Lithium Polymer Charging Cycle

[James Beck]

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

 

[Barry Lennox]

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.

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

 

[James Beck]

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

 

[Chris Jones]

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

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

 

[Robert Baer]

Barry Lennox wrote:




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.

 

[Barry Lennox]

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.

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.

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.

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

Barry

 

[James Beck]

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.

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.

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

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

 

[jasen]

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.

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

 

[Barry Lennox]

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.

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

 

[Jeff L]

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

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).

 

[Barry Lennox]

snip

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).

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