LiPo battery in T7C 2.4Gz

[Fred Schofield-graham]

I have been using a flightpower evo-tx 1500mAh 3s LiPo in my T7C for 2 years with no problems at all.Is there something i should know, am i living on borrowed time?                                                                                                                                         confused fred           

[Tim Mackey]

I have used a Lipo in my DX7 for over 3 years Fred, so you shouldnt worry !

[Fred Schofield-graham]

Thanks for the reassurance as your experience is the same as mine with no problems encountered. Do Futaba & JR/Spektum now approve LiPos in transmitters or are they still cautious? It would be nice to know if anyone has had problems with the increased voltage.

[ken anderson.]

wellcome to the forum fred----your right your'e living on borrowed time-take the lipo out and send it to me .....  'ss...

 

      ken anderson...........ne 1.

[Tim Mackey]

I dont think they yet approve officialy - although of course one or two specialized sets are already suppied with Lipo as standard. I am sure its only a matter of time before they become standard in all sets though - even if LiOn rather than polymer.

I should add that I did change the main voltage regulator in my DX7, and I think that this component is the bit that is susceptible to damage if not changed.

[Fred Schofield-graham]

My transmitter has not been changed in any way and I do not like the idea of modifying it as I do not have the electrical expertise to do this, so I feel my original posting has not been answered.                                                                                                                                                                                                                                                                                                                            still confused Fred

[jez]

hi fred

been using an evo 1500 lipo in both my futaba  ff7 trannies , 35mhz and 2.4ghz for over a year , no probs , i herd rumors when i got mine that they were not reccomended , so i contacted flight power (flighttechdistribution )(energon), and they said that they had tested them with no failures at all give them a ring and have a chat they seem very helpfull in the new company that now exists  

[email protected]

Tel: +44 (0)1763 848404

Fax: +44 (0)1763 848412

must get another  therrrrrrrrrr gggggggreat

jez

[Tim Mackey]

Well not sure what you want to hear Fred

The official reccomendation is dont do it - you have done it - for over two years and all is well. Many many people have also done it without incident, one or two that I have heard of have had problems. If you are a gambling man then keep it, and enjoy the benefits, if not, then replace with the original nickel pack. There is no other answer I can give.

 

[Bladerunner]

Posted by Fred Schofield-graham on 27/02/2010 18:48:54:
My transmitter has not been changed in any way and I do not like the idea of modifying it as I do not have the electrical expertise to do this, so I feel my original posting has not been answered.                                                                                                                                                                                                                                                                                                                            still confused Fred

Well if you'd like the damp squib version: Using Lipo's are at your discretion - manufacturer only recommends NiCd or NiMh for that transmitter. For the purpose of warranty (and possibly insurance) if something were to happen, you may regret using that there Lipo. Don't mess about, get an eneloop Tx pack and never think about it again.

Alternatively: It's a hobby, do what you like and forget about it  

[Clive Matthews]

I agree with Bladerunner. The LiPo packs offer little advantage over the new eneloop type batteries and are more complicated to charge. At around £10 a time a 2100Mah eneloop battery gives me enough flying in a day, including slope soaring. The advantage that the pack will remain fully charged through the longest spell of bad weather is great too.

 

I'm don't believe that the voltage from a 3 cell LiPo will harm the TX and the low voltage warning on TXs is about right to protect the LiPo.  It's the extra charging palava that puts me off!

Edited By Clive Matthews on 28/02/2010 10:30:43

[Tim Mackey]

The LVW on the standard Tx unit is around the 9 - 9.5 V mark and is way too low for safety when using Lipo.  The recommended minimum cut off voltage of 3V per cell is only really applicable under fairly heavy load conditions, and if they get that low with the very small currents involved in the Tx operation, then they really are low!  Remember that even at as "high" a voltage as 3.6V they are at less than 10% capacity remaining, and rapid voltage dump is occuring. This is not something I am happy with on a flight critical tem liem like the Tx!  I have a separate alarm system on my LiPo Tx which screams at me when my pack gets to 11.5V, and at this point I will normally land and consider it time for a recharge. On trials I did with a DX7, voltage was shown to fall off rapidly after 11V was reached.

Extra charging palava? Personally I find the recharging of Lipos the easiest method of the lot - whereas proper recharging of NiMHs can be very troublesome with false peak detects common with many chargers.

Edited By Timbo - Administrator on 28/02/2010 11:08:27

[Clive Matthews]

Well - you have to remove the battery and use a balancing LiPo charger. I know that you and a lot of flyers will already have such a charger. The eneloops will happily charge using the supplied TX charger in the transmitter. Personally, I remove mine every so often and check them with a quality charger (Schulze in my case), but never noted a problem.

 

So you've changed the voltage regulator, fitted a separate LVW alarm. What's the extra capacity gained and at what cost?

 

All I'm saying, is that to me, the eneloop route seems cheaper and easier! 

 

Forgot to ask, does the lower mass of battery improve the TX handling? I suspect that on the 'converted' 2.4Ghz sets, balance might be improved.

Edited By Clive Matthews on 28/02/2010 11:18:53

[Tim Mackey]

And I am not disagreeing Clive - LSD cells were not around when I did my conversion, and as I say, I find the charging regime of Lipos so easy these days. I never charge unattended, and simply plug my charger lead into the existing Tx socket - they are only being charged at around 1A. I only ever hook up the balance lead occasionaly, as dischrging at such low rates, and to well above minimum figures means that they hardly ever need balancing.

What did I gain when I did the work mentioned originally?

Hugely longer battery life than could ever be achieved with nickel.

