A PWM Controller For Each Cell?

[Randomly]

The water analogy for electricity is a very good one, although not perfect. However you need to apply it carefully.

A circuit is similar to a closed loop of pipe. A closer analogy of a battery is a pump, not a bucket. Here are a couple rough diagrams illustrating the point.


Each pump can increase the water pressure (voltage) in the system.
The total pressure available at the motor is the sum of all the pressures that each pump contributes.

With a series connection all the water in the pipe must flow through each pump.
Turn any pump off and the flow is blocked and no water flows in the loop.
Running pumps at different duty cycles does no good since no water can flow unless all the pumps are on at the same time.

The water in the pipe drives a motor.
The amount of work done by the motor is the water pressure x amount of water.
Double the pressure and you double the power out of the motor.
Halve the amount of water that flows through it (say by turning the pumps off 50% of the time) and you halve the power out.

In the Parallel case:

You CAN run the pumps at different duty cycles as their ability to pump water is not restricted by the other pumps.
BUT you cannot have a system pressure more than the pressure you can get out of a single pump (1 cell voltage). You can flow more water though.

 

[dirty_d]

safe, read this, the way you have that circuit, you lose just as much energy as heat as you put in the capacitors. http://www.olino.org/us/articles/2006/11/22/charge-efficiency-capacitor

 

[safe]

safe, read this, the way you have that circuit, you lose just as much energy as heat as you put in the capacitors. http://www.olino.org/us/articles/2006/11/22/charge-efficiency-capacitor

"So with a charge time of 20 RC, and that is 4 times longer than with the constant voltage source, we reduced the amount of lost energy over the ESR to 10 %!
Of course, when we allow for a longer charge time, we can reduce the energy loss over the ESR evern more!"

So the idea would be to be charging the capacitors all the time with the battery (which is a technique useful for combating things like the Peukert's Effect) and then only at the peak of the charge would you disconnect the capacitor from the batteries influence and send the pulse forward.

 

[safe]

Yeah I agree that water pressure is a good model for water and batteries. It's the inverse of gravity. (which acts like a pump in the downward sense)

 

[safe]

Improved Design

While being a million miles from solving anything this changes the battery setup so that the batteries are held together in a loop that has only capacitors in it. There is no complete circuit that loops around the batteries and yet the capacitors all charge up to their appropriate levels.

In the last chart I've tweaked the second battery to only deliver a shorter pulse than usual and you can see how that drops the voltage of the capacitor and it then drags every cell after it down a notch. Whatever "runt protection" balancing you do on a cell preceeding the others will shift the whole voltage levels down a corresponding notch.

This is the kind of behavior I'm after...

The next "big leap" is how to "harvest" those capacitors without losing the charge they hold as a pulse. That's where some MOSFET's will have to come into play... that's the "tricky part" after this being the "easy part".

This all makes sense so far right?

Those symbols that are like a circle for the batteries mean (in this program) that it's a "defined voltage source" that in this case means I'm created a pulse of a certain width and a certain period.

 

[fefifofob]

Wouldn't it be simpler to design a circuit that when a set of cells goes below a certain voltage, it just shorts those cells out?

You could get energy out of the rest of the pack while those cells were dying.

You'd have to replace the dead cells and eventually they would all have the same capacity through sheer attrition.

Carry on....

 

[safe]

Wouldn't it be simpler to design a circuit that when a set of cells goes below a certain voltage, it just shorts those cells out?

I've done a conceptual design like that. (never built it or anything) Yes, that would work too. You still need a PWM controller, and you still need to have a charger that can individually top off each cell. The idea here was to incorporate everything so that you solve all the problems in one fell swoop and eliminate all the layers.

I suspect that if someone used to using a variable resistor as a throttle back in the old days saw someone talking about some weird newfangled idea like "Pulse Width Modulation" there would be people saying:

"Well why the heck would you need THAT?"

