Ya out there Red?

how the hell did you get to that idea are you on drugs? a cc charger that changes the current and a cv charger that changes the voltage do read it back as its crap its either constant or its not

do grow up

1, you cannot have a pure CV charger for LiPo's as the initial current for a discharged cell would exceed the charge rate and shorten the life of the cell 2 you cannot fully charge a LiPo with a purely cc charger as it will never reach full charge with out going over the max voltage of the cell 3, and if you dont or cannot see 1 and 2 are correct then dont get involved as this is what the argument is over

Perhaps you can define the word "constant" for me. My Ph.D. in mathematics clearly left me unprepared for some usages.

I would say that a function f from the reals to the reals is constant if its image has a single element. In simpler terms, f is constant if f(x) = f(y) for all x,y in the reals. Apparently some folks would like to believe that the function

x \mapsto round(sin (x) + 0.5)

is "constant", but you'd have a hard time convincing ME of it.

It'd be reasonable to say that a function f: [a,b] -> R was "constant, at scale A, within tolerance e," if |f(x) - f(y) | < e whenever |x - y| < A, except on a set of small measure. Even with this rather liberal definition, from what I can see, the pulsing chargers are not "constant at any timescale" that's even close to, say, 5 seconds.

Even if you take "constant" to mean "2-valued" (i.e., the value is 0 some times, and some number C at other times), it's certainly possible to build a charger that doesn't use a 2-valued current or 2-valued voltage scheme over time.

And you keep telling me to integrate stuff. Well, take any electronic device you can name. Integrate its current use over the entire time it's used. You'll get a number. Divide by the time used, and you get a number, C. You COULD say that the device used a "constant current C", because "you just integrate." I hope no one would take you seriously.

So: tell me what interval to integrate over, and why; then tell me what "constant" means. Without knowing these things, I can't say whether I agree with you or not. (If "constant" for you means "blue with orange spots," for instance, then we don't have an argument -- just a difference in terms.)

--John

Apologies, Doug. I'd failed to properly notice that we have two others posting and you just making a quick comment. Your name was the one that stuck in my mind as I did a followup. My comment about baiting comes from reading your posts on other topics (which I usually find pretty informative...but sometimes provocative as well!).

--John

On Wed, 31 Jan 2007 20:56:33 +0000 (UTC), I said, "Pick a card, any card" and "John F. Hughes" instead replied:

In electronics, constant current means two entirely different things when seen from the perspective of the source and the perspective of the load. A power supply can be capable of delivering a constant current to a load but a load may be presented with a varying load by pulsing the source output either internally or by external components.

A load can present a constant current draw to a power supply the has no current regulation at all. A constant current supply presents a specific amperage to a load (the device being powered) but there is no requirement for the load to use all that amperage. Batteries, TV sets, radios, CD players and all manner of other equipment present an active load to a power supply which can only offer the maximum amount of current as it was designed to offer. The device draws what it can draw or needs to draw.

A constant current source is not an irresistible force of nature. It's governed by a variety of factors as noted above. What a constant current supply actually does for batteries is to allow the topping off of the electrons stored in the battery. When a battery nears full charge, the tendency is to stop drawing (needing) current and the number of electrons entering the device drop, almost trickling in, which can become either an exponentially longer charge time or result in the battery never actually reaching full charge. The constant current supply is like a compressor adding air to a tire until the maximum pressure of the compressor is reached. If that's set to 60psi, that's how much air is in the tire when the maximum pressure is reached. If you pulse that air, it will still reach the maximum pressure but the average pressure in the hose drops until equilibrium is reached on the entire system. As you can visualize, the air is still at a constant pressure based on the maximum that the compressor can supply but now but the air is no longer flowing having no place to go. As the compressor fills the tire, the pressure in the entire system is now at the maximum.

The same is true of a constant current supply. When there's no place for the current to go, it has to stop flowing but the potential to flow (pressure) is still there. It's still able to provide a constant current which won't vary according to the needs of a varying load. Difficult concept, yes.

