Technical Battery removed while running

I was asked today if an engine would keep running (and lights stay on) if the battery were disconnected. I believe it will on alternator equipped cars but not sure with a generator?

 

I'm pretty sure it would. The generator uses permeant magnets to excite the armature, so even with no battery at all as soon as it starts turning it generates power.

Phil

 

It will kill an alternator if the battery is left disconnected very long. A generator will tolerate a longer time, but it's hard on the regulator.

 

Yes it does keep running.
I see this all the time in motorsports where the sanctioning body requires a battery kill switch/isolator.

The generator wire must go to the battery, with the kill switch placed in between to prevent a feedback loop.

It is very common on homebuilt racecars to connect this up wrong

 

Yes on alternator. Was getting a new battery installed on an OT car and the guy left it running I was like WTF and he said this way you don't loose radio presets and computer learning curve.

 

That's why when I worked at Advance auto parts we had a device that plug into the analyzer port to keep the computer happy and the radio presets.
Before that we a Toyota that had to be towed to the dealer for repairs after changing out a battery. The dealer had to reinstall the basic computer information so the car would run. Then the customer had to reset the radio.
Very expensive for Advance and one very pissed off ex customer.

 

As the regulator is made to work against a battery you may get big voltage fluctuations w/o it connected, you MAY kill sensitive electronics, light bulbs and such. So yes, there's a good chance it keeps runnming, and there's a risk you'll damage something.

 

Interesting question, because I believe it might have to do with the RPM on a generator equipped engine, the cutout and all.

The battery is said to act like a "flywheel" to the electrical system. It absorbs spikes and prevents sags and smooths things out. One thing I've noticed is sometimes people who should probably know better believe the battery runs everything, and the generator/alternator is only there to charge the battery.

Technically, the battery really only has one purpose, and that is to start the engine. All the current for the ignition, lights and accessories is provided by the generator/alternator.

 

In my youth, when we were diagnosing an electrical problem, to determine if the generator or battery were at fault. We started the vehicle, then disconnected the battery. If the engine continued to run the battery was the problem. If the engine stopped, it was the generator. You have to understand that life was much simpler then, and we did not know or understand any of the other possible problems. Most of the time it was one of these to components that were the source of the problem.

 

I remember something like that too on my '58 Chevy years ago. With lights on and 8 track playing at full volume the Gen light would glow at idle, the go out when sped up.

 

Ditto...it was called grass roots diagnostics...just like turning the lights on and revving the motor. If they got
brighter, the generator was o.k. and you knew to look at the battery.

 

Disconnecting the battery while the engine is running is OK to do with a generator, but might cause a voltage spike and burn out some electronics in an alternator. Or it might be OK.

I've never seen an automotive generator with permanent magnets. They all have field windings. That allows control of the charging rate.

 

Good way to kill electronics(ecm's, tcm's bcm's etc) o OT cars and trucks................................

 

Mine is still running just fine with no problems.

 

Reluctance, Inductance, Resistance to the fore!

 

Sure both will keep running disconnected. With a magneto.

 

On my GF, now wifes, OT wolfsburg I solved this with a tip from the guy at Advance. Battery swaps require the dealership so the ECM is not affected. Gotta be careful but the gent let me know that my battery tender can fool the car into thinking the battery has never been removed. Saved me, her actually, a fortune and I had a great night

 

Wow you learn something new each day of your life!
Learning the proper way to change a battery without having to reprogram the computer or radio stations is interesting for sure.

Thanks for that information. Jimbo

 

There is also those little units that plug into either you acc. outlet or cig. lighter if you have one. They have a 9v
battery supply and work great! Saves a lot of headache. I think I got my last one at Harbor Freight.

 

Most times it will but it only takes one voltage spike to cost a small fortune.

 

Did it back in the 60’s to get a car started. Switched batteries to get it started then put back in the one that couldn’t start the car. Didn’t have jumpers. Worked fine. I have one of those 9 volt power outlet gadgets to keep the radio and shit from loosing their brain. Not sure if they work in the newest cars.

 

In 1968 I made five bucks getting a guys car started when we had no jumper cables. He had no idea we could start with my battery and switch out after getting it started.

 

A buddy had a new 63 Impala and he bought a boat. With car payments and all his budget was tight so he couldn't afford a battery for the boat. We would put the boat in the water, pull the battery out of the car, then park the car and trailer. Did this one whole summer until the diodes in the alternator went out. I wonder why?

 

I stand corrected, mr google has let me down again.

Phil

 

I am totally going to buy one of those!

 

Make sure the lighter or power outlet as they are now called work before you rely on it, can't tell how many times I've had techs plug it in and yank the battery only to find out the fuse was blown or the outlet was bad...............

 

Part of the answer to the question depends on the amp draw of the lights and the output of said generator or alternator.

Most of us do not nor have we raced off road. That said I have seen 200 watt bulbs and a stock alternator drain the battery once the battery is gone (which happens pretty quick) the engine dies. So even though the engine should run with the lights on a lot depends on amp draw v output.

 

I've heard of folks who have done it, at highway soeeds seemingly without harm in OT cars, but it can't do the VR any good. Idle is one thing, but spooling up the motor RPM with all the sensitive electronic$ ... no thanks!

I think I've read, maybe someone here even, said that to push start a generator equipped car, the battery can't be completely dead, some small amount of voltage is needed to excite the field coils or something like that. Otherwise voltage won't be generated to fire the plugs. Sounds right, though I don't know for sure. Filed it somewhere in the back of my mind in the "Interesting but probably useless information" section.

 

Opening the car door is another dependable way to smoke the 9 volt, because they can't power a dome light too good. Oops!

 

BatteryFaq.org or maybee AA1car.com , somebody has a list of the modern OT cars and all the debacles that can ensue by disconnecting the battery. It ain't just presets.

Mostly high end vee-hickles, but it usually involves fun stuff like a trip to the dealer for a proprietary scan tool. Things like power windows no longer functional, or the A/C no longer works. Nice. Some also monitor the battery age by date of installation and change the charging algorithm jiggery-pokery over time or somesuch. So a new battery gets installed we're supposed to let the car computer know too, I guess.