Steptoe Posted May 7, 2019 Share Posted May 7, 2019 Just wondering if a deteriorating battery harms alternator? No problems but just wondering as my old faithful heavy duty battery started to Peter out on cold cranking to get the old propane out and fresh stuff in to ignite. I found a suitable battery dumped in a carpark and grabbed it because old batteries can be useful but found it looked fairly new, charged it slowly over 36 hours and let it sit for a month or so. Swapped in without further charge - feels strong. So wondering if alternators get sick of charging old batteries not holding the cold cranking power Quote Link to comment Share on other sites More sharing options...
DaveT Posted May 7, 2019 Share Posted May 7, 2019 Only if the battery was so bad as to draw too much current. But it wouldn't likely hold charge for long if it were that bad. How old is the old battery? 5 years under ideal conditions is usually end of life by the specifications for flooded cell lead acid batteries. If the battery is over sized, it can continue to start the car for a year or 2 longer, but it won't have the CCA or reserve it did when new. Btw, ideal conditions are rarely found under the hood of a car. How many miles are.on the alternator? Every one of my OEM EA82 alternators wore out a brush at about 150k miles which reduces output until it won't charge the battery. And this failure mode doesn't light the alternator light on the dash until it is very far along, and then only very dimly. Have to be somewhere dark and look for it faintly glowing at idle. Quote Link to comment Share on other sites More sharing options...
naru2 Posted May 7, 2019 Share Posted May 7, 2019 The harder it charges,the quicker the brushes wear. Quote Link to comment Share on other sites More sharing options...
somick Posted May 7, 2019 Share Posted May 7, 2019 1 hour ago, naru2 said: The harder it charges,the quicker the brushes wear. Why? Probably the springs push harder on the brushes? Quote Link to comment Share on other sites More sharing options...
naru2 Posted May 7, 2019 Share Posted May 7, 2019 40 minutes ago, somick said: Why? Probably the springs push harder on the brushes? Because the field current thru the brushes is higher when charging harder. I`ve heard of new alternators(GM?) failing in short order after trying to charge quite dead(but otherwise good) batteries.Not sure if they were brush failures. They want you to charge the battery before swapping alternators. 1 Quote Link to comment Share on other sites More sharing options...
DaveT Posted May 7, 2019 Share Posted May 7, 2019 Normally, as batteries age, they get higher internal resistance. Not going to cause more current from the alternator. Higher current might accelerate brush eear, but I have no hard data on that. Brush pressure is from a spring, that does not change with current. A very thoroughly discharged but good battery can draw a lot of current. Might be able to fry the regulator or rectifier in a marginally designed alternator. Quote Link to comment Share on other sites More sharing options...
naru2 Posted May 7, 2019 Share Posted May 7, 2019 Here is some hard data for you http://www.j-mst.org/On_line/admin/files/07-M1-C-09-109_37-41-42백_.pdf Fuel pumps trying to push thru plugged filters wear out quickly for the same reason. I beg to differ,as batteries age they have less reserve capacity and a cold start will discharge them more deeply requiring higher charging current. Quote Link to comment Share on other sites More sharing options...
idosubaru Posted May 7, 2019 Share Posted May 7, 2019 8 hours ago, Steptoe said: I found a suitable battery dumped in a carpark and grabbed it is anyone else laughing at this? you found a battery? that's awesome! but i'd also be a little suspicious. is there a way to load test that or do a more thorough test than basic voltage/starts the car test? in my experience batteries don't take well to sitting or being exposed. Quote Link to comment Share on other sites More sharing options...
GeneralDisorder Posted May 8, 2019 Share Posted May 8, 2019 It is hard on alternators to "charge" a battery. This is NOT the alternators job. The alternator is there to provide electrical power for the vehicle and to replenish the relatively small amount of lost charge due to starting. The battery is also essentially a giant capacitor that smooths out the system. A bad battery that discharges when sitting will absolutely put a heavy load on the alternator resulting in premature failure. We OFTEN replace the battery (and terminals) at the same time we are replacing the alternator. And yes all alternators come with warnings that the battery should be charged or replaced prior to installation and operation. GD Quote Link to comment Share on other sites More sharing options...
Steptoe Posted May 9, 2019 Author Share Posted May 9, 2019 Wow hot topic! Thanks for the input. There are people out there with more money than brains. Likely had an alternator on its way out without knowing it. Battery is dead, so buy, beg,borrow or pinch another to keep rolling.....and ... just dump the dead one at their convenience. This find makes up for the time I grabbed a nice battery on the road side. Unknowingly at the time it leaked acid onto my new work strides. Don't know what that does? Try it on an old rag sometime The alternator is an AC Delco reman from Rock USA and only 30,000 km old if that. The General makes a good point in not using alternator to fill an empty battery for best alternator life. The old battery was about six years old and had been given to me by electrical engineer of all things coz he thought it was dead , good only for workshop testing etc I found out otherwise, got me through two winters and 65,000 km ! Quote Link to comment Share on other sites More sharing options...
sparkyboy Posted May 9, 2019 Share Posted May 9, 2019 (edited) Car batteries are the weirdest things, my factory Subaru Panasonic battery lasted 10 years! My oldest is six years old still good! Our family car, 1953 bel air has a 6 volt electrical system and the starter gets too hot for the battery to turn over on long drives. And 2 speed auto trans lol! Those use generators to maintain charge. Edited May 9, 2019 by sparkyboy Quote Link to comment Share on other sites More sharing options...
1 Lucky Texan Posted May 9, 2019 Share Posted May 9, 2019 had a 51 chevy with a generator - you REALLY need good grounds for those to be trouble free. (hated the stupid vacuum wipers - terrifiying trying to pass a semi in the rain!!!) 1 Quote Link to comment Share on other sites More sharing options...
carfreak85 Posted May 9, 2019 Share Posted May 9, 2019 3 hours ago, 1 Lucky Texan said: (hated the stupid vacuum wipers - terrifiying trying to pass a semi in the rain!!!) My Dad has voiced similar complaints about some of his first vehicles, his ire was towards a '48 Ford wagon, however. Also bad when shifting in heavy rain... 1 Quote Link to comment Share on other sites More sharing options...
sparkyboy Posted May 10, 2019 Share Posted May 10, 2019 Ford used vaccum actuated wipers well into the 80s! lol! Now the best part about post war era american cars were the 4 wheel drum brakes of course! It's funny that those cars were never considered dangerous but the little bitty corvair was a deathtrap cause politicians here couldn't wrap their heads around driving a chevy like a porsche! Anyway back to alternators...It's considered a wear part since there is typically a core charge and they will give you money back to have your old part rebuilt. Anyone here rebuilt one themselves? I understand subaru starters are easy to rebuild as well if you truly have nothing better to do ha! But a rebuild kit like $15, new alternator $100 or so? I have some old ones but i think they are still good! cheers boys Quote Link to comment Share on other sites More sharing options...
DaveT Posted May 10, 2019 Share Posted May 10, 2019 I have rebuilt many alternators, never bought a new or reman one. aspwholesale.com has just about every part for them. 1 1 Quote Link to comment Share on other sites More sharing options...
carfreak85 Posted May 10, 2019 Share Posted May 10, 2019 (edited) 11 hours ago, sparkyboy said: Anyone here rebuilt one themselves? I replaced the brushes in the alternator in my Tercel. $4 in parts, some time soldering and bam, good as new. I should mention that this was not the original alternator, but a remanned unit. Edited May 10, 2019 by carfreak85 2 Quote Link to comment Share on other sites More sharing options...
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