One of my co-workers semi-melted a wrench on a car battery yesterday and it prompted a discussion that we couldn’t resolve to our satisfaction; to whit, what would happen if you poured a steady stream of ball bearings on a car battery? would they fuse and melt or just continue to bounce and make the area mechanically unsafe to walk around? Let’s assume we use the same battery my friend did, a Series 34 Optima RedTop 800 CCA fully charged and you have a bucket full of Series 200 chrome steel bearings. Thoughts?
I don’t think ball bearings would be in contact with both terminals of the battery for any length of time.
Ball bearing density would be an issue.
One bearing every few seconds would be nothing. A completely full bucket with a (plastic) lid, turned over practically on top of the battery and the lid very quickly removed would cause enough sparking to get, um, results.
We need more data.
A ball bearing, by itself, it’s going to be connected to anything so it should bounce off harmlessly. This is only going to be an issue if the bearings are in contact with each other during this process and the reservoir of ball bearings is grounded, right?
This would have been an outstanding Mythbusters episode.
I don’t think any particular path of individual ball bearings between the terminals would exist long enough for any welding to occur, so at best you’d get some occasional sparking.
Yeah, individually they wouldn’t do anything, any more than pouring water on one terminal would. But a sufficient flow would bridge the gap, I would think, something about the size of a bicycle ball bearings. The real question is whether they would arc weld together or just sputter and spark a bit. Surprisingly, I haven’t seen anyone do this on Youtube which is my normal go-to for stupid things I want to do but am now old enough not to. The wrench glowed red in a very short period of time and deformed in about two seconds, so…
I might have missed, but: Was the wrench laid across both terminals, completing a circuit?
Inadvertently, yes. We were installing it in some equipment and the wrench contacted the +ve and _ve terminals. Very sparky and a cheery red glow to light up an otherwise frustrating afternoon…
I’m a little surprised it got that hot that fast. Sparks, I’d expect – but not an entire wrench melting (even partially) within a few seconds. Or was it longer?
An auto battery can supply, what, 35A? That’s 420 Watts. It doesn’t seem it would heat up a wrench that much.
Anyway, I’m not going to try this at home.
From the OP. “Series 34 Optima RedTop 800 CCA fully charged”…
That’s 880 cold cranking amps. 880 A times 12 volts = 10560 watts through a dead short.
That’s a nominal 12 volts. Car batteries usually test at 12.6 V fully charged.
I might melt a wrench at that. 
Oh it did. The really cool thing is you show someone that, then you stick your fingers on the battery terminals after they cool down. Nothing happens. It still makes you twitchy trying it though, even if science is on your side. i really do want to know what happens with the ball bearing scenario, but I’m reluctant to try it because a dead short across a battery, especially something as large as a car battery, can cause it to explode. Maybe a call to Mythbusters might still be in order.
OK, so what’s the science behind the wrench melting? Is it because the metal that the wrench is made of (aluminum?) has a suprisingly high resistance and thus throws off plenty of heat even while conducting current?
Unless you put the battery in the bottom of a barrel and poured enough ball bearings in so it was sitting under a pile of them, I’m sure nothing beyond maybe a spark or 2 would happen - in the randomness of the bearings bouncing around, you’d at best have a momentary circuit path, certainly not enough for any welding or melting to occur.
The great thing about Mythbusters is that they’d keep upping the ante over the course of the episode until something happened. So they’d probably wind up with a huge series/parallel network of batteries to get the voltage up to 1200 DC and 50,000 amps, then drop 50 cubic meters of ball bearings onto the 2 terminals.
You are adding a lot of energy to the material and it can’t transfer enough to it’s environment. So it heats up.
Makes sense, but I thought it was somewhat different with an electrical current.
Obviously, electrical wires in a circuit can get quite hot – well able to both shock you and give you a nasty burn.
But in the OP’s situation … shouldn’t the electrical energy be traveling through the aluminum fairly freely (at least compared to an insulating material like wood, rubber, etc.)? I know aluminum conducts electricity … but I don’t know how good of a conductor it is compared other metals. So something is making the aluminum wrench heat up rather than transfer a higher percentage of that electrical energy between the batteries two poles.
And I’m assuming aluminum, anyway. Maybe the wrench is made of a cheap alloy that conducts electricity a little more poorly? Don’t know.
You are taking an amount of energy that will turn over a truck motor, and producing heat with it. A lot of heat.
Not aluminum, a decent quality CrVa 10mm steel combo wrench with a box end ratchet. If I get the chance, I’ll find it and post a pic. Things like this are why playing with car batteries can be dangerous if you don’t know what you’re doing.
muldoonthief, that made me smile. Now I really want to see it happen!
The lowest setting on a welding machine is around often around the sixteen volts mark, just laying a spanner across a batteries terminals will easily melt it. You see thirty six volt batteries nowadays based on lithium chemistry ,the higher voltage gives better efficiency out of an electric motor but a bit scary if it gets shorted.