...and generally make the guy feel stupid for even proposing the idea. :lol:

 

[fefifofob]

"They laughed at Galileo. They laughed at Newton. But they also laughed at Bozo the Clown." -- Carl Sagan

 

[safe]

Sequential Capacitor Switching

Okay, so it doesn't take a rocket scientist to parallel the energy of a series of cells into a set of capacitors. But those capacitors lose their charge the moment the battery connection is lost.

How does one "harvest" the capacitor energy?

The only way I can imagine doing this is with a sequential switching process. What you would do is disconnect the last capacitor from the cell it's connected to and then go backwards through all of them until you reach the first cell. You now have a capacitor string that is holding the pulse. (if you don't do this your charge will be lost)

So Step One is to Unzip Backwards.

In order to reconstruct the voltage of all those capacitors in a way that you could recover it (since at this moment it's locked in the capacitors) you would now need to start from the first cell and add them together going forwards.

So Step Two is to Zip Up Forwards.

...and I would suppose the last step is to release the pulse, but it might be possible that the last switch opening could do that.

At this point people might be saying:

"Oh my gosh... I see where you're going with this, but that's just so darn complicated that I just don't see it working. KISS, this is just too much work."

...and they might be right, but I just want to make sure that this is technically possible to do even if it's more hassle than most people care to think about.

Are there any errors that anyone can spot?

Unzipping the capacitors should hold their charge - True / False?

Zipping the capacitors again should reconstruct the original voltage - True / False?

So in the diagram you would "zip" along the red line...

 

[safe]

Some Thoughts...

I've added another capacitor in a "position zero" and it's tied to the same ground as the first cell of the battery series. I'm looking at the diagram and wondering if zipping and unzipping is even necessary. Seems to me that as long as the battery is in the process of charging the capacitors the MOSFET that decides when to disconnect the capacitor could be INTEGRATED into the "runt protection" balancing concept. The capacitor would automatically disconnect itself when sufficent charge is attained. This is exactly what you would want.

The pulse width modulation part would actually serve a secondary role of disconnecting the capacitor once the charge is attained.

Also...

Since we are talking about a "pulse" and not a continuous current all we really need to do is cut the capacitors loose from "position zero" and the pulse will be released from the opposite end of the capacitor array.

This might be easier than I first thought... hmmm...

 

[safe]

Complete Compartmentalization

This diagram produces the same result as the previous one's, but is now 100% compartmentalized. It would seem to me that once you cut the red boxes free (close the MOSFETs) it would stop any capacitor charging taking place and isolate the capacitor array from the battery array. The charge should be maintained temporarily (until decay occurs) because both sides are terminated with capacitors. Whatever charge that has been pumped into the capacitor array is then ready for releasing as a "pulse".

 

[dirty_d]

what are you going to do to combat the 50% loss in charging the capacitors? you need an inductor on each cell. and a big one, one that can handle the full current through the pack. i think it will save money just to do away with this idea and spend the money to replace the runt cells.

 

[Randomly]

what are you going to do to combat the 50% loss in charging the capacitors? you need an inductor on each cell. and a big one, one that can handle the full current through the pack. i think it will save money just to do away with this idea and spend the money to replace the runt cells.

My guess is that he'll just ignore that like other unfavorable facts of physics, such as the fact that DC current cannot flow through a capacitor. The whole design is ill conceived, and he's fooling himself with transient analysis and ignoring the fact that he's setting up the initial conditions before each pulse. Is there any DC current actually flowing through this circuit that would drive a motor? no. What happens to charge transfers during successive pulses? etc.
I must admit though that I find this process fascinating.
Watching how peoples minds are capable of just ignoring evidence to the contrary of their beliefs and remaining secure in the correctness of their view of the world. I think it's a very direct insight into the process of how perpetual motion machines and such get 'invented'. It seems to be a very common human trait, and people apply it in all aspects of their life. Sometimes it's even useful by promoting behavior that though ill conceived turns out advantageous for some other unknown or unrelated reason. I think we all possess an amount of it, but in some people it's not sufficiently tempered and they end up going down blind alleys and never realize it, or never admitting to it.

