Can Engine Run Without Battery?

As the title states, is it possible to remove the battery, start the engine with a jump starter, and let it continue to run? Does the electrical system require a battery between the positive and negative cables?

I am having electrical issues and would like to remove the battery out of the equation (to make sure that it isn't the battery that is causing the issue).

I believe that the battery supplies all electrical power to your car and the alternator just keeps the battery charged. So if you remove the battery then your car will not run.

Thanks for the quick reply.

My understanding is the exact opposite - that the alternator provides power to the car and the battery is just used to start the engine. Am I wrong?

Incorrect. The battery does not "provide" the power. The alternator provides the power when running.



CAN it run? yes..


is it safe for your health? no.

The current and voltage produced by the alternator (which would be present at the power leads which normally hook to the battery) are DEADLY. not just harmful.. That and the fact that the output voltage of the alternator is based on battery voltage, load, etc. You never know what having NOTHING there would cause the alternator to do....

I would certainly NOT recommend doing this. There are other ways of troubleshooting.. try the troubleshooting forum for a nice write-up of your problem, be concise, but detailed. Get some help there.

yes i was doing some research right after i said that and i found this:


Charging System Basics:
The electrical system in an automobile is said to be a 12 volt system, but this is slightly misleading. The charging system in most cars will generally produce a voltage between 13.5 and 14.4 volts while the engine is running. It has to generate more voltage than the battery's rated voltage to overcome the internal resistance of the battery. This may seem strange, but the current needed to recharge the battery would not flow at all if the charging system's output voltage was the same as the battery voltage. A greater difference of potential (voltage) between the battery's voltage and the alternator's output voltage will provide a faster charging rate.

As long as the engine is running, all of the power for the accessories is delivered by the alternator. The battery is actually a load on the charging system. The only time that the battery would supply power with the engine running is when the current capacity of the alternator is exceeded or when engine is at a very low idle.



I stand corrected.

But as ray said its not recommended.:nonono:

From http://www.bcae1.com/charging.htm
Warning!

Some people tell you that you can check your alternator by disconnecting it from the battery to see if the alternator can produce enough current to keep the engine running. BAD IDEA! Disconnecting the battery will subject the voltage regulator (and computer and audio equipment...) to significant voltage spikes which may cause an otherwise good alternator to fail. Even if there were no damaging spikes, this test would not indicate whether or not the alternator was good because the engine will easily run with a weak or failing alternator.

Simple Test:
If you want to see if your alternator is producing current, turn on your headlights when you're parked and the engine idling with the headlights shining on a wall (at night). Notice how bright they are. Then turn the engine off. The lights should get dimmer when you turn the engine off. If the lights get brighter when you kill the engine, the alternator was not charging sufficiently. When doing this test, the lights should be the only load (turn the stereo, a/c and other accessories off). With a heavy load, an otherwise good alternator may not be able to produce sufficient amounts of current at idle.

Ray said:

...the output voltage of the alternator is based on battery voltage, load, etc. You never know what having NOTHING there would cause the alternator to do....

Click to expand...

Those were my thoughts, but I wasn't sure if the battery resistance was required or not. Thanks for you reply.

Ray said:

I would certainly NOT recommend doing this. There are other ways of troubleshooting.. try the troubleshooting forum for a nice write-up of your problem, be concise, but detailed. Get some help there.

Click to expand...

I plan on writing up a thread, but want to get more info before posting.

guy came into my shop with a blown pcm because he did just what you are talking about. DONT DO IT

GeoPappas said:

As the title states, is it possible to remove the battery, start the engine with a jump starter, and let it continue to run? Does the electrical system require a battery between the positive and negative cables?

I am having electrical issues and would like to remove the battery out of the equation (to make sure that it isn't the battery that is causing the issue).

Click to expand...

It would be much safer to substitute a known good battery. Although rare, I occasionally had to do exactly that to pin down a problem when I worked as a mechanic. One time I even pulled the battery out of my own car as a reference.

Pay attention to what others have said about the health of your car from trying to run the engine with the battery disconnected. Not only can it do such damage, the damage may not be immediately evident. DON'T DO IT!

GeoPappas said:

...
I am having electrical issues and would like to remove the battery out of the equation (to make sure that it isn't the battery that is causing the issue).

Click to expand...

