6.6 V LIFEPO4 BATTERY

[CARPERFECT]

I have started to use the 2 cell 6.6v Life battery in my Futaba t8j . What is a safe level to allow the battery to fall to before re- charging ?

[Martin Harris - Moderator]

It really depends on the accuracy of the voltmeter and the drop under normal load as the discharge curve is very flat.

I like LiFes for receiver packs where I can monitor the charge put back in and do an occasional discharge test but I'm not so sure about the wisdom of selecting them for a transmitter unless the charger gives you this info. Does the transmitter have a built in low voltage alarm?

I would discharge the cell to around 70% of its tested capacity on a suitable charger and check the voltage displayed when it's put into the transmitter - then use this voltage as a guide to maximum discharge.

Otherwise, LiFes don't mind being topped up so to be on the safe side, just recharge before every session.

[Frank Skilbeck]

Interesting point, my Tx uses a single cell LiFe battery, but measures the charge used and mah and run time remaining and alarms when there is less than 60 mins run time, but I charge up when the remaining runtime is less than 10 hours. But it also has an overiding voltage alarm which is set at 2.9v which would be the equivalent to 5.8v on your 2S LiFe. I'd err on the side of caution and use 6v as the alarm setting.

[Martin Harris - Moderator]

  If this example is anything to go by then at 2.9 volts, it really is a last chance alarm!

Although the discharge curve is very flat, there is a consistent decline in voltage during discharge but you would need very accurate measuring equipment in order to put a figure on a "safe" limit. With a transmitter you have the benefit of a fairly constant load to allow meaningful measurement but in the absence of any clever monitoring being built in, just err on the side of caution, establish the maximum duration, stay well within this and keep it topped up between outings.

The accuracy required for LiFe battery monitoring by voltage is totally different to nickel cells - or even LiPo/Li-Ion so I wouldn't even attempt to rely on the accuracy of a transmitter's voltmeter.

 

 

 

 

Edited By Martin Harris on 13/10/2014 10:34:39

[Lee Damms]

I have a Futaba 14sg currently using the provided NIMH battery and the low voltage alarm setting recommended is 5.6v the manual also states if using a 2 cell LiFe battery the low voltage alarm should be set to 6.0v. When the voltage drops to 3.9v the transmitter turns off.

Regards Lee

[Frank Skilbeck]

Posted by Martin Harris on 13/10/2014 10:25:40:

If this example is anything to go by then at 2.9 volts, it really is a last chance alarm!

 

Edited By Martin Harris on 13/10/2014 10:34:39

It is!, the Tx monitors the charge state and mah used and alarms when the run time is 60mins (but you can program this to be higher) and has a "last chance" alarm at 2.9v. But in reality being able to check the mah left and estimated remaining runtime it should never come to that. Just for info the Tx using a 1s LiFe consumes 120mA so plenty of run time on a 4,000 mah battery, with modern electronis and batteries we should never suffer from Tx flat battery syndrome.

Edited By Frank Skilbeck on 13/10/2014 11:57:53