FYI: the internal resistance of lipos, and the inevitable consequences...

[summa1988]

does anyone know where i can find the new gens ace 5300 30c lipos for my trex 550,
these batts have getting amazing results but everyones out of stock!!!!

somebodies got to be selling them

[2000SS]

Tell me if I'm doing this right. I'll use 1 of the 3 cells to make this easy.

At rest I get 4.13 volts.
I plugged battery into some LEDs pulling 1.17 amps.
The cell now reads 4.08 volts.

4.13 - 4.08 = .05
.05 / 1.17 = .04

Is this correct? What does the .04 mean? The cell is in the 0-5 range or do you have to move a decimal point?

[TignMeg]

0.04 is in ohms you want milliohms so divide by 1000 gives you 40 milliohm. (Well 43 milliohm actually 0.05/1.17*1000=42.7)

[2000SS]

So 20-25 won't hold a heli in the air and I'm at 40?

That pack will fly but has no punch.

[TignMeg]

If there's anything I've come to realize about IR its that its extremely difficult to get an ACCURATE reading but its relatively easy to get a PRECISE reading.
What I am saying is that you may find your calculated IR is very repeatable but it might be 10x higher than the actual value.
So your reading is really only useful as a monitoring method to compare one battery to another. You need to find and measure a battery you KNOW is bad to get an idea of what IR is bad for your measurement technique.

I have a commercially made meter that gives IR and the readings for a new battery are normally 20-28milliohms. The batteries work great but when the resistance gets to >100milliohm I doubt they will be much use.

So use your experience and feel of the heli to know whats bad. You can use the IR to gauge how quickly they are aging or if you have damaged cells.

Cheers

[REVOJohn]

REVOLECTRIX signs contract with Toll Logistics & DHL to ship LiPO cheaper than mail services within 4 days. Keep a look out on our site for new LiPO shiping rates all over the world. www.revolectrix.com

I have more technical info on IR so I'm writting a paper on it and will publish soon. But with conventional chargers........it just can;t be done with any consistancy

[markhull]

Hey guys... What are you getting for LIfe Source batteries? I am getting low 20s on new backs.

[ks9818]

What the best way too connect 1c batteries to a I charger 106b to test IR.? Not through my parallel charging board I presume....right?

[Gregor99]

Originally Posted by ks9818

What the best way too connect 1c batteries to a I charger 106b to test IR.? Not through my parallel charging board I presume....right?

IR measurement requires the both a balance lead and charge lead be connected to the pack. The balance leads must be connected directly to the cell and at no time should current from the main leads flow through the balance leads.

Because most 1s cells are wired with a single connector, there is always some error introduced in the IR measurement. While you can measure IR this way, the results include the cell as well as the wire and the connector.

[EBrom]

I don't know if it should, but this worries me.


Number six cell shows over 70! Never noticed any cells being that high before on any of my batteries. I really don't have very many flights on that battery.
What's up?!

[Slyster]

Did you try measuring that pack on the other channel? I bet after a flight your cell 6 is way high still in voltage. I think your ok until it puffs though.

[EBrom]

Actually, I didn't, but next time I charge it I'll switch over and check if the same..
Thanks Slyster..

[foolforspeed]

Originally Posted by redbird300

a) Packs that are as good as new: between 0 and 5 milliOhm/cell
b) Packs that have been used dozens of times, but still feeling fairly good: between 5 and 10 milliOhm/cell
c) Packs that have been used even more, and start to feel weak: between 10 and 20 milliOhm/cell
d) Packs that almost won't hold your heli in the air anymore: over 20-25 milliOhm/cell

Remember that the cells are wired in series, and the resistance values of the cells need to be added up to know the total resistance of the pack.
For example: a 3S pack with IR cell 1 = 4, IR cell 2 = 6 and IR cell 3 = 5 will have a total IR value = 4 + 6 + 5 = 15 milliOhm

So if these numbers are based on 3s then 6s should be doubled, right?

