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Old Feb 20, 2008, 11:57 AM
trying to kick the habit
United States, CA
Joined Mar 2006
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Question
Why LiPo's in a TX?

Why do people use Lipos in their TX's. I just dont get it. It cant be a capacity issue since most of the similarly sized AA packs actually have more capacity. From what I gather, the common TX LiPo is 2100-2500 mAh and the common AA NiMH's are around the same. If it is a self discharge thing, well I can argue that with the advent new low self discharge NiMH cells (Eneloop, etc.) this is not really an issue (especially if you just leave the TX plugged in). Is it a weight thing.... really?

Or is it just the hey, look how cool I am thing?
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Old Feb 20, 2008, 12:33 PM
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Smells like a straw man argument to me, as I doubt that many people
actually do it. I've yet to fly with anyone who uses lipos in
their Tx. I could see it in the electric crowd where everything is lipo powered
anyway so it's consistency of charging strategy. And there's nothing wrong
with saving weight and low self discharge though. Having a lightweight spare
to carry around that you know will still be fully charged could be handy.

Why does it matter?

ian
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Old Feb 20, 2008, 12:43 PM
trying to kick the habit
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Joined Mar 2006
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Quote:
Originally Posted by Daemon
Smells like a straw man argument to me, as I doubt that many people actually do it.
http://en.wikipedia.org/wiki/Straw_man

I am assuming that by straw man you are referring to this type of setup:

"Presenting a misrepresentation of the opponent's position and then refuting it, thus giving the appearance that the opponent's actual position has been refuted"

I dont think there has been any misrepresentation. Just the facts as I see them. I did outline many of the reasons that may have been presented and then provide an opposing point of view, but that does not constitue a straw man.

Quote:
Originally Posted by Daemon
Why does it matter?
People do indeed fly with them regardless of whether you have seen them or not and I am curious why they made the decision to go that route. Maybe something will be presented that will convince me to switch.

Why does it matter to you why I ask?
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Old Feb 20, 2008, 01:05 PM
Deletedfor proving Nauga wrong
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LiPos have essentially no self-discharge.

You can charge up... set the radio in a corner for 2 to 3 months (potentially over a year...) and its still charged.

The higher capaciy is debateable as a reason to use them in a TX. The average non-computer TX will operate for 2 to 3 hours using a 700 mah NiCd pack. You can easilly ge a 1800 mah NiMh pack to get at least the same durration (probably more) from a computer TX.

Leaving a TX plugged in all the time using the original wall-wart charger (especially with NiMh) is bad for the batteries. I don't recommend it.
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Old Feb 20, 2008, 01:12 PM
trying to kick the habit
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But isnt it also bad to leave LiPOs fully charged for an extended period of time also? I thought that degraded the cells. The new NiMH's with the extremely low self discharge are nice and happy being stored with a full charge.

I could see the consistency of charging argument if you only have one kind of charger. I just find it easier to plug the TX in while I am charging my LiPOs on my LiPO cahrger and not have one more battery to put on and take off the charger.

The weight difference is less than 3 ounces.
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Old Feb 20, 2008, 01:20 PM
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If there is any problem with leaving them charged... I haven' seen it. I left a cell phone full charged on a shelf for 3 years... and the LiPo battery tested at rated capacity. I have 3 1800 mah 3S packs that sometimes sit for 2 to 3 months full charged. They have always worked just as well as the 4th pack that gest used more often... (bought all 4 at once for a 6S 2P project and then decided to use different batteries)
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Old Feb 20, 2008, 01:31 PM
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Perhaps I misread your tone with the "I just don't get it" and "Really?" and
"look how cool I am thing" comments.
If they are roughly the same capacity, have lower self discharge and lower weight
then I'd say people use them because they *can*, and there's no
more compelling reason why they shouldn't than there is that they should.

As far as low discharge NiMHs, they're relatively new to the market,
aren't sold as tabbed cells yet, and thus few places that sell pre-made battery
packs offer them as an option. I know, because I just looked into
ordering up a Tx pack with low discharge cells myself. Lipos have
been an option for Txs for a lot longer.

