Can vehicle run without battery?
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Originally Posted By: severach
Both right and wrong.
A car cannot reliably run on the alternator alone. The battery cleans the power like a capacitor and puts out during bursts only to be immediately refilled when the alternator catches up. Without a battery a sudden load from the headlights or the heater fan will kill the engine all the while you may be destroying electronics with the dirty power. Old cars with few electronics and low power usage would tolerate an alternator without a battery but new cars require a lot of electrical power that must be clean so are unlikely to run at all.
However when running all things run off the alternator, not the battery.
A car with audio stiffening capacitors would probably run as well with or without a battery. The handful of small capacitors in various vehicle electronics aren't enough.
Magneto engines are usually designed to run without power. That doesn't prove that coil spark engines can also.
Originally Posted By: eljefino
There are milliseconds between diodes in the rectifier when zero current is being produced.
Maybe in single phase power but an alternator is 3 or 4 phase power. The waveform is bouncy but there is always current.
Originally Posted By: Gary Allan
I subscribe to the theory that all power is supplied by the battery and that the alt merely replaces it.
Any ammeter will prove this theory. My meters always say current is going into the battery.
EXACTLY RIGHT. excellent summary.
Both right and wrong.
A car cannot reliably run on the alternator alone. The battery cleans the power like a capacitor and puts out during bursts only to be immediately refilled when the alternator catches up. Without a battery a sudden load from the headlights or the heater fan will kill the engine all the while you may be destroying electronics with the dirty power. Old cars with few electronics and low power usage would tolerate an alternator without a battery but new cars require a lot of electrical power that must be clean so are unlikely to run at all.
However when running all things run off the alternator, not the battery.
A car with audio stiffening capacitors would probably run as well with or without a battery. The handful of small capacitors in various vehicle electronics aren't enough.
Magneto engines are usually designed to run without power. That doesn't prove that coil spark engines can also.
Originally Posted By: eljefino
There are milliseconds between diodes in the rectifier when zero current is being produced.
Maybe in single phase power but an alternator is 3 or 4 phase power. The waveform is bouncy but there is always current.
Originally Posted By: Gary Allan
I subscribe to the theory that all power is supplied by the battery and that the alt merely replaces it.
Any ammeter will prove this theory. My meters always say current is going into the battery.
EXACTLY RIGHT. excellent summary.
In theory, yes. In reality, no. Without a battery to keep things in check, the alternator may do strange things. A buddy of mine told me of the day he disconnected the battery on his motorcycle and the voltage went crazy high, making several lights get very bright and burned out. My MG has a big warning under the hood saying never to disconnect the battery while the engine is running. In short, the battery is there to stabilize the alternator's output, and without it you might get big fluctuations in voltage. In addition, if very few loads are turned on, the alternator might put out too much voltage because even though the regulator may be trying to reduce the alternator's output, the residual magnetism in the rotor might be more than enough to generate enough output, which the battery would be able to absorb.
I had a friend that had a charging or battery problem in his '87 Mazda B2200. For 4 months, his routine when he left work was to push it through the parking lot, hop in, pop into gear, and drive it home. I know this is a little off topic, but it sure was a good laugh watching a grown man sprinting with a truck across the parking lot everyday. He had it down to a science.
Once while on a trip, we left the our '01 Accord parked at the airport and accidentally left the dome light on. When we came back, the battery was dead. The airport sent us an assistance truck, and we started the car off his battery, then (to my surprise) he immediately removed the jumper cables. You could tell the battery was depleted, though, because the lights flickered.
I don't know if this necessarily answers the question - it's possible the battery had just enough charge to be of some use?
I don't know if this necessarily answers the question - it's possible the battery had just enough charge to be of some use?
A lot of cars' PCM will shut the engine off if the battery voltage drops below about 9 volts. Also I think the battery has to connected to complete the circuits on some cars.