[Relisys190]

Excellent writeup. Thank you very much.

Seeing these numbers makes me realize my old turnigy blues with an IR of 10 on cell #1 and the rest from 4 to 6 doesnt sound bad at all.

[peteski]

I've also found IR measurements to be very battery size dependent. I have some top quality Optipower batteries for my 180 CFX and OXY 3. I measured their IR when brand new using my iCharger 106B+ at storage charge (as they came) and got the following average results:-

3S 450 mAh IR 33, 33, 33 mOhms
3S 1300 mAh IR 6, 6, 6 mOhms

I thought maybe I could normalise by capacity, but even if you do that then the smaller capacity batteries still have much higher IR when new.

I've since re-measured the 3S 1300 mAh batteries after 33 cycles and the resistance has gone up by around 2-4 m.Ohms per cell and they still seem very strong in flight - as new as far as I can tell. I also measured them after only 6 cycles and there was no significant change from new.

Edit: I have just re-measured the 3S 450 mAh batteries after 28 cycles and the resistance has actually reduced by on average about 2 m.Ohms per cell. Again they still feel like new in flight.

So I think it's very important to measure IR when new to get a meaningful reference point and then keep monitoring them as they age - using the exact same measurement method and state of charge too. You cannot presume that 0-5 milliOhms is the starting point for all batteries and certainly not for smaller capacity batteries. For 1S batteries, I find the IR is all over the place even when new, so I don't bother measuring those at all.

[emederos]

My packs that have 15 flights have average 6mo per cell . They are like new to me and I'm just going to stick to 0-5mo like new, 6-10 good, 11-15start to maybe notice some slight output power loss ( slightly) 16-20 noticeable power loss and 20+ keep an eye as power is not constant and may voltage sag at any moment

[peteski]

Originally Posted by emederos

My packs that have 15 flights have average 6mo per cell . They are like new to me and I'm just going to stick to 0-5mo like new, 6-10 good, 11-15start to maybe notice some slight output power loss ( slightly) 16-20 noticeable power loss and 20+ keep an eye as power is not constant and may voltage sag at any moment

I think that's only valid if your packs are the same capacity as the ones the OP tested. Otherwise you just have to determine your own IR profile from usage. If I went off that guide, I would be throwing away brand new smaller packs!

[emederos]

All my packs are the same 4s 4000mah

[Mikker 75]

We have purchased multiple batteries for this new found hobby of mine. Bought a mcpx bl, 230s, and 360cfx. And two batteries for each bird. It was suggested that I buy a better charger for my bird batteries. I have a Onxy 245 for my car batteries. It has done a great job to date. Now that I have the 360 CFX, I needed a charger capable of handling 6s packs. The Passport ultra force 220 watt is the unit I purchased. It is capable of measuring internal resistance of these packs. As I have been breaking in these packs I am noticing extremely high resistance #s and it is concerning. They are reading in the 100+ mAhs and this is bothersome. We took the packs back to LHS and they swapped them out. New packs.....same issue. What gives?

[peteski]

Originally Posted by Mikker 75

We have purchased multiple batteries for this new found hobby of mine. Bought a mcpx bl, 230s, and 360cfx. And two batteries for each bird. It was suggested that I buy a better charger for my bird batteries. I have a Onxy 245 for my car batteries. It has done a great job to date. Now that I have the 360 CFX, I needed a charger capable of handling 6s packs. The Passport ultra force 220 watt is the unit I purchased. It is capable of measuring internal resistance of these packs. As I have been breaking in these packs I am noticing extremely high resistance #s and it is concerning. They are reading in the 100+ mAhs and this is bothersome. We took the packs back to LHS and they swapped them out. New packs.....same issue. What gives?

Is that 100+ mOhms per cell or total for the battery? I presume you are talking about your 6S packs here? If it really is 100+ mOhms for each individual cell then that is very high, but across all 6 cells that would be okay. The really small packs for say your mCPX will have very high internal resistance anyway.