Lithium Polymer Charging Cycle

Do you have a question? Post it now! No Registration Necessary

Translate This Thread From English to

Threaded View



Is ther any type of charging cycle for these cells that does not end up
just being CC/CV?

This is not really for any design, just a conversation I am having about
LiPo chargers.  


                                 Jim


Re: Lithium Polymer Charging Cycle


On Wed, 31 Jan 2007 10:48:24 -0500, James Beck

Quoted text here. Click to load it

I'm not really aware of any, most of the manufacturer's app notes just
suggest CC/CV or something very close to it. I have not yet seen the
re-invented pulse or "burp" charging and it's wonderous benefits, but
I'm sure it's coming soon enough !

For a number of years, I have just used a Thurlby LB-15 bench PSU. You
just set the CC section to any value up to 2A and the CV section at
any value up to 15V. It works perfectly. I'm still a little nervous
about leaving them connected for long periods, but it has been done
accidentally without any signs of distress.

Barry

Re: Lithium Polymer Charging Cycle


snipped-for-privacy@spamgourmet.com says...
Quoted text here. Click to load it

Same thing I have done with SLA batteries, just don't leave the LiPo
connected for more than a couple of hours and keep them in a fire
resistant container.

Anyway, I made the comment that all the LiPo chargers out there are just
CC/CV units just some of them have a few more bells and whistles than
others.  Like preconditioning, cell count guessing, and so on.  I was
pretty much called an idiot and a pulsed CC method was mentioned.  When
I looked it up, the beginning of the cycle is just like any other, but
when it came to switching over to CV the unit did a PWM 1C pulse.  I
contended that since the width of the pulse was determined by the
voltage on the cell, it was just a fancy CV cycle, nothing more.  Look
at the data over time and it looks just like a tapering CV charge.

                        Jim

Re: Lithium Polymer Charging Cycle


On Wed, 31 Jan 2007 16:56:14 -0500, James Beck

Quoted text here. Click to load it

I have charged LiPo cells, possibly for 100+ cycles now and never once
seen distress, or even mild overheating. They have been left on
accidentally, once for maybe 4 hours, the other time closer to 8
hours, in both cases the cell was just sitting there at ambient.

However I'm well aware of some folk having experenced fires, etc, I
wonder if their charging setup was not correct. It's hard to go wrong
with a bench CC/CV PSU.

The fireproof container might be a good idea, I have an old ammo box
that would be perfect. OTOH, I could just as easily make up a 2 metre
lead and leave them outside the door.

Quoted text here. Click to load it

Hmmmmm.....,, I smell another re-invention of the "Burp" charge, or
some variation of it.

Barry

Re: Lithium Polymer Charging Cycle


snipped-for-privacy@spamgourmet.com says...
Quoted text here. Click to load it
I have never had any problems with amy of mine either, but I believe
that "Floating" the cells isn't recommended, BUT I cn't remember where I
read that either.

Quoted text here. Click to load it
Yeah, me too.
I did find a Maxim part that did that very thing, but you had to provide
a CC wall wart in their example.  I don't remember seeing many of those
laying around.  

                      Jim


Re: Lithium Polymer Charging Cycle



Quoted text here. Click to load it

The only thing that I would add to that setup is some provision so that a
single component failure (e.g. the power supply pass transistor shorting)
cannot cause a fire.  The other poster suggested what is my preferred
option, put the battery in a fire-proof container.  Otherwise some sort of
overvoltage protection e.g. resistive divider, TL431 and a relay, might be
worth having.

Chris

Re: Lithium Polymer Charging Cycle



Quoted text here. Click to load it
...The relay NO contacts carrying the charging current, a piece of paper
in the magnetic gap to prevent magnetic stiction, and the relay mounted
upside down so gravity can pull it open if the spring fails.

Re: Lithium Polymer Charging Cycle


Quoted text here. Click to load it

AIUI the limits are the only important bits.
if you're charging from an under-powered supply (eg solar)
current-limited, voltage-limited will work.

CC/CV is just fastest.

Bye.
   Jasen

Re: Lithium Polymer Charging Cycle



Quoted text here. Click to load it

And it's (almost) the easist. If you have a bench PSU with independant
CC and CV controls, it can't get any easier.----Just:   "Dial and
Charge"

The next hardest is an incredibly simple design using 2 x LM317. One
in a CC config, feeding another in a CV config. I have not made one
for my own use, but am aware of a few folk that are very happy with
them.

Barry

Re: Lithium Polymer Charging Cycle



Quoted text here. Click to load it
about

Why use two? You can add a transistor and a sense resistor to add current
limit to a LM317. Been charging a 24V lead acid bank for years at almost 5A
that way (with the 5A version of the LM317).

Quoted text here. Click to load it



Re: Lithium Polymer Charging Cycle



snip

Quoted text here. Click to load it

Quite right, whatever approach floats your boat. I guess the original
person who wrote this up just took the idea from the Nat Semi VR
handbook. Although the 317 + transistor limiter is in there too.


Barry

Site Timeline