Thanks Blueshift for the up date on super caps. But did I miss what the OP is using this cap bank for?

 

'competition audio' i believe.

 

'competition audio' i believe.

Wouldn't that put this in the 'buffer' type situation? Who runs their audio on just supercaps after an amount of time? Unless there's a competition on a desert island without a car.

Still say there's a railgun hidden in this thread.

 

You may be right, but what then? Many projects here could be used to do all sorts of nefarious things. We don't generally require proof.

 

You may be right, but what then? Many projects here could be used to do all sorts of nefarious things. We don't generally require proof.

Indeed - the inverter for a xenon strobe or CDI is just as useful for a stun gun.

Except in the UK; a stun gun is covered under firearms law and carries a 5 year sentence!

 

Indeed - the inverter for a xenon strobe or CDI is just as useful for a stun gun.
Except in the UK; a stun gun is covered under firearms law and carries a 5 year sentence!

I have heard about some of those UK laws. No guns, no stun guns, no knives unless you have an excuse, and their government is working on toenail clippers (much like the TSA in America). I feel so safe!

 

Still say there's a railgun hidden in this thread.

"Don't ask, don't tell" policy is fine for me (in most cases).

I am sometimes dismayed and sometime entertained when an OP is trying to get his project to work, then on the 5th post, the OP mentions his ignition switch, lead-acid battery, or any other car part. Then, with the speed of ECL logic, a Moderator puts the cuffs on the thread.

 

Who runs their audio on just supercaps after an amount of time?

That is exactly what I'm up to - I build capacitor-powered portable speakers.
Granted, they run on about 1/3 W, not 15,000 W...but for a super-efficient speaker it actually makes sense.

Does this make sense? Um, kinda...

Still say there's a railgun hidden in this thread.

I had that thought, too, but then why bother with the insane charge rate? Unless its a railmachinegun...



(FOR THE RECORD I DO NOT BELIEVE IN RAILMACHINEGUNS)

 

Oh I don't care, just making a statement. Just doesn't make sense to do all this for car audio. Why not just use home audio and an inverter?

 

My question is this: How would I expand this circuit out to work with 7 of them in series? My question is mainly around R3 between A1 and T1, but no resistor between A2 and T2
http://blueshiftpdx.com/blog/2013/a-new-method-for-capacitor-balancing

 

Or would I be better off building 6 of them and overlapping the wiring across pairs. Did that make any sense?

 

I guess my other question is: What would be my best bet for building these? Buy some blank circuit boards and wire/solder them as needed?

And what sort of parts would I need? I'm lost on the ratings I'd need for the op amps and transistors

 

"Don't ask, don't tell" policy is fine for me (in most cases).

I am sometimes dismayed and sometime entertained when an OP is trying to get his project to work, then on the 5th post, the OP mentions his ignition switch, lead-acid battery, or any other car part. Then, with the speed of ECL logic, a Moderator puts the cuffs on the thread.

I use lead acid batteries for a variety of things totally unrelated to automotive - unless you include bicycle lighting sets.

 

Yes, it is for a car, but I was more going by the spirit of the law vs. the letter of the law. I read that rule as: Don't go asking how to mod the stuff on your car.

I'm asking for advice on balancing capacitors, and although they are going in a car, it's not necessarily a car part and it's nothing automotive specific. Capacitor balancing is nothing new/ground breaking. I'm just trying to wrap my head around a better way of doing it.


If I was totally off-base with this assumption, the I apologize.






Would someone mind telling me what op amps/transistors I'd need for doing blueshift's circuit and explain why I need those parts? Or equip me with the knowledge I'd need to shop for myself? I tried looking at op amps on mouser and I see a bunch of different noise ratings, voltage ranges, etc. And there are lots of different transistors available to. I'm kind of lost on it and I'm not exactly sure where to start

 

Well...that's not a trivial task.

Especially given the currents you're talking about. Specifically, for the top capacitor in your 17V stack: if that capacitor is over voltage, then it needs to drain as much as 130 amps, either to ground (130A * 17V = 2kW) or into another undervoltage capacitor...and it would need to know which one to drain into...


If you called an electronics deign firm and asked them to design this for you, they would quote you...I don't even know. Thousands of dollars?


One of my projects for the next week or two is to build this up for my application: 5.4V / 350F / 10A charge current. I have started picking out some parts that I think should work, I'm going to build one up and see how it goes.

I'll post pictures, BOM, etc. once I get there.



As far as my methodology for picking components...

I just started writing that down - ha, it was a total failure. Informatively failure-y.

There are too many variables to just fire off all the criteria I'll be using. I need to work this all out before I write anything or I'll say some real dumb stuff.



snowdrifter, do you have either:

1. An electrical engineering degree
or
2. A good book?


You probably need at least one. I bought:
Practical electronics for inventors by Paul Scherz and Simon Monk.

It was $40 at Powell's Books. Worth it! Has great descriptions of how most things work and formulas for things like the current across a transistor in a given state...stuff that is sort of in the datasheet, but requires a little more calculation.

