amps? I thought it was the other way around. On my fiance's buick the delco died and wasn't putting out squat when I checked it. No voltage at all, and it was only 2.5 months old. New one worked fine, and its been almost a year so far.

It depends on the particular failure, remember in electrical circuits you have 2 basic types, open circuit failures, (circuit opens somewhere and no current/voltage) or short circuit failures (circuit shorts and creates excessive current flow, possibly in some cases lower voltage caused by the excessive draw)
If the alt has a short in the control (regulator) part of it, it can go haywire and do all sorts of interesting things, including overcharging the battery and cooking it from the inside out, thinking that it is seeing a flat dead battery and feverishly trying to bring it back up.

[Hatterasguy]

Originally Posted by pawoSD

So when an alternator goes bad it pumps out extra amps? I thought it was the other way around. On my fiance's buick the delco died and wasn't putting out squat when I checked it. No voltage at all, and it was only 2.5 months old. New one worked fine, and its been almost a year so far.

Sometimes yep.

[SD Blue]

Did the "tech" at Autozone disconnect anything? If he didn't, he could not have measured DC amps correctly.

He tried to measure amps by a guesstimation of voltage through a parallel shunt to produce a number for amps and if he didn't have the correct settings, the readings would be way off. (With those numbers, he should have deduced incorrect settings right away.)

A quality multimeter will tell you if the alternator is working correctly. On start-up you should see about 13-14VDC across the battery. (Checks the regulator) Switch to VAC and you see less than 1VAC. (Checks the alternator rectifier diodes.)

To test a battery correctly, you need to place a very high wattage resister across the terminals of a disconnected battery and check to see how well it maintains voltage over a period of time. If you go to a place that specializes in batterys, you will see that these things have large cooling fins as they have to dissipate a lot of heat, and can leave nasty burns. Just ask one of them!

[TwitchKitty]

If your alternator is putting out anywhere near that much current it will be a very temporary condition. There will be very high temperatures involved. Melting, smoking, firetrucks and emergency rooms may be involved.

[Ether]

The alternator does not "put out" current per se. It is a device that develops a voltage (around 13.5 volts if it's working properly) and the amount of current that is drawn from it is dependent on the load.

Good old Ohms Law at work here, the current draw from an alternator will increase only if the load resistance decreases or the voltage output increases.

A bad voltage regulator could result in increased voltage and overcharging of the battery.