Dead car battery and alternator strain?

[caphair]

I haven’t driven my car in just over a week and we’ve had snow and freezing temps since.

Went to start it today and as expected it tried and tried until nothing but the relay clicking.

My question, if I get the battery jumped and drive on the highway for more than 30 minutes will the battery recharge without affecting the alternator? I know a completely depleted battery can put strain on the alternator causing it to fail prematurely so I want to avoid that.

Is there a voltage limit on the battery to indicate whether or not the alternator will work too hard resulting in damage? Right now it measures 11.92v

The battery is about 4-5 years old and never gave me any issues when I used to drive daily but recently don’t drive as much.

[eccerr0r]

Re: Dead car battery and alternator strain?

As long as you're over 11 volts I think the alternator is fine. It's a 'new' battery with shorted cells that hurts; an old battery or old battery with shorted cells is not that bad because internal impedance has gone up.

4-5 years is about time for a new battery, though you should ensure that you don't have a very high parasitic load on your battery. Even with modern cars, you should be able to stand about 2 weeks before needing to charge, even in winter. Shorter than that, you probably needed a new battery.

All bets are off if you left the lights on...

[stj]

Re: Dead car battery and alternator strain?

just do it, the alternator is rated to atleast charge the battery while running the headlamps.
however, 30min's is fuckall - it takes that to put back what you use to start the car.

btw, a dc clampmeter like a ut-210e is good for these situations, you can see how much current is being drawn by the car when it's parked.

[caphair]

Re: Dead car battery and alternator strain?

Thanks for your response. I think what contributed to it was last time I drove the battery struggled slightly to get it started (again cold temps and car sitting) and I only drove for about 15 minutes. Then temps dropped and it’s been sitting for a week.

Now would it be ok to not jump start it for a day or two? Or should it be attended to ASAP? Just trying to avoid any damage to the battery and alternator if possible.

Also could I use a pc 12v power supply to apply a charge to the battery or it would be so minimal that I shouldn’t even bother?

[eccerr0r]

Re: Dead car battery and alternator strain?

Based on what you said, the battery is probably still discharged.
You should attend to it right away, charge it. The longer you leave it discharged, the more likely you have to go to a car parts store and open your wallet.

A 12V PC PSU will not likely do what you need. You have to mod it to around 14V to get the charging going.

[redwire]

Re: Dead car battery and alternator strain?

You can't charge a block of ice - so if the battery went dead and froze, you'll probably have to bring it inside and thaw it out to charge it.
It depends on how cold and how low the battery is. Don't add water to cells when it's really cold as that can ice up.

Alternators have inherent current-limiting so they do not cook and burn up under heavy load. It's cold out too so they also get extra cooling.

It sounds like the battery is just old and weak, one cell is toast.
The recovery time, or amount of energy you take out to start the car verses how long to put back into the battery... it's complicated. An idling engine the alternator does not have full output. I would use a battery charger and give it 14V for a day.
Boosting is hard on a car due to transients that are generated.

[momaka]

Re: Dead car battery and alternator strain?

4-5 years is about time for a new battery

It depends on the vehicle. Perhaps it is normal for new cars these days or for folks living in climate extremes. But an older garage-kept car with less complex electronics (read: no constant drain from a silly onboard "smart" computer) and smaller engine/starter could go much more than that. The battery in my car, for example, is 9 years old now. If it makes it past this winter, it will probably go for another year until next season's cold weather. (But I don't know, the other day I cranked it and went to the grocery store and... it barely was able to start. So it surely is on its way out.) That said, if my battery dies, I might try bringing it in, adding some distilled water in the cells and then charging it? Good/bad idea?

I've also read about the "pickled solution trick" and that it can restore dead batteries as long as they don't have shorted cells. What's your take on that one? Too good to be true? Something is telling me yes, to good to be true indeed.

[redwire]

Re: Dead car battery and alternator strain?

Modern cars have high drain with the key off. 50-100mA so battery life is short, it's always discharging.

Car battery main failure is usually corrosion of the plates. What do you expect to happen with metal in an acid solution. The lead just crumbles. So no amount of pickle juice can fix that.

Other data shows lead sulphate crystals are always forming on the plates and grow bigger and bigger with every cycle. Eventually the plate's pores get blocked with (insulating) lead sulphate crystals and this is why the lifetime is limited to like 500 cycles and batteries have less capacity as they age. I think this (sulphate crystals) is what newer cars are aggravating with high quiescent drain.

