Need help with charging 9 Li-Ion 18650 cells

[protocol217]

Ok, thanks for all the help, i will make a pack of 4 groups of two cells making together 16.8V when fully charged, and will charge them with 4 separate charging modules (with 400ma each) and 4 separate USB cell phone chargers.

 

[MrAl]

I don't remember where I got this design, but I use it to charge 2 in series and then take that 8 volts down to 5.1 to charge my phone, I also have a 4 cell charger using 4 of the single cell designs. Haven't had any problems.
View attachment 96787

Hi,

That design cant possibly work right with a 1N914 diode. 888ma will blow that diode out.
Looks like a redesign of a charger i designed many years ago, without that diode. A diode like 1N4004 might work though.

 

[audioguru]

Two battery cells will not charge when they are in series with the C3 capacitor.

 

[MrAl]

Two battery cells will not charge when they are in series with the C3 capacitor.

Hi ag,

You got good eyes
I looked fast and only saw two cells in series, not expecting to see such a DRASTIC flaw.

That charger will not even charge one of a fly's eyeball. WELL ok, maybe that, but surely not two Li-ion cells unless they are as small as a fly's eyeball

 

[audioguru]

I got good eyes? I was blinded with cataracts and now I have perfect vision with synthetic lenses in my eyes.

 

[kinarfi]

Two battery cells will not charge when they are in series with the C3 capacitor.

SORRY ABOUT THAT, yes, I'd be willing to bet I got this design here, so it probably it your's, thanks MrAl, let me explain the purpose of the cap, it's for simulation purposes only, to show the charging function, notice the cap is 20f and the cell is 2v, when you run the sim, it shows the slope of the constant current and the roll over to constant voltage, the diode is just the first one to show up in the pick a new diode drop down box. It's a good thing the LTSpice doesn't get so realistic that it shows smoke, I think it's a fantastic program and use it constantly, I'll try to remember how exact some of you are maybe delete some of my adaptations I've thrown in, Please forgive.
Jeff

 

[audioguru]

The "F" (Farads) is missing on the schematic.

 

[kinarfi]

I blame that on LT spice, they never throw the F on, just like they don't throw the ohms on resistors.

 

[MrAl]

The "F" (Farads) is missing on the schematic.

Hi ag,

Believe it or not, in LT Spice i think the 'F' stands for the prefix, "Femto", which of course is 1e-15, so 20F or 20f would be 20e-15 Farads

 

[MrAl]

View attachment 96808
SORRY ABOUT THAT, yes, I'd be willing to bet I got this design here, so it probably it your's, thanks MrAl, let me explain the purpose of the cap, it's for simulation purposes only, to show the charging function, notice the cap is 20f and the cell is 2v, when you run the sim, it shows the slope of the constant current and the roll over to constant voltage, the diode is just the first one to show up in the pick a new diode drop down box. It's a good thing the LTSpice doesn't get so realistic that it shows smoke, I think it's a fantastic program and use it constantly, I'll try to remember how exact some of you are maybe delete some of my adaptations I've thrown in, Please forgive.
Jeff
View attachment 96808

Hi again,

Ok yes, that's good for testing in a simulator. You can then see the current wave as it gets nearly charged. You can also figure out other things too like how much charge is lost if you dont allow it to charge for the entire voltage limited period.

But the diode should still be changed, at least to type 1N4001 or 1N4002 or equivalent. Anyone building this will blow out that diode the first time they turn it on.

 

[audioguru]

Yes, like milli is tiny and Mega is huge, then femto is tiny and Farad is huge.

 

[kinarfi]

Yes, like milli is tiny and Mega is huge, then femto is tiny and Farad is huge.

No, Farad is a unit of capacitance, 1 Farad is a very large capacitor though & 20 Farad is REALLY big, some of the super caps I've seen get that large, but they're only good for 2.5 volts

 

[MrAl]

View attachment 96815 No, Farad is a unit of capacitance, 1 Farad is a very large capacitor though & 20 Farad is REALLY big, some of the super caps I've seen get that large, but they're only good for 2.5 volts

Hello,

Nobody disputes that Farad is a unit of capacitance, and 1 Farad is considered a large capacitance. What was disputed here is what LTSpice *uses* for the femto prefix. They use "F" or "f" i think, so 20f or 20F would be an extremely tiny capacitance while in real life 20Farad would be a huge capacitance. They should not have done that i think, but they probably wanted to stick with the convention of using "u" for a capacitance prefix too so 20u would be 20 microfarads to both us and LTSpice. 20F to LTSpice is 20e-15 Farads to us. If you want 20 Farads in LT Spice then just type "20" without anything else for the cap value.

 

[kinarfi]

would a Femto be the same as a nano nano? or should I ask Mork, AKA, Robin Williams

 

[MrAl]

would a Femto be the same as a nano nano? or should I ask Mork, AKA, Robin Williams

Hi,

You could ask but he wont be able to answer :-(

A nano nano would be more like 1e-18. Femto is more like a micro nano.
Long time ago they did use micro micro, so you'd see 200uu for example. Today we use pico.
The femto suffix is sometimes used in spice model statements.

 

[alec_t]

Expanding on that 'gotcha' with LTspice, "1Meg" is interpreted as 1 Megohm for a resistor value, but the text "1Farad" is still interpreted as 1 femtofarad for a capacitor value. Only the first letter is significant for that.
Incidentally, LTspice is case-insensitive, so "m" and "M" are equivalent.

 

[audioguru]

I notice the case-insensitive in LTspice, when I want 3.3M ohms I need to use 3300k ohms.

 

[kubeek]

You can use 3.3e6 or 3300k or 33e5 if you want, but 3.3meg or 3meg3 is the usual way to do it.