As far as the alternator I know that at least with some cars if the alternator is not plug in the whole car will be dead. One car I remember had extra positive lead from the battery and the schematic showed it powered the car. Yet without the alternator hooked up, the whole car was dead, no constant hot even dome light, headlight etc. I can't really explain that.
As far as the alternator I know that at least with some cars if the alternator is not plug in the whole car will be dead. One car I remember had extra positive lead from the battery and the schematic showed it powered the car. Yet without the alternator hooked up, the whole car was dead, no constant hot even dome light, headlight etc. I can't really explain that.
I know dad and I did it with a 1990's Honda Accord. We boosted it and then he drove it with two feet keeping the idle at 1200 rpm. He made it the 55km's we had to go with it.
Steve
Steve
Originally Posted By: NateDN10
Once while on a trip, we left the our '01 Accord parked at the airport and accidentally left the dome light on. When we came back, the battery was dead. The airport sent us an assistance truck, and we started the car off his battery, then (to my surprise) he immediately removed the jumper cables. You could tell the battery was depleted, though, because the lights flickered.
I don't know if this necessarily answers the question - it's possible the battery had just enough charge to be of some use?
Yes because it started charging the moment the last jumper was connected. This is called a "surface charge" and wouldn't have turned the starter over, but was enough to convince the alt that there was "something there".
Once while on a trip, we left the our '01 Accord parked at the airport and accidentally left the dome light on. When we came back, the battery was dead. The airport sent us an assistance truck, and we started the car off his battery, then (to my surprise) he immediately removed the jumper cables. You could tell the battery was depleted, though, because the lights flickered.
I don't know if this necessarily answers the question - it's possible the battery had just enough charge to be of some use?
Yes because it started charging the moment the last jumper was connected. This is called a "surface charge" and wouldn't have turned the starter over, but was enough to convince the alt that there was "something there".
Originally Posted By: Chris142
Originally Posted By: beast3300
Depends on the car. Some with run with no battery, some will not.
Yup most cars wont run. It's a safety thing to prevent sending voltage spikes to the computer.
A 69 Chevy pickup will run w/o a battery. A 99 Chevy wont.
I'll take the '69!
Originally Posted By: beast3300
Depends on the car. Some with run with no battery, some will not.
Yup most cars wont run. It's a safety thing to prevent sending voltage spikes to the computer.
A 69 Chevy pickup will run w/o a battery. A 99 Chevy wont.
I'll take the '69!
On our 60's and 70's cars,it was not uncommon to get the car running and then lift a battery terminal connector to see if the car would stay running. That provided a quick check of the alternator to verify it was putting out charging voltage.
If you try this on a modern car, you risk frying 100's of dollars worth of computerized control equipment.
It is good to hear that at least a few manufacturers have a means to shut down the engine as a safety precaution, but I would never recommend that anyone do this. One spike or surge is all it takes to destroy some expensive parts.
If you try this on a modern car, you risk frying 100's of dollars worth of computerized control equipment.
It is good to hear that at least a few manufacturers have a means to shut down the engine as a safety precaution, but I would never recommend that anyone do this. One spike or surge is all it takes to destroy some expensive parts.
I wouldn't do it - the battery acts as a buffer and helps maintain the correct voltage to the computer.
Originally Posted By: TallPaul
Originally Posted By: Chris142
Originally Posted By: beast3300
Depends on the car. Some with run with no battery, some will not.
Yup most cars wont run. It's a safety thing to prevent sending voltage spikes to the computer.
A 69 Chevy pickup will run w/o a battery. A 99 Chevy wont.
I'll take the '69!
Thank you for this classic thread!
Originally Posted By: Chris142
Originally Posted By: beast3300
Depends on the car. Some with run with no battery, some will not.
Yup most cars wont run. It's a safety thing to prevent sending voltage spikes to the computer.
A 69 Chevy pickup will run w/o a battery. A 99 Chevy wont.
I'll take the '69!
Thank you for this classic thread!
Originally Posted By: brianl703
http://en.wikipedia.org/wiki/Load_dump
This. Once I killed electronic tach in a boat by simply disconecting battery when running. Transients will kill any sensitive electronics.
