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I was told that if I took the positive

JimmyJuneau

JimmyJuneau

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I was told that if I took the positive cable off of the battery. When the truck is running that my alternator is fine. And the reason my truck wont start after turning it off is because I have a dead battery. So before I go and buy a new battery. Can you guys let me know if this is the right way to test it?
 
If the alternator works and all of your connections are good, you can remove the pos+ cable from the battery and the truck will still run.
if it stalls, the alt is bad. You need to make sure all positive connections and ground connections are good. I guess you don't have a volt meter to check the battery volts and alternator charging volts?
 
No I do not. I jump started the truck and then took the positive cable off the battery. The truck kept running. So does that mean the battery is dead?
 
yep battery is bad.or something drained the battery before you jump started it.you gotta make sure that the battrery connections are clean also or the battery will not charge even if it is good.
 
Pulling the bat cable while the vehicle is running is a great way to fry the alternator.

The way to test it is with a voltmeter. A cheapy is all of $2 at harbor freight. Personally if you don't have one, you will need it, and will end up using it a bunch, so pay decent money for a digital multimeter, I paid like $50 years ago and that multimeter is still going strong.
 
dyeager535 said:
Pulling the bat cable while the vehicle is running is a great way to fry the alternator.

The way to test it is with a voltmeter. A cheapy is all of $2 at harbor freight. Personally if you don't have one, you will need it, and will end up using it a bunch, so pay decent money for a digital multimeter, I paid like $50 years ago and that multimeter is still going strong.
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Thats what they say, and who am I to disagree? But, I've done it a hundred times and never had a problem.:confused:
 
The question really is, why would you do this when it's known to be potentially harmful and a voltmeter is a necessity for checking electrical stuff of all sorts anyway?

On top of that, carbed you don't need but probably 8 volts for it to RUN, that doesn't mean the charging system is up to the task. You can't trust your gauge unless you've verified the output of the alternator. Nor does disconnecting the battery wire show that the output of the alternator increases as load on the electrical system increases.

I'm not arguing or anything, just throwing it out there that you can damage your electrical system this way, if that's an acceptable risk, go for it. Voltmeter is cheaper than a new alternator, that's for sure. :)
 
dyeager535 said:
The question really is, why would you do this when it's known to be potentially harmful and a voltmeter is a necessity for checking electrical stuff of all sorts anyway?

On top of that, carbed you don't need but probably 8 volts for it to RUN, that doesn't mean the charging system is up to the task. You can't trust your gauge unless you've verified the output of the alternator. Nor does disconnecting the battery wire show that the output of the alternator increases as load on the electrical system increases.

I'm not arguing or anything, just throwing it out there that you can damage your electrical system this way, if that's an acceptable risk, go for it. Voltmeter is cheaper than a new alternator, that's for sure. :)
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I know what you're saying. I asked him if he has a volt meter in post 2.:wink1:
 
Actually, the big trouble is if the alternator is charging hard and you pull the battery cable. The alternator has a lot of inductance and that current can't drop to zero instantly. It produces a big voltage spike which can be bad for any electronic device on the vehicle. This is called "load dump" and can be as high as 100V, depending on the alternator, the vehicle and the current level. If your battery is fully charged or just a piece of crap that doesn't charge, then pulling the battery cable is not very dangerous with a good alternator.

A safer test is to test the battery instead. Just let it run long enough that the battery would be fully charged. Turn on the headlights and then turn the engine off. The lights should dim a little as the alternator quits and then stay steady for several minutes. You SHOULD have a voltmeter and the battery should stay above 12V.

Or you can just go to a place like Autozone and let them test the battery and alternator for free.
 
The way to test it is with a voltmeter. A cheapy is all of $2 at harbor freight. Personally if you don't have one, you will need it, and will end up using it a bunch, so pay decent money for a digital multimeter, I paid like $50 years ago and that multimeter is still going strong.
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got my craftsman (at sears, of course) many years ago, for about $15 (on sale) and it's still one of my most useful tools. used it just yesterday, actually and it saved me a ton of time in finding the circuit i needed to tap into. any decent meter that meaures dc and ac volts, impedence, and amperage is a good place to start.

when i know i may not be driving the blazer for a week or two, i stick my trickle charger on the battery, especially during the dead of winter or the 100+ degree summer days. much more convenient than having to jump it.
 
You can take the battery up to autozone or advance they will test it for free. they will also test the alternator for free too
 
If it is your battery, no matter how you figure it out, you need to figure out what killed it so you don't go through this again next week. For that you will need a voltmeter so you can check various things and make sure they turn off when you turn the key. The cheapo that was submitted earlier will be fine, though a nice digital will be better in the future. I went overboard and got a Fluke, but I use it for other things too. Ebay can help get you something on the cheap. You need a voltmeter. Badly. They can save you lots of time and wasted effort when troubleshooting.
 
When working on the charging system, a clamp on current probe is pretty handy, too.
 
redbeast24740 said:
You can take the battery up to autozone or advance they will test it for free. they will also test the alternator for free too
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Yeah I'm picking this stuff apart, but I've been there.

Whatever the auto stores use to test, is NOT an accurate test of how the battery performs in your truck. (same as the ignition modules, starters, etc)

Battery in my truck wouldn't turn the truck over for more than about 5 seconds, before it was so weak it wouldn't turn over at all. That was with a full charge.

Took it to parts store, they tested on their machine, said it was good. Took battery home, hooked it up to a 12V load for a week, took it back, now it was dead. New battery, truck would crank for minutes if I wanted it to.

If your alternator is putting out over about 13V, and doesn't go below about 12.5 under a heavy load, then it's almost a certainty your battery is toast.
 
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Is it a walmart battery?

They seem to be the worst batteries
 
spend the money on a tester, fortunately a buddy had one before i bought a new battery since i had the same issue..my batt to alt. cable end was bad and that caused no charge to the battery. cost $10 for 40 connector things, just trust me!
 
dyeager535 said:
Yeah I'm picking this stuff apart, but I've been there.

Whatever the auto stores use to test, is NOT an accurate test of how the battery performs in your truck. (same as the ignition modules, starters, etc)

Battery in my truck wouldn't turn the truck over for more than about 5 seconds, before it was so weak it wouldn't turn over at all. That was with a full charge.

Took it to parts store, they tested on their machine, said it was good. Took battery home, hooked it up to a 12V load for a week, took it back, now it was dead. New battery, truck would crank for minutes if I wanted it to.

If your alternator is putting out over about 13V, and doesn't go below about 12.5 under a heavy load, then it's almost a certainty your battery is toast.
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yea yea. :bow: i just saying if you dont have the stuff to test it. it's free.
 
howdiy said:
Is it a walmart battery?

They seem to be the worst batteries
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Wal mart batterys are great! Just take them back and get a free one.
I had a chepo 3 year wally world batt in one of my cars and got 3 free batterys over a 10 year period. Cant complain about that.
I am on my 1st free replacement Maxx battery in 7 years on my K5. It died a little after 5 years. They gave me a brand new one for free.
Why do Wal mart batterys suck?
 
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