bad battery or alternator

[james s]

driving home from work my 97 ex's gauges quit working and when i got home the battery was dead.so i put a charge on it but when a load is put on it the batt shows bad another battery makes it run but should i replace the alt too?

 

[jd4242]

I wouldn't if its not bad

 

[MDmounty]

I'd go to autozone or somewhere and get your alt tested cause if your battery keeps dying your alt might not be putting enough power out to power all of the truck

 

[Robman]

Using a multimeter you can easily test to see if the alternator is putting out around 14v when the truck is running.
If the gauge in the truck is very low even when the truck is running, that doesn't sound like a good alternator.

In all likelihood, your alternator probably crapped out and sucked the life out of the battery to keep the truck running.

When you put the new battery in the truck, does the volt gauge sit in the middle?(When it's running)

 

[jd4242]

I mean this sounds clear cut too me..battery cell went bad...old battery goes bad as soon as load is put on it..

You need a good battery to supply voltage to the alternator for it to even work...

He replaced bad battery and it works fine..unless he comes back and says the new battery has gone dead then it sounds clear cut to me...bad battery. .

 

[Robman]

Ever pulled your battery terminals off while the truck is running? ... Keeps running.

I agree though, sounds like a cell went bad or whatever... but yeah never know! We aren't there to look at it, hehe.

 

[jd4242]

Ever pulled your battery terminals off while the truck is running? ... Keeps running.

I agree though, sounds like a cell went bad or whatever... but yeah never know! We aren't there to look at it, hehe.

Off the residual voltage field in the alternator will keep the truck running for a couple seconds to a minute with no accessories running. But once that field dies the truck will too..

Take a alternator and put it on the bench..hook up a meter to it only with absolutely no voltage going to it,spin it and tell me what the meter reads??

 

[Robman]

Well, while I'm certainly not arguing with you, I can only tell of my experience.

I have 3 Explorers currently and 1 is basically a field truck, '97 4door XL 4L OHV - A while back, my cousin and I had a debate on whether the truck would run or not with no battery. We marched out to the truck, fired it up and I took the battery terminals off and the thing didn't even bat an eye, kept running... mind you I didn't have the blower running, lights on or anything. I can't tell you how long it ran for because I can't remember how much time elapsed before putting the terminals back on, I just remember that it didn't stall. (Which proved me wrong, because I had declared that it wouldn't run without the battery, lol)

In the OP's case, I would put the good battery in, fire the truck up.. let it run for a few minutes and then test the voltage with a multimeter... doing this of course with all electronics/blower/lights off. If the gauge in the truck read in the middle and the voltmeter(multimeter) read 14ish, I would leave the alternator alone and call it a day.

 

[jd4242]

This is a alternator not generator..

Alternator has DC field which generates constant magnetic field in Armature.it requires a dc voltage to generate that field...

A generator has a permanent magnetic field..

Yes a vehicle will run but it wont run long..once that voltage drops to below what the alternator needs to produce that field,it will die...depending on whats running and how old the vehicle is,depends on how long it will run..

Try that test again with the lights on or heat on or drive it around for couple minutes. .bet it dies..

 

[Robman]

Yep, I agree with all that.

 

[koda2000]

Yes, pulling the battery cable while the engine's running is the redneck alternator test. If the truck keeps running the alternator is charging. Not a good idea to do this, but people have been doing this since they replaced generators with alternators back in the early 60's.

 

[james s]

Tried the"redneck" alternator test and the vehicle continued to run with the new battery and no positive cable

 

[jd4242]

Tried the"redneck" alternator test and the vehicle continued to run with the new battery and no positive cable

If the new battery hasn't died by now you should be fine