Been inspecting the innards of my Colaier Lii-500 a few hours ago. My initial plan was to somehow solder a wire from the board cathode contacts to the rail tabs, as this would minimize contact to rail resistance. However, soon I realized that due to the limited space inside and the need to allow the tab to slide freely over the rail, the only proper way I found was to tightly coil some patches of fine wire with nearly 10cm/4in of lenght which would be attached beyond the rail contact, as if they were attached exactly to the contact there would be no room for the coiled wire with the rail tabs nearly extended. A patch of AWG28 wire of such lenght has ≈22mΩ of resistance, thus I realized this was only going to be a laborious a patch. At the other side there's the steel spring, so good luck setting a coil of wire nested inside it and hoping for it to last (+patch anyway).
Read on!
Rails are long metallic retangles over which the tabs seat, making contact. The tab receives power from the steel coil linked to it (a lot of combined resistance) and from the rail. The problem is that there's too much play between tab and rail, this is caused by a too short set of supporting plastic rails which give seat to the slot cathode rectangular rails, two for each one in the base cover. My solution has been to carefully cut some pieces of electrical tape to carefully wrap the plastic seating rails. Ended up setting 4 layers with good results, the rails now feel noticeably tighter and there's much less measuring variance. I may put another layer, but as it is now I can get all rails with “low” readings with some wiggling and a couple power cycles, maybe another because I'm finicky.
This is of importance if you aim to capacity bin cells, all rails should display consistently low resistance as any cell in a high resistance rail will score lower (less charge in and out due to earlier cut-offs).
It was about time!
Added a 5th layer and now the rightmost slot's tab has slight difficulties getting all the way down. I guess this is as tight as it can practically be.
This possibly explains (partially) the differences in IR I see from my Opus BT-C100 to my MiBoxer C-3000. It had not occurred to me the variance could be within the chargers themselves.
In HKJ’s test the IR reading seemed to not have any correspondence to the actual DC resistance, not just that there was a lot of variance. Does your fix address that problem?
As you can read there EasyB, 1KHz cell AC impedance is not very useless for our needs. There's no real correlation between measured values and the actual cell DC figure. For example a 30Q/25R may show ≈30mΩ, this measured value is sum of the actual cell AC impedance (maybe ≈15mΩ) plus contact resistances (another ≈15mΩ more or less).
Do you mean to say AC impedance is not useful for us? That I agree with. But there are meters that display values consistent with the real DC resistance. For example see HKJ’s reviews of the zanflare C4 or the popular opus charger.
Ok, I wasn’t sure what method any of these chargers used. But even an AC method should measure a simple DC resistance such as a resistor. That is what HKJ does in his tests of the IR functions. The reading should go up by 100 mOhms if a 100mOhm resistor is put in series with the cell. The zanflare and opus IR functions do this, but the lii 500 doesn’t. The lii 500 IR function seems to return nonsense.
