Noob question about wiring a charging circuit...

[Rocketman]

Ever wonder how laptops charge series stacks of cells?
Or how some of the camera or cellphone 7.4 volt packs are charged?

A current limited (CC) regulated voltage (CV) supply and one of these
PCB/PCM for 7.2V(7.4V) Lithium Battery Pack
to protect from overvoltage, undervoltage, and overcurrent might help.

 

[kaddigart]

Ever wonder how laptops charge series stacks of cells?
Or how some of the camera or cellphone 7.4 volt packs are charged?

A current limited (CC) regulated voltage (CV) supply and one of these
PCB/PCM for 7.2V(7.4V) Lithium Battery Pack
to protect from overvoltage, undervoltage, and overcurrent might help.

As a matter of fact I have wondered - I disassembled a couple not too long ago and it appears that some of them (all maybe) have a series of 4-6 and then a single or a pair separated from the stack. Is this loner a part of the series or is it parallel to the stack? It seems I read that it was the latter somewhere too (hopefully not this thread...). Maybe I need to take better notes...

 

[Rocketman]

I can't say "ALL" but laptop packs using the typical UNPROTECTED 18650 are organized
as 3 in series with 2 parallel strings (6 cells) or 4 in series with 2 parallel strings (8 cells). Extended life packs are 3 in series, with 3 parallel strings (9 cells).
It may not be straight forward how they are connected until you look closely at the circuitry.
All, that I have seen, have a 3 or 4 cell protection charge/discharge board.

 

[cadcoke5]

Good point about laptop batteries. I know the older NiCad batteries were just charged in series.

I just did a quick internet search, and the schematics I came across for Li-Ion batteries all had the ability to charge each individually, using a micro chip to manage it all. But, I am not clear if this was something required for standard practice, or rather an ideal way that may prolong the life of the batteries. Perhaps in can be done more simply by charging in series.

I would like to find an authoritative source of information that can state the issues and solutions. There seem to be a lot of chips available just for the purpose of charging batteries individually, when they are normally used in series to stack the voltage.

-Joe Dunfee

 

[Rocketman]

Joe,
most have a tap to 'monitor' voltage at each series junction.
The control chip switches from tap to tap and when any one voltage level drops below or goes above a preset threshold it turns off the whole pack. Charging is still through the whole series stack with each cell monitored.
Even the more complicated 'balancing' circuits usually charge the whole sting until one cell reaches the cut off then it is drawn down to match the others.

Look at where the charge terminals are connected on the circuit you saw and what the charging voltage is.
Here's a typical schematic for a 2S board. What looks like 2 Mosfets is really a single device with back to back Mosfets on board. One for charge control, one for discharge control. Cell voltage is 'monitored' but the entire string is either turned on or off by the Mosfets.
Higher current boards will have more than one of these dual chips mounted in parallel.
Higher voltage packs will have more taps for each series junction.

Here's one for a LONG series string
http://www.batteryspace.com/prod-specs/pcm37V_20A.pdf


here's a 4P3S pack and a 3S protection board from a Lenovo laptop.

and a 3S2P pack using an aftermarket 3S control board.

and a board for a 4S string of LiFePo4 20 amp hour cells




A control board from a Dell Laptop Pack

 

[cadcoke5]

Rocketman, thank you very much for that clarification/correction. IN regards to the "charging" circuits I had come across, I really didn't evaluate their exact function. I do recall seeing the word "balancing", so the thing you are describing, is probably what I was looking at.

-Joe Dunfee

 

[kaddigart]

Ok, so most of those boards wouldn't be practical for use in an e-cig mod obviously - are there smaller versions available that are designed for fewer cells? I can do the searches myself, I'm just not sure what keywords to use or what parameters to input into a parametric search like Mouser's...scrolling through 100's of 1000's of parts can be very tedious.

 

[Rocketman]

What you would be looking for is Chinese parts for e-cigs
If you want to charge a 2 cell stack, similar to a 7.4 volt camera or cell phone pack look for
2S Li-ion protection circuit board - Yahoo Image Search Results
They should be easy to get from battery suppliers like Batteryspace or Fasttech for just a couple of bucks.
If you want to build your own then search for the components at Mouser or DigiKey.

 

[kaddigart]

Thank you, I just needed the right keywords, I wasn't sure what they would be called or how to describe it in search enginese.

Edit:
Well, I finally found one on a site that provided prices and I could peruse without thinking I was reading Yoda's diary (Too good not Chinese-English translations). It is also not gigantic like some I saw, there's a huge form factor difference between these things, even if they're all 2S.

By the way, for any one else that may want to dig a little farther I had better luck with this search string:

"2S" Li-ion pcm

Without wrapping 2S I got very random results that had just the number 2 and any other one keyword used. Using the acronym helped with that too. It returned more sites that actually sold them as well.

