Lithium Polymer Charging Cycle

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

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

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

...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.

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.

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

Barry

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.

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

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

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

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).

snip

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