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RC Radios, Transmitters, Receivers, Servos, gyros Discussion all about rc radios, transmitters, receivers, servos, etc.

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Old 04-12-2014, 03:30 AM   #1
FlyWheel
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Question LiFe battery pack for older Hitec

I have an old HiTec Flash5X (72MHz)) transmitter that currently uses a 1000mAH 8cell nickel metal hydride pack. it works OK, but if I want it to last for more than a few flights I have to charge it the morning of or at least the night before or it will lose it's charge sitting. I know a 3 cell LiFe pack is close to the same voltage and lithium batteries can hold a charge for a very long time (lithium-iron can better tolerate full charge storage also). They also last a lot longer and I have even seen them made in an 8 AA battery size for transmitter use.

HOWEVER, I am concerned by the voltage differences and discharge curve. Also the low voltage warning in my older TX which is calibrated for 8 NiCd or NiMH. Can I use a LiFe pack in my transmitter without harming it or the battery pack?

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Old 04-12-2014, 03:59 AM   #2
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Originally Posted by FlyWheel View Post
I have an old HiTec Flash5X (72MHz)) transmitter that currently uses a 1000mAH 8cell nickel metal hydride pack. it works OK, but if I want it to last for more than a few flights I have to charge it the morning of or at least the night before or it will lose it's charge sitting. I know a 3 cell LiFe pack is close to the same voltage and lithium batteries can hold a charge for a very long time (lithium-iron can better tolerate full charge storage also). They also last a lot longer and I have even seen them made in an 8 AA battery size for transmitter use.

HOWEVER, I am concerned by the voltage differences and discharge curve. Also the low voltage warning in my older TX which is calibrated for 8 NiCd or NiMH. Can I use a LiFe pack in my transmitter without harming it or the battery pack?
H'mmm
Lets see.

A typical Nih 8 cell battery pack will charge to 1.35 Volts per cell, times 8 cells or 10.8 volts, right off of the charger. While in use, that Nih battery will operate at about 1.2 Volts per cell, or 9.6 Volts DC. And, when that Nih battery is pretty flat at 1.1 Volts per cell, the Nih pack will read about 8.8 volts DC.

Now, a LiFe 3 cell pack will measure 3.6 Volts DC per cell times 3 cells or 10.8 Volts right off the charger. While in use, that LiFe battery will operate at about 3.3 Volts per cell, or 9.9 Volts DC. And, when the LiFe battery hits 3.0 Volts per cell, or 9.0 volts for the pack, it is pretty much flat.

One difference on these LiFe's, their voltage during a discharge curve is pretty flat, so when it is nearly flat, that voltage will drop like a rock.

So, just top it off before a flying day. They hold their charge for many months, if you don't fly. And, storing them at full charge doesn't hurt them.

Just be aware that you must use a LiFe balancing charger to charge these type cells. Not using balancing can damage them over a long period of time.

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Old 04-12-2014, 12:27 PM   #3
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The LiFe works great in the TX. On discharge when it gets to 9.3 v recharge. You should be just fine with the discharge curve. The voltage will stay flat at 9.6 for a good long time. That is plenty for the TX in fact most of the TX uses much lower voltage and it uses a regulator to drop the volts anyway. So this slightly lower voltage is easier on the TX regulator!

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Old 04-12-2014, 12:40 PM   #4
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Great. My charger has a LiFe mode, will balance and I think my TX low battery alarm, a preemptive audio warning that the battery voltage will soon be too low, starts beeping somewhere just below 9.6V (I'll have to double check).

I knew they worked fine in the newer radios (I think some even come with lithium cells), I just wanted to be sure about my fossil.

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Old 04-12-2014, 08:53 PM   #5
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Originally Posted by FlyWheel View Post
Great. My charger has a LiFe mode, will balance and I think my TX low battery alarm, a preemptive audio warning that the battery voltage will soon be too low, starts beeping somewhere just below 9.6V (I'll have to double check).

I knew they worked fine in the newer radios (I think some even come with lithium cells), I just wanted to be sure about my fossil.

Yup
As previously indicated, just make certain to "Top off" your LiFe battery on a regular basis. When these LiFe batteries are near totally discharged, their output voltage drops like a lead brick. Much faster than a Nih battery pack will drop off.

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Old 04-13-2014, 08:41 PM   #6
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Originally Posted by FlyWheel View Post
I have an old HiTec Flash5X (72MHz)) transmitter that currently uses a 1000mAH 8cell nickel metal hydride pack. it works OK, but if I want it to last for more than a few flights I have to charge it the morning of or at least the night before or it will lose it's charge sitting. I know a 3 cell LiFe pack is close to the same voltage and lithium batteries can hold a charge for a very long time (lithium-iron can better tolerate full charge storage also). They also last a lot longer and I have even seen them made in an 8 AA battery size for transmitter use.
HOWEVER, I am concerned by the voltage differences and discharge curve. Also the low voltage warning in my older TX which is calibrated for 8 NiCd or NiMH. Can I use a LiFe pack in my transmitter without harming it or the battery pack?
As above, LiFE can be used but remove and charge before use each time as the LBW of the Fhash 5X
is well below the danger level of new chemistry batteries.
. Transmitter - Replacement Battery Packs NiMH, NiCD & Lipo - DIY.
- use the diodes as shown in attached picture if using Lipo.

Be wary of your battery level monitor on those Tx as they are a guide only, not accurate.
. Transmitter - Voltage Display - How To Read & Interpret Remaining Battery Time

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Old 04-14-2014, 12:26 AM   #7
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oh. Well if I have to top them off anyway before I go out them I may as well stick with the NiMH, as that was what I was hoping to avoid.

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Old 04-14-2014, 01:23 AM   #8
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Originally Posted by FlyWheel View Post
oh. Well if I have to top them off anyway before I go out them I may as well stick with the NiMH, as that was what I was hoping to avoid.
IMHO, there is nothing wrong with Nih batteries for transmitter use. That's what my DX7 and DX8's have.

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Old 04-14-2014, 02:26 AM   #9
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Originally Posted by FlyWheel View Post
oh. Well if I have to top them off anyway before I go out them I may as well stick with the NiMH, as that was what I was hoping to avoid.
I use them in several of my TX's. I never top them off. I just watch the voltage as indicated. Not a big deal.... The voltage curve is steep but very manageable.

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Old 04-14-2014, 03:21 AM   #10
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Originally Posted by rcers View Post
I use them in several of my TX's. I never top them off. I just watch the voltage as indicated. Not a big deal.... The voltage curve is steep but very manageable.

Mike
Yeah, my Spektrum DX8 transmitters battery voltage reading is low by about a half volt DC. Surprising results, considering how accurate those A/D converters are in these microcontrollers.

At any rate, I ran my DX8 continuously until the original Nih battery went down to where the DX8 issued a warning. It took some 9 1/2 hours.

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