Supercapacitors

[kiloran]

Worth adding that those capacitors are incredibly dangerous, even the garden shed version could probably kill you if you touched the wrong bits, so safety is a big issue.

While it's true that, as the old saying goes, it's mills that kills and volts that jolts (mills = milliamperes, i.e. current), and it's generally reckoned that 100mA is lethal, with as little as 10mA being able to cause muscle contractions, these 400F capacitors are just 2.7V each.

So, with the guy having wired eight in series the bank will be charged to only 21.6V, and while the effective 50F of the bank will store a lot of coulombs, the "mills" that flow out of it will depend on body resistance and it's extremely unlikely that you'll get even a mild shock from the 21.6V ... unless you connected one side to, say, the inside of your mouth and the other side to another soft and moist part of your anatomy.

For someone who was into electronics in his yoof, when 400 micro Farad electrolytics were considered big, these supercapacitors are kinda gob smacking ... indeed, I remember our physics teacher at school (quite a few decades ago now!) telling us that a one farad capacitor would have to be the size of a house ... although maybe he was talking about Leyden jars ....

Perhaps it's the thought of an accidental short-circuit across the capacitor terminals which causes alarm. A short across battery terminals would not be good news for sure, but I suspect a short across a charged 400F capacitor might cuase a sudden and significant explosion to the detriment of the capacitor and any nearby human.

--kiloran

[mc2fool]

While it's true that, as the old saying goes, it's mills that kills and volts that jolts (mills = milliamperes, i.e. current), and it's generally reckoned that 100mA is lethal, with as little as 10mA being able to cause muscle contractions, these 400F capacitors are just 2.7V each.

So, with the guy having wired eight in series the bank will be charged to only 21.6V, and while the effective 50F of the bank will store a lot of coulombs, the "mills" that flow out of it will depend on body resistance and it's extremely unlikely that you'll get even a mild shock from the 21.6V ... unless you connected one side to, say, the inside of your mouth and the other side to another soft and moist part of your anatomy.

For someone who was into electronics in his yoof, when 400 micro Farad electrolytics were considered big, these supercapacitors are kinda gob smacking ... indeed, I remember our physics teacher at school (quite a few decades ago now!) telling us that a one farad capacitor would have to be the size of a house ... although maybe he was talking about Leyden jars ....

Perhaps it's the thought of an accidental short-circuit across the capacitor terminals which causes alarm. A short across battery terminals would not be good news for sure, but I suspect a short across a charged 400F capacitor might cuase a sudden and significant explosion to the detriment of the capacitor and any nearby human.

--kiloran

Indeed, and reminds me of a story from someone I knew a while back who was out shopping for a marine battery (like a car battery but larger capacity and deep cycle-able), and decided to check the spacing between the terminals of one ... using a metal tape measure.

There was apparently an almighty flash and bang, and a good part of that section of the tape just disappeared. Fortunately nobody was hurt (other than with totally red faced "I don't believe I did that" embarrassment under the "we don't believe you did that" stares from others in the shop!) but he did have to buy the battery 'cos of the cosmetic damage on the top....

[kiloran]

Indeed, and reminds me of a story from someone I knew a while back who was out shopping for a marine battery (like a car battery but larger capacity and deep cycle-able), and decided to check the spacing between the terminals of one ... using a metal tape measure.

There was apparently an almighty flash and bang, and a good part of that section of the tape just disappeared. Fortunately nobody was hurt (other than with totally red faced "I don't believe I did that" embarrassment under the "we don't believe you did that" stares from others in the shop!) but he did have to buy the battery 'cos of the cosmetic damage on the top....

And going further off-topic, that reminds me of a capacitor-related event back in the early 70s. I was working in a development lab designing phones and other bits of telecoms gubbins for the GPO (now BT). One of the tests we had to perform on equipment was a lightning test, to conform to a GPO spec. We had a special test rig for this, consisting of a bank of capacitors which could be charged up to 10kV. This was connected to the equipment by a Heath-Robinson switch, a modified rat trap which snapped onto a lead bed, the idea being that it would be an instant connection with no bounce. The rat trap was triggered by a hand-held 3ft rod of perspex. One day, some guys were testing a phone (might have been a TrimPhone, remember them?), and there was a mighty bang and the innards of the phone flew out of the plastic case, sailed down the lab and hit the lab manager on the back of his head. Ah, those were the days, fresh out of Uni and messing about with high voltages.

--kiloran

[GoSeigen]

Worth adding that those capacitors are incredibly dangerous, even the garden shed version could probably kill you if you touched the wrong bits, so safety is a big issue.

While it's true that, as the old saying goes, it's mills that kills and volts that jolts (mills = milliamperes, i.e. current), and it's generally reckoned that 100mA is lethal, with as little as 10mA being able to cause muscle contractions, these 400F capacitors are just 2.7V each.

So, with the guy having wired eight in series the bank will be charged to only 21.6V, and while the effective 50F of the bank will store a lot of coulombs, the "mills" that flow out of it will depend on body resistance and it's extremely unlikely that you'll get even a mild shock from the 21.6V ... unless you connected one side to, say, the inside of your mouth and the other side to another soft and moist part of your anatomy.

For someone who was into electronics in his yoof, when 400 micro Farad electrolytics were considered big, these supercapacitors are kinda gob smacking ... indeed, I remember our physics teacher at school (quite a few decades ago now!) telling us that a one farad capacitor would have to be the size of a house ... although maybe he was talking about Leyden jars ....

Ah I stand corrected. I didn't pay attention to the voltage of the shed bike system and just assumed it would be somewhat higher.

GS

[Gerry557]

I remember late on evening riding back to Didcot along a cycle way under some pylons. I could see sparks tracking in my mates carbon seat post.

[UncleEbenezer]

I remember late on evening riding back to Didcot along a cycle way under some pylons. I could see sparks tracking in my mates[sic] carbon seat post.

What was he wearing? Sparks come from static: for example, walking on the carpets of some offices I've worked in.