Yo, Geo! If it was recent like in the past 2 weeks during the 99 degree spell. It was probably just the hot weather with the ac running non stop. My 18 month old battery went flat within one hour of in town driving. I thought it was the alternator but it turned out to be a completely flat battery. I charged the battery overnight and it has been at 12.4 or so ever since. When the battery went flat, it was about 10.5 volts. When the car was running, it was fine. The last time I managed to start it before it "died" was when the wipers and speedometer (and ABS light) came on by itself.

just take a voltmeter and measure battery voltage with the key off. should be around 12.6 then start the engine. voltage should then be from 14-15. let us know what you get

And whatever you do dont put anything metal down between the terminals and if you do dont be holding on to it or expect it back. I did that once when someone behind asked me a question and I got shocked plus wet my pants. It was a very odd day.

not something i'd be proud of... lol :laugh:

Oh I'm not proud of it at all. It was a bad day at work to say the least.

You touched the pos to the neg. and got a shock? That sounds odd to me. I have never experienced that I have always got sparks and once when I accidentally touched the 3rd battery wired in series in my Lowrider which is 36volts to the battery frame it arc welded the wrench and turned it so hot you couldn't touch it for 5 minutes and burnt 2 layers of skin off the top of my hand!:shocked:

Dyoel182 said:

And whatever you do dont put anything metal down between the terminals and if you do dont be holding on to it or expect it back. I did that once when someone behind asked me a question and I got shocked plus wet my pants. It was a very odd day.

Click to expand...

I just got done wiring my amp on my svt and my gf took the car the into town and 5 miles down the road the negative popped off the battery and the car died. That was my lesson of seeing if the car ran w/o the battery lol.

Ray said:

Incorrect. The battery does not "provide" the power. The alternator provides the power when running.

CAN it run? yes..

is it safe for your health? no.

The current and voltage produced by the alternator (which would be present at the power leads which normally hook to the battery) are DEADLY. not just harmful.. That and the fact that the output voltage of the alternator is based on battery voltage, load, etc. You never know what having NOTHING there would cause the alternator to do....

I would certainly NOT recommend doing this. There are other ways of troubleshooting.. try the troubleshooting forum for a nice write-up of your problem, be concise, but detailed. Get some help there.

Click to expand...

This is the ANSWER!

The alternator supplies the power needed for "nearly" all requirements of the vehicle. (once started of course)

When running the battery is only a stop gap to help the alternator, when the demand for power (i.e. AC/DC current) surpasses the alternator output, at "said" engine rpm level. This is where a proper battery is key (i.e. big stereo!, HEI/Magneto ignition, etc...) Otherwise a battery is only used for the starting of the engine.

---FOR REF---

The "old school" pulling of the battery cable to see if the alternator is working is STUPID!!! DO NOT DO IT!!! This normally creates a voltage (amp) spike in the line and kills the alternator. If it was not dead, it sure is now. Best bet to test for a bad alternator at a place like AutoZone or the such. They'll test it (on or off the car) for free.

A bad battery (dead cells) will also kill an alternator because of the extra load it puts on it 100% of the time. Beware the extra maintenance bill here!

DemonSVT said:

This is the ANSWER!

---FOR REF---

The "old school" pulling of the battery cable to see if the alternator is working is STUPID!!! DO NOT DO IT!!! This normally creates a voltage (amp) spike in the line and kills the alternator. If it was not dead, it sure is now. Best bet to test for a bad alternator at a place like AutoZone or the such. They'll test it (on or off the car) for free.

A bad battery (dead cells) will also kill an alternator because of the extra load it puts on it 100% of the time. Beware the extra maintenance bill here!

Click to expand...

Unlike a generator, which has a permanent magnet field and will generate usable power by simply turning the shaft, alternators use a rotating field winding that needs some power from an external source, in the case of an automobile, that external source is the battery.

When the battery is disconnected from the electrical system of a running engine, you get what we in the automotive industry call "load dump". Load dump results when the alternator (magnetic) field rapidly collapses, and the collapsing field cuts across the alternator stator (fixed) windings. This uncontrolled field collapse causes a voltage transient that can exceed 80V. For the most part, modern automotive electrical systems are designed to withstand the load dump transient, but the energy dissipated in the transient suppression circuits can be pretty high, and repeated load dump events will eventually destroy the transient suppression circuits. As DemonSVT said, load dump can also blow the diodes in an alternator.

Don't disconnect the battery on a running engine.

Gary M.