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HELP new alternator popped and smoked when battery connected

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New User

Sep 8, 2016, 7:19 PM

Post #1 of 4 (1022 views)
HELP new alternator popped and smoked when battery connected Sign In

Hey everyone,

Not sure if this has been posted before but my search did not come up with results so I hope I am not repeating.

I am no expert mechanic and I am actually just trying to figure things out as I go with help from youtube and forums etc...

I have a 1991 Chevy s10 Blazer 4.3 v6 project vehicle. I drove it for a few days on a brand new battery and then let it sit and the battery went completely dead. I went to replace the alternator and serpentine belt today and everything was going smoothly until I went to connect the battery. After bolting down the new alternator I reconnected the wire harness and the 2 ring connectors to the bolt. I tightened them down pretty tight. The battery uses bolts rather than ring connections so I screwed in the negative and then when I got the positive in half way it started to arc. Before I could get it disconnected the new alternator popped, shot sparks and smoked for about a minute. It did not start on fire or anything. I put all the wires back the way they came off...I had disconnected and reconnected the new battery several times and nothing like this happened with the old alternator (possibly because it was dead already?)

I would appreciate any input on something I did incorrectly or thoughts on why this happened. I was thinking there may have been a short somewhere inside the alternator as the wires did not melt or smoke...all the smoke came from inside the alternator.


Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

Sep 9, 2016, 1:01 AM

Post #2 of 4 (1013 views)
Re: HELP new alternator popped and smoked when battery connected Sign In

This is tough and naturally lots of questions first.

Did you just get this vehicle for the purpose of learning some automotive repair?

It seems it worked a few days as you said till a new battery just went dead or you thought so? Did you test that out or try to recharge it or test anything?

For much of any battery/charging system work you need some basic tools and basic know how even at this age/vintage some basics haven't changed.

You need to have a battery charger, best if one that will automatically shut off, a volt/ohm meter, plain test light always handy, battery brush for cleaning connections and strongly suggest some dietetic grease for connections on hand for this and in general.
Add to the list a "memory saver" handy for all and super handy for newer vehicles than this.

Know how to use each tool.

# 1 basics: When disconnecting a battery always take negative off first and on last. Many reasons - the first is nothing is empowered till the last connection and the tool used to tighten the last one if it touches something that is ground wont matter if it's the ground battery terminal. Putting positive on last you can short out just with the tools if positive is put on last. Newer than this other reasons come into play.

So what was wrong with the first battery that it required replacement? Do you know if in fact it was bad?
You didn't say but specific to this and many GM vehicles the battery is held by a block and bolt from the bottom that is easily frozen and breaks off. Some difficult to properly repair and batteries get left loose or perhaps some creative way to hold it OR a proper hold-down kit to replace the original as specific vehicles will allow for room.

The GM side post battery terminals have been in total use since the very early 1970s - not new and same issues now as the first ones. The eyelet inside if rubber covered rots out and makes a weak connection or none at all so need to know those are good, cleaned and grease prevents future damage. It's unlikely these are originals but could be now rubber would be hard like plastic and impossible to take eyelets out to clean or even inspect very well.

Replacement cables may or may not be whole cables or color coded as RED or Black for positive and negative so easier to make mistakes and cross up which is which for connections or for jump starts, charging - anything to do with them.

I suspect somewhere recently this vehicle has suffered cables or a jump start was crossing polarity and some damage happened not mentioned or not known by you or admitted to just yet.

I'll quit the novel and it would be a whole series of books but for now your alternator for whatever reason near certainly has shorted inside itself newly rebuilt or not or just plain defective for any reason.

This battery could also be a dead short inside from running dead if it did at all really go low or dead showing zero voltage, fully drained at the battery bolts - the cables do not necessarily make contact to the battery well or at all so test by the bolts on GM side post type or others from the center posts for those the use "u-bolts" for batteries.

Perhaps for now gather up some of the tools mentioned.