Edit Too:
I did stumble across these holders with built in PCB while searching using Rocketman's string - they're a bit pricy but could be very useful to those like myself that have tons of laptop batteries laying around...

 

[cadcoke5]

I was looking at some of those protection circuits, and was a little uncertain about their function.

It says you need to connect your charger to the circuit. So, apparently they don't have the necessary electronics to actually control the charging process. It seems that the connection to each battery is for the purpose of balancing them after they are charged. The charge voltage is applied in series.

I just wanted to be sure I understood their function.

-Joe Dunfee

 

[Rocketman]

The 'typical' protection board is connect to the negative and positive poles of all the cells.
It needs these connections to be able to sense cell voltage. Most put the Mosfet on/off switches at the negative pole, and give you a 'controlled' negative pole to use for both charging and discharging. Once connected to the cells (1S, 2S, 3S) you can forget it's even there.
The most positive pole and the negative pole of the control board are now your 'new' battery pack terminals. You could put the cells and the board in a 'black box' and it would be difficult to even know it was now a protected pack.
Like a laptop battery pack. You don't notice the protection board in it until you take the pack apart.

In order to charge this pack, you still need an appropriate charger. A single cell charger won't work.
For a 2S application, you would need a 7.4 volt Li-ion charger.

 

[Visus]

rocket that fuse mod is kewl
okr mod:
question two fused round li po in series
8.4v

I was thinking use https://www.fasttech.com/products/1284905
this charger on a timer with v meter

thoughts on safety?

 

[Rocketman]

That would probably work (the price works ).
It is probably regulated at 8.4 volts, which is appropriate, but the CC/CV charging profile will probably not be optimum.
Might be.
As the combined 2 cell voltage approaches 8.4 volts the charging current will decrease. That's good.
But it may not ever cut off like a real charger. Not a big problem if you monitor charge progress.
Charging should hit a termination and then stop. Most resume after the cells drop a small amount, but they stop.
Will this one?
The laptops I've played with hit the battery pack pretty hard, and let the pack control board cut off charging. They don't actually get into a constant voltage tapering off. I guess laptop users are too impatient

For the money (and shipping delay) buying one of those probably (see how I use that word a lot?) wouldn't be a bad idea. The 1000ma output would be a little hot for smaller cells. Stick with 18650.
Put a 5.5mm X 2.1mm jack in your mod.

Setting it up with one of their cheap volt meters (red display is the cheapest)
$1.93 0.36" Display 3-Digit 3~30V Voltage Tester for 18650 Battery - red LED at FastTech - Worldwide Free Shipping
and a timer in case you fall asleep would do fine.

Buying some of these cheapo components is good for experimentation.
The better components are often cloned and end up about as reliable as the real deal.

You mentioned "fuse". The control board has a built in current limit. The OK-R-6 for less than 10 bucks would be a good choice. It's not VW, doesn't have an OLED display, won't tune in shortwave stations (but will generate a little RF interference ). Remember that loaded voltage from your 2S pack will not be 8.4 volts. More like 8 for one puff, then 7,6 after a few more. Eventually getting down to about 7. That still leaves enough for the OKR to put out about 5.5 volts. Plan on that. There are threads on that module. I've used the OKR for some car powered pass throughs (great for long trips).
The last time I checked Digikey was cheaper (real US postage charged).

Sounds like you are looking forward to this DIY modding stuff

Postscript: You will probably find people that don't like protection circuits. Claim they fail all the time. I think that came from using low quality, low current cells (like ultrafires) a few years back and overloading them. The board cut off flow. They try to overload it again, it cuts off. Duh.
Figure it's a bad protection board. I've never had a problem with the cheap cells if I didn't load them over about 2.5 amps (where they should be operated). I think the protection circuits are very reliable. Do what they are supposed to. Since no one vapes at 6 watts anymore, better cells with a little higher current capability are the way to go.
The Ultrafires also didn't have any where near the labelled capacity, but for about $3, not bad.
Those that sell them for $10 or more are cheating us. That 3S3P pack in the earlier picture runs a 35 watt 12 volt HID ballast. Those are selected Ultrafire cells.

 

[Visus]

you are a wealth of happy battery mod play
Thanks

I am eventually doing a MAMU mod Denali with the caps for resonance so it should be much less whiny
I did see the cheat sheet on using a 500ohm direct no caps but I hate siney wave form sounds

They say with the okr after an all day vape, loss to 8.1v after
My New Mod- the Denali by Mamu

That flashlight I figured was running a led would have never guessed hid

 

[Azmo]

Can you charge batteries directly off the Evolv charging board without going through one of the chips?