what next?...
4 eyed Lizards? lol
- Seriously, 4 legs?!
[quote author=ebay-selller ]
no worry about the quality[/quote]My mind is at ease now 
strykeroz:
[quote author=ebay-selller ]
no worry about the quality
My mind is at ease now
[/quote]
Joking aside, they actually sell them on digikey, etc:
And yes, they can discharge at 237 amps. (although they're only rated for a pathetic 86 amps). That's quite scary...
Soooo the other 2 legs? What do they do?
cjdelphi:
Soooo the other 2 legs? What do they do?
They're "blank". Probably for keying it — so it can't be hooked up backwards?
2.7v, 400f. Hmmmm.
Sub this into a solar pummer circuit somehow? Would it drive a standard LED all night?
cjdelphi:
Soooo the other 2 legs? What do they do?
Have you ever connected an electrolytic capacitor backwards? (If not, try it...)
Now imagine doing it with a 400 Farad device...
bigred1212:
2.7v, 400f. Hmmmm.Sub this into a solar pummer circuit somehow? Would it drive a standard LED all night?
If it can do 86 amps for 5 seconds then it can do 20mA for about six hours...but that's to discharge to half voltage so your LED would be dim. If you run at 10mA you might be OK but it would take two connected in series to keep your LED at 20mA all night.
Hmmm. I would have thought "connected in parallel" not series.
Capacitors with extra legs are not uncommon. The extra legs serve TWO purposes. The first is to "key" the capacitor such that it only fits into the circuit one wya. When working with this level of energy density it is a good idea to do this. Second, they serve as additional mechanical connections to the board in order to stabilize and support the capacitor. These capacitors are large and heavy; note that it is 64mm (2.44 inches) long and 35mm (1.38mm) wide and weights 67g. This will have significant force in areas subject to vibration, often enough to either pull out the leads, break the solder joint or worse pull the cap right out of the board. As such, it is actually quite common to find 3 and 4 legged capacitors in larger can sizes. I have some Mallory caps in an old (but VERY nice) HP Precision 6114A power supply that have three and four legs. They are quite large (the largest is roughly the diameter of a can of red bull.
cjdelphi:
Soooo the other 2 legs? What do they do?
Partly for mechanical support, to protect against vibration fatiguing the other leads.
strykeroz:
[quote author=ebay-selller ]
no worry about the quality
My mind is at ease now
[/quote]
we have sold many in our other shop, and all positive feedback, so you can buy directlly. no worry about the quality.
We only have to worry about the spelling.
I have 2 400F caps and 2 200F caps.... i'm a little too scared to wire them wrongly, i have an attiny85 driving a 7hc595 and it goes for around 3 - 4 hours before the leds dim too much (wired in series making 5v)
cjdelphi:
Soooo the other 2 legs? What do they do?
3-6 legs is common for "snap-in" style capacitors like this one.
Primarily they provide mechanical stability. They can also help to reduce the ESR.
I found this 1 legged transistor with arms.
bigred1212:
Hmmm. I would have thought "connected in parallel" not series.
A white LED won't even make it to 20mA at 2.7V.
fungus:
If it can do 86 amps for 5 seconds then it can do 20mA for about six hours...but that's to discharge to half voltage so your LED would be dim. If you run at 10mA you might be OK but it would take two connected in series to keep your LED at 20mA all night.
For a capacitor, the fundamental equation is Q = CV where C is the capacitance, V is the change in voltage, and Q is charge. If the current is constant, then Q can be replace by It, where I is current and t is time. So if you charge your 400F capacitor to some known voltage and then discharge it at a constant 20mA, it will take (400 * 1)/0.02 = 20000 seconds (about 5h30min) for the voltage to drop by 1v.
In practice, to drive any LED other than a red one, you would need to use a boost converter.
dc42:
In practice, to drive any LED other than a red one, you would need to use a boost converter.
Or two of them in series.
fungus:
dc42:
In practice, to drive any LED other than a red one, you would need to use a boost converter.Or two of them in series.
Yes, but then you would have the problem of making sure that they charge equally. A switch mode converter would also make use of the energy more efficient than a series resistor or linear current regulator.
dc42:
Yes, but then you would have the problem of making sure that they charge equally.
Making a switch mode converter work well down to 1V isn't much easier...