Subaru have issues with high battery drain and an ECM firmware update that helps lower that, but they still eat batteries and go dead if the car sits for a short period.

[eccerr0r]

Re: Dead car battery and alternator strain?

Yeah my climate is like -20°C to 40°C but more typically like -15°C to 35°C, and I'm averaging 7 year battery lives without too much ±. But rule of thumb is when the battery hits the 5th birthday, be ready to open your wallet; it may last 4 more years but more often than not, it will die on you in an inconvenient spot within the next 2 years. Quite possibly even less than 5 years if you abuse your battery (high parasitic load/leaving lights on overnight, running radio when engine not running for hours, not mounting it properly, running off road, etc., etc.)

My last battery died during the summer/fall when a cell shorted out*. The one before then, one cell just ended up with a huge internal impedance, and also during the summer. You never know when they will fail.

* I was a few miles from home, but was able to squeak out one last start from it, lucky it wasn't cold that day (60s I think). I should have just driven it straight to the car parts store as I was pretty sure what was wrong, but drove home and bought a new battery with another car. Of course I was cheap and at least tried charging it before giving up but it was to no avail.

[stj]

Re: Dead car battery and alternator strain?

i just replaced a battery in a family members car at x-mas.
it was factory fitted in 2010!!!
(ford)

[Curious.George]

Re: Dead car battery and alternator strain?

i just replaced a battery in a family members car at x-mas.
it was factory fitted in 2010!!!
(ford)

The norm, here, is 3-4 years for a battery -- regardless of "quality". The heat just cooks the sh*t out of them!

The optimal battery maintenance strategy (here) is to buy your first replacement from a place like Costco (inexpensive yet decent replacement warranty -- the non-prorated term is about 3 years) and then just bring it back to them at the end of the non-prorated period for a free replacement. They don't even bother testing the returned batteries as short-term failures are so common.

(A battery need not "fail" for it to be considered as defective in terms of bench testing)

[redwire]

Re: Dead car battery and alternator strain?

I see temperature has a big effect on lifetime.

Johnson Controls revenues $6 billion for car batteries, 135 million made per year. They are pretty much the big dog making almost all car batteries, so I don't see a huge difference other than marketing hype between "brands".

Optima AGM spiral plates are 3X the price of a vanilla car battery and last 2-3X... so what's the point? Especially since Johnson Controls bought them out and destroyed the quality years ago.

[petehall347]

Re: Dead car battery and alternator strain?

jump start it but let it charge up with jump vehicle running at fast idle for 20 minutes . then start it up and leave jump leads connected for a further 10 minutes .

[stj]

Re: Dead car battery and alternator strain?

i'm sure they could harden batteries to take temperature swings - just not good business to do so.

maybe add some alcahol to lower the freezing point, and seal it a bit more with an expansion area and a pressure release valve - to handle hot weather.

[eccerr0r]

Re: Dead car battery and alternator strain?

No, they cannot add alcohol to depress the freezing point. Water is part of the reaction when charging, all that water needs to be there to let the sulfuric acid to go around (not to mention sulfuric acid probably reacts with alcohol). Besides, a charged battery won't freeze: that's all one needs to do. A fully charged battery will go down quite cold. But a half charged battery will freeze sooner...keep that in mind during the winter.

During the summer it's not pressure that's the problem, it's faster reaction/decay of the plates. They already are adding stuff to the plates to ensure the plates don't decay as fast. Making the plates thicker will help, but it will reduce the specific power of the battery as well as increase cost and weight. So there's a lot of trade offs here.

Actually I'm not sure how the alternator limits charge current. Then again, they can support many many amperes of current -- but if the battery isn't shorted I don't think it will be a problem for any alternator to charge its typical battery. If you're worried, don't turn on accessories. It still will take a while to charge no matter what.

[redwire]

Re: Dead car battery and alternator strain?

Older (car) generators and dynamos needed output current limiting so they would not burn up under heavy load. This was done by a current-sense winding on the relay coil in the mechanical regulator, like Lucas in the 1950-60's.

Alternators are power-limited by the leakage inductances of the stator. At higher speeds and higher currents, the impedance gets in the way of more output current. They pretty much self-protect themselves.
You can't get 100A out of a 50A alternator due to this and the stator's copper winding resistance, which is about 50% of the losses, 25% in the rectifier diodes and the remainng losses in connection resistances and the rotor and bearings. I find the car's wiring and fusible-link resistances also limit output current. Of course a short-circuit would damage an alternator.