The making of the BLF UC4 charger: the start of a new venture, INTEREST LIST, UPDATE 7 (Ramping up slowly...))

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CvR_XX's picture
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I’m interested in one!

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Looks like the project has been placed on hold, however, I will throw in that I am interested in 2 if these ever make production.

Thank you,

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Interested. Let’s make it capable of charging 21700 and 26650 cells, too.

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@def_nvar, I knew it applied to lithium-ion cells, but NiMH cells? I did not actually know.

I’ll do some research on the subject and how easy the charging implementation would be.

My very own high current Beryllium Copper springs Gen 3:
Liitokala Aliexpress Stores Battery Fraud:

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also I found some nice Application Notes on inflection point charging from ST:
that’s detecting the point where a curve transitions from rising to falling and it’s even better for the battery than fast charging with -dV/dt since it allows to stop at 99-100% pretty much exactly instead of relying on the slight overcharge until the voltage drops by a bit.
It’s what panasonic used in flagship chargers BQ-CC55 and BQ-CC65
ST recommends using back-up -dV/dt, temp and voltage termination but that config could also be permanently stored in eeprom, configurable in the UI.

sorry for giving you homework Big Smile

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it’s slightly different for the chemistries

for li-ion, it’s good if you don’t charge them all the way to 100%.
this increases how many charge cycles you can get out of the battery as a higher voltage / SOC, especially together with higher temperature accelerates aging-induced wear.
It’s also why, for RC LiPo packs at least, recommended it’s recommended to store them at 3.85V = just above 50% SOC per cell and then charge them fully right before using them.
In RC a full charge makes sense since they want maximum runtime and don’t care if they only get 200 cycles but for Li-ion in flashlights, you can avoid charging it that high altogether if you don’t really need maximum capacity.

for NiMH, there are 2 relevant effects:
if you charge them up (e.g. to 100%) and then discharge them a bit afterwards (FDK goes down to 70%), they can keep the charge you put in for longer, i.e. you temporarily decrease self-discharge until the next charge cycle
when you charge a NiMH to 100% (or in reality, a bit beyond) with -dV/dt termination, you make them hot, which also accelerates aging processes for the duration it’s hot. for the same temperature, the effect on NiMH is less severe but with -dV/dt on a used battery they can go well beyond 45°C / 113F. Especially as the internal resistance increases with cycles/age, you get higher and higher temperatures at termination, “quickly” degrading the battery more and more.
That’s why I suggested adding inflection point charging, to stop a bit earlier than above 100%, decrease termination temperature and thus get more cycles out of the battery for trading a few % of mAh.

at least that’s how I understood it

I’d make a settings menu with submenus in UI and save the settings to EEPROM.

for Li-Ion
target charge and discharge voltage selectable from 2.50V to 4.20V in 0.05V increments
slow, stepped current reduction before reaching target charge voltage, especially above 4.0V (see AN859 Li-Ion current curve in last post)
minimum detection voltage, default 2.5V but changeable by the user, with a big fat warning in the manual that charging overdischarged Li-Ion batteries can form dendrites and thus internal short-circuit, leading to anything from increased self-discharge current to venting or even serious fire during charging or even up to months after charging (time bomb) and is thus not recommended.

for NiMH charge
charge current
primary mode selector: inflection point / -dV/dt / target voltage / temp
with -dV/dt and temp serving as backup termination methods in inflection point mode
-dV/dt value (2.5mV and above in 2.5mV increments)
target temp value
max. temp value (for overtemp protection)
inflection point parameter, i.e. how much the smoothed battery voltage derivate is allowed to drop after peaking, causing charge termination (see AN417 in the post above, Fig 5). Good defaults will be key here (soon enough after inflection but not succeptible to measurement noise (higher ADC resolution and smoothing will help here), and allowing this to be adjusted by the user allows for getting closer and closer to the charge level -dV/dt would produce.
target voltage value
max. voltage value (for overvoltage protection)
post charge mode selector: nothing / trickle charge / selfdischarge-reduction discharge
trickle charge current: from your preset currents
selfdischarge-reduction voltage, default 1.42V, in 0.01V increments.
selfdischarge-reduction discharge current
bothering with converting NiMH voltages to % is wasted effort in my opinion since voltage-to-SOC curves are so different between NiMH manufacturers / product lines, let alone capacitiessee lygte/HKJ battery comparator
minimum detection voltage, default 0.7V but you should be able to lower it to 0.1V to revive “dead” cells

