OPUS BT-C3100 V2.2 Resistance test upgrade mode

[EGOksy]

Hi,
so i stumbled on nice mod for more accurate resistance testing on OPUS BT-C3100 V2.2





Of course you should choose the silicon protected wires .. and they should be ~26 AWG or0.5mm (5A max)
AND wire resistance for 26 AWG ~ 5cm is ~ 0.007Ohms (7mOhms) that is when current flows only through it , but it will flow and through contacts of slider, so resistance will be less from this mode

After this mod i get resistance always with in 5mOhm

The solder sticks quite well to the spring holder(slider) so there should be no problem

 

[Korishan]

YAY!!! Thank you for confirming EXACTLY what I've been saying for months about bypassing the spring for resistance testing.

You're the first who has actually done this mode and posted the results. I give you "Like" and "+1 Rep"

The second question is, does the mAh rating now become more accurate as well? Further testing is needed, I would gather

 

[EGOksy]

Not sure .. maybe will help a little bit, but the mAh calculation is more specific to REAL Voltage and REAL Current flows, maybe it will help a bit, but if OPUS is miss-reading the voltages ....

if you somehow make read out correct for voltage... it will help on mAh and on Resistance to , because it involves the Voltage in calculations... not sure what type of calculation is used here for Resistance ...

I'v tested the mAh on both my beast-diy tester and opus and have a chart ... that shows that opus gets closer to readings from beats when readings are from ~ 2100mAh. but way off when less. Will add that later

 

[Korishan]

I was wondering because a coil of wire increases resistance. Not to mention the contacts between the spring and the terminals was loose, so there is a lot of wasted energy at these connections.

Across the forum the knowledgeable guys will tell you to make sure your solder joints are done right and not cold soldered, bolts/nuts are tight, crimp connections are done correctly and securely, etc etc etc.
But then most of them will break out the opus to get a capacity test on the cells and not fix the one issue that was probably plaguing it from the start. Loose connections on the spring ends. Loose connections cause resistance which is wasted in the form of heat. No wonder the opus would consistently read wrong values.

 

[tremors]

As a precaution, anything that is moving often should be hot glued at points in case the wires snap at the solder joint and fly around shorting all the lovely things. At least where you can.

 

[EGOksy]

I was wondering because a coil of wire increases resistance. Not to mention the contacts between the spring and the terminals was loose, so there is a lot of wasted energy at these connections.

Across the forum the knowledgeable guys will tell you to make sure your solder joints are done right and not cold soldered, bolts/nuts are tight, crimp connections are done correctly and securely, etc etc etc.
But then most of them will break out the opus to get a capacity test on the cells and not fix the one issue that was probably plaguing it from the start. Loose connections on the spring ends. Loose connections cause resistance which is wasted in the form of heat. No wonder the opus would consistently read wrong values.

i think the best decision to upgrade OPUS would be to get 1% resistors and replace the existing ones from the PCB ... also make a bigger bottom case with 3d printer ... and add bigger fan to cool the new resistors and add the more air flow for other parts and more powerful supply.

As a precaution, anything that is moving often should be hot glued at points in case the wires snap at the solder joint and fly around shorting all the lovely things. At least where you can.

This is a good point !! No one wants the loose ground wire to go around the pcb ) I'll add the glue after it finishes this batch of 4 batteries



PS: here is the result of about 120 tested batteries on my tester and on OPUS. % is how much you add from measured capacity to match the OPUS capacity(Opus shows way more for weaker cells )

 

[Korishan]

PS: here is the result of about 120 tested batteries on my tester and on OPUS. % is how much you add from measured capacity to match the OPUS capacity(Opus shows way more for weaker cells )

This is due to the opus reading higher capacities than what they really were. So now you are seeing what the cells really are in capacity.

 

[Mazlem]

I added the wires to my Opus but weirdly I'm seeing higher values on most of the 24 cells I've tested so far, not lower. Like up to 100mAh higher than when they tested on an unmodded charger.

There's a difference in that the cells were previously tested only using the unmodded Opus. Now I'm charging with TP4056's and discharging with the modded Opus. There may be too many variables to accurately test like this.

 

[rev0]

I added the wires to my Opus but weirdly I'm seeing higher values on most of the 24 cells I've tested so far, not lower. Like up to 100mAh higher than when they tested on an unmodded charger.

There's a difference in that the cells were previously tested only using the unmodded Opus. Now I'm charging with TP4056's and discharging with the modded Opus. There may be too many variables to accurately test like this.

This makes sense to me, the TP4056 probably has a lower cut off current in CV mode (the opus stops charging around C/10 whichis a bit high), and adding the wire means the voltage the opus is reading is closer to the real cell voltage, so with less voltage drop the cell will discharge to a real value closerto the 2.95V cut off.

 

[EGOksy]

I added the wires to my Opus but weirdly I'm seeing higher values on most of the 24 cells I've tested so far, not lower. Like up to 100mAh higher than when they tested on an unmodded charger.

