Batteries

[Old Man]

I only have a couple questions with the mAH/gm thing. One can obtain advertised weights and battery capacities off the internet or a battery labe. Has anyone performed actual measurements to verify the claimed ratings? We are living in a world where advertising statements have been known to be bit over stated, yes?

 

[fltundra]

I only have a couple questions with the mAH/gm thing. One can obtain advertised weights and battery capacities off the internet or a battery labe. Has anyone performed actual measurements to verify the claimed ratings? We are living in a world where advertising statements have been known to be bit over stated, yes?

Here are the IR readings for my Multistar 10AH4S,tests out currently at 14.1C.

 

[Ronan]

Here are the IR readings for my Multistar 10AH4S,tests out currently at 14.1C.

That's insane... your 4s weights so much less than my 6s...

 

[gtranquilla]

Its very difficult and somewhat dangerous to replace one or more cells in a battery pack..... although I did witness a technician do it behind the counter in a local hobby shop and without any assisted fan ventilation or fire extinguisher! even then there might then be a reliability issue etc.

I have 6 of the 8000 6s nano techs. So far, all are good as I've not pushed my flight times so no real stress. Curious, how do you replace a cell on those in case I ever run into a bad cell.

I have that on 2 of 5000 4s batteries, 1 hard case, 1 soft, so maybe I can learn something today.

 

[jfro]

Ok, I just did a test tonight. I flew 1 of my 80000 6s batteries till my alarm went off.

Here's what I got. Landed with cells in the 3.55 range. Put 7438 mah back in. Didn't write down the ir values, but it's a good battery and during charging the internal resistance values are around 1.2 to 1.4 per cell.

I'm confused over the 80% figure. If it's 80% of 8000 mah, then I shouldn't use more than 6400 mah. I went over that substantially.
I thought I read I should never let a cell go below 3.35 or so. It's been mentioned that 3.5 is very safe so I was over that at landing.
So what do I take from this....

 

[gtranquilla]

Time for a new thread/spreadsheet battery power/weight ratio..

Desire Power 6S 35C continuous

5200 mAh 736g
6200 mAh 883g
8300 mAh 1115g
10400 mAh 1591g
20000 mAh 2492g

..without discharge connector

..or put another way..

7.06 mAh/gram
7.02
7.44
6.53
8.02

With such high prices per pack for the larger capacities I would like to see someone develop a LiPo battery pack that could be quickly pulled apart and rebuilt cell by cell so that bad cells could be easily replaced!!!! But I suspect the energy density would drop due to the extra wiring etc. needed to allow for this.

 

[Quinton]

Here are the IR readings for my Multistar 10AH4S,tests out currently at 14.1C.

How exactly did you come to the conclusion that your pack is rated for 14.1C?
I have not seen a charger that can tell you this, or are you going by some calculation based on IR, which would constantly change anyhow depending on what state the battery is going through.

 

[fltundra]

How exactly did you come to the conclusion that your pack is rated for 14.1C?
I have not seen a charger that can tell you this, or are you going by some calculation based on IR, which would constantly change anyhow depending on what state the battery is going through.

Based on IR at any given time during the lifespan.
http://www.soko-heli-tools.com/en/lipo-battery-calculator/lipo-battery-calculator.html

 

[Quinton]

Based on IR at any given time during the lifespan.
http://www.soko-heli-tools.com/en/lipo-battery-calculator/lipo-battery-calculator.html

I am no expert but sorry I do not accept the results of that tool for 1 second.
The IR changes even when you are charging, the hotter your lipo the less IR, the more heat in the battery the more damage you could be doing.
If a battery is cold you probably have higher IR rates etc.

If you charged your lipos at 1C then charged them again at 5C I would imagine you would get completely different IR amounts.
The only true way to get the C rating would be to actually draw a very large current from a battery, which then may damage it.

The tool may be used as a reference I would imagine, but thats all.

 

[R_Lefebvre]

I started one.

https://docs.google.com/spreadsheets/d/1w9q_FbrBPAP8LMWmLNRe3lyF9J1yJXdhu3pNmemVJtg

I was thinking about opening it up to anybody to change it, but I'm not sure if somebody would vandalize it. This would be nice info to have though.

Time for a new thread/spreadsheet battery power/weight ratio..

Desire Power 6S 35C continuous

5200 mAh 736g
6200 mAh 883g
8300 mAh 1115g
10400 mAh 1591g
20000 mAh 2492g

..without discharge connector

..or put another way..

