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2.4G Spektrum Radios Spektrum 2.4 Gigahertz Radios and Technology


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Old 09-17-2010, 08:15 AM   #1
Jotto
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Default LiFePo4 TX battery and voltage alarm

I just killed my TX lipo because I forgot to turn off the transmitter. Oh well, fortunately I had a spare one.

I'm considering using LiFePo4 instead, but I'm worried about the discharge curve. Voltage on LiFePo4 batteries is constant until it drops FAST, right? Can I trust the voltage alarm on the radio, and will I have time to land?
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Old 09-17-2010, 11:05 AM   #2
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Not sure what radio you are using. I have read where you can change the alarm voltage in a DX7 through the service menu. If you set it at the right voltage I think you would be OK.
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Old 09-17-2010, 01:20 PM   #3
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Yes you can adjust the alarm level in the DX7. One idea is to do a monitored deep discharge test of your battery choice and determine the rapid fall-off voltage then set the alarm a few tenths of a volt above that.
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Old 09-17-2010, 02:54 PM   #4
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I have a DX7. The suggestion to create a discharge curve myself is good. The question is whether the curve will fall too rapidly.
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Old 09-17-2010, 07:47 PM   #5
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I guess your asking is can you land "in time" after the alarm trips. The DX7 manual says don't fly below 9.0v, so again you should be able to test the batt/Tx combo and achieve a safe margin. I'm sure you'll quickly adapt to the battery's characteristics.
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Old 09-18-2010, 09:42 AM   #6
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Quote:
Originally Posted by Jotto View Post
I have a DX7. The suggestion to create a discharge curve myself is good. The question is whether the curve will fall too rapidly.
Well I'll offer this thought about using LiFePO4's on tx's.....

I use A123's (identical chemistry and charge characteristics) and I really like 'em for flight packs. If there is a downside to the A123 type chemistry, it is the voltage discharge curve being relatively flat and then pretty much dropping off a cliff so to speak. So with flight packs, you time your usage and charge according to whatever the particular model uses since volt checking these batteries is a pretty worthless activity.

I wouldn't use 'em in my tx for that reason. An excellent alternative for tx packs is the Eneloop cells and that's what I run in my tx's now. Very low self discharge rate, good capacity at 2000 mah, NiMH chemistry and similar voltages so you can use your existing charger and the volt meter on the tx will provide a reliable voltage readout so you know when to charge.
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Old 09-22-2010, 06:07 AM   #7
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Where do you buy "Eneloop" cells?
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Old 09-22-2010, 11:39 AM   #8
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NoBS, Sin City Jets, ElectroDynamics are just a few places to get 'em. IIRC, Radical RC, Batteries America and such places also have 'em.
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