How long can you drive a car with a broken alternator with a freshly charged battery?
January 3, 2004 4:55 AM   Subscribe

How long can you drive a car with a broken alternator with a freshly charged battery? [more inside]

I picked up a POS car a month or so ago because my previous car got destroyed in a freak snow/hail/rain storm/flood (in L.A.?). The car has something wrong with it's electrical system. Tonight the car just stopped and after hassling with it for a while it became obvious that the car was not getting any energy from the alternator. I would jump start the car but a minute after disconnecting the jump cable the car would die again. So I'm thinking I can pull the battery, charge it, put it back in and drive the car to my mechanic. My mechanic is about twenty miles from where I'm at. Does this plan make any sense?
posted by rdr to Travel & Transportation (11 answers total)
Go during the day when you don't need headlights. No radio or fan on the heat or A/C either. You should be fine. IF it is the alternator.
posted by spartacusroosevelt at 5:44 AM on January 3, 2004

What spartacusetc said. Many, many years ago I drove VW Bug for about three months just charging the battery each night at home. I seem to recall once getting 30 miles *with* the lights on. Your mileage may vary.
posted by mojohand at 6:03 AM on January 3, 2004

This sounds stupid, but it's often overlooked-- make sure that it's not a simple bad connection from the battery posts to the terminals. It's possible that there's a bad connection due to corrosion, wear or loose fit and when you're jumping it, you're really just moving the terminals slightly and restoring the connection temporarily. I've seen this personally on a few occasions.

Grab a wrench and disconnect the terminals. Clean the posts and the terminals and reconnect the terminals so that they're in at least a slightly different position from where they are now and quite tight. Additionally, make sure that they battery is still capable of even holding a charge. Either of these are as likely suspects as the alternator and a lot cheaper to correct.
posted by Mayor Curley at 6:15 AM on January 3, 2004 [1 favorite]

Your mileage may vary.

posted by dash_slot- at 7:39 AM on January 3, 2004

it's also possible the battery simply won't hold a charge anymore.
posted by quonsar at 8:05 AM on January 3, 2004

You can drive a damn long time if you have a solar panel on your car roof to re-charge the battery.

Otherwise......if you give the battery a full charge (overnight is best) you've got an excellent shot at making it those 20 miles, especially during the day with your car headlights off. But bring your jumper cables along! (also - no radio, heater fan, no nuthin' - save the juice for the ignition and your car will go a lot further)
posted by troutfishing at 10:23 AM on January 3, 2004

I once drove an old hulking station wagon around Ventura county for about three days with the alternator out. It was only when I got caught out after dark on the third day (and the lights ran for about 15 minutes before dying) that I was in trouble. Older cars doen't need much electricity at all to start and very little to run.

I would like to know if anyone knows about increased electricity demands of cars with more modern electronics, though.
posted by weston at 10:23 AM on January 3, 2004

From personal experience on a 1986 Toyota Corolla with 170K miles on it and enough other problems for it to qualify for "just run it until it stops" mode: A 12+ hour charge usually gave me enough juice for a 28-mile workday roundtrip, plus going out on a 1-mile-or-less lunchhour errand (2 starts) and putting on the lights for the trip home. I already had a charger, and I ended up getting a used battery for $20 as a backup if I miscalculated (or, as happened once, a traffic jam left me creeping at 10MPH for a half hour with the lights on). The car eventually died of other causes (leaky radiator and overheating).
posted by wendell at 11:57 AM on January 3, 2004

Well, one time my generator went out on my VW bus and I drove it basically from indianapolis to St. Louis (250 miles) on a single full battery.

Might not get that far on a car with EFI, but if I were in your situation, I would Bring a spare battery and stay in the slow lane in case I had to get to the shoulder quick. People can and do die getting creamed while being broken down in the way of traffic.

In the end it is your decision, and your judgement that counts here. While myself or others might be comfortable taking the risk, you are responsible for your own safety. Decide accordingly.
posted by jester69 at 1:49 PM on January 3, 2004

How long can you drive a car with a broken alternator with a freshly charged battery?

not long, esp if you need that battery to start the car.

what Q said.
posted by clavdivs at 3:23 PM on January 3, 2004

Thanks for the answers. I can't tell you the outcome of the experiment because it turns out that my sister has AAA^2 and they towed the car.
posted by rdr at 2:31 AM on January 4, 2004

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