Testing a 10S 36 Volt BMS

[newb123]

I have included a picture of the BMS with heat sink removed

So, I should charge each cell to 4.2 V, then connect the BMS and let it sit for a few days at 4.2V in parralell config?

The blue light is on,meaning the cells are charged to 4.2V now, so how do I know the BMS is balancing the cells? Once each cell has
reached 4.2 V, then the red charging light on my CC/CV converter changes to blue

 

[john61ct]

I feel like I'm repeating myself.

The BMS only balances while charging is active, and the pack is hooked up in its xPyS layout.

If the BMS does not indicate balancing status, you need to read the cell voltages to check how closely balanced they are.

Many BMS will let you check from a cell phones or tablet.

 

[john61ct]

But, if this is like your first time "pre-assembly commissioning" top balancing:

Once you get them close to the same voltage, you could put them **in parallel** no BMS, bring them up together a bit higher than they are now at rest

and **hold** that termination voltage until amps accepted drops to .01C.

That requires an ammeter.

Then keep them hooked up in parallel to **sit** isolated for a night, or couple days if you can.

They will all equalize to each other. Or should, measure each isolated after before assembing back into a pack with the BMS.

 

[Dak77]

I know I'm gonna get slapped for asking this , but is a cheap bms more liability than benefit? If so , what are some suggestions for "some of the least expensive , yet reliable bms modules ?

 

[newb123]

Then keep them hooked up in parallel to **sit** isolated for a night, or couple days if you can.

Yes, I have them all charged to 4.2.

So your saying, without the BMS, parallel them all up, set the CC/CV converter to a bit higher than 4.2 like 4.3, then charge them without the BMS. I say a bit higher because, the converters blue light comes on at 4.2 since I charged them all to the voltage, at .5 amps. if 10 of these batteries, in parallel are being connected to the converter, when the blue light is one, nothing is happening, correct?

 

[john61ct]

I know I'm gonna get slapped for asking this , but is a cheap bms more liability than benefit? If so , what are some suggestions for "some of the least expensive , yet reliable bms modules ?

Depends on the situation.

BMS is not just one gadget but a list of functionalities, all the gear that protects the battery is included AFAIC.

Individual owners's capacities for DIY, preferences and budgets dictate the solutions chosen.

There is no one size fits all, and if there were it would not be cheap.

Make sure in any case you thoroughly understand what you use, and if cheap enough, use multiple redundant layers of protection and have spares ready to swap in when (not if) they fail.

Many go without "a BMS", but usually you do need devices that act as a failsafe, an innermost last layer of defense.

 

[newb123]

Then keep them hooked up in parallel to **sit** isolated for a night, or couple days if you can.

They will all equalize to each other.

oh your saying let them sit without using a charger, and they will self equalize

 

[john61ct]

Yes, I have them all charged to 4.2.

So your saying, without the BMS, parallel them all up, set the CC/CV converter to a bit higher than 4.2 like 4.3

Woah!

Check your cells' spec sheet for max voltage.

A whole 100 mV above maximum is not a little increase.

After sitting isolated in parallel, get an accurate reading, will be much lower than your charge voltage.

I do not know your converter, but if it claims to do CV stage then maybe the blue light means it has reached that.

Say it's 4.05, going back up to a 4.2V the group is going to accept charging further to the current endpoint I spec'd, may take a fair time.

Use your DMM and ammeter to monitor until that point then stop, 35Ah you said? Should be charging at up to 20A rate, then stop when trailing amps fall to say 3A at the 4.2V Absorb.

 

[john61ct]

Then keep them hooked up in parallel to **sit** isolated for a night, or couple days if you can.

They will all equalize to each other.

oh your saying let them sit without using a charger, and they will self equalize

Yes, wired in parallel will start the process.

You are then driving them to a higher than normal SoC, together wired in parallel,

then letting them sit again 12-24 hours, since they're not perfectly matched have reacted differently to the balance charge.

Then assemble your pack.

Hopefully from then on your correct use of the charger+BMS will keep them balanced.

You will need to monitor that, figure out how to make it easy for yourself.

 

[john61ct]

Note "CC/CV" is inherent to holding a charge past hitting the setpoint, not a feature of the charge source.

 

[amberwolf]

So your saying, without the BMS, parallel them all up, set the CC/CV converter to a bit higher than 4.2 like 4.3, then charge them without the BMS.

No.

Don't overcharge the cells.

The BMS doesnt' need to balance htem if they are already all teh same voltage; there is nothing for it to do.