Instant ready to go state at all times.

Simple and foolproof charging ( for me anyway )

 

As for the handling ...cnat sya I noticed a great difference - sure the box is lighter, but the balance was never an issue to me. I actually now hate those heavy "full house" tx booxes, tried one of the fancy 11 channel JR 2.4 sets the other day - didnt like the weight at all.

To clarify..... I like and recommend the instants too - in fact I use them in my wifes DX6i - I was just answering the points you raised about charging "palava" and LV warnings

 

[Clive Matthews]

Your LV warning advice is well made and worth following. I wouldn't go as far as to say that I was wrong - but you are definitely more right

[John Privett]

Posted by Timbo - Administrator on 28/02/2010 11:05:22:

The LVW on the standard Tx unit is around the 9 - 9.5 V mark and is way too low for safety when using Lipo. 

 

Actually,  if we're still talking about Fred's (Futaba) T7C, the manual states that the LVW doesn't kick in until 8.5v.  So that's even worse for LiPos. 

 

I can't say I've ever let mine get that low, so I'm assuming the manual is correct!

 

 

[Clive Matthews]

I've been doing some experiments with a 2200Mah 3 cell LiPo (well the weather has been miserable). The LiPo is in good condition and is at it's stated capacity.

 

Timbo is taking reasonable care in landing when the voltage reaches 11.5v. When my LiPo reaches that voltage at a low load (50 milliamps) it requires  a charge of 0.91ah to bring it up to full charge. I must stress that because of the time this takes, I have only been able to do this experiment once and with only one battery.

 

My conclusion so far is;

   11.5v cut off is over cautious.

   Utilising less than half the battery capacity is counter productive.

 

[Clive Matthews]

I've been doing some more tests (forgive me it's been a very slow year so far).

 

The following information whilst based on tests, experience and out sourced knowledge, is purely my opinion. 

 

Charging in the transmitter;

 

Whilst most transmitters have a charging socket, not all allow charging with a smart charger. This is because some transmitters have a protection diode in the circuit preventing the charger sensing the battery. Many people remove this diode. I have an old 35Mhz TX and a brand new 2.4Ghz TX which both come under this catagory. I also have a JR DX9 which allows smart charging. I believe Spektrum TXs also allow this. Fast charging in the TX is not recommended due to heat and gas emission.

 

LiPo v NiCd v NiMh

 

This is where it gets a bit opinion biased. I am attempting to be objective, so please bear with me.

NiCds, most wall chargers supplied with TXs are designed with NiCds in mind. They are happy to receive a low rate charge and 'float'. They will suffer from the so called memory effect and to counter this need cycling every so often. A TX with a protection diode will prevent this and so they will have to be removed to achieve this. NiCds have a 'slow' voltage drop which is ideal for use in TXs. Unfortunately they are no longer available on the market due to the use of cadmium.

NiMhs, These are now the most common rechargeable battery in cylinder form. For their size they generally have a larger capacity than NiCds. They are not suitable for charging by typical wall chargers. Whilst in practice, they can be charged in this manner without obvious problem, they are at risk. A smart charger is highly recommended and they are best charged at 1C (source Schulze and Panasonic). They should not be charged at this rate in a TX. If the TX allows smart charging, they can adequately be charged at a lower rate with reduced capacity. NiMhs have quite a steep voltage drop and for this reason should not be used when 'low'. Both NiMhs and NiCds self discharge. This can lead to cell imbalance in packs. This leads to cell failure when the pack is subsequently recharged or discharged. They both need regular cycling.

Low Discharge NiMhs, Becoming more common, these cells reduce the problem of cell imbalance due to there charge retention characteristics. When new, they are charged ready for use. Can be left for long periods without charging and retain good capacities (about 2100mah for an AA cell). They have higher internal resistance and should not be recharged at more than 0.5C. They also require smart charging, though it is possible to get away with using a wall charger with care. Their characteristics should result in a longer life due to requiring fewer cycles. Other characteristics are similar to NiMhs.

LiPos, With a cell voltage of 3.7v, they do not add up to ideal voltages for TX and RX use. This will change in the near future as TXs and RXs will be designed to utilise these excellent batteries. They MUST be carefully charged using a dedicated smart charger. Incorrect handling and charging can lead to combustion. Whilst it is possible to charge in TX, it must be with a smart charger and a low current. I would prefer to charge on the bench. The minimum discharge voltage is 3v per cell (source Kokam) beyond this, the cell will be damaged. Many TX low voltage warnings will be to late to prevent damage. LiPos have a sharp voltage drop towards the end of their capacity. The biggest advantage of the LiPo battery is it's capacity/weight ratio. They are often less than half of the mass of similar capacity NiMhs.

 

My opinion;

 

If you've got NiCds, hang onto them, they are ideal for TX use though tend to have relatively small capacities. If you need a new battery for your TX or want to fly all day on one battery, the new Low Discharge NiMhs are ideal and cheap (£9.95 for an 8 cell 2100mah pack). Just take care on the rare occasions that you will need to recharge, and don't recharge for the sake of it. Whilst LiPos will increase in popularity and usage (until the next type arrives) using them in a TX is at the moment is pushing the boundaries slightly and you need to take extra care. In an RX, you will either use a voltage regulator or be prepared to replace servos regularly (the RX itself will probably be fine). This extra complication doesn't make sense to me for now but I know that higher voltage servos are coming. NiMhs, probably the most common battery for now, use a smart charger to cycle them occasionally and don't keep topping them up.

 

 

 

[Bladerunner]

Been a while, but just read it all. Nice summary.

Regards