There's a difference in that the cells were previously tested only using the unmodded Opus. Now I'm charging with TP4056's and discharging with the modded Opus. There may be too many variables to accurately test like this.

maybe tomorrow will do some rechecks .. grab some oldest cells that were tested on opus and give it a go ..
it all depends how accurate is the voltage readings .. if they where lower because of bad connections now they should be higher. After adding the wire .. because of parallel resistances now ... resistance that was in there will be always lower then the lowest value of parallel resistances .. i don't have a 5 digit multimeter so cant test the resistance that it is in the slider... but wire should be about 7mOhms so while 1A is flowing it should be no more then 7mV drop on wire

 

[EGOksy]

As a precaution, anything that is moving often should be hot glued at points in case the wires snap at the solder joint and fly around shorting all the lovely things. At least where you can.

This is a good point !! No one wants the loose ground wire to go around the pcb ) I'll add the glue after it finishes this batch of 4 batteries

Ok this was a good point but a bad material to use
OPUS gets HOT as wee all know soo ... what did you all think happened with hot glue
Yes it melted good thing that pcb is facing bottom : and all the glue ended on the bottom of the casing

 

[Korishan]

Hot glue isn't conductive. So even if it dripped on the electrical parts, you'd still be fine. Just be a mess to pull back off At least with the glue on it would help protect the board from leaky cells.

 

[EGOksy]

Hot glue isn't conductive. So even if it dripped on the electrical parts, you'd still be fine. Just be a mess to pull back off At least with the glue on it would help protect the board from leaky cells.

I guess it could do some mess if you use additional fan .. like others in this forum do .. Dripping on the fanwhile it is spinning ... you get inedible "sugar" wool everywhere
I think the right one would be some kind of thermal silicon ... that is not conductive

 

[Korishan]

Hahah, that'd be kewl effect. glue wool Any takers on making this happen? If so, set up 2 or 3 cameras to get the effect from all angles

 

[snuf]

YAY!!! Thank you for confirming EXACTLY what I've been saying for months about bypassing the spring for resistance testing.

You're the first who has actually done this mode and posted the results. I give you "Like" and "+1 Rep"

The second question is, does the mAh rating now become more accurate as well? Further testing is needed, I would gather

Hi, this won’t work, because the spring is NOT part of the electrical circuit…..

 

[Korishan]

Hi, this won’t work, because the spring is NOT part of the electrical circuit…..

The spring itself is not directly connected. however the metal sleeve that the contact slide rides in "is" directly connected. So whether it's the spring or not, adding the hard wire connection will get far better results across the board.

 

[Ruky]

Could this mod also work with the LittoKala Lii-500? Since it uses a similar spring design and it too has a internal resistance test.

 

[Korishan]

Could this mod also work with the LittoKala Lii-500? Since it uses a similar spring design and it too has a internal resistance test.

Should be able to. Making a solid connection between the cell and the circuit board is way more accurate than connecting through a sliding piece of metal that can develop corrosion or debris/dust along the surface, which increase resistance, and can alter the capacitor/resistance values.

 

[Wolf]

Besides all of these slide tester having woefully inadequate IR calculations ( whether you update the slide cell contacts or not) which are derived from a simple voltage drop measurement, they also lack a way to adjust the charging mA cutoff and the actual discharge cutoff voltage.
Li-Ion cells have different cutoff discharge voltages some at 3.0V some at 2.5V and some high performance cells at 2.0V
Most of these "reasonably" priced cell analyzers have a way of changing the charge amperage however the rest of it runs a canned C/D/C program and splitting the cutoff voltage usually to ≈2.75. This can cause some discrepancy in the mAh results. Not earth shattering as long as you use the same model cell analyzer for all your cells, if you have multiple units, and are planning on testing your cells for a multiple XpXs Battery.
The only affordable cell analyzers that have adjustable setting for this purpose are the SKYRC MC3000 and the Mega Cell Charger.
Unfortunately both of these units also rely on the same voltage drop method to calculate the IR. Highly inaccurate.
.
The only way to properly test the IR/Impedance of a cell is to use a 4 wire internal impedance tester.
It measures the cells impedance at AC 1kHz which is what the manufacturer details in the spec sheet of many cells.

This will give you an accurate IR/Impedance reading that will not fluctuate no matter how many times you test the cell at its present condition.

The reason DC IR is so inaccurate is due to the contact resistance which can vary a lot.
The DC voltage drop test runs this way.
Lets say your cell is at 4.2V you jump the pos and neg with a 5Ω resistor.
Ohms law says we have 0.84 A or 840mA flowing.
We also measure the Voltage drop and it ends up at 0.05V
Calculating the DC IR of this cell at 59.52 mΩ
This is in a perfect world however if we add just .5Ω to the 5Ω resistor circuit because of contact resistance
our current goes to 763mA giving us an IR reading of 65.48mΩ.
You can get pretty accurate DC IR readings but it must be done with a 4 wire Kelvin tester.

Wolf

 

[Ruky]

So I did the mod to one of my LittoKala chargers, but found that it didn't make any discernible difference, but while I had the unit taken apart, I did find room for another mod regarding the heat sinking on the MOSFETs responsible for the discharge mode, but I'll save that for it's own thread on another day.