Topics

Ubitx batteries / charger #ubitx

Bill Lamm
 

George, have you seen this thread?

https://groups.io/g/BITX20/topic/homebrew_li_ion_battery_pack/31181951?p=,,,20,0,0,0::recentpostdate%2Fsticky,,,20,2,0,31181951

Similar adventure..  I ordered a buck/boost converter and I will have more info when it hits my bench

_Dave_ K0MBT
 

For my model batteries I recharge at 1c the recommended rate. It isn't hard to have more than one battery.

I have battery powered my ubitxs but kept the battery outside the case. and put a volt meter on the front panel. I put the xt60 connectors for power on all the hf radios. To match the batteries.
Cell imbalance does happen and is the most serious issue with these batteries.

The batteries use a balance charger where each cell has a separate charging lead straight back to the cell.
73

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. 


Arv
_._


On Fri, Apr 19, 2019 at 4:39 PM Jerry Gaffke via Groups.Io <jgaffke=yahoo.com@groups.io> wrote:
Daniel's three cell lithium ion 18650 holder with protection from fasttech.com 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 fastech.com 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:
    https://www.amazon.com/11-1V-Balance-Lithium-Battery-Protection/dp/B075D96HVV

Here's another, totally different design (don't see the big FET's),
has a somewhat better description even if it is rather mangled:
    https://www.newegg.com/Product/Product.aspx?Item=2S7-00MH-048Z3

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:  https://www.fasttech.com/product/1161200-3s1p-18650-11-1v-battery-holder-case-li-ion-pcm

Jerry Gaffke
 

Daniel's three cell lithium ion 18650 holder with protection from fasttech.com 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 fastech.com 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:
    https://www.amazon.com/11-1V-Balance-Lithium-Battery-Protection/dp/B075D96HVV

Here's another, totally different design (don't see the big FET's),
has a somewhat better description even if it is rather mangled:
    https://www.newegg.com/Product/Product.aspx?Item=2S7-00MH-048Z3

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:  https://www.fasttech.com/product/1161200-3s1p-18650-11-1v-battery-holder-case-li-ion-pcm

Jack Brabham - KZ5A
 


For powering the radio from batteries look for an "automatic buck-boost" regulator. This type will maintain your desired output V as the battery runs down.   A "step down" regulator will only work if the battery voltage is higher than the desired output V.

For charging Li-ion packs look for a "BMS - Battery Management System" rated for your pack's size.  These these handle all the over- under situations, control charging and maintain a balance between the individual cells.

I'm planning on a 3 cell pack, giving 11 to 12 volts.   I can recharge them from the shack 13.8V supply or charge directly from a solar cell. 

73 Jack KZ5A



On 4/19/2019 12:49 PM, George Blass via Groups.Io wrote:
Hi All

I’m designing my case and have a question. I plan on using 18650 batteries inside the case with this voltage regulator. 

Voltage regulator

Then for charging I’ll have one of these inside the case. 

Charger

My plan is to have everything inside the case with just the charging and USB ports exposed. This way to charge up the batteries you would just plug it in like a cell phone. 

Will this work?  Am I missing something?

George


Daniel Conklin
 

Arv Evans
 

George

There seems to be a potential for problems, unless I have misread what you are planning
to do.  If using only a single Li-Po or Li-Ion cell (3.8 to 4.2 volts) you can charge them with
relatively simple chargers but there must be voltage limiting in the charge scheme to insure
that the voltage never exceeds the manufacturer rated voltage (usually 4.0 volts). 

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.  Over-voltage charging of Lithium based cells has been documented as a cause of
overheating and possibly fire. 


The small brick style cell phone auxiliary power banks usually include built-in charge control
circuitry that protects the Lithium cells from abuse.  This makes them relatively safe for most
applications. 

Most Li-Ion and Li-Po 18650 type cells include built-in FET switching that prevents discharge
to less than 2.0 volts.  If you do manage to discharge your Lithium based cells all the way to
zero they may refuse to accept re-charging current and thus become unusable. 

There are charge management boards available from several vendors.  These are needed
if you want to make up your own Lithium based battery packs that use multiple cells in series.



Maybe this helps...?

Arv
_._


On Fri, Apr 19, 2019 at 12:49 PM George Blass via Groups.Io <georgeblass=icloud.com@groups.io> wrote:
Hi All

I’m designing my case and have a question. I plan on using 18650 batteries inside the case with this voltage regulator. 

Voltage regulator

Then for charging I’ll have one of these inside the case. 

Charger

My plan is to have everything inside the case with just the charging and USB ports exposed. This way to charge up the batteries you would just plug it in like a cell phone. 

Will this work?  Am I missing something?

George

George Blass
 

Hi All

I’m designing my case and have a question. I plan on using 18650 batteries inside the case with this voltage regulator. 

Voltage regulator

Then for charging I’ll have one of these inside the case. 

Charger

My plan is to have everything inside the case with just the charging and USB ports exposed. This way to charge up the batteries you would just plug it in like a cell phone. 

Will this work?  Am I missing something?

George