My new “battery charger” :-)

[Barkuti]

Received one a couple days ago. Onboard voltmeter is within ±0.02V, and it features internal trimpots for both voltmeter and amperimeter adjustment. Ampmeter is spot on according to my multimeter. Maximum output voltage goes up to ≈31.6V.
I have this BF-2A battery holder on the way. Together with the KPS3010DF it will allow me to precisely determine cell DC IR.

Cheers

 

[Rossum]

The biggest problem with using a supply like that as a charger is that there's no cut-off when the current the cell is willing to take at 4.20V drops below a threshold (50-100 mA).

 

[Barkuti]

The biggest problem with using a supply like that as a charger is that there's no cut-off when the current the cell is willing to take at 4.20V drops below a threshold (50-100 mA).

Nothing wrong with that. Current just keeps tapering down slower and slower. But end of charge condition is easily spotted in the supply's display: once you see the power supply is in CV phase and output current tapers down below selected thresold (100mA, for example).
And I can select lower maximum voltages for improved cycle life.
Can also charge cells in series, gonna test it soon with 6x Samsung ICR18650-30B cells (4.35V, 6A specced).

Cheers

 

[Rossum]

Nothing wrong with that. Current just keeps tapering down slower and slower. But end of charge condition is easily spotted in the supply's display: once you see the power supply is in CV phase and output current tapers down below selected thresold (100mA, for example).

I prefer not to have to watch my charger quite that carefully.

And I can select lower maximum voltages for improved cycle life.

That's a feature I do wish more chargers offered.

Can also charge cells in series, gonna test it soon with 6x Samsung ICR18650-30B cells (4.35V, 6A specced).

 

[Barkuti]

…

Yes I know. Genuine brand name cells are very tightly binned, very consistent. They've come at ≈3.701V ±0.001V, and you can be sure they will barely drift, if at all.
I am going to select just up to ≈4.1V, for a binning in series discharge test, and they'll be set in parallel for passive balancing before testing.

Cheers

 

[Barkuti]

There it goes!

Cheers

 

[stols001]

I'm totally scared your charger may show up in my nightmares, argb!!!

LOL, the main thing is you like it and I'm going to assume you know how to use it safely. I sure wouldn't but I hope you have (non explosive) fun with it. Congrats.

Anna

 

[Rossum]

LOL, the main thing is you like it and I'm going to assume you know how to use it safely. I sure wouldn't but I hope you have (non explosive) fun with it. Congrats.

@Barkuti sometimes takes an unconventional approach to things but I'm confident that he does know what he's doing, and that he's got a fire extinguisher handy.

 

[Barkuti]

Results: no measurable cell voltage drift after tapering down under 10mA at ≈24.6V (PSU voltmeter readout). As they came lowest one was measured at 3.700V while highest at 3.702V. After end of charge the lowest cell voltage readout was 4.095V, highest 4.097V.
I've set them in parallel for passive balancing before binning discharge test. Cells seem so tightly binned it's gonna be splitting hairs to get maybe a few mAh of drift even down to ≈2.7V/cell (via manual cut off at ≈16.2V).

Cheers

 

[Mooch]

Received one a couple days ago. Onboard voltmeter is within ±0.02V, and it features internal trimpots for both voltmeter and amperimeter adjustment. Ampmeter is spot on according to my multimeter. Maximum output voltage goes up to ≈31.6V.
I have this BF-2A battery holder on the way. Together with the KPS3010DF it will allow me to precisely determine cell DC IR.

Cheers

How are you measuring DC IR with a CC/CV supply?
You’ll need, at least, a load (or two, depending on your testing methodology) and a voltmeter on the kelvin connections to the cell.

