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Old Aug 20, 2012, 06:46 PM
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Originally Posted by Wayne Giles View Post
I agree. You cannot expect to take meaningful comparative measurements of cells with an IR of 2 - 3milliohms with a resolution of 1 milliohm. The potential error with a perfectly accurate sytem is up to 50%.
This is not a criticism of the i charger; it is fine for smaller and older cells where the figures are 10 milliohms and up.

Wayne
+1 it seems that many over look the resolution on many things......
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Old Aug 20, 2012, 07:04 PM
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Thanks guys, that is what I was thinking. And I do have to say, in harmony with Wayne, the iCharger 3010b has served me well as a charger, which is why I bought it.

As far as the batteries this thread is about...I flew 4 in my 48" MXS yesterday. Hard to tell, but it seems like they performed better than my Gens Ace batteries usually do...had more power longer--didn't notice as much decline in power toward the end.

Still waiting to find time to get a CC log on them. I plan to compare one of the new batteries (since they are all measuring about the same) to one of my best and one of my worst gens ace 25C. So 3 batteries.

I'm thinking:

1. Freshly charged for 10 seconds full throttle, use CC BEC.
2. Storage charged, full throttle for 10 seconds.

All in same plane in same conditions...static WOT for 10 seconds.

This should be, it seems to me, a fair comparison.
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Old Aug 20, 2012, 07:10 PM
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But here is the kicker.

In the iCharger, is the ir measurement only one significant digit or is that all that is displayed.

There is a huge difference between low resolution and rounded out display digits.

Not being an expert, I would say that a cell with an ir of 1mO should be better than a cell reading 3.123456789mO don't you think?
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Old Aug 20, 2012, 07:18 PM
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Originally Posted by bigroger View Post
But here is the kicker.

In the iCharger, is the ir measurement only one significant digit or is that all that is displayed.

There is a huge difference between low resolution and rounded out display digits.

Not being an expert, I would say that a cell with an ir of 1mO should be better than a cell reading 3.123456789mO don't you think?
Yep. I'm not saying it is inaccurate, but even a reading of 5 mOhms could be anywhere between 4.5 and 5.49, even if it was perfectly accurate.

I know for one of my gens ace batteries, I was getting a reading of 25 mOhms, until I noticed the balance connector was askew. Then I reseated it, measured again, and the "bad" cell fell in line with the other readings.

The major point is, it's a charger.

Comparing what I get on mine to what somebody else gets on a different charger and different battery, even if it is the same charger model and battery line, isn't all that valid in my opinion...unless we've at least calibrated our chargers to each other using the same battery in the same conditions, or compared our chargers to calibrated test equipment, and ensure that all of the connections are sound.

To measure these low resistances, you would need some good equipment, as well as consistent connections.
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Old Aug 20, 2012, 07:33 PM
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I aggree.

I take the charger reading as just a guide.
In the end it all comes down to voltage sag.

I have some Turnigy blue 30C4s3600 packs that measure IR down around 3-4mO per cell that I run in series in my 70" slick. They start out powerful but within a couple of minutes they say heaps and really lose punch.

On the other hand my sky lipos 40C6s3300 in my 60" edge now reads IR around 4-6mO per cell and the punch is strong from the first minute till the end of 7 minutes at which time I land based on my timer because there is little to no noticeable sag in performance through the entire flight.

I'm sure the modern cell chemistry plays a major role in how the stored energy is delivered and thats it gotta be more then just IR effecting the voltage sag these days.

My Skylipo mentioned above come down warmer then my blue 4s3600 packs and the skys fly longer and harder IMHO.
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Old Aug 20, 2012, 07:34 PM
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Originally Posted by yurstruly View Post
yes you are correct but no one has the guts to say point blank that 60 to 65c is just a marketing hype and it doesn't exist today for Rc Hobby.
I must be more brazen than most as I have said precisely this on many occasions!

Here are a few:

http://www.rcgroups.com/forums/showp...54&postcount=2

http://www.rcgroups.com/forums/showp...&postcount=106

http://www.rcgroups.com/forums/showp...52&postcount=4

http://www.rcgroups.com/forums/showp...1&postcount=38

Here's one more...

60C+ LIPOLYS DO NOT EXIST! There are no lipolys currently available that can repeatedly sustain a 60C+ discharge to nearly 100% DOD and not be quickly destroyed due to extreme overheating. Point out some test results and I will happily delete the above.