If you want to test the balancing function, the cells have to be at differnet voltages, below 4.2v.

So just ride the bike with the BMS attached and then check cell votlages.

If they are different at that point, hook it up to your charger set to 42v, and measure cell voltages as it charges, so you can see the process happen.

 

[john61ct]

Some balancers will keep going until they are all **exactly** the same voltage, much closer than you would get manually with imprecise tools.

50mV or even 5mV is not uncommon.

Not saying the cheap Chinese necessarily **are** in fact that accurate, but they can try to be.

And if you **have** properly top-balanced at say 99.99% SoC relative to 0A flowing, then at lower and lower SoC points, it would be natural for some imbalance to start to emerge, imperfectly matched cells can really only be balanced **at** a narrow SoC range, not throughout say the whole top 10%.

 

[Dak77]

What is an acceptable voltage variance between cells , at which point you can string them in parallel to allow them to balance themselves naturally before assembling the pack ?

 

[john61ct]

I use .1V or 100mV, but that's with thick wires, closer is better

 

[newb123]

is there a tutorial on here, for li ion charging and BMSs?
I know battery university has some basic info

terms like SOC , 20A rate, etc are new to me

 

[newb123]

I charged each cell to 4.2 and then paralleled them all up and let them sit, they balanced out over night as you suggested. Why does it take so long to balance out?

Also, I set the CC/CV buck to .5 amps but it will charge the cell up to 3.7 ( I have it set at 4.2 V) then the blue light comes on. I turn the screw pot a 1/2 turn, then the red charging light comes back on. (CC amp screw pot) it seems it needs more than .5 amps to push above 3.7V....is this correct?

He seems to go into great detail about charging/discharging cutoff testing
Seems there needs to be a trigger voltage when discharging
https://www.youtube.com/watch?v=w8xtSTspFCE

 

[john61ct]

I charged each cell to 4.2 and then paralleled them all up and let them sit, they balanced out over night as you suggested. Why does it take so long to balance out?

If you had a voltmeter that was very precise and very accurate, you could tell when they were within say 5mV of each other.

To get there may actually take days, but I figured you were impatient and couldn't tell anyway.

This top-balancing is a once-off (hopefully) commissioning procedure and if the cells match capacity and resistance and you also care for them properly, hopefully they won't get much out of balance, at least stay close enough your BMS (or whatever device you end up using for regular balancing) doesn't take forever to bring them back in balance.

Short answer: because as voltages get closer and closer, current flow gets slower and slower.

 

[john61ct]

What is the Ah/mAh capacity of your cells, and the pack as a whole?

What does the manual for your DC converter say is the meaning of the red vs blue lights?

Have you followed its instructions for setting the target voltage - under load, as opposed to OC unloaded?

And what are you using to measure actual V & A independently of charge sources?

 

[newb123]

The pack I think was 12 Ah, already got rid of that. now just using the basic 18650 cells

the converter red is charging the blue is full

there were no instructions that came with it

Using a mulitmeter with DC volts and series Amp reading capacity. I check it every 10 - 20 min manually, I could code some simple code with the arduino and Analog input w/voltage divider resistors and ADC pin with display or tone() to call but its no issue to check it by meter for now

 

[john61ct]

In general, details & precision will get you better answers.

Every pack has an Ah capacity, please answer my question. If you can't figure it out tell me your xPyS layout and link to the new "basic"cells.

So since you can measure V&A, you can tell us exactly what the blue light means. There are myriad definitions of "full", that doesn't help.

A logger that lets you plot the curves on your PC would be ideal.

You really should find the instructions online, even if Chinglish, contact the seller, look for identical units for sale.

Could you link to the unit you're using?

You can use any battery to test, use a V setpoint a bit lower than the mfg max spec.

Charge from 50% depleted, log the CC stage (both V&A) as voltage climbs (blue) then when your setpoint is reached

CV stage then continues at that voltage, depending on the Ah capacity and batt chemistry maybe for hours.

All this should happen without you touching your set screws on the converter, if you figure out how to set your parameters in advance of starting to charge.

Record the current rate as it falls until it hits 0.005C, or could even wait until zero.

When did the light go to red? At the CC to CV transition? Some time later, at a certain amps rate, or perhaps based on just a timer after that?

 

[docw009]

You have been getting good advice, but let me add a comment. Here's a picture of your BMS. There is no solder on the C- pad.


Here's how you were supposed to wire up the charge connector.


I hope you did it this way, but the lack of solder on that pad suggests you are charging thru the output port. Do not do that, especially if not using a 42.000 volt charger.