 

[Barkuti]

…How are you measuring DC IR with a CC/CV supply?
…

Voltage reading right at the battery terminals is going to be accomplished with the aforementioned battery holder plus my handy multimeter.
Since cell DC IR is about the same no matter if current goes out or in, this is my procedure:

1. Settle initial cell resting voltage at some moderate value, ≈3.7V.
2. Proceed to charge/pump 5 - 10A of current into the battery for a brief timed lapse at which exact half time the loaded cell voltage is noted down.
3. Final cell resting voltage is also noted down (a little while after the current is stopped to allow the voltage to settle).
4. Cell DC IR is calculated by substracting average cell resting voltage (½(VRinitial + VRfinal)) from the noted down loaded cell voltage to attain a dV value from which cell DC IR is obtained by dividing it by the charge current value.

Of course this is just a sort of smartass… and unconventional way of doing it. But I am pretty sure it'll work.

Cheers

 

[DaveP]

Barkuti's charger should be safe. As a cell is charged the cell's voltage approaches and finally reaches the charging voltage. Charge current drops as cell voltage rises. When both are equal, current flow drops to a minimum and finally equalization occurs. After that, the cell is in maintenance mode.

It's a lot like water flow. When the flow from one vessel (side by side) causes the other to fill, there's a point where the two are equally filled and water movement stops, assuming that one isn't at a higher level than the other.

 

[Rossum]

Barkuti's charger should be safe. As a cell is charged the cell's voltage approaches and finally reaches the charging voltage. When both are equal, current flow drops to a minimum and finally equalization occurs. After that, the cell is in maintenance mode.

I dunno. No dedicated charger works like that, nor does the spec sheet for any Li-Ion battery allow for it to be continuously float-charged at 4.2V.

 

[sonicbomb]

I think someone wants to be Mooch

 

[DaveP]

Rossum wrote: I dunno. No dedicated charger works like that, nor does the spec sheet for any Li-Ion battery allow for it to be continuously float-charged at 4.2V.

It depends on the charger design. Some lithium chargers, like the one you use with a cell phone, are constant voltage chargers. As the battery charges the current it draws from the charger diminishes due to rising voltage of the battery. Eventually, the battery voltage balances with the charging voltage and current draw drops accordingly as the internal resistance of the cell increases in a full charge state. At that point the current draw from the charger drops to a tiny trickle charge level and rises again if the cell voltage drops over time.

My Efest LUC 4 drops current to almost zero when the cell is charged. Over time, if the battery begins to drop voltage, the current will rise and begin to charge the cell again to top it off.

 

[Barkuti]

… Charge current drops as cell voltage rises. When both are equal, current flow …

stops. Cell voltage cannot go above supply's output voltage.

… It's a lot like water flow. When the flow from one vessel (side by side) causes the other to fill, there's a point where the two are equally filled and water movement stops, assuming that one isn't at a higher level than the other.

Yes.
Tapering can prolong for very long but this is due to lead and connection resistances (can be up to 0.2Ω, mostly due to connections). When they're minimized (like when I do balance close voltage cells with copper/aluminium sheet and neodymium magnets) they equate relatively fast.

 

[Mooch]

Voltage reading right at the battery terminals is going to be accomplished with the aforementioned battery holder plus my handy multimeter.
Since cell DC IR is about the same no matter if current goes out or in, this is my procedure:

1. Settle initial cell resting voltage at some moderate value, ≈3.7V.
2. Proceed to charge/pump 5 - 10A of current into the battery for a brief timed lapse at which exact half time the loaded cell voltage is noted down.
3. Final cell resting voltage is also noted down (a little while after the current is stopped to allow the voltage to settle).
4. Cell DC IR is calculated by substracting average cell resting voltage (½(VRinitial + VRfinal)) from the noted down loaded cell voltage to attain a dV value from which cell DC IR is obtained by dividing it by the charge current value.

Of course this is just a sort of smartass… and unconventional way of doing it. But I am pretty sure it'll work.

Cheers

I urge you to compare your results with the more conventional method of using a discharge to measure DC IR as what’s going on in the cell is completely different for a charge than a discharge. Without this comparison you have no way of knowing how accurate your method is.

