Ya out there Red?

Here is his web page.

Also his email. snipped-for-privacy@bellsouth.net

ka8jvx

| Been trying to contact Red S @ Battery Clinic. Yer e-mail keeps | bouncing. I could use a little help.

To be fair, the people on this group generally know a fair amount about batteries, and generally aren't unwilling to help ...

and if its a LiPo question I dont think Red is an expert in this field judging by some of his replies on chargers IE "Most Lipo chargers employ a tapering current as they approach cut off, what we would term as a soft cut off" as that just plain old physics nothing to do with the charger

You must have found the right combination snipped-for-privacy@rcbatteryclinic.com since I got your message regarding the charger question.

OK, just hook your constant current charger Ni-Cd to your LiPo pack and see what physics does for you. :-(

Say Hi to the firemen when they arrive.

who said constant current I never did? a constant voltage but current limited charger as in all Lipo chargers the current has to reduce to approx zero by simple physics, it has nothing to do with the charger its all to do with the cells voltage rising to the charge voltage

You forgot the most important law of physics, which is that Red Scholefield is always smarter than you. Just ask him.

Much as I agree that Red is not the greatest Guru on LIPOS, his statement in this context is correct, and yours is wrong.

How the current falls as the charger approaches full LIPO voltage is entirely a function of its design.

Well it cam be anything from a taper from full to nothing gradually decreasing, or full current charge until the moment it exceeds the 4.2v per cell, at which point it switches off. Or like the Astro, continue to put 1 second bursts of full current in, until the voltage stays at 4.2v for 30 seconds, and THEN switch off..

I guess physics is a tad more complicated than you think...

No, he forgot the all imnportant law of Usenet, it's wise to not open your mouth if all you can manage to do is put your foot in it.

"A man would better remain silent and be thought a fool, than speak and remove all doubt"

Hey Zeus Christ, I didn't want to stir up the shit. I just wanted Red's e-mail address. DH er I mean NP why don't you go off in a corner and F*#k yerself.

full voltage maybe but not full current as the cell voltage would go above 4.2v , until the voltage stays at 4.2v

er no its not not unless you have rewritten ohms law

the decreasing current has nothing to do with the charger per say The charge current cannot and will not stay at max until it reaches 4.2v a cell, it has to decrease by simple physics, you can charge a lipo pack with nothing more than a work bench supply that has variable current and variable voltage, at the beginning of the charge the current limiter is the primary control as the cell voltage will be below 4.2v volts and at maximum set current as the cell voltage rises and the current will decreases and the voltage will be the primary control and the current will continue to decrease gradually to zero until the cell is charged and the bench charger wont not even know it charging a LiPo and it will happily follow the graph below even your Astro will

current graph for a simple voltage charger below

and have a look at this graph of a charge on a capacitor its the same, voltage increases current decreases its not rocket science

the trick with charging Lipos is doing it safely by correctly sensing the number of cells the max current and the max voltage ETC

*Per se*, actually, and yes, it has EVERYTHING to do with the charger, which is responsible for controlling it.

It can. And in many cases does.

A charger is not simple.

Chargers - commercial chargers - are not simple voltage chargers.

LIPOS are not capacitors either.

First bit you actually got right....

Well that would all be true if the output impedance of the charger were some finite positive constant value.

Electronics however can be used to make it whatever you wish. Non linear, very non linear, even negative and so on. Perhaps a very very simple explanation will serve.

Consider a very high voltage source, and a variable resistor controlled be a computer that senses the output voltage. For every output voltage the computer looks in its memory and sets the variable resistor to a particular value, or even switches it off altogether, needing a manual rest button to start it again.

With such an arrangement you can have a COMPLETELY arbitrary arrangement of current with respect to voltage. It is not controlled by the load at all, or 'simple phyiscs'. It is controlled entirely by software and the circuitry. It can have as many completely arbitrary values as the computers ability to sense voltages, and store (or calculate) an appropriate current.

The only interesting possibilty is if you had two of hem back to back, fighting each other..;-)

It is perfectly possible to have a totally constant current, or even and INCREASING current, with voltage. Then all you need us a voltage detector that trips the thing off at a point, and you have a current which steadily increases till the voltage reaches a preset value, and then stops completely. For example. Not that such a circuit is desirable for charging LIPOS.

