Lii-500 IR accuracy

S

Santiago

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Apr 6, 2018
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trying to figure out why i'm not having consistent IR measurements with Liitokala Lii-500.
I did some simple tests to find the root of the inaccuracy:

Tested one fully charged, cold 18650 cell for IR, i got readings from 30 to 40 mOhm, some weird 50, 60 or so but most of them in that range.

Opened the case and found that springs are soldered to the pcb and hooked to the holder.
I soldered the spring to the holder, heated it good enought for the tin to stick very well.
Tested again with roughly the same readings.
So looks like the spring is not the main cause.

Then i soldered 20 cm of 2.5 mm2 new shiny cables to pcb.
Tested again pressing (hard) the cables to the cell with my fingers with bit more consistent readings.
Something like 30 to 37.

Then i went all the way and soldered the cable to the cell.
Tested pluging in and out the power source.
Got a bit more consistent results, but still 29 to 34 mOhm.

In Conclusion Lii-500 doesn't look to be very accurate (consistent) and holder contacts add some more inaccuracy.
May be accuracy could be improbed a bit with something like Crimp Daddy did: https://secondlifestorage.com/t-Int...g-Ultra-Low-Resistance-18650-holder-accessory
But Lii-500 is what it is.
 
We all know that :) You should not expect any accuracy from any tester below 100 bucks ;P You get what you pay for and yes you can do alot to get it better but still i would say its +-10% at best for most of them.

Even with 500USD testers you can easily get some variations with bad holders. Best way to test Ir is with 4wires and not 2.
 
daromer said:
We all know that :) You should not expect any accuracy from any tester below 100 bucks ;P You get what you pay for and yes you can do alot to get it better but still i would say its +-10% at best for most of them.

Even with 500USD testers you can easily get some variations with bad holders. Best way to test Ir is with 4wires and not 2.
Click to expand...

Yes, i readed it from you an others in this forum, i was just curious about what is the cause and to what point it could be improbed.
I think that more than soldering cell to pcb is not possible :D

4 wires???

rev0 said:
The Lii-500 internal resistance measurement function is basically useless, this site does detailed charger reviews, where he adds a 40 and 100mOhm resistor in series with the cell, it still reports the same resistance! https://lygte-info.dk/review/Review Charger LiitoKala Lii-500 UK.html
Click to expand...

just... lol
Btw nice review, i confirm that discharge cutoff is around 2.85V
 
Yeah Lygte is a nice site. I say it over and over and most cheap chargers are crap.. Not all because some 5 buck testers do actually come close but can you guarantee it? :)

4 wires as in 2 wires for the current part and 2 wires only for measuring the voltage. Doing that you dont get any voltage sag over the wires for the current. This gives you a very accurate reading in terms of outer interference. As long as the internal part of the tester is good enough :)
 
daromer said:
Yeah Lygte is a nice site. I say it over and over and most cheap chargers are crap.. Not all because some 5 buck testers do actually come close but can you guarantee it? :)
Click to expand...

I wouldn't say it's crap, just that it is intended for certain uses, Lii-500 looks like something to charge a few batteries to use in flashlights or cameras or so, and have an approximate idea of the capacity and IR.
Using it to build powerwalls is perhaps out of it specs, but is a budget option for many people.
And i think if you know how it works and what are the limits it can do the trick.

For example there is an interesting thing about IR tests i did:
The inconsistency of the IR readings seems to be in "upper side"... i mean: in all readings i did, the minimum is almost the same, around 30 mOhm, and the better consistency with better contacts drives to readings closer and closer to 30... how do you think about taking 30 mOhm as the "real" value and the offsets as increased resistance due to other factors?
For "real" i mean a value that is consistent betwen readings. As far as i know there is nothing like THE REAL IR of a cell.

daromer said:
4 wires as in 2 wires for the current part and 2 wires only for measuring the voltage. Doing that you dont get any voltage sag over the wires for the current. This gives you a very accurate reading in terms of outer interference. As long as the internal part of the tester is good enough :)
Click to expand...

Ok... good tip!
 
Santiago you can of course offset the value but the value is still way around the ball park. I would have said its a decent charger if they would have left out the IR testing function. Because adding functions that doesn't even come close to a real value is in my world not a good practice :D Same goes with the Opus that I personally prefer... Its a crappy tester but it works for my purpose.
 
I was trying to be kind with Lii-500. But indeed IR measurement is real crap, useless.
Looks like is depending on the day, the moon, planet alignment and maybe some others.

Wondering if there is some way to get an idea of what is going on.
Doesn't need to be a precise IR, but something coherent that can be used to compare cells.
For example put a load of lets say 1A to fully charged, rested, cold cells.
Let the voltage stabilize and use that volt. drop to compare cells.

Feeling like i can see your thoughts: "Buy a decent charger" :D
 
Santiago said:
I was trying to be kind with Lii-500. But indeed IR measurement is real crap, useless.
Looks like is depending on the day, the moon, planet alignment and maybe some others.

Wondering if there is some way to get an idea of what is going on.
Doesn't need to be a precise IR, but something coherent that can be used to compare cells.
For example put a load of lets say 1A to fully charged, rested, cold cells.
Let the voltage stabilize and use that volt. drop to compare cells.

Feeling like i can see your thoughts: "Buy a decent charger" :D
Click to expand...


Yeah you can do "manual" IR measurement by taking the voltage just before/and right at the start ofa 1A discharge. R = V/I, so at 1A your IR is just the voltage drop.
 
Yeah manual work. If you want an even better test this one did a pretty darn good job in my eyes.



 
Nice video (btw this video doesn't work here for me).

The iCharger seems to do it pretty well.

There is something interesting/weird:
If you compare cells 1 and 4 for SM8124 and iCharger.
SM8124: cell 1 higher res than cell 4.
iCharger: cell 1 lower res than cell 4.

The values of these two cells are pretty close, but still looks weird for me.



rev0 said:
Yeah you can do "manual" IR measurement by taking the voltage just before/and right at the start of a 1A discharge. R = V/I, so at 1A your IR is just the voltage drop.
Click to expand...

Nice... i din't think about that: 1A load then R = V.
 
The values are close enough and im pretty sure if I would have run through 100 cells they would be spot on. +- a couple of mOhm is not much :)
 
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