Diodes for capacitor balancing?

[AMI CUSTOMS]

In electronic lab, every diode I have ever tested has a .7 volt drop across the diode.

[SnowDrifter]

Explain to me how in a series bank you would have some running at 2 volts and some at 2.7, it is a cap not a battery.

Not all the capacitors have the same leakage current. Over time that can (and will) create a variance in voltage. With a battery, you can overcharge a cell with nothing spectacular happening except a bit of heat (typically too small to measure). But if you overcharge a capacitor they will grenade.

They may all start at the same voltage but if you have one cap that self drains faster or slower than another it will be a different voltage. Expand that out over a bunch of time and bad things happen. Without any sort of balancing I had a ~.25v difference between the lowest cell and the highest cell after about a week

[SnowDrifter]

In electronic lab, every diode I have ever tested has a .7 volt drop across the diode.

Different diode

Zener diodes act as voltage regulators and aren't the same as a traditional diode

[justin0943]

get 5v if you get one 2.4v it;ll be like sticking a wire in it what a diode does it keep current from comming backwards it keeps it flowing one way.

Why do you say 5v? My caps are rated at 2.7v and during usage don't see more than 2.36v ea

like I said if you have a 2.7v and get a 2.7v diode it will kinda short itself here what I mean if you have something thats pushing 2.7v and get something thats rated 2.7v it will give out that why you get a little bit bigger.diode lets current flow one way

[SnowDrifter]

Ok guys, if you aren't familiar with this stuff please don't try to help. We can have a separate "learning" thread if you all want to know about this stuff though

Zener diodes are different than normal diodes. And if you aren't familiar with the concept of cell balancing you will have no idea what I'm even trying to do

[AMI CUSTOMS]

hmmm.....I see what you are trying to do, and it will work, a zener between each cell will do what you are after.

[Wicks]

Explain to me how in a series bank you would have some running at 2 volts and some at 2.7, it is a cap not a battery.

All caps, even high quality ultea-caps have an ESR (Equivalent Series Resistance) and each one will be slightly different.

Series a bunch together and those varying ESR's will given you different voltages across the caps.

Differences won't be huge but they could add up and maybe cause issues.

[AMI CUSTOMS]

Here ya go

[AMI CUSTOMS]

Explain to me how in a series bank you would have some running at 2 volts and some at 2.7, it is a cap not a battery.

All caps, even high quality ultea-caps have an ESR (Equivalent Series Resistance) and each one will be slightly different.

Series a bunch together and those varying ESR's will given you different voltages across the caps.

Differences won't be huge but they could add up and maybe cause issues.

If you abuse them and over a long time, years, I do agree. For the most part a balancing circuit isn't necessary.

[justin0943]

I work on electronics all the time their pretty much the same is that the zener can go both ways so if one 2.5 the other 2.7 the 2.7 will feed the other until they balance.