7.06 mAh/gram
7.02
7.44
6.53
8.02

 

[Quinton]

I started one.

https://docs.google.com/spreadsheets/d/1w9q_FbrBPAP8LMWmLNRe3lyF9J1yJXdhu3pNmemVJtg

I was thinking about opening it up to anybody to change it, but I'm not sure if somebody would vandalize it. This would be nice info to have though.

Thanks for that.
After studying it a bit, I notice that you are using Energy Density.
This is where I need to get my head around things a bit better.
When would the C rating actually come into it weight wise, as we would never really reach the maximum C rate.

Is a 6000mAh 35C lipo not the same as a 6000 20C lipo with actual flying time as long as its not being taken to its limits?
Am I thinking the wrong way?

 

[Motopreserve]

I started one.

https://docs.google.com/spreadsheets/d/1w9q_FbrBPAP8LMWmLNRe3lyF9J1yJXdhu3pNmemVJtg

I was thinking about opening it up to anybody to change it, but I'm not sure if somebody would vandalize it. This would be nice info to have though.

that would be a really helpful spreadsheet to have. I think you're right - probably best dealt with by a
"moderator" so that someone doesn't mess it up.

What is the W-H measurement???

 

[Quinton]

that would be a really helpful spreadsheet to have. I think you're right - probably best dealt with by a
"moderator" so that someone doesn't mess it up.

What is the W-H measurement???

Watts per hour is it, voltage x current?
Looking at the sheet it is
number of cells x volts per cell (3.7) x mAh/1000

I was not much good at power equations, wish I paid more attention in physics now!

 

[Motopreserve]

Watts per hour is it, voltage x current?
Looking at the sheet it is
number of cells x volts per cell (3.7) x mAh/1000

I was not much good at power equations, wish I paid more attention in physics now!

Aha. Makes sense.

 

[R_Lefebvre]

Yeah, the 3.7V is just a nominal per/cell voltage. Could be 4.2... but industry seems to label nominal voltage as 3.7 for whatever reason. Doesn't really matter as long as you use the same number across all batteries.

Also, could use mAH/gram, but Watts allows you to compare energy density across the the voltage range, 4S vs. 6S, etc.

 

[R_Lefebvre]

Thanks for that.
After studying it a bit, I notice that you are using Energy Density.
This is where I need to get my head around things a bit better.
When would the C rating actually come into it weight wise, as we would never really reach the maximum C rate.

Is a 6000mAh 35C lipo not the same as a 6000 20C lipo with actual flying time as long as its not being taken to its limits?
Am I thinking the wrong way?

C rating doesn't affect energy density at all. Well, actually, there's a loose, inverse, correlation between C-rating and energy density. Typically, the higher the C-rating, the lower the energy density. But there's no consistency in C-rating across brands, so it's hard to say for sure.

Yes, I should think that a 6000mAH 35C should fly about the same length of time as a 6000mAH 20C. However... the 35C may actually deliver more Watts than the 20C, because it's internal resistance is lower, it's voltage under a given load will be higher, so amp-for-amp, the watts will be higher. Now, how big is the effect? Needs more study.

 

[R_Lefebvre]

If you guys want to throw out some input on your favorite batteries, I'll see if I can add them.

Just need:

Name, xS ymAH, C rating, weight (excluding shipping packaging, obviously), dimensions, and price. Though the last two are technically not required, nice for comparison.

 

[Quinton]

C rating doesn't affect energy density at all. Well, actually, there's a loose, inverse, correlation between C-rating and energy density. Typically, the higher the C-rating, the lower the energy density. But there's no consistency in C-rating across brands, so it's hard to say for sure.

Yes, I should think that a 6000mAH 35C should fly about the same length of time as a 6000mAH 20C. However... the 35C may actually deliver more Watts than the 20C, because it's internal resistance is lower, it's voltage under a given load will be higher, so amp-for-amp, the watts will be higher. Now, how big is the effect? Needs more study.

How exactly would the manufacturers come up with a C rating, is there any kind of tool out there that can test this without going to the extremes of damaging a battery?

 

[R_Lefebvre]

I don't know. Clearly there is no industry standard. Didn't one of the more expensive brands get caught labelling some batteries at 65C, but they were really only good for 5C? I'm not even entirely sure how they come up with mAH ratings. I mean, if draining past 80% of the battery damages it, aren't they all over-rated?

 

[gtranquilla]

Watts = Power = current squared x resistance = Voltage x Current
E = I * R
i.e., Volts = current x resistance. Units are typically amps X ohms

Energy density should be considering only the output power when compared to total battery weight and should not take in to account the battery size.

Watts per hour is it, voltage x current?
Looking at the sheet it is
number of cells x volts per cell (3.7) x mAh/1000

I was not much good at power equations, wish I paid more attention in physics now!