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Old Feb 08, 2013, 12:09 PM
Detail Freak
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Harbor City, CA
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I'm still waiting for someone to come forth with the voltage of a fresh 5 cell 2/3A Elite pack....
I think that is someone bothers to measure, they will discover that the 6.6v of a 2S life is not the issue that they think it is for the majority of the servos out there.

R<
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Old Feb 08, 2013, 12:37 PM
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Quote:
Originally Posted by fnnwizard View Post
Most nixx cells when they fail , fail close. So if a cell does go bad it becomes a 4 cell pack = more reliable if 1 cell goes bad.
One of the biggest benefit for me is the consistent voltage of the Life cells throughout the day. You start at 6.6v, you end up at 6.6v even under load. You can't say that for a 5cell nimh pack. It'll be more than 1v difference depending on flight loads from begining of day to end of day. It may not matter for most of our flying, but I think for competition work (speed in F3B), getting consistent speed/torque out of the servos is very important.
Frankly this was one of the reasons I was warned away from LiFe. No way to read charge level. They stay flat, then voltage drops off the table. True?
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Old Feb 08, 2013, 01:09 PM
Detail Freak
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Harbor City, CA
Joined Oct 2003
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Not really.
If I ever get down to 6.4v on the data logger (which can be replaced with a loaded voltmeter) I recharge.
Essentially, all the same rules apply, check your average consumption of battery power, figure out what your time limit is to fly (with safety margin), and there you go.

R,
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Old Feb 08, 2013, 01:31 PM
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United States, CA, Midway City
Joined Dec 2003
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Quote:
Originally Posted by target View Post
I'm still waiting for someone to come forth with the voltage of a fresh 5 cell 2/3A Elite pack....
I think that is someone bothers to measure, they will discover that the 6.6v of a 2S life is not the issue that they think it is for the majority of the servos out there.

R<
TARGET
Here you go T... man has it been that long ago?

http://www.rcgroups.com/forums/showp...&postcount=255

Here's one where a brand new Perfect went in and some were speculating that my Life cells were to blame.... over 4yrs ago...
http://www.rcgroups.com/forums/showp...&postcount=212
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Old Feb 08, 2013, 01:41 PM
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Quote:
Originally Posted by aeajr View Post
Frankly this was one of the reasons I was warned away from LiFe. No way to read charge level. They stay flat, then voltage drops off the table. True?
Well, yes you are right. The majority of their discharge cycle is at ~6.6v so if a voltmeter says 6.6v you don't exactly know how much charge is left. But there are quite a few benefits to LiFe that win out over NiMH packs. Greater energy density per ounce of pack weight, negligible self discharge rates, more consistent voltage under extreme (high G) loads, no weird cell discharge states that require cycling to recover, etc, etc.

When you use LiFe packs you get in the habit of watching how many mAH you put back in after a day's flying. If you find a charge cycle requires either way more or way less than what you expect, that's a sign to do a full discharge/charge cycle to verify the pack's capacity.

In the 2+ years I've been using Hyperion 1450mAh LiFe packs in my planes I have never had one go bad or even test funny. Never.

The only downside to using LiFe is that servo manufacturers are still playing a bit of catchup to offer products that are spec'ed to handle LiFe voltages.

Chris B.
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Old Feb 08, 2013, 01:59 PM
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Chris, I am flying HV servos on LiFe's with very good results, would not even considering going back the other way or going to LiPo, just so easy to work with these cells. And even though Ed brings up what happens when they are run down to nothing, why is that a problem? I fly half the day, and top off which can be done fast and easy and you are ready to go. In any contest, I have never had to put in more than 500mah and as Chris pointed out, not so much as a single funcky charge or voltage numbers that made me wonder if something was up in the charge. Just such great cells to deal with all the way around.

Marc
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Old Feb 08, 2013, 02:17 PM
Detail Freak
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Harbor City, CA
Joined Oct 2003
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Its just funny to me that people are using a 5 cell Nixx pack to avoid low voltage Rx glitches, and no regulator, but if they think about using a LiFe pack, they immediately want to use a regulator (even though a fresh 5 cell pack is higher voltage initially).

I will say this:
If you have a binding problem with one of the servos in your plane for any reason, the servo likely will not survive with a Life pack, but may with a NiXx pack, solely due to the voltage droop under load that the round cells experience normally.
That in itself is a good thing, but if the RX browns out because of it, then its not.
I'd rather have control of 5 out of 6 servos, then 0 out of 6 servos....

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Old Feb 08, 2013, 03:15 PM
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LiFe, good; NiMH, never again.

JT
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