 

[TylerDurden]

Amazing, ain't it? :lol:

 

[Ypedal]

Randomly : now do you understand my position on this a few pages back ? lol.. :lol:

I have read most of Safe's 4000 + posts, and on many occasions i've stepped up and provided examples and real life personal test results to explain why most of his " Theories " won't ever work in a practicle fasion... this is not the 1st time we'v been down this road..

However, on a positive note.. i do apreciate your input on all this.. very informative stuff you put forth !!! thanks !

 

[Randomly]

Randomly : now do you understand my position on this a few pages back ? lol.. :lol:

I have read most of Safe's 4000 + posts, and on many occasions i've stepped up and provided examples and real life personal test results to explain why most of his " Theories " won't ever work in a practicle fasion... this is not the 1st time we'v been down this road..

However, on a positive note.. i do apreciate your input on all this.. very informative stuff you put forth !!! thanks !

I can certainly sympathize, but we should try and restrain ourselves from trolling and sniping regardless. I think it makes us better people to exercise that restraint, it's like living with 'Freedom of speech'. I also find it difficult at times to restrain myself and slip over to the dark side, but hopefully we'll keep working on it. 4000+ posts? you're a better man than I

Thanks for the support on the comments. I was hoping to clarify a few things to a larger audience than just safe as I seem to run into those misconceptions or knowledge gaps all the time. It can also be an interesting exercise to try and figure out how to explain a concept clearly. Hopefully it helped somebody. I certainly don't feel it was wasted time.

 

[safe]

Is there any DC current actually flowing through this circuit that would drive a motor? no.

But I'm not that far yet...

All I've done is focused on building the correct framework for building up the pulse energy, I've made no attempt to cross that other bridge towards releasing it. You are prematurely assuming that I'm "done" or "near done" on this. Maybe as it evolves you will end up saying:

"Oh, well had I known you would have gone down that path... of course I would have been more supportive."

...at this stage all I've proven (and I think you agree... I suspect... that a SPICE analysis tool should be a fairly reliable a tool) is that a series of batteries can transfer their corresponding voltages to a series of capacitors. I'm at that "bridge point" of having to throw the switches and that probably is where the idea falls apart.

Don't you at least want to see me fail first?

So far the basic premise is still actually working.

(I conceed that down the road on this that maybe I'll fall into a known trap, but even that trap is educational for people reading :wink: )

 

[safe]

Looking Closer

These two charts represent the behavior of the capacitor charge.

In the first chart the timing and pulse width is identical and you get exactly what you would expect in that the voltage at the last cell is 30 volts since each of the three cells are set to 10 volts in this example.

In the second chart the timing is the same, but the pulse width for cell two has been cut in half.

There are a lot of possible timing variations to fiddle around with as well as pulse width possiblities too. I can't say much except that when you reduce the pulse of the second cell it does create the reduced peak voltage as hoped for.

And if nothing else... if this stuff doesn't interest you then just skip over it... some people might find it at least mildly interesting even if it's just a exercise in futility...

What's kind of weird is how the voltage at cell one actually goes up when the others are going down. (actually even exceeding the 10 volts of the first cell) Hmmm... it's just weird... :?

Anyone want to impress us with your knowledge and explain why such a thing would happen? Remember cell two is being given a pulse width modulation that is half of the others.

 

[safe]

Diodes Help To Simulate the MOSFET's

At some point I'm going to need to get more sophisticated and actually place MOSFET's in between the cells and the capacitors. For now it's easier to play around with some diodes that will allow me to watch the charge I'm able to build in the capacitor array.

In the voltage chart you can see that with the diodes in place the capacitor array will step up. The second cell is being given a really, really short pulse and yet since you are applying it again and again you see the stepping up of the voltage. With MOSFET's you would attempt to control this very carefully. Diodes introduce some loss, so the 30 volts max isn't ever getting reached.

 

[safe]

...if you just have a capacitor shorted across a battery do you realize that its only charged at 50% efficiency? im not sure how to show the work, but it just works out like that unless you start charging at the same voltage that the capacitor is at. if you could calculate the RMS current from t=0 to t=considered charged then i guess you could show the energy dissipation due to resistance. if you charge a capacitor through an inductor, the voltage appears across the inductor instead of the capacitor and the current through the capacitor is slowly increased then slowly decreases and you can charge it efficiently.

