Turnigy Reaktor screen question

[nathanotis]

Hi. Thanks for looking. I've got a question about this screen on my charger. I have the stock 350mah battery from my SCX24 plugged into it, balance charging @ .3

The first screen shows battery type, charge rate, etc. Pictured is the second screen. The manual isn't clear on what I'm looking at. Those of you more familiar with chargers (or if you have the Reaktor chargers):

Is this showing a badly out of balance cell?

 

[Xx Losungen xX]

That's far from badly balanced

 

[nathanotis]

What's the second line showing? I can't find information on exactly what the screens are showing.

 

[nathanotis]

FOUND IT! It's internal resistance... So, 120 seems ... high.

Right?

 

[Xx Losungen xX]

FOUND IT! It's internal resistance... So, 120 seems ... high.

Right?

120 of what?

What number do you think should be there?

How are you getting to that screen?

 

[nathanotis]

120 of what?

What number do you think should be there?

How are you getting to that screen?

I assumed ohms. But you know what they say can happen when you assume... Sometimes you're wrong :lmao:

This is how I start. I set up to balance charge a 2 cell lipo at .3 amps (350 mah battery).

<a href="https://lensdump.com/i/0NqrKo"><img src="https://i.lensdump.com/i/0NqrKo.md.jpg" alt="0NqrKo.jpg" border="0" /></a>

Then I press start and the charger confirms and starts charging:

<a href="https://lensdump.com/i/0Nqg1i"><img src="https://i1.lensdump.com/i/0Nqg1i.md.jpg" alt="0Nqg1i.jpg" border="0" /></a>

After 1 minute you can go to the second page, where it shows the individual cells. According to the manual, the second line shows resistance. The battery isn't the least bit warm. I'm guessing that's 1.2 ohms... But I hate guessing.

 

[Xx Losungen xX]

I downloaded the manual which is why I asked where you got that. In the manual I ended up with there is a special function to check resistance where it properly displays as megaohms.

120 would be to low as ohms and 120 would be to high as megaohms, by a massive margin either way, to the point that the battery would be beyond fugged up so seems weird that it's resistance.

Trying to say that I wouldn't rely on that 120, there's no way it correct. It just can't be right if that battery is even usable.

 

[nathanotis]

Trying to say that I wouldn't rely on that 120, there's no way it correct. It just can't be right if that battery is even usable.

Ok. Going forward I'll ignore the other pages outside of a cursory glance to see if the cells are balanced... Focus on the first page and it's settings.

Thanks.

 

[Xx Losungen xX]

Have you tried seeing if a new firmware update is available? I can't find any reference to that screen you're on

 

[AC49]

120 would be to low as ohms and 120 would be to high as megaohms

The internal resistance on batteries is often measured in milliohms. (small m)
Small batteries that run in the 200-400mah range often have an IR in the 150 milliohm range. Larger RC batteries have a much lower IR often ranging in the 2-10 milliohm range.

Your total battery resistance will be the sum of the resistance in each cell.
so your battery at 120 milliohms would be a 240 milliohm or 0.240 ohms.

120 ohms would be insanly high not too low. A toaster typically runs around 75 ohms. Your RC would light on fire in seconds at that resistance.


We can confirm that this is a reasonable number by checking the voltage drop across the battery.
The stock battery is a 25C at 350mah which means it has a max output of a little over 8 amps.
Ohm's law (V = I x R)
1.9v = 8a * .240amps

So you'd have a 1.9 volt drop across the battery on an 8 amp draw.

 

[Xx Losungen xX]

The internal resistance on batteries is often measured in milliohms. (small m)
Small batteries that run in the 200-400mah range often have an IR in the 150 milliohm range. Larger RC batteries have a much lower IR often ranging in the 2-10 milliohm range.

Your total battery resistance will be the sum of the resistance in each cell.
so your battery at 120 milliohms would be a 240 milliohm or 0.240 ohms.

120 ohms would be insanly high not too low. A toaster typically runs around 75 ohms. Your RC would light on fire in seconds at that resistance.

Yes sorry, milli I meant

 

[AC49]

Long story short. 120 looks pretty much perfect for a new battery that size. Your charger is working well and you can use that IR to keep an eye on overall battery life/health.

