What else controls the alternator to charge? New DMW 120 Amp installed, won't charge

[captainneo]

So I thought my alternator went out this winter while it was cold. Took the battery in, thinking it was damaged and froze, but after being charged, tested perfect. so I bought the new 120 Amp alternator from DMW. Installed it, with the new belt. Thinking it would be good. Well, to test drive it today and volts were low. And after about 7 min of driving with no lights or heater on, it drained completely out.

My battery light works in the dash.

Is there a fuse or relay involved that could not be working?

[Michael]

If it's draining that fast it has to be the battery, or the charge circuit. When is the last time you checked grounds?

Even if the charge circuit is broke somewhere, a fresh good battery should give you more than 7 minutes.

[captainneo]

battery was trickle charged and tested by advanced. Said it checks out 100%. Cleaned the entire cluster of wires when I put in the new alternator. Even used the wire dremel brush, to clean the eye hole rings of each one, before I stacked them back on the post to clamp them down. What else is involved? Maybe my red wire is bad? It was suppose to be a plug, but I couldn't get it apart.

[Michael]

Charge the battery and check voltage at the alternator and at the battery both while running and after stopping. My first thought is that battery is knackered. I suppose it's possible a high draw item like a starter is sucking it down if the solenoid is bad but surely you would hear that, and smell a melted starter. Also possible there is a broken or corroded cable in the charge circuit but I am assuming when you say the battery is dead it is dead and not just a loose battery cable.

This may be hard to believe but Advance Auto Parts is not totally without fault.

As far as grounds, there is a big ground on the frame right behind the alternator and about a half dozen more. Still a charged GOOD battery should run that car for an hour with no help from an alternator.

[Ron]

Once the engine is running, the battery should have nothing to do with it, unless it is internally shorted so bad that it consumes everything the alternator puts out. In which case it would never take a full charge or start the engine w/o a jump to assist it. (Although it is extremely hard on the voltage regulator, you could remove the battery while the engine is running and it would keep going. The battery's job is to start the engine, not supply it while running. Don't try this at home;-)

I agree that you should check the battery's voltage, while shut off and running. It should be ~12v when off and 14.2v+ when running. Watch & record the voltage as it warms up and dies for the best clues...

If you suspect the alternator's ground, run a jumper cable from the Battery (-) to the alternator's casing/bracket and recheck the battery voltage.

[Michael]

Once the engine is running, the battery should have nothing to do with it, unless it is internally shorted so bad that it consumes everything the alternator puts out. In which case it would never take a full charge or start the engine w/o a jump to assist it. (Although it is extremely hard on the voltage regulator, you could remove the battery while the engine is running and it would keep going. The battery's job is to start the engine, not supply it while running. Don't try this at home;-)

A lot can be lost in translation but I never got from the OP that the car dies, just that the fully charged battery is dead after a few minutes of running. If it is indeed the ENGINE that dies, then that changes things completely. Time for the OP to elaborate a bit more.

[Ron]

A lot can be lost in translation but I never got from the OP that the car dies, just that the fully charged battery is dead after a few minutes of running. If it is indeed the ENGINE that dies, then that changes things completely. Time for the OP to elaborate a bit more.Agreed.
...if the engine doesn't die, the light should be on way before the battery does.

[David T]

Replace the battery. It should keep the motor running a lot longer even with no alternator. Clean all of the connections and get the alternator tested.

[CFI]

(Although it is extremely hard on the voltage regulator, you could remove the battery while the engine is running and it would keep going. The battery's job is to start the engine, not supply it while running. Don't try this at home;-)


Definitely do not try this at home.

You could probably get away with disconnecting the battery on an old, carbureted, pre-computerized car without doing any harm. However, trying this on anything with an ECU is likely to cause more problems than it solves. The battery is an integral part of the electrical system on modern cars. It’s job is NOT finished simply because the engine is running.

[Elvis]

funny ... some weeks ago on Facebook -> THE source for technical information when you have a classic car - I was taught
that if you car suddenly dies while drving on highway speeds - it's the battery.
Therefore you can only crank the engine for another 30-60 seconds.

And of course fuel pump and battery die in the same moment.




... and now you guys tell me the car can run without the battery once it is running ?

:-P


OK I go and wake up Delorean and MGB from the winter sleep and then I'll continue to look for the
CAN-Bus problem on my daily driver before I put the steak on the grill and beer in my hand while thinking
about how I got my EE degree...without facebook... :-D

[dn010]

Buy a universal battery ground cable at the auto store, you'll obviously need one long enough and one that has loops on both ends and not a battery terminal on one end. Disconnect and bypass the cluster of brown wires with the ground cable, running it from the alternator large post directly to the bulkhead +bolt. Then see what your voltages are.

[David T]

"Back-in-the-day" before cars got so complicated, a quick and "dirty" test of an alternator or generator was, once the motor was running, disconnect the battery and if it kept running it meant the alternator or generator was making at least some electric. If you try that today you risk damaging the sensitive electronics because the battery dampens out the pulses from the alternator and "sinks" or stabilizes the voltage. No need to do that, most auto stores will test your battery and alternator for free.

[Josh]

I remember in highschool shop class we had no batteries. So to get a car going we would start it with a battery charger to the battery leads, then disconnect it after it was running so we could drive the cars around the shop/building.

[Bitsyncmaster]

I remember in highschool shop class we had no batteries. So to get a car going we would start it with a battery charger to the battery leads, then disconnect it after it was running so we could drive the cars around the shop/building.

It would work with no electronics. But the battery acts like a big capacitor and filters the rectified AC from the alternator. Most electronics should have capacitors that filter the car voltage and may work fine but your really testing unknown voltages at different RPM on the alternator.

[Ron]

I remember in highschool shop class we had no batteries. So to get a car going we would start it with a battery charger to the battery leads, then disconnect it after it was running so we could drive the cars around the shop/building.LMAO! Man, does that bring back memories!...a red shop rag and one of those wide oversize red rubber bands for the hot terminal...
Next up, 6 foot of hose and a can of ether. Makes a car with a bad fuel pump jump like this guy -:flamed:

And since we're in a playful mood- I hereby promise to never mention disconnecting the battery while the engine is running again, with or without mentioning it is extremely hard on the regulator, underlining it, and stating not to try it, never, ever. So help me God and keep me steadfast in the due and true performance of the same.

[Bitsyncmaster]

My battery disconnect relay disconnects the ground on the AUX relay that powers the ignition then waits one second before turning the battery off.