Dirty_D you seem to have best anticipated the "traps" that I would stumble into.

It's seems that charging up the capacitor array isn't the hard part... and in fact you could pretty easily set up something that could PWM the charge into each capacitor and get what this thread was about a "PWM in each cell".

The problem is in releasing the capacitor back to the battery at ground. This diagram and chart shows how in the simplest case you can indeed charge up a capacitor, switch the gates, then release the energy as a pulse. However, I've been unable so far to figure out a way so that I can get all the energy back... in this case I get a charge voltage up to 3.2 volts (full) but then I'm unable to get more than 50% of it back again. I'm guessing that this is the "trap" that Dirty_D was talking about.

The problem is not in the charging, but in the releasing of the capacitor energy...

Also, I did play around with inductors a little and I can see how that might be a way to shift the voltage in such a way as to make the full voltage apply forward to the load. Another one of those things to play around with...

The problem with this design (diagram pictured) is that when the exit gate is opened it creates a situation where it lacks a ground on the other side of the capacitor to release the second half of the energy. If I could somehow ground it then all the energy would be released... any ideas? (without going to the extreme of another gate?)

 

[dirty_d]

the 50% loss i was talking about isn't in the discharge, its in the charge, if you charge a capacitor with a fixed voltage 50% of the energy is lost due to resistive losses. you need an inductor in series with it to get an efficient charge. and they need to be large value capable of handling the full pack current, inductors aren't cheap but maybe you could make your own, they will probably be pretty big.

 

[safe]

the 50% loss i was talking about isn't in the discharge, its in the charge, if you charge a capacitor with a fixed voltage 50% of the energy is lost due to resistive losses.

Where did you learn that? Any links that talk about losses that high... it seems wrong, but I'm not sure... Below is a link to the general idea I'm after:

http://electronics.howstuffworks.com/capacitor1.htm

Here you have a battery, a light bulb and a capacitor. If the capacitor is pretty big, what you will notice is that, when you connect the battery, the light bulb will light up as current flows from the battery to the capacitor to charge it up. The bulb will get progressively dimmer and finally go out once the capacitor reaches its capacity. If you then remove the battery and replace it with a wire, current will flow from one plate of the capacitor to the other. The bulb will light initially and then dim as the capacitor discharges, until it is completely out.

What makes this easier is that they are running the current exchange in both directions through the load. (a lightbulb) How the heck would you do that in a real battery with a motor as the "load" in the way? It's the ability to connect the grounds in the right fashion that will be the way to make it work. Some switching needs to take place somehow. (and NOT like my previous example)

 

[dirty_d]

i already sent you a link to a site explaining it, its in one of the previous thread pages.

 

[safe]

Capacitor Was Waaaay Too Big

I had stumbled upon the right configuration, but when I tested it the results looked wrong because I was using too big of a capacitor. Reduce the capacitor to something "just right" for the desired pulse size and everything works great.

Okay, so the "single cylinder" machine works, now I'm going to need to work on the "multi cylinder" (multiple battery cells) version.

One comment: I switched from the "normal" N type MOSFET's to the P type so that the voltage is forcing the gate closed rather than the other way around. Seems that over the years they've been trying so hard to get the "on" resistance down that they've been allowing a lot of leakage through the MOSFET's. Using the P type closes the gates really tight and actually makes more sense because for the battery to capacitor array we mostly want that wide open except when the pulse is being released out the other end. P type MOSFET's mean that we can assist the "runt" by closing the gate a little sooner. However, I'm sure I'll be trying other versions that use the N type eventually because those are more common and cheaper to buy.

 

[safe]

Well Gosh Darn... It Works!

The "one banger" and the "three banger" seem to work correctly. Next step is to validate the ability to implement balancing by modulating the length of the pulse that the capacitor is allowed to be filled.

The nice thing about not knowing much is that you are willing to try stuff that others have already written off as impossible. This does seem to validate the concept... so at least I've got that on my side now. :lol: (whether it could ever be practical is another matter)