Keep in mind that when it's warm you'll always have a lower IR than if it's been sitting. So just be consistent when you measure it.

 

[Xx Losungen xX]

Long story short. 120 looks pretty much perfect for a new battery that size. Your charger is working well and you can use that IR to keep an eye on overall battery life/health.



Keep in mind that when it's warm you'll always have a lower IR than if it's been sitting. So just be consistent when you measure it.

120 ohms is near perfect?

 

[AC49]

120 ohms is near perfect?

milliohms yes. RC chargers measure in milliohms and 120 is right on par for a 350mah battery.

 

[Xx Losungen xX]

I've always heard around 6mO per cell is decent, my graphenes measure around 2-3 per cell. 120mO seems awfully high.

 

[AC49]

Larger batteries have lower IR. The 3 to 10 mohm range is pretty normal when you get into the 2000 and up range. But small batteries found in the scx24 have much higher IR. usually you'll see drone guys happy with a 150 mOhm battery.

It makes good sense when you do the math on the voltage drop and consider the C rating.

25C rating on a 350mah battery means it's capable of an 8 amp load.
25C rating on a 3000 mah battery means it's capable of a 75 amp load.

V = load * IR
so for a small battery 2S (120 milliohms per cell)
1.9 volt drop = 8amps * .240 ohms

For a Larger battery also 2S
18v = 75 amps * 0.240 ohms.

As you can see a full punch on the battery would draw more volts than a 2S even has. so it's mathematically impossible. So you are right. 120mohm resistance in a larger battery would be a massive issue.

So what we commonly see in a larger battery:
IR per cell of 0.006 ohms. (6 milliohms) which would be 0.012 ohms total.
0.9volt = 75 amps * 0.012 ohms.

This makes a lot more sense, full load on a battery and you see a 0.9 volt drop.

So that's the really long way to show that 'good IR' is relative based on battery size and C rating.

 

[Xx Losungen xX]

My Turnigy 350mah sit around 2mO. Doing some digging on the idiot box, 1.5 to 3 is around normal on cells that's size, 120mO STILL sounds off the charts. I can't find any reference to any lithium cells ever reading even close to that high, 30 to 40 and the cell should be toast no?

 

[AC49]

My Turnigy 350mah sit around 2mO. Doing some digging on the idiot box, 1.5 to 3 is around normal on cells that's size, 120mO STILL sounds off the charts. I can't find any reference to any lithium cells ever reading even close to that high, 30 to 40 and the cell should be toast no?

The turnigy battery (if I have the right one) is a 65C. so it should have a lower IR than most. the stock battery that comes with the scx24 is only a 25c or 30c I believe and is probably not the best battery money can buy.

It's really hard to compare batteries of different specs when looking at internal resistance.
If you take the Turnigy battery at 65C that means it's capable of a 22.7 amp load. Well if that battery didn't have a low IR value then it would overheat really fast and it's voltage drop would be brutal.
over 5 volts drop, so basically you'd punch it, your voltage would drop down to 2 volts.. which is a problem as we know on a Lipo.



This study looked at 800's of a variety of chemistry and IR was typically above 150 in all cases.
https://batteryuniversity.com/learn/archive/how_does_internal_resistance_affect_performance


"As I mentioned, as packs age, the internal resistance goes up and the warmer they run. Lower discharge rated packs and small capacity packs will generally have higher internal resistance readings. It is not unusual to measure internal resistance numbers in the region of 200 milliohms on smaller 100 to 200 mAh micro park flyer LiPo packs when they are brand new for example."
https://support.teradek.com/hc/en-us/articles/360037175073-LiPo-Batteries

I'll check the battery that came with my SCX24 just to make sure I'm not completely full of crap.

 

[Xx Losungen xX]

Thanks for the info, enjoy the opportunity to learn and hopefully not taken as arguing. I honestly didn't think there would be that much difference between these batteries even accounting for C ratings. I appreciate the back and forth man, seriously [emoji106]

 

[AC49]

I'm really happy to have the back and forth with people too. Especially because I might think I know something only to find out I didn't. For example I had no clue you could get a small 350mah battery with such low IR!

I might actuallym order one of those turnigy batterys for the scx24, but I'll save that for another post.