for NiMH discharge
target voltage value
discharge current
discharge delay in minutes (wait X minutes between charging and discharging if cycling / measuring capacity to allow the battery to cool between cycles)

for NiMH cycling
charge cycle number 1-10000
there should be a counter available to display how many cycles the cell has already done if this mode is active
end state: charged / discharged
I’d add an internal resistance test between the pause after charge and the discharge (a cool battery always has higher/more realistic IR), then here the user can set:
rejection on internal resistance yes/no
maximum internal resistance value before rejection (10-5000 mOhm, default 2000mOhm)
this, together with logging capabilities makes the charger an automated AAcycler-worthy test machine

for NiMH capacity testing
I’d always do charge-discharge test-charge

best add a way to manually calibrate channel voltage readings or even currents and internal resistance measurement current

to save the user from having to select the channel by button each time:
When you insert a battery I’d display a what-to-do-dialogue for this channel (operating mode: charge / discharge / measure IR / capacity test / cycle) and also set desired charge / discharge current for each.
If a battery/channel was previously configured since the charger was powered on, you could pre-select the last entered operating mode and currents.
If there was no battery inserted yet, default to charging and the default current set in the settings menu.
If the user inserts multiple batteries, have the charger remember the order in which they were inserted and ask for each channel before starting any operation. (an array could be used here)
If there is at least one operation going on and the user inserts a battery, continue the operation in background and ask what’s to be done with this channel.
Should a battery be removed before it’s decided what’s to be done that battery is either crossed from the what-to-do-dialogue list or its dialogue is closed again, if it’s the one being displayed.
then during charging I’d only leave an option to change current up/down for the selected channel, but also to pause or abbort, which returns to main menu, showing voltages and allowing to access the settings menu.

that’s all I can think of for a “simple”, powerful user-friendly UI for now.
of course the manual would need to explain every parameter and what-does-what very well but if it’s clear enough people will learn it quickly.

During the operations I’d permanently cycle the display through each active channel, showing voltages and mAh charged / discharged with the option to view other metrics by button.

again, sorry for all the homework BlueSwordM.
If I’d be paying my own bills I’d set aside time to help you in development but studying is more important rn.

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I’m interested in one too.

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Interested, when and if. Thanks.

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I’m interested in one too.

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Interested, if we go forward

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Just saw this thread today, as someone that have:
Opus BT-C3100 V2.2
LiitoKala Lii-500S
Miboxer new C4-12
Sanyo NC-MQR06W
I would edit the 

BlueSwordM wrote:
4. 4 cell channels, with support for 10180 cells all the way up to 78mm 21700s.

for a simultaneously support 4 cells, size at least up to 26800 if not 26950 for future-proofing on length, or even 32950 (to accommodate the 32650 cells) 

We really need 4 slot 26800 charger.

Ps. If you are worried about the overall size, you could just have sliding plastic covers with the metal end, for each slot, and not robust plastic body, with just metal sliding inside.

And we need to test the AAA cells fit, because it's very common for them to not fit easy, on this type of chargers (lose contact on the button head, or tail, or just jump out of slot by spring tension). 

BlueSwordM wrote:
11. Adjustable max charging voltage for lithium-ion: 3,50V-(n1+0,1V)…(n6+0,1V)-4,2V-4,25V-4,30V-4,35V-4,40V

This can be what I could be sold on, I would love to charge my Li-ion up to max 4.10V, or 4.15V (and I wish it could be programmed and memorized)

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I’m interested for one if it makes production.

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