Velocity, if your engine starts OK and runs now - you’re fine. That said I’m assuming that you left the lights on, was a cold morning, was the original battery, etc. and it just didn’t have enough stored energy to crank. If the car is dead again I’d be looking at a new battery and/or testing the alternator.
The “flooding” hysteria shows a lack of basic automotive systems knowledge.
The Ohms law discussion shows a lack of of high school physics.
E=IR; R-starter is constant, E-applied battery voltage is reduced, therefore I-current is LESS and the starter wasn’t getting enough power to turn the engine.
That might be true if you had a fully charged 10V battery. You don’t. You have a damn near flat 12V battery. The battery can’t supply the power the starter needs. So resistance is constant voltage goes down and the current flow goes down.
Here’s a tip: we something isn’t working, don’t keep doing it. I’m kinda dumb, so I learned this lesson the hard way several times, long ago.
All my examples are for obsolete designs, but still: avoid operating anything way outside its design envelope. You never know just what might happen. Fortunately cars are more idiot-proof than they used to be.
Running a battery way down can cause it to leak flammable gases that can ignite when jumped. Saw this happen; glad it wasn’t me. A bit of an explosion, nobody harmed thank goodness, but acid in the eyes is no fun.
Trying to crank a car when it’s barely turning over can overheat the starter and damage it.
Used to be, when you run out of gas and kept cranking in vain hopes, you’d run all the gas out of the lines and make it way harder to start when you put gas in.
The stories get longer and more embarrassing. Basic lesson: as soon as it stops working, don’t foolishly keep trying, fix what’s wrong and save yourself more trouble.
I don’t know much about electric motors, so I don’t what the limitations are to that statement: does it mostly apply to certain kinds of electric motors?
Stalled electric motors run higher currents than rotating electric motors. They have “lower resistance”
I don’t know much about electric motors, so I don’t what the limitations are to that statement: does it mostly apply to certain kinds of electric motors?
Stalled electric motors run hotter than rotating electric motors. They are normally designed for self cooling using their own rotary motion.
Running your starter motor for a long time will cause it to overheat. They aren’t designed for that. That’s more of a problem with a fully charged battery and a dead engine.
A stalled electric motor is essentially a short circuit (at least compared to a spinning motor). A spinning motor produces counter EMF which produces a lot of the impedance normally “seen” in a motor. So yes, a stalled motor will draw more current than a spinning one HOWEVER on a dying battery that can’t provide enough current to get it going, the voltage sags and it just causes it to go flat quicker.
I’m a bit loopy tired, so I’m not sure if I just made sense or butchered my feeble EE training from a thousand years ago that I never use…someone feel free to correct me.
No, lead-acid automotive start batteries don’t “like” being fully discharged at all. 2 to 5 complete discharges and they are completely done for. Even one time, while not necessarily ruining the battery will reduce its lifespan considerably.
Another factor is, anytime the voltage drops below 11 volts if not recharged asap there is danger of cell reversal. Yet another, a discharged battery can freeze. A fully charged battery is protected from freezing to -40F, a discharged or “flat” battery will freeze around +20F.
In turn, a frozen battery may explode if jump started. Very bad ju-ju.
Finally, a discharged or “dead” battery presents a tremendous load on the charging system and may ruin the alternator stator or diodes and other components. Re-charging a dead battery with the vehicle is something to be avoided, any battery that needs a jump start should always be fully charged with an outboard charger as soon as possible.
Rick is correct here. The starter should not be modeled as a constant-power load.
At work we spent months measuring input current & voltage on a DC starter generator (SG) used to start a small aircraft engine. When the supply voltage was decreased, the current automatically decreased. This resulted in a decrease in RPM, which further resulted in the engine taking more time to start. Which resulted in more “heat build up” in the SG.
Ah, fascinating. This must be why my starter motor burned out in an instant when I applied zero volts to it - it was pulling an infinite amount of current.
I repeated the experiment just to be sure, because mucking about with infinities is always dubious. I applied one microvolt to a 1kW electric motor and sure enough it pulled a billion amps and burned like the desert sun.
Although lacking any electrical knowledge it seems obvious to me that if a starter motor is jammed, and you keep trying to use it, the power has to go somewhere and will either melt the cables or burn the motor out. There is a **lot **of power stored in a car battery.
Yes, if you have a jammed starter motor and the battery is in good order then what you have is a motor with zero dynamic resistance, not much static resistance, and a huge current going through it. You’re right about the power storage of a car battery too - and even smaller batteries can be dangerous. Rechargeable packs (lead-acid or otherwise) often have low internal resistance and can pump out a lot of current if the resistance is low - shorting out a battery through a wedding ring is a favourite way for either a mechanic or a modeller to give themselves a severe burn.
However, this happens not because “as the voltage decreases, the current rises to compensate”. If you have a nearly-dead battery then what you’re actually after is the V = IR application of Ohms’ Law; with the resistance unchanged and the voltage lowered, the current drops proportionately with the voltage. The power, obviously, also drops; with half the voltage and also half the current, you’re looking at a quarter of the power.
If you don’t have the volts to turn the motor at all, then it’s true that your remaining voltage is not experiencing much resistance, but by the same token, it’s not driving much current either.
This doesn’t make sense. An engine won’t “vroom to life” if the battery is dead. If the engine cranks normally, then starts but only runs for a second or so, it’s not a battery issue. Kindly tell us clearly and accurately what the symptoms are. “Dead battery sounds” is vague and apparently inaccurate.
You’ve never really explained the sequence of how you came to have a problem nor even whether it’s currently running. “Fizzled” doesn’t mean anything and it’s hard to offer advice.