There is also this: cars with EPS, will pull as much as 100A peak current from battery while turning at low speeds. This is why in some modern cars you can't just jump dead battery and drive away.
http://en.wikipedia.org/wiki/Load_dump
This. Once I killed electronic tach in a boat by simply disconecting battery when running. Transients will kill any sensitive electronics.
There is also this: cars with EPS, will pull as much as 100A peak current from battery while turning at low speeds. This is why in some modern cars you can't just jump dead battery and drive away.
Originally Posted By: friendly_jacek
Originally Posted By: brianl703
http://en.wikipedia.org/wiki/Load_dump
This. Once I killed electronic tach in a boat by simply disconecting battery when running. Transients will kill any sensitive electronics.
There is also this: cars with EPS, will pull as much as 100A peak current from battery while turning at low speeds. This is why in some modern cars you can't just jump dead battery and drive away.
I prefer to jump with a self-contained jump starter rather than a live car battery. It's a lot easier and has fewer issues with length of cables as well as position of the vehicles. I don't even recall how many times I've offered the use of mine with a dead battery.
However, the one thing I generally do is let it sit there for a minute. I figure it should get slightly recharged, and the other thing I've heard is that by sucking up a little bit of charge, it should limit the charge going into the dead battery initially. I heard that a dead battery is probably better off starting off without a full charge. It might also help somewhat if there is a sudden demand for high current that the alternator can't meet and the "mostly dead" battery still can't deliver.
I have some experience with notebook computer batteries. They generally need to have a live battery installed because there can be short spikes in current demand that can't be met with a small AC power supply. A charged battery is capable of meeting current demand that the AC supply simply can't. On some machines, if it's sensed that the battery is disconnected, the system is designed to cut the clock frequency in half to reduce potential current demand.
Originally Posted By: brianl703
http://en.wikipedia.org/wiki/Load_dump
This. Once I killed electronic tach in a boat by simply disconecting battery when running. Transients will kill any sensitive electronics.
There is also this: cars with EPS, will pull as much as 100A peak current from battery while turning at low speeds. This is why in some modern cars you can't just jump dead battery and drive away.
I prefer to jump with a self-contained jump starter rather than a live car battery. It's a lot easier and has fewer issues with length of cables as well as position of the vehicles. I don't even recall how many times I've offered the use of mine with a dead battery.
However, the one thing I generally do is let it sit there for a minute. I figure it should get slightly recharged, and the other thing I've heard is that by sucking up a little bit of charge, it should limit the charge going into the dead battery initially. I heard that a dead battery is probably better off starting off without a full charge. It might also help somewhat if there is a sudden demand for high current that the alternator can't meet and the "mostly dead" battery still can't deliver.
I have some experience with notebook computer batteries. They generally need to have a live battery installed because there can be short spikes in current demand that can't be met with a small AC power supply. A charged battery is capable of meeting current demand that the AC supply simply can't. On some machines, if it's sensed that the battery is disconnected, the system is designed to cut the clock frequency in half to reduce potential current demand.
I used to have one of the portable jump boxes ... but it seems to be too much trouble to keep them charged. When I had one, I never once killed my battery and never used it for myself!
I have a spare car battery hooked up to a solar charger. I use that if I need to jumpstart anyone.
I have a spare car battery hooked up to a solar charger. I use that if I need to jumpstart anyone.
"Sensitive"? Guess I've been around electronics too long, I tend to think of 100V killing something not being the fault of the electronics. I mean, something meant for running on 5V just isn't meant for high voltage spikes. That said, load dump testing is done at least for the silicon products I'm familar with, and I would have to guess the OEM's test each of their boxes for load dump too.
Load dump testing is an interesting test. I find it wild that you can have a part that would die if exposed to anything above say 30V withstand this long pulse of 100V. All about power disapation; how long until something melts?
Load dump testing is an interesting test. I find it wild that you can have a part that would die if exposed to anything above say 30V withstand this long pulse of 100V. All about power disapation; how long until something melts?
