Capacitor exploded while soldering

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cory2067
 
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Capacitor exploded while soldering

Post by cory2067 »

So, I have previously had bad luck with my motor shield, and ended up destroying my arduino and the motor shield.

I just got a replacement, and my bad luck unfortunately continues.
While soldering on the headers, a capacitor (I think) exploded near the M3/M4 terminals.
Image
Can I salvage a capacitor from my other broken motor shield to fix this?

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adafruit_support_bill
 
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Re: Capacitor exploded while soldering

Post by adafruit_support_bill »

That is very strange. There are no solder joints nearby. Even so, I've never seen damage like that from a capacitor overheated in soldering. About the only way soldering could have caused that is if your soldering iron is defective and is injecting voltage into the circuit.

Capacitors explode like that if exposed to a reverse voltage, or a voltage much higher than they are rated for. With luck, that voltage did not cause damage to the ICs on the board too. You can probably replace the capacitor with one from your other shield, but I'd try to understand what caused the first one to blow.

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cory2067
 
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Re: Capacitor exploded while soldering

Post by cory2067 »

Hmm, I used a butane soldering iron.
Doesn't seem like that would be able to inject any voltage.

Edit: Anyway, swapping out the capacitor for the one on the other board was succesful, as far as I can tell. Ran a stepper on it for a couple minutes, seems normal.

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adafruit_support_bill
 
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Re: Capacitor exploded while soldering

Post by adafruit_support_bill »

Good. Glad that worked out for you.

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cory2067
 
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Re: Capacitor exploded while soldering

Post by cory2067 »

Interestingly, my poorly-soldered capacitor fell off, but the stepper continued running normally.
Is the capacitor even relevant to running steppers?

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adafruit_support_bill
 
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Re: Capacitor exploded while soldering

Post by adafruit_support_bill »

The capacitor is relevant, but not absolutely essential for operation. It helps to satisfy the instantaneous current demands of the motors. Your motor will probably run OK without it, but will have slightly less torque.

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adafruit_support_mike
 
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Re: Capacitor exploded while soldering

Post by adafruit_support_mike »

Thinking about it, you could probably blow a cap with simple heating.

Electrolytic caps explode because they contain a layer of paper soaked in a water-based dielectric. If the cap gets too hot, the water boils, creating steam. Liquid water is about 1300 times as dense as water vapor, so the steam *really* wants to expand. It can't do that while contained in the can, so the pressure rises until it breaches the can, and then bang.

A soldering iron will boil water too, so it's possible that heating the can or the leads long enough could make a cap pop off.

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DanGR
 
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Re: Capacitor exploded while soldering

Post by DanGR »

I have used a butane soldering iron for a few Adafruit boards including the motor shield. You have to be careful about where the flame heat is venting. Mine vents in a radial pattern so I have to be careful with the tip angle to keep the excess heat from the board.

Dan

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