I suggest the Black and Decker dual purpose battery maintainer/charger which is fully automatic but slow for charging. It will do rapid blinks if all is wrong. Oddly these are more available at Home Depot specifically more than automotive parts places in their tools section and have to ask for where they hid them that day! Might be at other places or on line as well just like that one and brand best myself in use right now. Still about $30 bucks and they are good but slow. Others do the same at double the cost and this one is weather proof not ever recommended to leave chargers out exposed to possible weather ever.

Everything begins with a known good and fully charged battery then some testing can be trusted,


New User

Sep 9, 2016, 1:25 AM

Post #3 of 4 (1010 views)
Re: HELP new alternator popped and smoked when battery connected Sign In

I got the vehicle in part to learn to work on it but it was running with working 4x4 so I could get more adventurous with my camping excursions.

I had the battery tested and it was only testing at about 54 of the theoretically available 600 so it was not actually DEAD DEAD...just mostly dead...I had it recharged for free as it is under a 2 year warranty. After charging the new battery tested at 600 again. The old battery tested at 0.

Sounds like the fact that I put the negative on first may have had something to do with it and I have also read that tightening the charging post nut too much on the alternator can cause a short so maybe that was part of it? The block that holds the battery in is in tact and works fine. I cleaned the connections with a brass brush prior to reconnecting and made them shiny again. I am fairly certain the wiring is original which may mean worn out since it is 25 years old? Not 100% on that though...

Tom Greenleaf
Ultimate Carjunky / Moderator
Tom Greenleaf profile image

Sep 9, 2016, 3:39 AM

Post #4 of 4 (1004 views)
Re: HELP new alternator popped and smoked when battery connected Sign In

Ok - I'm getting some of the picture with some guessing as to why stuff happened. Know that "automotive" batteries are plates and lead/acid electrolyte that must also keep plates inside (you don't see these anymore) separate so any trauma to even a good new battery can make on plate touch another inside.

Trauma can include just tipping them over, handling before or during you got it, even how it rides in vehicle. Those plates flake like dandruff to the bottom very slowly too so when that pile (unseen as well) reaches the bottom of plates the battery shorts out either moments or a show of instant failure - dangerous gasses. They seriously do NOT like being discharged or charged quickly! Odd - that's what you expect but not so with them unless specific types for harsh conditions and use - forget that for this.

When discharged or even low enough including strong usage by vehicle the alternator works hard trying to just leave the battery mostly out of the scene and at full charge as for the most part it's really only hard job is to crank the engine then part of stabilizing spikes and dips in usage while running.

So alternators that work hard get hot, very hot sometimes up to melting the plugs and wire insulation inside and outside them. That can make an alternator short, just quit charging or strange acting. That one will fail usually and sent out for a rebuild job of unknown what was done to fix it except they are nice and pretty all cleaned up you really don't know. If you got one the shorted and was fixed with only what was obvious you got a bad one. It does happen with some expected % unfortunately.

This in turn has harmed the battery and becomes ping-pong having them both good at the same time so there isn't a battle always going on which may be a lot of reason for you troubles.

The OE cables were tons better quality than what you will commonly find new. With just some care can last indefinitely.

Still need some tools so you can do some tests yourself. The main wire to the back of this alternator is hot all the time to the battery positive and subject to touching things - tools or any strange reason so a rubber boot was on it new (cable) which must be long gone. It's too close to fasten that with battery connected in many.

Other stresses on this exact problem. You said you tightened the terminals real tight? How tight do you mean which is hard to describe? You can easily strip the lead threaded hole of the battery with the bolt plus that is torqueing on the plates inside the battery so snug is good without overdoing tightening those there. IDK - go by tight enough so you can't twist cable easily and stop there.

For right now get some testing tools and things listed. Look at the current alternator and see if you get a glance inside at what looks like a braid of copper colored fine spaghetti if it's burned up and probably is. Each of those wires in that winding are isolated from each other and if can touch by heat or trauma will short out the alternator.

I know you are YouTubing and searching for all kinds of info. An awful lot will end up being your specific vehicle and what has happened to just yours not all that are out on video, forums or one hit idea. Many things on the web are plain wrong such that it's really up to you to know enough to know it's bull or not,


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