The BMS will NOT balance if you don't hook the charge connector as above. In addition, the BMS will NOT protect against over charging if the charge is hooked to the P- or if you charge thru the load connector.

A month ago, I carelessly plugged my charger into the load port, and I used the wrong charger. Battery was destroyed, and would surely have escalated into one of those youtube fires you see when they overcharge a cell. It was still pretty hot though, and I had to toss it in a bucket of water.

 

[newb123]

I have not charged yet using the bms, just using a buck CCCV and charging each individual cells. I need a 42 V source so I ordered a boost converter

 

[newb123]

I have included pics of the buck CCCV charging a cell with red light on set at about .6 amps and set point at 4.2V; now reading 3.9V

and the other cells are resting in parallel balance config, the red wires on the positive side are soldered to the existing nickel tabs and pulled out so the dont touch the sides. Had that happen once with some not so good results. maybe latter I will make some plastic cut outs and hot glue them on the pos side for extra protection

Every pack has an Ah capacity, please answer my question. If you can't figure it out tell me your xPyS layout and link to the new "basic"cells.
I threw away the cover for the pack, but I remember it at 12 Amp hours. these cells arent new. Got them for free. Trashed the ones under 3.7 volts, charged the other ones to 4.2. there are ten of the green ones. Have included a pic of their model #. What is xPyS layout? The red cells (18650) are for my light set (12 volts) the green ones are for my motor (36 volts in series, for now) no range but its all I have right now. specs for the panasonic CGR26650 B are as follows:
--------------------------------------------------------------------------------------------------------------------------------------------------------------
3300mAh
Nominal Voltage:
3.7V
Type:
Li-polymer
Voltage:
3.7V
Application:
E-bike,Computer ,Mouse,Battery pack,etc
Color:
Light Green
Warranty:
1 Year
Capacity:
3300 MAh
Battery type:
26650 Rechargeable Li-ion
Cycle life:
1000 Times
Material:
Lihtium Polymer
--------------------------------------------------------------------------------------------------------------------------------------------------------------

A logger that lets you plot the curves on your PC would be ideal.

anywhere I can get one of these or make one...got some spare nano arduinos and use the serial monitor, so something like this?

When did the light go to red? At the CC to CV transition? Some time later, at a certain amps rate, or perhaps based on just a timer after that?

red to blue occus at 4.2V

Could you link to the unit you're using?

I posted a pic below of the model and company mfg. specs/instructions follow:

Description:

the maximum current is 8-9A

(Spot: the maximum current is 8-9A, the input voltage is the highest 40V output voltage is about 35V or so)

(Due to 12A current chip manufacturers to stop production, replace the chip current from the previous 12A down to 8A current (actual test maximum current in 9A or so), the input voltage from the previous 32V to 40V, the output voltage from the previous 28V to 35V. Power supply for 10 strings of high power LEDs 12A chips are subject to change.



QS-2405CCBD-12A power supply module

Size: 65 (L) * 47 (W) * 23.5 (H) mm

typical application:

Adjustable power supply (12A power is large enough), high power LED driver, LED display driver, lead battery charging, lithium battery charging, car power, car notebook power supply (buck), power supply, low voltage system power supply (such as children Toy car with 12V battery buck to 6V), 24V to 12V 12A \\ 12V to 5V 12A \\ 24V to 5V 12A \\ 24V to 19V20V and so on, the application range is very wide.

1. Fixed turn lamp current is 0.1 times the constant current value (used when charging to identify whether the battery is full);

2. Using a dedicated reference IC, and high-precision sampling resistor, so that constant current more stable, (20 degrees to 60 degrees constant current 5A when the temperature drift less than 5%). Especially for LED driver

3. Output current, the maximum output current can reach 12A, to meet most of the needs.

4.4 high-frequency capacitors, effectively reduce the output ripple, improve work stability

5. Double heat sink design, MOS tube Schottky diode independent heat sink, heat is good, do not affect each other

6. At the cost of large-size iron-silicon magnetic ring, improve work efficiency, and with pure copper and Rao, reduce heat, improve efficiency.

7.3296 multi-turn potentiometer, voltage and current regulation of high precision, good stability.

8. Special current sampling resistance Current sampling accuracy High stability and good temperature drift small. LED essential.

