Blowing up capacitors

[Max Demian]

I would have thought that a supercapacitor has as many volts as you charge it to (if it can stand it). It's only chemical batteries that will have a particular voltage due to electrochemistry.

[Mark Lloyd]

[snip]

I thought the usual maximum was 5.1V.

[Jim Jackson]

I think you misunderstand. The voltage quoted is the maximum voltage that can be applied. SuperCaps often have quite a low Max. voltage.

[invalid unparseable]

You don't have to put "three" 12V lead acids in series to see the adverse effect. A 12V lead acid battery is in itself 6 lead acid cells in series. That's why when you over-discharge a 12V lead acid battery, you risk killing the weakest cell by being reversely charged from the electric current driven the remaining good cells in the circuit, and then the second weakest cell will be the next to go.

I have bought some gel-ball toy guns from Amazon recently. Most of them use 7.4V lithium-ion battery pack. Each 7.4V is two 3.7V connected in series. I notice that the charger is designed to charge the internal

3.7V separately. The charging plug is 4-prong. That will eliminate the risk of overcharging each 3.7V and thus weakening it.

[The Natural Philosopher]

Bollocks. Think lightning. Air is not a chemical insulator

[Commander Kinsey]

I've never seen one.

[Commander Kinsey]

I've never seen one.

[Commander Kinsey]

I've never seen one.

[Max Demian]

Why 5.1 and not 5?

[The Natural Philosopher]

E24 series standard logarithimic progession

1.0 1.1 1.2 1.3 1.5 1.6 1.8 2.0 2.2 2.4 2.7 3.0 3.3 3.6 3.9 4.3 4.7 5.1 5.6 6.2 6.8 7.5 8.2 9.1

[Clive Arthur]

Small low-voltage electrolytics have been used in the past for film effects. Buried in plaster and wired to a big selector switch connected to a high voltage (probably mains), they make a convincing machine gun effect when the switch is rotated and bullets appear to spray along the wall.

I used to have some baked bean can sized 400V electrolytics from a skip. Charged up from the mains through a diode (and maybe a lamp, though I don't remember that), they'd make impressive holes in your sandwich wrapping foil at school when you threw it on them. It never crossed my mind that they could have blown up.

[Mark Lloyd]

Could it be because a 5V power supply may not be EXACTLY 5V?

[Commander Kinsey]

It is assumed when one cell of a battery goes, the whole battery was almost ready to throw out anyway. But if one cell of a poor battery dies, it can take out an entire good battery.

What I did with my electric drill, which used to be NiCad, was I put in Li Ion cells instead. The charger I removed the circuitry from and just use it as a connector to the battery and use a bench power supply, set at 4.2V per cell and a sensible max current. Inside the battery pack, I connected a cheap (a few dollars) equaliser, which boosts the weakest cell from the strongest at all times, charging, discharging, or idling. I have the same on my UPS battery system with lead acids. They could put one inside a lead acid for each of the 6 cells.

[Commander Kinsey]

Why would they blow up? You weren't exceeding 400V, or were you using 3 phase?

[Commander Kinsey]

What?

[Commander Kinsey]

Isn't it more to do with what nature wants and not us? We didn't want NiCad batteries to be 1.2V. 1.5V would have worked better to replace duracells.

[invalid unparseable]

I have not seen a 12V lead acid battery that provides easy access to the

6 internal cells.

The 2-cell, 4-connector setup is the ultimate solution to prevent charging the 2 internal cells in series. The 7.4V battery charger has two sets of 3.7V charging circuits to connect to the two 3.7V cells individually through the 4-prong plug. When the battery is unplugged from the charger and plugged back into the toy, the toy's 4-prong receptacle visually has a short wire shorting out the #2 and #3 to connect the two internals cells in series, and use #1 and #4 to connect the combined 7.4V to the toy. It will be quite tedious to apply this principle to a 6-cell, 12V battery.

[John J]

Poly Chlorinated Biphenyl anyone?

[Bob Eager]

Back in the 1960s, I thinbk it was relatively common. The interconnects were on top of the case, not inside, and one could tap at whatever multiple of ~2v one desired.

[jon]

True