I am not responsible for bad information on other peoples web sites.

I am well aware that the behaviour you describe is characteristic of a bench power supply. And those can be used to charge LIPOS. It is not the only characteristic possible however, and is most definitely NOT the behaviour of the Astro 109, which is computer controlled to maintain full charge current right up to cutoff, and then pulses full charge current - and I mean FULL - until the *resting* voltage reaches the maximum.

Other commercial LIPO charge chips do similar, or just cut off when the voltage reaches full, or taper down to full voltage.

The problem with constant current to cutoff, is that the resting voltage of the cell will be somewhat below the allowed maximum. That is why a taper is normally used..but the taper is a very slow process..the charger approaches full voltage asymptotically, and in fact never reaches *full* charge, The Astro shortens that process by taking the LIPO OVER full voltage under charge, then disconnecting the charge to see what the resting voltage is. This allows the voltage to be brought up to maximum relatively quickly, and still safely.

A LiPo charger is nothing more than a CC to CV system. That is why the guys that were early adopters of the technology used big lab supplies to charge them. They just set the max charge current on the CC control and the max voltage on the CV control. There is a natural taper when the unit is in the CV mode because the pack is filling up, but the "charger" is not allowed to ramp up the voltage. The taper is just a natural extension of the CV part of the cycle. Now the charger may have a time limit on how long it says in the CV top off mode, but the taper is just plain 'ol physics.

Jim

the only thing the charger limits is the voltage it has no idea during the charge process when its going to end its not some ultra smart algorithm ,the cell limits the current by pure physics LiPo chargers are exactly the same as a CV lead acid battery charger (but not the crap you buy at your local car shop)put 14.6v across a lead acid battery and the current will fall as the cells charge

crap again, prove it show me any website/document where any LiPo charger can charge a cell at 4.2v at max current for the whole charge sequence

it can be read up on it

they are all based on cc/cv (constant current start/constant voltage finish)

No but the physics are the same

but that is not got anything to do with a LiPo charger its a bit like saying the more I put my foot on a brake the quicker I stop which is true but totally Irrelevant

but not on a LiPo cell its not, its not physically possible

but you are for the crap you type

it cannot give a full current pulse as it limits the voltage to just over 4.2v a cell RTFM I have "the charger goes into mode three and the charge current is turned on and off and the charge cycle is slowly reduced until the cell voltage approaches 4.2v

possibly but not constant current charge the current has to taper it cannot do anything else

you do type some crap you cannot charge a Lipo to full charge with a constant current it cannot and will not happen is that the resting voltage

its not "used" its fact it cannot be any thing else .but the taper is a very slow process..the

it goes over 4.2v a cell very slightly in pulses next time you put a battery on charge have a look at the charge current it falls towards the end it has to , then disconnecting the charge to

Thanks but he wont believe you

The facts are the facts. All you gotta' do is look at the datasheets for the cells. Classic CC/CV charge cycle. Sure, you can add some nice touches with an MCU, like pre-CC conditioning/testing, usually done to attempt to guess the cell count, but you still have to go by the rules. I have designed many of them.

Jim

is it true you can leave a LiPo battery permanently connected to a charger without any damage?

The quick and safe answer is NO. UltraLife Battery says : "Float Charge A charge at a low rate of current to compensate for self-discharge of a cell or battery. Not recommended for lithium ion or lithium polymer batteries."

Portable Design says : "In order to obtain maximum charge in the battery, the Li-Ion cell must be provided a constant current source to charge the battery up to the

4.2-V level. Once at this point, the battery is only 70 to 80% charged. A voltage termination is necessary in order to ensure maximum charge. When the voltage reaches its maximum level and the voltage termination portion of the charging circuit takes over, the current to the battery begins to decay. At some point, the charge must be terminated; Li-Ion cells have a very low self-discharge rate, and keeping a float voltage applied to the battery will result in overcharge and damage the battery. The termination point cannot be set by the voltage level. As stated earlier, when the voltage reaches the maximum battery level, the battery is only partially charged. When the charging current drops off to a minimum level, the battery can be determined to be fully charged. During constant voltage mode, the current decays down to a minimum level where charging can then be terminated. "

I would imagine if the charger is designed right, there should be a shut down point and not just a float.

Jim