9. Two-color indicator light, working status at a glance. Charging must be.

10. Voltage and current are adjustable, so adjustable power supply effect, 12A current, power enough.

Module parameters

Modular nature: non-isolated step-down constant current, constant voltage module (CC CV) charging module

Applications: High-power LED constant current drive, lithium battery charging (including ferroelectric), 4V, 6V, 12V, 14V, 24V battery charging, nickel-cadmium nickel-metal hydride batteries (battery pack) charging, solar panels, wind turbines

Input voltage: 7-32V (without constant current 5-32V)

Output voltage: (1) continuously adjustable (0.8-28V)

(2) fixed output (0.8-28V between any choice), please tell the treasurer when buying. (For the time being only for bulk customers, all the sample adjustable type)

(3) If you need higher voltage please contact me directly

Output current: up to 12A (power tube temperature exceeds 65 degrees please add fan cooling, 24V to 12V 6A or less open environment generally can not fan)

Constant current range: 0.2-12A (adjustable) (no constant current without this function)

Turn current: constant current value * (0.1), turn the lamp current and constant current value linkage, such as the constant current value of 3A, turn the lamp current is set to constant current 0.1 times (0.1 * 3A = 0.3A), when the constant When the flow rate is adjusted to 2A, the turn lamp current is 0.1 times the constant current (0.1 * 2A = 0.2A).

The secondary version is fixed for 0.1 times (the actual turn lamp current is probably not very accurate) is used to charge if the fill is full of instructions.

Minimum pressure difference: 1V

Output power: maximum power of about 300W, power tube temperature over 65 degrees please add fan.

Conversion efficiency: up to about 95% (the higher the output voltage, the higher the efficiency)

Operating frequency: 300KHZ

Output ripple: 20M bandwidth (for reference only)

Input 24V output 12V 5A ripple 50mV or so (no noise)

Operating temperature: industrial grade (-40 ℃ to +85 ℃) (the actual use, please pay attention to the power tube temperature, the temperature is too high, please strengthen the heat)

No-load current: typical 20mA (24V to 12V)

Load regulation: ± 1% (constant voltage)

Voltage regulation: ± 1%

Constant current accuracy and temperature: the actual test, the module temperature from 25 degrees to 60 degrees, constant current value of less than 5% (constant current value of 5A)

Dynamic response speed: 5% 200uS

Potentiometer adjustment direction: clockwise (increase), counterclockwise (reduced) close to the input potentiometer for voltage regulation (CV), close to the output of the potentiometer for the current regulation (CC)

Indicator light: two-color indicator light, red light in charge, charging complete indicator green (no load is green) without constant current indicator light is red.

Output short circuit protection: Yes, constant current (current set constant current value)

Input Reverse Protection: None,

Output to prevent backflow: none.

Wiring method: terminal block

Battery charging method:

1. Make sure you need to recharge the battery's float voltage and charge current, the module's input voltage;

2. Adjust the constant voltage potentiometer, adjust the output voltage to about 5V.

3. With the multimeter 10A current block measurement output short-circuit current, while adjusting the constant current potentiometer so that the output current reaches a predetermined charge current value;

4. Adjust the constant voltage potentiometer so that the output voltage reaches the float voltage;

5. Connect the battery, try charging.

(1, 2, 3, 4 steps for the module input power supply, the output is not connected to the battery.)

LED constant current drive use:

1. Make sure you need to drive the LED's operating current and the maximum operating voltage;

2. Adjust the constant voltage potentiometer, adjust the output voltage to about 5V.

3. With the multimeter 10A current block measurement output short-circuit current, while adjusting the constant current potentiometer so that the output current to a predetermined LED operating current;

4. Adjust the constant voltage potentiometer to make the output voltage to LED maximum operating voltage;

5. Connect the LED, test machine.

(1, 2, 3, 4 steps for the module input power supply, the output no load LED lights.)

Package Included:
1 x DC-DC CC CV Buck Converter Step-down Power Module 7-32V to 0.8-28V 12A 300W USA

 

[john61ct]

Are you really poor or something?

Otherwise I would not bother messing with secondhand cells.

xPyS layout means, for example 5P10S to get a 36V pack at 16.5Ah, or would be when new.

Might give 3 hours range supported by pedaling, and without big hills?

If 12Ah maybe 4P10S?

______
Many chargers, dummy loads include PC connectivity besides dedicated loggers, no need to roll your own.

Stopping at 4.2V, not holding CV is fine. 4.1V would be better for longevity.

At 8A output current you can charge 7 cells in parallel at a time, around 0.3C.

Follow the instructions there for setting volts and amps so no adjusting needed while actually charging.

 

[newb123]

oh ok thats a new # for me...I will check a similar pack for its xPyS config #

if I get a charger with a data logger, what am I looking at? how long to hold the CV?