Cheers,
Mark
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Old Aug 20, 2012, 07:48 PM
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How long would a flight last even if there were a 60C battery? Am I having a brain fart in thinking one minute?
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Old Aug 20, 2012, 08:05 PM
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I personally don't care what crap they write on the labels.

I care about hitting the throttle for instant punch out and having the volts there when I need them.

3D flyers have needs different to heli pilots, different from speed racers, different from pilon pilots.

We are all after different things, but we all need maximum voltage sustainability under load.
Racers and edfs etc, need huge amps over very short periods, in some cases I've heard people speak of power delivery over 15-30 seconds and its all over.
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Old Aug 20, 2012, 08:09 PM
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I agree. Ideally, I'd like as much power the last 10 seconds of a 7 minute flight as I have the first 10 seconds. I guess this is an area where IC beats electric.
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Old Aug 20, 2012, 08:19 PM
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Originally Posted by N6145k View Post
I agree. Ideally, I'd like as much power the last 10 seconds of a 7 minute flight as I have the first 10 seconds. I guess this is an area where IC beats electric.
I'd agree with that.

I'm currently working on an EF 88" electric that will run on 12s and will pull over 5500W peak.

Feedback is that it will pull as well as the DA60 on tuned pipes but flight time will be around 5 minutes if running high throttle the whole time.

Gas set ups don't get sag, but if I had a $$ for every gas plane dead stick landing/crash I've seen at my club in the last month I'd already be in the 88" setup and flying.
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Old Aug 20, 2012, 08:29 PM
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Quote:
Originally Posted by mrforsyth View Post
I must be more brazen than most as I have said precisely this on many occasions!

Here are a few:

http://www.rcgroups.com/forums/showp...54&postcount=2

http://www.rcgroups.com/forums/showp...&postcount=106

http://www.rcgroups.com/forums/showp...52&postcount=4

http://www.rcgroups.com/forums/showp...1&postcount=38

Here's one more...

60C+ LIPOLYS DO NOT EXIST! There are no lipolys currently available that can repeatedly sustain a 60C+ discharge to nearly 100% DOD and not be quickly destroyed due to extreme overheating. Point out some test results and I will happily delete the above.

Cheers,
Mark
It is pathetic and you would think that a company like thunderpower who gets much praise and respect would not do such a thing, like you said, perhaps there are cells that can produce those kinds of loads but they wont last very long, maybe only a few cycles, a true rated 25c battery will cope with 95% of my needs, end of rant.
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Old Aug 20, 2012, 08:31 PM
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Quote:
Originally Posted by bigroger View Post
I'd agree with that.

I'm currently working on an EF 88" electric that will run on 12s and will pull over 5500W peak.

Feedback is that it will pull as well as the DA60 on tuned pipes but flight time will be around 5 minutes if running high throttle the whole time.

Gas set ups don't get sag, but if I had a $$ for every gas plane dead stick landing/crash I've seen at my club in the last month I'd already be in the 88" setup and flying.
thats my biggest fear with a gas engine, I hate dead sticks, and it seems that even the best engines quit in the air every now and then.
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Old Aug 20, 2012, 08:50 PM
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Yep,
and out of all the electric planes I've had and got currently, only a few have had power issues in flight that cause me to land/crash so forth.

I'd say that at ,my club, which all the big birds 60" and up are either glow or gas powered, almost all of them get a dead stick either from out of fuel or motor stall, idle too low or something almost every week.

Its so common that they make dead stick landings part of the bronze wings standard requirement of the Australian model flyers specs etc......

They didn't bother testing that out for me on my 70" slick, did have to learn to non-harrier land though!! lol...
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Old Aug 20, 2012, 11:20 PM
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Quote:
Originally Posted by bigroger View Post
I personally don't care what crap they write on the labels.

We are all after different things, but we all need maximum voltage sustainability under load.
Agree 100%. Lipoly manufacturers happen to call the ability to hold voltage under load the 'C rating'. Some are honest about this, some are less than honest, and precisely why I personally depend on my own measurements and those of others rather than manufacturer ratings.
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Old Aug 20, 2012, 11:45 PM
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Quote:
Originally Posted by N6145k View Post
How long would a flight last even if there were a 60C battery? Am I having a brain fart in thinking one minute?
Well, if it were a "true" 60C battery AND while flying, it was pulling a constant 60C then you would almost get a minute out of it! With a load of 60C there will be some voltage sag and perhaps prior to the 60 second mark (of pulling 60C) the loaded voltage might drop below what is required!

Of course, figuring for a 75% DOD (depth of discharge) 60 seconds X .75 = 45 seconds!

Michael (if your not fryin, your not tryin!)
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