Originally Posted By: Miller88
I used to have one of the portable jump boxes ... but it seems to be too much trouble to keep them charged. When I had one, I never once killed my battery and never used it for myself!
I have a spare car battery hooked up to a solar charger. I use that if I need to jumpstart anyone.
I remember finding myself with a dead battery in a remote location in the Cascades driving my wife's car. That was back when the driver door sensor switch would cave in and the light chime and key chime failed to sound. Used it a couple of times that trip.
I generally don't have too many problems, but my wife has a habit of staying in the car and leaving the map lights on. Sometimes we don't take that car out for a couple of days and it won't start. She's done that with my car too, and with an older battery it wouldn't start after draining overnight. She's getting better about that though.
I've helped my folks out with a dead battery after they got back from vacation, but I think a better thing for them would have been to charge the battery overnight. I think a 1.5A maintainer overnight would have been enough for them to start their car, although I'm thinking of getting a higher capacity charger; I want to build up a collection of tools. The last time they went on vacation I hooked up the maintainer to their battery about a week in and disconnected it a few days before they got back. Sure beat getting a panicked call to come over and give them a jump.
I used to have one of the portable jump boxes ... but it seems to be too much trouble to keep them charged. When I had one, I never once killed my battery and never used it for myself!
I have a spare car battery hooked up to a solar charger. I use that if I need to jumpstart anyone.
I remember finding myself with a dead battery in a remote location in the Cascades driving my wife's car. That was back when the driver door sensor switch would cave in and the light chime and key chime failed to sound. Used it a couple of times that trip.
I generally don't have too many problems, but my wife has a habit of staying in the car and leaving the map lights on. Sometimes we don't take that car out for a couple of days and it won't start. She's done that with my car too, and with an older battery it wouldn't start after draining overnight. She's getting better about that though.
I've helped my folks out with a dead battery after they got back from vacation, but I think a better thing for them would have been to charge the battery overnight. I think a 1.5A maintainer overnight would have been enough for them to start their car, although I'm thinking of getting a higher capacity charger; I want to build up a collection of tools. The last time they went on vacation I hooked up the maintainer to their battery about a week in and disconnected it a few days before they got back. Sure beat getting a panicked call to come over and give them a jump.
Old vehicles would, my old 300SD could be pull started and would run just fine with no battery.
Perfect EMP vehicle.
Perfect EMP vehicle.
That happened to my Kawasaki KZ650 once. Battery was broken and had an open condition, as if it wasn't there. After a push start, it ran fine, except the higher I revved it, the higher the voltage went, and more and more lights burned out. First to go were instruments, then turn signals, and finally brake lights. The headlight survived because I parked the thing after riding around the block.
I've read (on a car forum) that the voltage regulator needs the battery voltage or resistance (or something) to make the circuitry work properly. And judging by the 5 wire connector, and the way my lights burned out, I have to believe that.
(BTW, if it matters, this 1979 bike's ignition was "points". That's where a magnet on the crank pulls a lever which closed a switch which sends 12 volts to the respective coil. Basically like a car's distributor cap, but without the lateral friction. By 1984 the 900 Ninja from Top Gun had digital ignition. My '85 fzr400 did also, as did pretty much all bike's from the mid 80's on. Thankfully, I've never had an "open" battery on one of these bikes.)
I've read (on a car forum) that the voltage regulator needs the battery voltage or resistance (or something) to make the circuitry work properly. And judging by the 5 wire connector, and the way my lights burned out, I have to believe that.
(BTW, if it matters, this 1979 bike's ignition was "points". That's where a magnet on the crank pulls a lever which closed a switch which sends 12 volts to the respective coil. Basically like a car's distributor cap, but without the lateral friction. By 1984 the 900 Ninja from Top Gun had digital ignition. My '85 fzr400 did also, as did pretty much all bike's from the mid 80's on. Thankfully, I've never had an "open" battery on one of these bikes.)
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