Re: Ubitx batteries / charger #ubitx

Arv Evans

I have and use several of the 3S and 4S charge controllers.  These have between-cell connections
for charge balancing.  Seems to work well because I have rebuilt a number of old Ni-Cad drills
so that they now use Li-Ion cells.  Drills work really well with Li-Ion or Li-Po battery packs.  

From on-line anecdotes it seems that people trying to use Ni-Cad chargers on Li-ion cells is culprit
in many of the horror stories. 

My one complaint about the Ebay sourced 3S and 4S charge controllers is that they usually like
source voltages that are only a couple of volts above the string you are trying to charge.  This
limits what voltage wall-wart you can use to trickle charge your Lithium based battery packs. 

This Li-Ion thing has spawned some research and design work here to see just how much radio
can be powered from a single 18650 cell.  The current is more than adequate but making sensitive 
circuits that run on 3.4 to 4.0 volts is a challenge.  End result I seem to be looking for is ability
to use a simple 1S charge controller (they are less than US$1.00 from Ebay) to manage several
18650 cells in parallel.  Transmitting using MOSFETs in class-C or class-E is not difficult but
at low voltages there is not much margin for noise immunity and overload in receiver circuits. 

If doing much work with 18650 type cells it is probably worthwhile to make a simple spot-welder
for attaching the cell connectors. 


On Fri, Apr 19, 2019 at 4:39 PM Jerry Gaffke via Groups.Io <> wrote:
Daniel's three cell lithium ion 18650 holder with protection from looks promising.
Unfortunately, from the "discussion" section there, I doubt it does charge balancing across the cells.
Would like to hear of a 3S or 4S holder like this that does do charge balancing,
and is designed for standard issue 4.2v max lithium ion 18650 cells.

Arv said:  "Most Li-Ion and Li-Po 18650 type cells include built-in FET switching
that prevents discharge
 to less than 2.0 volts." 
Arv must be spending more money on his cells, the ones I get generally don't have protection.

Arv also says:
"If using multiple 18650 Li-Ion or Li-Po cells you have to manage the voltage on each individual  
cell during charge to insure that no cell exceeds the rated voltage.   While I abhor the "it won't 
work" and the "it will explode" scare tactics, this is one place where the nay-sayers may be justified"

The model aircraft guys might discharge a battery in 5 minutes or less of aerial acrobatics.
Then land it, and do a quick charge to almost full capacity in 3 minutes or so from 
a 100 Amp source, send it back up for more fun. 
That's the usage case where most of the explosions come from.
If charging at a fraction of an amp, explosions are much less likely.

Charge balancing is a very good idea, but if starting out with a set of all new
cells from a quality manufacturer, they will all charge and discharge at about the same rate.
Maybe back off from the spec max of 4.2v per cell, 4.1v max per cell would be safer.
Unlike lead-acid batteries, a fully charged lithium ion cell can get damaged if you push
a charge current through it while any slower cells catch up. 

If I were to buy that 3S 18650 holder, I would charge the cells in place
from a 3*4.1v=12.3v voltage source, limited to a max of perhaps half an Amp.
Could use an adjustable 3 terminal regulator set to 12.3v, plus a series resistor to a 20v supply.
And check for balance across the cells with a voltmeter every few charge cycles.

But looks like most of the balance boards are sold separately from the the cell holders.
That's fine, just an extra 4 wires to solder.

Here's a cheap 3S balance board, though from the user's comments, the balance function is rather weak:

Here's another, totally different design (don't see the big FET's),
has a somewhat better description even if it is rather mangled:

Too bad they don't include a schematic of the thing so I can figure out what all it does.

Any suggestions for a good balance board along these lines?
Can it charge the string of batteries from something like a 20v source
without any external voltage regulator?  Without external current regulation?
How large can the balance currents be?
That sort of thing is often missing from the description.

Jerry, KE7ER

On Fri, Apr 19, 2019 at 12:45 PM, Daniel Conklin wrote:
You need a 3 cell protected holder, like this one:

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