While the ohmic resistances won’t change for a charge or discharge the electrochemical equivalent resistances (AC IR component) will be different. How much? I don’t know as I’ve never seen anyone use charging to determine IR.

I would advise using the cell voltage before the charging pulse starts as the initial voltage as the post charge pulse resting voltage will take a long time to settle.

Why are you calculating the average resting voltage? Just use the difference between the pre charge resting voltage and the charging voltage and divide by the current. That will give you the equivalent resistance that causes that voltage rise at that current level. Perhaps I’m misunderstanding something here though.

How

 

[Barkuti]

I urge you to compare your results with the more conventional method of using a discharge to measure DC IR as what’s going on in the cell is completely different for a charge than a discharge. Without this comparison you have no way of knowing how accurate your method is.
…
I would advise using the cell voltage before the charging pulse starts as the initial voltage as the post charge pulse resting voltage will take a long time to settle.

Why are you calculating the average resting voltage? …

Because as we pump current into the cell, it's resting voltage raises. Averaging initial and final cell resting voltages gives about the resting voltage figure at exactly the moment I read and note down loaded voltage.
Will compare my results to those inferred from discharge curves, no problem.

Cheers

 

[Rossum]

It depends on the charger design. Some lithium chargers, like the one you use with a cell phone, are constant voltage chargers.

You can't really see what's going on with a modern phone's battery because the dang thing isn't accessible to an external meter, and using an app that shows voltage while the phone is running isn't very telling either because the phone itself is presenting a constantly varying load.

As the battery charges the current it draws from the charger diminishes due to rising voltage of the battery. Eventually, the battery voltage balances with the charging voltage and current draw drops accordingly as the internal resistance of the cell increases in a full charge state. At that point the current draw from the charger drops to a tiny trickle charge level and rises again if the cell voltage drops over time.

Agreed, this would happen if you allowed it. Yet no spec sheet I've seen for the cylindrical cells we use allows that. They all demand that charging stop when the current the battery is accepting at final voltage drops below some specified value, generally 50-100 mA.

My Efest LUC 4 drops current to almost zero when the cell is charged. Over time, if the battery begins to drop voltage, the current will rise and begin to charge the cell again to top it off.

Huh? That graph clearly shows the charger stopping the charge at the 450 minute mark when then current the battery is pulling from the (then constant voltage) drops below the charger's threshold. It looks to be doing exactly what a charger is supposed to do, but @Barkuti 's power supply won't do that. It will sit there supplying 4.2V (or whatever he's got it set to) until he manually intervenes.

 

[Mooch]

Voltage reading right at the battery terminals is going to be accomplished with the aforementioned battery holder plus my handy multimeter.
Since cell DC IR is about the same no matter if current goes out or in, this is my procedure:

1. Settle initial cell resting voltage at some moderate value, ≈3.7V.
2. Proceed to charge/pump 5 - 10A of current into the battery for a brief timed lapse at which exact half time the loaded cell voltage is noted down.
3. Final cell resting voltage is also noted down (a little while after the current is stopped to allow the voltage to settle).
4. Cell DC IR is calculated by substracting average cell resting voltage (½(VRinitial + VRfinal)) from the noted down loaded cell voltage to attain a dV value from which cell DC IR is obtained by dividing it by the charge current value.

Of course this is just a sort of smartass… and unconventional way of doing it. But I am pretty sure it'll work.

Cheers

Because as we pump current into the cell, it's resting voltage raises. Averaging initial and final cell resting voltages gives about the resting voltage figure at exactly the moment I read and note down loaded voltage.
Will compare my results to those inferred from discharge curves, no problem.

Cheers

Sorry, I’m missing something as that doesn’t seem like it will work but I’m sure that’s my fault. Looking forward to your posted test results!

Don’t use my discharge curves to derive DC IR as the one second sampling rate and the inability to see the start of discharge clearly makes that problematic and subject to a lot of error. Use the DC IR spec in my ratings graphic for most cells tested over the past few months.