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Will bad battery damage alternator?
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Supernaut
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Feb 10, 2014, 12:05 AM
Post #1 of 10
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Will bad battery damage alternator?
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I have a 2004 Pontiac Sunfire with 345,000km (214,000mi) which I have had to abandon tonight and take a cab home. It was the classic signs of a dead alternator, voltage drops, won't start and eventually dead. The battery light came on intermittently so I parked at my local Canadian Tire and tried to see how long it would run. After about 10 min it was dead.
The obvious thing I need to do is go back and replace the alternator. However I knew since last summer this battery is on its final days at its original and showing signs of weakness last summer.
My questions as follows
Since this car is well used and I probably don't plan to have it for long, If I just change out the alternator can I run on that old battery for a day or so and maybe get a used one from a wrecking yard? Or if the battery has totally failed would that make it impossible to complete the electric circuit and run the engine? I could just get a new battery from Canadian Tire while I get the alternator from there, but I'm just wondering if there was a way to save a few bucks on this.
Though I highly doubt it, could there be a chance that this is just battery failure and the alternator may still be ok?
(This post was edited by Supernaut on Feb 10, 2014, 12:10 AM)
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Feb 10, 2014, 1:00 AM
Post #2 of 10
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Re: Will bad battery damage alternator?
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Battery and alternator depend on each other and can harm or kill each other. Test away - charge battery and test it then charging system right down to the belt tension.
If an alternator is overworked it gets hot and can fail new or used. Battery could fail from frequent cycling of states of charge and discharge. Also know since you said Canada that a very low charge on a battery the electrolyte (acid water in it) can freeze, damage likely up to cracking the thing, acid leaks out and can cause assorted problems just from that.
Both need to be good at the same time is the answer. If that isn't the fix alone it has to begin with that much,
T
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Hammer Time
Ultimate Carjunky
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Feb 10, 2014, 3:44 AM
Post #4 of 10
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Re: Will bad battery damage alternator?
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A bad alternator can ruin a good battery and a bad battery can ruin a good alternator so forget trying to get away with either one. Don't forget that there are other possible reasons for an alternator not to work beside the alternator itself being bad.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Feb 10, 2014, 3:57 AM
Post #5 of 10
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Re: Will bad battery damage alternator?
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Quote">>
Hypothetically speaking. If the battery had failed and the engine is running. Should the alternator (assuming that its working) be able to power the car indefinitely as long as it is running? Or would a failed battery break the circuit and the whole electric system fail?<<"
If battery became a dead short inside car would quit w unknown electrical problems/damage. A working alternator requires at least a partially charged battery or can't work. If "alternators" are exposed to running engine with NO battery either removed or a wild total failure damage is likely to occur and car may run for a short while and should quit. DON'T DO THAT as it can/will harm expensive electrical things. That is NOT a test of a good alternator either. That dates back to "Generators" which are not used anymore in cars for ages.
As said first time both need be OK for each other. Rock and hard place with dead/flat batteries as you don't want to speed charge them either as battery doesn't like that much on or off car charging.
Normal is battery starts the engine, alternator restores what it just took to crank it and remains fully charged while running and can cover quick spikes of electrical use beyond alternator but not forever. Hope that gives you the idea,
T
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Discretesignals
Ultimate Carjunky
/ Moderator
Feb 10, 2014, 5:44 AM
Post #6 of 10
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Re: Will bad battery damage alternator?
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Another thing also is the alternator in your car wasn't designed to recharge a dead battery. That is why they make battery chargers. The alternator is designed to maintain a battery's charge and to provide power to the vehicle's electrical system. Using an alternator to charge a dead battery is one good way to destroy an alternator.
Since we volunteer our time and knowledge, we ask for you to please follow up when a problem is resolved.
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Supernaut
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Feb 10, 2014, 6:09 AM
Post #7 of 10
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Re: Will bad battery damage alternator?
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All good advice. I'll have to find a ride into town, pick up a new alt and battery at the Canadian Tire. Call my towing service to bring the car and parts home so I can work on it with some shred of comfort. Good thing its probably the coldest day so far this year at -30c and I don't have a garage. 
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Tom Greenleaf
Ultimate Carjunky
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Feb 10, 2014, 7:02 AM
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Re: Will bad battery damage alternator?
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Cool thing that I think many people should own, small and inexpensive is a battery "Maintainer/Charger" fully automatic on and off when done.
SLOW! But cheap. Assorted brands of them. Can clip direct to battery, put in power port not for every model so AYOR if done that way. Benefit is small and cheap. (still about $20ish USD) Does require 110 house current. That could be a snag if you needed an extension cord where vehicle is. Something just right or not with assorted widgets and gadgets but these are great for low use, seasonal stuff and if you are not in a hurry, Tom
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Supernaut
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Feb 17, 2014, 11:29 PM
Post #9 of 10
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Re: Will bad battery damage alternator?
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I have the problem all squared away. I bummed a ride to the Canadian tire in town from the nice old lady who lives next door (I live 30km out in the country) where my car was abandoned and the store conveniently had a new battery and alternator in stock for me. I had my tow service, which was well worth the $75 for the year which gives 5 tows, bring me and my car home so I could fix it in the driveway.
The old battery was not leaking but at a glance it seemed to have been somewhat bulged out on the ends which suggests it may have froze. For Sh!ts and giggles I charged up the old battery to see what would happen. It charged to 13.4 volts and had dropped to 12.5 by the next day.
The alternator wasn't too bad to change out as the GM "J-body" cars have a large engine bay for a small car, and the ecotec engine and connected systems as a unit seems pretty well organized.
With a new (rebuilt) alternator and battery that's one less thing to worry about. Maybe I'll even get another 100k out of the old bugger... not that I exactly want to keep it around that long.
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Tom Greenleaf
Ultimate Carjunky
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Feb 18, 2014, 3:23 AM
Post #10 of 10
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Re: Will bad battery damage alternator?
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Just notes now as it seems you are all set now:
Dead batteries can freeze the "electrolyte" (battery acid) and not leak or crack the case but damage is likely brand new one or not. Just had one left in windy below zero Fahrenheit temps go dead. Didn't leak but not response from the dang thing.
Like you I charged it up mostly just to see and it did! Your reading for volts alone where fine but you don't know if it could deliver the AMPS (power) it should be able to just from that reading.
I don't trust a battery that has frozen especially now new. One in my hands was ~ 6 years old never to be used again but probably would in that one case but not good as it showed signs that the cold had made it short inside itself - a real problem and horror show if one does that while installed and driving - seen it - yikes. Those can not only harm all sorts of things but plain explode blowing a hood right off! They can fail to produce lots of hydrogen gas quickly sometimes you can smell a tell-tale rotten egg like odor.
If or when a battery is flat dead there's risk in even charging it, best to do so out of vehicle and out of harm's way well ventilated but probably best to toss those known to have frozen.
Battery killers include: Fast charging, vibration or trauma, running to low charge too much, heat isn't their friend either and the cause of many surprise failures. Plain age makes the failure rate much more likely. Know how old your battery is best from the month it was made not just when you purchased it! They are marked either boldly or encrypted on the case of them.
One more: Not all of even same rated new batteries are equal in quality. It's hard (for me anyway) to get "brand" loyal about them anymore. Cheap is not a bargain with the things - trust me,
T
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