If there's enough juice to power a fuel pump, ignition coil, etc there should definitely be enough to excite the alternator. Old alternators' excitation terminal used to be powered through the "battery charge" indicator lamp so very little current would get through (and indeed the wire gauge was very thin).
This checks out with me anecdotally, at least. I bought a new car just as the first COVID lockdown let up and right on the forecourt it was complaining about a low battery, apparently due to sitting around for a month or two. "It'll be fine by the time you get it home" they said. Wrong. Even a few hours on a charger and a 300 mile drive only bought me a few weeks of time. I ended up having to trickle charge it for 24 hours to permanently resolve the problem.
Anecdotal confirmation yes, 3 months out the gate my new Subaru had a drained battery due to a 250mA cold draw while parked that they traced to some random electrical unit and replaced.
I think so. It was in a Land Rover Defender. Luckily due to the shortages, I sold it after a year for the same I bought it for! :) Sticking to Ford now, too many bad LR experiences.
For most battery chemistries, if you drain them low enough the battery will be permanently damaged. Had to explain this to a friend that let their car sit every winter and completely drain the battery and would repeatedly have to buy a new battery every year.
Battery tenders are great things to have if you don't drive often enough to make up for natural discharging. Especially so if you're in a very cold climate.
> Have you ever seen or driven a car where, as you sped up, the lights got brighter? That's because the battery was dead and all the electrical power was coming from the alternator with no battery to act as a load-balancer.
Not in a long-long time. Voltage-regulated alternators have been a thing for decades now. By the 90s, most companies had solid state internal voltage regulators. Also, most (probably every) modern cars feed the alternator signal through the ECU/PCM before it gets to the battery specifically because it's crucial that computer-controlled component receive a clean, reliable voltage signal. I learned this the hard way.
Some good stuff there, but I think this article suffers from not distinguishing between a "dead battery" that's dead because, eg you left your headlights on, and a battery that's "dead" because it's aged to the point of suffering internal defects.
A "dead battery" in the former case (maybe we should just call it a "very discharged battery") can, in my experience, often be recharged by your alternator and it doesn't necessarily take a super long drive to do it. That's assuming you're able to get the car started in the first place, possibly by jump-starting from another car, or "roll it down a hill and pop the clutch" which will work IF there's "just enough" juice in the battery for the ignition coil to fire (and enough to provide the "seed" excitation current to the alternator).
OTOH, a "dead battery" in the latter sense (maybe we should call it a "dying battery") simply needs to be replaced, ASAP. It won't ever hold a charge reliably, could (in an extreme worst case scenario) develop an internal short and catch fire, or damage your alternator.
Fortunately most auto parts stores (here in the US anyway) offer a battery testing service that can tell you if your battery is truly shot or not. They'll also often have an alternator tester, but that usually means removing the alternator and bringing it in, which can be a lot of work on some vehicles. But a simple test is to start your engine and then disconnect the positive battery terminal. If the engine dies immediately, you know the alternator isn't emitting any current (the engine dies because there's no current for the ignition coil(s), ECM, fuel-injectors, etc).
> But a simple test is to start your engine and then disconnect the positive battery terminal.
Do not do that. The battery acts like a buffer to smooth out voltage spikes put out by the alternator. Without it, system voltage can spike to dangerous levels and potentially damage electronics.
That's true, but I'm not talking about disconnecting it and keeping it disconnected for an extended period of time. I'm talking about just as a quick test to see if the alternator is charging or not.
Also keep in mind that all modern alternators have a built-in voltage regulator that provides first-order protection against such spikes.
Empirically, I can say that I have done this very many times in my life, and I have never once observed any negative consequence as a result. YMMV, of course.
Is there a solar panel solution for this? Like a solar panel you can leave on the back window or something, that will slowly trickle-charge the battery?
They already make battery powered jumpstart devices, that are not so different from the phone recharging blocks. It wod probably be pretty easy the wire one of those up to a solar panel so that it’s always at 100% charge. But if you’re going to do that, you might as well just fully charge it from the car battery when the car battery is not dead.
This is one of those science gotcha posts that threads an incredibly narrow line of reasoning. If your battery is (A) dead but (B) you can somehow start the vehicle (how?) and (C) you don't have time to call a tow company to come recharge it or replace it and (D) the battery isn't completely defective and needs to be replaced and (E) you do have time to drive around in hopes that your alternator can charge the battery and (F) I got bored with this list
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[ 3.0 ms ] story [ 61.9 ms ] threadNot in a long-long time. Voltage-regulated alternators have been a thing for decades now. By the 90s, most companies had solid state internal voltage regulators. Also, most (probably every) modern cars feed the alternator signal through the ECU/PCM before it gets to the battery specifically because it's crucial that computer-controlled component receive a clean, reliable voltage signal. I learned this the hard way.
Yes, VW Bettle ;)
A "dead battery" in the former case (maybe we should just call it a "very discharged battery") can, in my experience, often be recharged by your alternator and it doesn't necessarily take a super long drive to do it. That's assuming you're able to get the car started in the first place, possibly by jump-starting from another car, or "roll it down a hill and pop the clutch" which will work IF there's "just enough" juice in the battery for the ignition coil to fire (and enough to provide the "seed" excitation current to the alternator).
OTOH, a "dead battery" in the latter sense (maybe we should call it a "dying battery") simply needs to be replaced, ASAP. It won't ever hold a charge reliably, could (in an extreme worst case scenario) develop an internal short and catch fire, or damage your alternator.
Fortunately most auto parts stores (here in the US anyway) offer a battery testing service that can tell you if your battery is truly shot or not. They'll also often have an alternator tester, but that usually means removing the alternator and bringing it in, which can be a lot of work on some vehicles. But a simple test is to start your engine and then disconnect the positive battery terminal. If the engine dies immediately, you know the alternator isn't emitting any current (the engine dies because there's no current for the ignition coil(s), ECM, fuel-injectors, etc).
Do not do that. The battery acts like a buffer to smooth out voltage spikes put out by the alternator. Without it, system voltage can spike to dangerous levels and potentially damage electronics.
Also keep in mind that all modern alternators have a built-in voltage regulator that provides first-order protection against such spikes.
Empirically, I can say that I have done this very many times in my life, and I have never once observed any negative consequence as a result. YMMV, of course.
New verb: To chernobyl your car's electronics.