-- Ray

I believe that the paragraph above describes a "current-limited source" rather than a "constant current source." In general, a constant-current source really DOES supply constant current, over some specified range of loads. These used to be used in the old Model 33 teletypes, for instance, in their "20 mA current loop" transmission lines. For sufficiently-low-frequency to DC circuits, this means that when the load resistance rises, the applied voltage has to rise to keep the current the same. Given that there's usually some maximum voltage that the source can provide, you end up with something that provides constant current over a certain range of resistive loads. (All this ignores non-resistive loads and complex impedances, which would just muddy the issue.)

The "compressor" is much more closely analogous to a constant-voltage source.

Or at least, that's what Horowitz and Hill would lead me to believe.

The interesting thing about a constant-current source is that (within the specified load range), the current coming from it tends to be constant over time, in the mathematical sense of "constant" that I described before, at least over the interval of time when it's operating, rather than on the whole real line (i.e., for all time). So that's a notion of "constant" that I've got a pretty good grip on. What I can't see is how something that looks like a pulse-train can be considered "constant." Probably just a problem with my narrow world-view.

-John

Ray did a very good job at explaining the terminology. In this case constant current means that the average current is kept at a certain value over a certain time frame. Constant voltage means the same thing. The average voltage is maintained over a certain time period. Peak voltage and peak current can be vastly different, but you get the idea. I didn't invent the terminolgy, but it is what we are stuck with in this case. Jim

Why don't you weigh in on the subject? I'm sure you have seen how the current array of chargers handle the charge cycle. I'm pretty much done with this thread, but I would like to know your take on things.

Jim

On Wed, 31 Jan 2007 21:46:08 +0000 (UTC), I said, "Pick a card, any card" and "John F. Hughes" instead replied:

Voltage is a potential, in electronics and current is a pressure. The electrons are presented in a maximum level limited by the voltage. The electrons are presented in a maximum number or quantity by the current. An ordinary, run of the mill, power supply with a voltage rating of 12 volts and a current of 500 milliamps will have the capability of developing that much pressure whereas a constant current supply with the same ratings WILL develop that much pressure. Both present to a load the maximum as required but the constant current device will not waver with load. The current will be there but not always used. In the case of LiPo batteries, they will continue to absorb the electrons even when the devices are absolutely full to capacity. This tends to destroy the innards (I'm using baby talk here for those who are following what has become a very deep thread) and the battery can be damaged and even catch fire if a constant current (pressure) is presented to the battery.

There are constant current power supplies that will safely charge LiPo batteries. The Maxim company makes integrated circuits that monitor the level of charge (they call it the gas gauge) on a cell. Some even 'remember' the batteries under charge so that subsequent charging of those batteries can be done safer each time. They present that constant pressure of electrons until about 70% of the charge is met and then they begin to taper the actual time that the current is presented by pulsing the output eventually cutting it off completely when the battery is charged. The constant current supply still presents the same pressure to the circuit but only in dribs and drabs. It's the fastest way to charge LiPo batteries without causing too much damage to them. Unlike other types of batteries, they do degrade when fast charging is done.

Sometimes I think that those who debate the issue are rubbing their hands in glee with a word such as constant can present many meanings to the discussion allowing for others to interpret them as they will. The word does imply some sort of permanence and stability in most usages but in electronics, due to active loads versus constant loads, the meaning is very clouded.

It's common, John, to those who don't live in the world of electronics or physics. Remember, we've had to deal with hole flow and electron flow to explain what you probably know as quantum physics or quantum mechanics. The limited world view concept applies there. Why learn all the complicated theory behind the workings of a transistor when the analogous holes/electron theory fits exactly.

-- Ray

If you're trying to make the standard analogy with fluids, Ray, it goes like this:

(a) Voltage represents electrical potential.

(a') For a fluid, the height of the water-tower represents the potential energy stored in the tower; a higher tower gets you higher water pressure at the tap.

That water PRESSURE corresponds to voltage.

(b) Electric current is the net flow of electrons along a conductor.

(b') Fluid current is the net flow of the fluid in a pipe. Fluid FLOW is the analog of electric current.