BTW, my charger can charge two lipos of any size at the same time.

ian
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Old Feb 20, 2008, 01:35 PM
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Cell phones probably don't charge to 4.2 volts per cell. Many users of lipos charge to lower voltages for more cycle life.

And yes, leaving lipos fully charged for more than a couple of weeks can damage them and lead to lower capacity.

And when you leave you Tx on overnight/for several days, most Txes that actually shut down, do so at too low of voltage for lipo safety.

Overall, I agree, I don't see it. I have a 2700 mAH NiMH pack that has very low self discharge. Should last some 16+ hours. And isn't killed by forgetting to turn the Tx off.

And BTW, at least Spektruim and JR specifically say to NOT use lipos in their Txes as they can be damaged.
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Old Feb 20, 2008, 01:39 PM
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There aren't any 2700mAh low discharge NiMH cells available yet.
They currently range from 2000-2100.

ian
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Old Feb 20, 2008, 02:11 PM
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Define low self discharge.
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Old Feb 20, 2008, 02:17 PM
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The top voltage input you can give your TX is determined by the voltage regulator in the TX.

I contacted Futaba about what can be used in thier TXs a couople of years ago (before Futaba had a 2.4 ghz radio...) and they said that you could use up to 14 volts without hurting anything. (Appx voltage of 8 new AA Alkalines)

So.. any TX that can use 8 Alkalines or 8 cell Nicd, should be able to use a 3S LiPo.

The low volge issue... some radios have a method to adjust the alarm and auto-shut-down voltages. But if you hit the low volage alarm even after adjusting it... you need to pay more attention to your batteries.
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Old Feb 20, 2008, 02:17 PM
trying to kick the habit
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I consider this to be low self discharge:

http://en.wikipedia.org/wiki/Eneloop

"It is generally claimed that the batteries retain 90% of their charge after six months, 85% after a year and 70% after two years, when stored at 20 degrees Celsius (68 F)."
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Old Feb 20, 2008, 02:23 PM
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The "new low self discharge cells" that the OP is talking about
are the likes of Eneloop and related. http://en.wikipedia.org/wiki/Eneloop

Defined as cells that will retain upwards of 70-85% of their charge
after a year of storage. Any current 2700 mAh AA cell will self discharge
much faster than that. I've also found that the bleeding edge high capacity
cells tend to be more easily damaged by peak charging in a large pack (as
opposed to the way they're peak charged in pairs in off the shelf
consumer quick chargers). There are some in the 2300-2400 mAh range
that are much more stable (lower discharge, less prone to damage
from peak charging, and give rated capacity over more cycles)
but they still don't meet the low self-discharge criteria.

ian
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Old Feb 20, 2008, 02:48 PM
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Lipo's in my TX !

OK.. Im one of those that have bought Lipos' for my TX's .. I had all the charger's for my parkfly'ers already , and It's so great that Im useing one-two , high end TX's for several aircraft models each ... that I don't have to be concerened about flying all day and haveing the possibly of running low on TX battery.. I have 2700 mAh battery's in them ... I just got them for the capasity issue. Mike/Cepilot
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Old Feb 20, 2008, 03:12 PM
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I Use Lipos In My Tx

I also use a 2500 mAh 11.1 volt lipo battery in my Futaba 9C. Why you ask? Because with the stock battery that came with it I could get about 4 to 6 hours of flying with it before I was within 30 minutes of the alarm sounding on the TX. Now with this Lipo, I can go for nearly 16 to 20 hours of flying without dropping below 10.0 volts. I can go for over a week of my normal daily flying without having to worry about needing to recharge. I switched to a Lipo battery in TX because I got tired real quick of the inconvenience of having to recharge nightly. As for the "looking cool" thing, nobody knows what kinda battery I have in there unless I tell'em! Oh, and you can "argue" with yourself all day long about if my lipo is better than your new low discharge technology metal batteries. I'm not going to argue or debate it. I did my own real world tests and made MY decision based on the results I lived. I could care less if I'm the only idiot out there using a Lipo in his TX, it works very well for me. There you have my story!

Troy
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