 

I use lead acid batteries for a variety of things totally unrelated to automotive - unless you include bicycle lighting sets.

Ian - I'm glad that someone else is working on bike projects, but why are you using lead acid batteries?

So many options...so many.

 

@BlueShift

Here's my goal for this: I'm currently using resistors which have a measured bleed current of 50ma (as per Maxwell's guidance). The whole idea behind doing something else is a convenience factor of not having to keep a close eye on voltage if the battery/capacitor sits for a couple days. Given that if the capacitors were perfectly balanced, they'd only see a maximum voltage of 2.37v each, is it really necessary to invest that much into assuring that they will never go above that mark? Given that the resistor's current is only 50ma and it seems to do a good job at it, I'm really seeking an answer as to why I need a circuit capable of passing hundreds of amps.

Because in all honesty, it's not worth a several thousand (or even more than about a $100) investment to me just so I don't have to plug it in when it sits for a few days. If it's more than that I'll either stick with using resistors or just run without balancing and replace units as they break. I got the capacitors for 18 bucks each, to put the cost of this project in perspective.


Not trying to sound like I'm arguing here, I'm just genuinely trying to understand why there is a need for such heavy duty hardware when a resistor passing 50ma does the balancing part just fine.


To answer your questions, no I do not have an electrical engineering degree. And I don't have a book

 

I don't have a book

Get a book! Spend $40 and you will receive near-infinite benefits.



This was the topic of a post of mine earlier, but to recap: There are different sources of the 'error' voltage between cells:



Your balancing resistors deal with one source: leakage.

Different cells have different leakage currents, and by adding another 'leakage-like' source that
1. greatly exceeds the capacitors' built in leakage
and
2. acts to equalize the voltages between cells

you can limit this source of error voltage.

To effectively deal with leakage current your balancing current in this mode must be much larger than leakage current. 50mA is much larger than 1.5mA rated current so you're good.




Your balancing resistors DO NOT DEAL WITH the difference in capacitance between cells. During the charge time (< 1 minute) the balancing resistors hardly move any charge - 400,000 mA charge current vs. 50mA balance current.



Q = C*V
(from physics)

There is a 33% range in capacitance for in-spec capacitors: +20%/-10%.
(from datasheet)

THEREFORE: In-spec (new) caps given equal charge (as they necessarily do when charged as a series bank) can have voltages that differ by 33%.




So if you charge your bank to 2.37V/cap, you could have some caps as high as 2.96V (2.37/((1.1-.9)/1.1) assuming they are under nominal capacitance and others are over.

I just did the math: not going to transcribe it here, but I get that your maximum stack voltage - absolute worst case, all cells +20% except one -10% - would be 2.14V with 7 cells, or total stack voltage 15V to keep worst case cell voltage to 2.7V.



So, you can probably charge the stack to 15V and ignore most of this, for a while.

Maybe you got lucky and all of your capacitors are at precisely the rated capacitance, but you can bet that their capacitances will change over time, at different rates.

The less you charge them, the longer they'll last...

 

Ian - I'm glad that someone else is working on bike projects, but why are you using lead acid batteries?

So many options...so many.

At the moment, I'm not as I switched to a MTB and a Shimano hub hasn't arrived via the usual salvage channels.

Previously I had an ancient Raleigh with the notoriously feeble Sturmey Archer hub dynamo, I charged a 1.3Ah SLA to run home made switchmode LED drivers front & rear.

With the effect of speed (frequency) on the inductive reactance of the coil, the generator is regulated so it doesn't keep blowing the bulbs (doesn't work so well on the Miller rubwheel dynamo!). My theory is that the generator will produce more net power if the current draw is reduced, allowing the output voltage to flourish - On receipt of a round-tuit, I plan to develop a buck regulator to see just how much power I can get out of a hub.

 

The owners of All About Circuits has elected not to host discussions of automotive electrical system modifications/enhancements due to safety concerns, the potential of legal ramifications and the possible circumvention of vehicle regulations at the state and federal level.

I apologize about the length of time it took for use to respond to this thread, but our rules are very clear.

This thread is against the AAC forum rules, Chapter 6, as seen here:

6. Restricted topics. The following topics are regularly raised however are considered “off-topic” at all times and will results in Your thread being closed without question:

• Any kind of over-unity devices and systems
• Automotive modifications
• Devices designed to electrocute or shock another person
• LEDs to mains
• Phone jammers
• Rail guns and high-energy projectile devices
• Transformer-less power supplies

This can be found in our Terms of Service (ToS)

Automotive modifications of any kind are strictly forbidden. Therefore, this thread will be closed.

Please try to understand the reasons behind this action, and feel free to browse and use the forums.

You might find answers to your questions in one of these forums:

http://forum.allaboutcircuits.com/showthread.php?t=54400

Another good forum that shares many of the same membership is http://www.electro-tech-online.com/ . Good luck.