I messed up, big spark, but not sure how

wattwatt

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May 21, 2018
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I needed to quickly test a 48v inverter just to make sure it actually works, so I grabbed four (4) 12v batteries to put them in series. The first battery is aAGM car starter battery (automotive post terminal), the second one is a solar AGM battery (1/4" inserted screw terminal) and the last twoare deep cycle AGM batteries (2 x 5/16" nut & bolt terminal). Again, this was just a quick test, just to make sure this inverter powers on.In my haste I started with the terminals opposite of me because they were harder to reach. First I connectedthe negative terminal of the car battery to the positive terminal of the next battery.Then I connected the positive of the car battery to negative of the next battery and that's when second battery's negative terminalgave a big ol'spark, it's1/4" screw broke off and part of the screw hole chipped off too. I figured my mistake was rushing and not paying attention to details likeconnecting the negative terminal first of the first/car battery instead of the positive terminal first. Then I thought maybe it was because the first/car battery pushed too many amps initially upon connection(hundreds of amps as if it was starting a car, maybe?) and the second battery's screw terminal just couldn't handle the current(side note:in previoustests with this second battery where I was using a 12v inverter,I could only pull 33 amps/400 watts before the voltage dropped significantly and the terminals got extremely hot). Then I realized I should know why and embarrassed I wasn't sure. I've connected batteries tens of times with no problems so far and obviously had some spark upon connecting to terminals, but never this big and this damaging.Any ideas why this sparked like this?


image_tuavxb.jpg


P.S. - I checked the voltage of both batteries in question after a couple of minutesand they still both had 12.6 volts, so I guess I didn't short them or destroythem...?
 

Korishan

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Glad you're ok.

First, it's hard to follow what happened considering you have only 1 paragraph and many run-on sentences.
Second, from what I could extrapolate is you connected Neg->Pos then Pos->Neg, but i can't tell if that was all 4 battery connected or not
Third, a bolt shouldn't get electrically sheered off from current flow like that with the level of equipment the average person, the most of us on this site, deals with. Especially at the low voltage you were working with.
Lastly, a lead acid battery can take a lot of abuse and be fine. They aren't as fragile as lithium batteries.
 

wattwatt

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May 21, 2018
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Korishan said:
Glad you're ok.

First, it's hard to follow what happened considering you have only 1 paragraph and many run-on sentences.
Second, from what I could extrapolate is you connected Neg->Pos then Pos->Neg, but i can't tell if that was all 4 battery connected or not
Third, a bolt shouldn't get electrically sheered off from current flow like that with the level of equipment the average person, the most of us on this site, deals with. Especially at the low voltage you were working with.
Lastly, a lead acid battery can take a lot of abuse and be fine. They aren't as fragile as lithium batteries.

Yes, I connected Neg->Pos then Pos->Neg then spark! This is just the first two batteries, to make the 24v leg of the series (the last 2 batteries weren't connected yet).
 

gokalex

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Apr 10, 2020
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Did you connect the two batteries in series (Negative of Battery1 with Positive of Battery2) and then short the main Positive with the main Negative (Positive of Battery1 with Negative of Battery2)?

That creates a short, and would explain the big spark and heating
 

daromer

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Nothing will happen when connecting batteries in series. Spark comes from short somewhere. So you must have had a connection all the way around or you did parallel 1 battery to another and therefore created the short.

Paralelling batteries wrong way around easily pushes 1000s of A between them causing a big nice bang and spark :D
 

Redpacket

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Feb 28, 2018
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You said you could only low amps from the battery #2 before the voltage dropped - this could be a symptom of terminal corrosion hence the terminal breaking when there was a short.
Ie the resistance in the corrosion worked like a fuse & "blew". Probably saved you from worse....
So like others have said, sounds like you connected two batteries in parallel & opposite polarity, effectively shorting 24V.

Series is 0V here > (-)[bat](+)<wire>(-)[bat](+)<wire>(-)[bat](+)<wire>(-)[bat](+) < +48V here
 

wattwatt

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May 21, 2018
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gokalex said:
Did you connect the two batteries in series (Negative of Battery1 with Positive of Battery2) and then short the main Positive with the main Negative (Positive of Battery1 with Negative of Battery2)?

That creates a short, and would explain the big spark and heating

Yup! This is what I did wrong - connect the positive of the first battery to the negative of the second battery causing a short. Wow, that's embarrassing. Chalk it up to rushing and cockiness.

Thanks everyone!
 
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