[cman]

Hi

I did a search I did not find the answer but if there is already a thread here please post the link

I am wondering if anyone is using a 2 cell lipo for a receiver pack? do you have to step down the voltage?

I'm slowly getting the nutros ready and do not really like the nihm packs mainly because of charging them I would not be able to use my old chargers and because I have had bad luck with them only lasting a year, where as before my NiCads lasted many years.

I have seen batteries advertised as 2 cell RX packs I'm assuming the RX is for receiver.

any insight would be great

thanks

C

[cosmith]

You can use a 2 cell lipo with high voltage servos or with a regulator and standard servos. Another option is a 2 cell Life battery. They put out 6.6v and can be used with standard servos bearing in mind a fully charged NIMH battery puts out more.

I've done all of the above without any issue.

[Daren71]

This is what I use.

http://www.castlecreations.com/products/ccbec.html

I have several small lipos, 2 and 3 cell 750mah batteries that get used for receiver packs. These bec's from Castle are programable, and have updates occasionally. You can set the output voltage to whatever you want. I check the voltages of my packs after every flight, and they have tons left in them.

One airplane, my Beast 60e, has 6 servos, I fly for 7 minutes each flight, fly 3 times every time I go out, and the receiver battery could probably go for at least 6 more flights.

The bec gives me a bit of redundancy that I'm looking for in my planes. I'm not concerned about the extra weight.

Daren

[Cougar429]

Chuck, as you know you are limited by the lowest capacity component in your system. You will need to check each and every one to confirm they can tolerate the voltages.

On that note, there is a better option than LiPo. For the last several years I have been exclusively installing 2S LiFE, (A123) packs for flight power and they have been flawless. Got rid of the previous favourite NiMH packs in both flight and transmitter due to age and their annoying self-discharge that required rewinding the day or night prior to flight sessions. With LiFE I can leave either the craft or transmitters alone for months and find them at close to the charge level they had when left idle.

Along with confirming your charger can discriminate and handle that chem, (most do now) there are a few other factors to know. The listed voltage should have them running at 6.6V, but can start with a short jolt of 7.2V. Sounds critical, but I have been finding no problem on all but one particular servo that may have suffered other problems.

Unless special-purpose such as heli tail servos, most spec for 4.5-6V, what you would get from 4-5S NiCad or NiMH. You may note even these in the 5S config can light off higher than 6.5V, but also quickly normalize.

Due to concerns the first two installations had the 20A rated Castle BEC PRO to drop the output to 6V and could sustain even the most demanding power drains, (servoless retracts) while mounted inside the fuse with minimal cooling air.

The at least half dozen subsequent installations have run straight off the LiFE packs and so far have also worked fine.

That is the good, now for what you need to know to keep them healthy.:

LiFE and LiPo are similar chems. However, LiFE does not seem to suffer the overdischarge, (still, no reason to go there) and can rewind incredibly quickly. Using either the Cellpro 4 or 10 I can fully balance a 2500MAh pack in slightly more than 5 minutes. Because of that rate, if doing so through the balance connector you need to watch for overheating, at least for the first few times.

That same power density means it can supply just like a LiPo, so the standard slide switches likely could not handle the demands. Take note that regardless of the capacity, NiMH do not have high current outputs so system components were never rated to handle more than approx 4A max. With modern components like the aforementioned servoless retracts and digital servos, the current requirements can easily exceed than.

Here is one that could be very important. A while ago I contacted Western Digital and Fromeco to look into a charge state indicator. The response was two-fold: First was that the voltage differences between full and leaning over the cliff, (right where the voltage takes a dramatic drop to nothing) are so minimal no equipment then available outside a lab would work. Second was that the balance between the cells is almost as important as their level.

The first may no longer be as true since I found several indicators that can pretty accurately show the charge state. The balance however is still treated with the same concern.

One other final item that may gum up the works is that any previous internal watch and warn systems set for NiMH or NiCad will NOT work if LiFE are installed. You best do time/use monitoring to see how much drain you place for different length sessions and try and maintain at least 80%, the same as with LiPO.

So, my own experience with LiFE has been positive. In the flight packs not one failure, good power output and very quick rewind times. With the 3S Tx packs the same, with even the 1500MAh installed lasting at least a full day or more of flying.

The only complaint would be their greatest advantage. For the same rating they are considerably lighter than NiMH, so if used to set the CofG in your craft you may have to be creative in a direct swap to keep things in range. If the Tx is designed to balance for them you may find it antenna heavy once swapped over. Since I have often gone with a 2.4 module in place of the telescoping antenna not so bad.

[stegl]

Gary : To clarify a couple of items. Starting with the weight of nimh vs. Life/A123 comparable battery packs if comparing premium AA Eneloops ( white) 5 cells of Eneloops weight 481 grams and the two life/A123 weight 515 grams. These are unwrapped loose cells . Also if running small aircraft ; Eneloop also make a AAA cell rated 800 mah as another possibility .

Pricewise ; comparable Nimh are less expensive than Life/A123 ;about half the price.

One advantage of Life/A123 over Eneloops ... faster charge, requires special charger (disadvantage ? )and have higher discharge rates for large aircraft with high power digital servos. Now, Eneloops rating holds 85% of the charge over 5 years and 2100 cycles but not sure what cycle rating is of the Life/A123 batteries.

The 5 minutes to balance/charge a 2500 mah discharged Life/A123 pack would be really stuffing a high rate charge into it and would be running pretty warm to hot; but then if only say discharged 30% can be quite possible in 5 minutes.

On the other hand if using cheap nimh then the comparison would not touch the Life/A123 batteries.

Lastly , not sure if you mentioned it ; the receiving/servo arrangement would have to be able to handle 6+ volts as some servos specifically state no more than 4.8 volts ( older Futaba for example) . Of course you find guys that do run 6v on these but then when failure occurs , would be blamed on something else.

You have made a lot of good points in your last statement for users to compare for their needs.

[cman]

Thanks for all the info

I just want it back to where I plug the charger that came with my radio into the wall, and one lead into the radio the other to the jack on the side of the plane, then go to sleep and wake up the next morning and go flying. but things change I guess.

Thanks for all the good info a lot to read

[cman]

Another quick question

My DX 7s uses a nihm battery my Dx8 uses a LiFe batter, the adaptor to plug into the wall is the same for both, as far as I can tell I can put a life pack in my DX7s, and it will charge or a nihm in by DX8 and it will charge. Am I right on this? I thought nimh and LIFE required different chargers, or does the radio figure it out.

[Cougar429]

Not sure since NiMH packs would best work with a Peak Detect charger to prevent overcharging, (or one with a temp sensor?).

Stegl, I would think even the Eneloops 800MAh output would fall short when digital servos are used. Some I have worked with can pull up to 1.5A or more EACH if heavily loaded or stalled.

I remember the days when a 400MAh flight pack would last us all day. Things have sure changed.

[Cougar429]

Chuck, those wall warts are incredibly low current and lack any monitor circuitry. If left unattended you run the risk of battery damage.

Check the manual for both transmitters. I would think the ports may be identical, but the power requirements would be different.

[Frank Klenk]

Chuck
You can use a Lipo combined with a regulator for the standard receiver and servos. Servos and receiver that run on HV can use a Lipo with no reg.
For me the simplest and most reliable solution is use LiFe batteries. I run non HV stuff and find these work just fine. Most chargers support this chemistry. You can quick charge these and they don't get hot.