Internal Resistance 6s Nanotech's

[bikerflier]

Always an interesting read about LiPo's.
Thanks for all the technical stuff.

My 6s 3300 Nanotechs 45-90C were measured on 'Enterpryse' 'i' charger and showed between 5 and 9 mohms.
No more than a maximum range of 3 on any one battery.

First time I have ever had the internal resistance checked on any of my cells so can't offer anymore details.

I am keeping a full record of discharge and charge cycles as these are my first Nanotechs.
I am hoping careful use and especially charging, will get a good life, better than the reported poor performance of Nanotechs.
I've been more than happy with the blue Turnigys, especially against my poor performing Optipower cells.

[Mark_T]

New batteries should be less than 5. Useable batteries less than 10, old batteries 10+

Just to avoid confusion for anyone else reading this, that is not a bad target for a 3300 packs, but cannot be applied directly to packs of other sizes.

[GIXERMAN]

I would be nice for someone to just put in basic terms, rather than brainwashing, most of the people on here are not nuclear scientists or electricians.

Thanks

[Mark_T]

I would be nice for someone to just put in basic terms, rather than brainwashing, most of the people on here are not nuclear scientists or electricians.

Not sure if this helps, but feel free to ask again if this isn't on point.

1. Don't compare PL6/8 to iCharger to Wayne Giles as they will give different results for the same pack.
2. Don't compare results taken in different temperatures, colder packs will give worse figures, warmer packs better figures.
3. Do compare the readings between cells on the same pack and different packs tested on the same device at the same temperature
4. Small capacity packs will always have higher IR, this is normal, smaller the pack the higher the IR that is acceptable
5. Generally a good pack will have all IR values within 10% of each other.
6. On some devices (PL6/8) be suspicious of higher IR values on cell 1 or 6 as this can just be a problem with the charger/balance board wiring.
7. On split packs (typically large capacity 6S) you may get false readings on cell 3 or 4

[xygax]

Not sure if this helps, but feel free to ask again if this isn't on point.

1. Don't compare PL6/8 to iCharger to Wayne Giles as they will give different results for the same pack.
2. Don't compare results taken in different temperatures, colder packs will give worse figures, warmer packs better figures.
3. Do compare the readings between cells on the same pack and different packs tested on the same device at the same temperature
4. Small capacity packs will always have higher IR, this is normal, smaller the pack the higher the IR that is acceptable
5. Generally a good pack will have all IR values within 10% of each other.
6. On some devices (PL6/8) be suspicious of higher IR values on cell 1 or 6 as this can just be a problem with the charger/balance board wiring.
7. On split packs (typically large capacity 6S) you may get false readings on cell 3 or 4

What he said..

Steve

[mahbouni]

All that asside in the comercial world we condem cells / blocks when their internal resistance is double that of their piers.

This is why for HV setups where I use 2 packs in series, I pair up packs with similar IR's . I normally buy my packs in batches of 6 or even 12 so that I have a good sample set. I charge them first and write all the IR's on a sticker then sort them into pairs.

[cjcj1949]

When we talk about internal resistance we are really talking about how much the voltage drops on load. The way it is measured is actually measure the drop in voltage for an increase in current. So if a cell drops 1 volt when you increase the current by 1 amp it has an internal resistance of 1 ohm. Or it can be said to have an internal resistance of 1 ohm. The "it can be said bit" is important as all we can really say is that that cell at that state of charge at that temperature dropped by 1 volts when the load increased by 1 amp. The confusing bit is all the other things that we didn't mention. Like how fast did the current increase and what current was it taking when we did the test. The how fast bit is what Steve mentioned in the ac impedance test. The Wayne Giles meter gives a pulse test. It gives a short blip of load of around 16amps for less than a second. It is very close to the way we use our batteries. It also measures the voltage change across the cell and so ignores the connector and some of the intercell wiring.

Chargers measure the change in voltage during charging. They can do the measurement at any current and either drop or rise in volts or both. My icharger sometimes gives different results from my Wayne Giles meter and sometimes the same. This should be expected though as lipos are complicated things and internal resistance or voltage drop with load, varies in how you measure it. Different makes of lipo will probably behave differently as well.

I wouldn't bother testing nanotechs. They are not as good as the cheap blue ones. But they may get better or worse. We have no guarantee on what we are getting.

If a charger indicates one weak cell, it may be important. I would certainly get it tested on a proper Wayne Giles type meter or do a simple load test. All you have to do is to increase the load by a fixed amount, like connecting a 12V car bulb across the battery and measuring the volt drop across the suspect cell and compare it to a good cell. It is a fiddle, but it is a proper test. You can also do it more easily when charging. Charge at say 0.5 amps until the cells are balanced and then increase the current to say 2.5 amps. On a good battery the cells will still be balanced. If one cell has twice the ir of another it's voltage will rise by twice as much. The balancing circuit should also kick in and reduce the charge by about 300ma so the rise in voltage will only be for 300ma less than the increase in current.

The ir or voltage drop is very important on discharge. It will lower the voltage on the cell with the highest ir (in fact it is the voltage drop we measure anyway) and this cell will be damaged more than the others on each cycle. It will also take longer to balance as the balancing circuit will see it as a high cell for the high current part of charge and will reduce it's charge until the current is reduced. As the current reduces it will see it is a low cell, or more accurately, it will see all the other cells as high and start to discharge them until the weak cell catches up.

Knowing that ir means voltage drop for a fixed current we can see that if one cell drops 0.5V for an increase in load of 10 amps, then if we put two cells in parallel, each cell will take about 5 amps ( This is not quite true but best ignored for the moment as it involves more maths that doesn't help). Each cell will then drop 0.25V and so the ir depends completely on capacity. Roughly speaking 3 mohms si good for 2000mah, so 6mohms would be good for 1000mah. For larger cells divide by the amp hour. So 5000mah is 5Ah so 6/5 mohms is good for 5000mah cells.Or about 1mohm. Roughly 2mohm is average and above 4mohm is doubtful for normal heli use.

[iceuk]

17 ohms is just wrong on a 6s 3300 battery that is new. I would be giving someone a ear bashing.

[enterpryse]

Re: Internal Resistance 6s Nanotech's

Well thanks guys for all this good info. I never thought my simple posting would start such an informative thread :-)

Interesting comments about the quality of the Nanotechs. I may buy two blue turnigy's for the 600 (25 or 30 C) and compare.

Once again, thanks.