(c) Electrical resistance is the resistance to the flow of electrons through a conductor (or not-so-good conductor, which is called a 'resistor').

(c') Fluid resistance is the resistance to the flow of fluid through a pipe, typically the result of viscosity and a bunch of other stuff. Narrow pipes correspond to large-value resistors; fat pipes correspond to small-value resistors.

So (at least in the usual analogies) current isn't a pressure. It's a flow. (Funny...it means that when you talk about the ocean, too. Current is the FLOW of water, while TIDE describes the water LEVEL, although those two terms are often misused/swapped as well). Indeed, if you replace the word "pressure" with "flow" everywhere in the paragraph you wrote below, you'll get something that's more or less correct. Of course, I could be completely wrong; maybe Ray's really an expert.

But I think I feel safe in suggesting that anyone who doubts me or Ray should take a look at Horowitz and Hill, "The Art of Electronics". They're pretty clear and pretty authoritative. Used in a bunch of courses at MIT, for instance. So you can probably trust them...

--John

Unbelievable ;-))

The fact that you don't see the point, proves the point, to those who can.

Ignorance is bliss.

Th astro algorithm allows 100% charging..a CC/CV charger dare not go to

100%..except by tapering over an extremely long time..you might say it approaches 100% charge after an infinite time..

The astro gets you 100% charge in about 1 hour and 15 minutes from almost flat. No other charger I am aware of does that.

The simple ones that 'stop' when they get they 4.2v/cell will generally show 10-15% more charge can be taken when stuck on an astro,.

The CC/CV stuff will take about 5 hours estimated to get to 95% charge.

A SMPS will always be more efficient than a linear regulated power supply anyway..and you have to use SMPS to charge more than a 12v battery from a 12v DC supply.

On Wed, 31 Jan 2007 23:11:08 +0000 (UTC), I said, "Pick a card, any card" and "John F. Hughes" instead replied:

Correct.

Not exactly. The total water regardless of height is the voltage analogy. Height would be directly responsible for pressure since we have gravity in play.

Pressure is the amount of force applied by the water at end of the pipe which would correspond to the electrical load. Look, I'm trying to make this work for CONSTANT CURRENT, not for all conditions, OK? Remember, this isn't about something that everyone here can understand. I could go into FFTs and a variety of other instantaeous current calculations and blow smoke all over the place but we are dealing with a variety of people here, some of whom are ignorant of the math involved. Thus, I use analogy that explains things. The pressure represents the CONSTANT current, not relating to the total current which is analagous to the flow itself. Understand? Actually, I am sure YOU do but not everyone else. Stop trying to help other readers here unless you truly aren't getting the concept yourself. Fair enough?

Did I state otherwise? I gave my analogy to represent what happens with a CONSTANT CURRENT power source.

Duh. Has this moved into the realm of complete Ohm's Law?

Double duh.

I am an expert. Thanks for asking. Retired from Electronics Engineering in 1999. Taught it for a while, too. Still teach it part time at local colleges here.

I believe. I really do. Am I saved now?

John, I think we're actually on the same page. The constant current power supply is a strange beast since it is absolutely non responsive to varying loads. An ordinary power supply is not able to provide a current source when the load demand drops. The constant current source can but doesn't absolutely have to do so. It's a distinction worthy of note when your goal is to gather as many electrons as you can into a battery. Our goal is to make the battery so full it nearly, but not quite, overflows with electrons.

-- Ray

It has been covered very well by those with at least a basic knowledge of electronics, not much I can add. The charge profile is essentially a function of the charger's design as many have stated.

Red S.

thats the trouble its not? stick a cell across a fixed 4.2 volt source and the current at the start will be high and it will decrease as the cell charges, the decrease in current is not a function of the charger its physics try it if you like and prove me wrong the only thing the charger does to this curve is limit the current at the start to prevent damage to the cell

Which is "a function of the chargers design"....

Oh dear.

I bet he still thinks Bush is an intelligent man..

As a matter of curiousity , what are some of those products ?

Thanks

Ken

Ah yes -- another anonymous self-proclaimed expert with a phony E-mail address -- PLOINK!