I need to update my receiver batteries. My Ni-Mh are a few years old now, though they have not seen a ton of use. Do youse guys use 2s li-po's? I would also need to update my charger, but the li-po's are significantly lighter, and not too expensive. Of course I would have to deal with the cg change with a lighter battery. Any thoughts?

I use nothing but 300 and 350 nimh packs for 1/2A. I've heard that Berg RXs run fine off of 7.2 volt packs, but haven't tried it and don't know which servos are OK with 7.2 volts. Lighter weight lipos might make a big difference if you're into 1/2A 3D [hovering] or all out speed in a tiny air frame.

I personally prefer lipo's over any other battery for my 1/2a's. They are light and there is no fear of voltage drop while using them. I usually run a diode or 2 inline depending on the rx I use. They are light and drop the voltage .7v for each diode used. I also use TP chargers for home and the field. They are top notch but expensive. I also use A123's for my .40 size and larger planes. It is nice to be able to charge in under 15 minutes safely. I only use one diode with them. I guess it depends on how much your willing to pay for the change. Some sell lipo chargers for as little as 20 bucks but they are not the best quality. I have 2 of the 610C's from TP and 2 of the 1010C's from them as well. Never had a single issue and they out perform most any charger out there. They also charge Pb so it comes in handy for the field battery once home too.

Kevin

I use lipo's in everything now, I like the charge time, I use a 2100 3s in my 9z tx. been going great for over a yr now.
They are exspensive but once set up, they are so convenient. for my planes I use a small 450 3s TP battery and the castle creations 10 bec between it and the rx, the bec and the battery still weigh almost the same as my old 350 nimh batt's I think there is 4g difference and I get way more flights out of the setup than I did with the old fashion bateries. The switching bec converts the higher voltage into 5.1 volt without heat build up. on my Helis, I use the 1320's and get 8 flights on digi sevos in my furys per charge. so convenient.

I stick to the K.I.S.S. metheod of battery management:
I use 1200 mah nicads for .40 size, 270 mah nicads for .15
size and smaller. My nitro cars get 6.0v nimh packs from
Trinity. I check the voltage every few flights, and charge
when nessessary. I replace packs every few years. In fact,
I have three packs I'm rotating out at the end of this flying
season. I have never had an in-flight battery issue in nine
years in the hobby.[sm=shades_smile.gif]

I just started looking at what flight pack to use with my first 1/2A RC effort. I'm building a stick built 38" Citabria which is designed around the old "schoolyard scale" catagory and will have a throttled Cox .049TD. It has about a 10oz-12oz weight minus radio gear.

Since I would like to build it close to scale, I would like to add seven LED's for strobe, dash and nav lights.

I have four eFlight 9g servos, and planning on getting a Berg 4L reciever.

I like the idea of running a voltage regulator due to the LED setup.

I guess my question is this still in the bounds in which you guys are talking? If so, I'm hoping someone like Tower Hobbies carries it.

LiFePO4 cells are the way to go!

They have many of the advantages of LiPos but a much lower output voltage (2-cells come to about 6.2V after they've settled off the charger).

There are a growing number of different cell-sizes now available and they're *dirt* cheap ([link=http://www.dealextreme.com/details.dx/sku.1880]an example[/link]).

I've been using the 1350mAH cells in my .40-.90-sized planes and will be using those 350mAH cells in my 1/2As. At $4.50 per pack/2-cells (plus lead and heatshrink) they are pretty cheap and can be fast-charged in under 30 minutes from flat.

There's more on the difference in the battery technologies [link=http://www.rcmodelreviews.com/baffledbybatteries.shtml]here[/link]

Thanks for the link. I didn't realize these were out there. I will be picking up a few packs right now and testing them out.

Kevin

I'll admit up front that I'm a battery idiot. 99% of my batteries are still NiCd, and I have one NiMH pack. My charging bench consists of a Hobbico Accu-Cycle and 2 wall warts that I got from Tower years ago.

LiFePO4 batteries sound interesting, but 3.6V is too low and 7.2 is too high for my gear. How does one get these batteries into our 4.8 - 6v sweet spot? And what kind of exotic charger would I need?

EG

I don't think anyone has mentioned the only advantage of lipo for rx that I recognise.
The shelf life of the charge.
I use them on my F3F slope racers only so I don't have to charge immediatly prior to flight. nothing worse than getting off work at 5:30 and the wind is ripping and having to charge a rx pack. The lipos will retain 90% charge for 2 weeks.

I am not convinced that the extra bulk, more fragile construction, extra components (bec/regulator), more failure modes, monumental charging danger add any benefit to use in my gas/diesel planes.

Having said that they are the only battery used in my electrics for power but still use nimh for extremely high amp applications for the rx power.

Xjet, Do these LiFePO4 need a lipo charger?

I think people use an diode type item to regulate the voltage.

http://www.hobbycity.com/hobbycity/s...idProduct=3735

well, it looks like the link to hobbycity is not allowed?

just tell us what to input in the **** spot.

3.6V per cell is for LiPo and Li-Ion.

One of the benefits of LiFePO4 is that they're only 3.2V per cell (6.4V for a 2-cell pack) which is well within the acceptable range for the vast majority of receivers and servos out there (HS50s excepted I believe).

The 6.2-6.4V of LiFePO4 is *very* good for 2.4GHz systems because it gives you a lot more headroom against low-voltage induced receiver reboots than even a 5-cell NiMH/NiCd pack does.

You should use a LiFePO4 capable charger to charge these cells but most new chargers have settings for these cells now.

Xjet...I really like your site and found it very useful! It takes a heck of an enthusiast to do that for folks. I appreciate it! I too am a nut of the A123's... So are these LiFePO4's the same thing or a touch different? Or is that the technical terminalogy for A123's? I went to A123's site and did not find LiFePO4 anywhere so I wondered if they are different.

Kevin

A123 cells are a particular type of LiFePO4.

The A123 cells use nanotechnology to significantly improve the ability of the cells to deliver high currents (up to 50C) whereas a standard LiFePO4 cell is rated to about 3-5C.

I use A123 cells in my gas planes where the large number of hi-torque digital servos can produce peak current draws of up to 15A or more but on my smaller models regular LiFePO4 cells work just fine. I fly a lot of 3D stuff with .46-sized profiles and even with the very large control surfaces plus large throws I've never had a problem running 5 standard servos and a 2.4GHz receiver on a regular LiFePO4 pack.

I use the 370mah NiMH packs I bought from Radical R/C in my sub-.15 models. They weigh 1oz. I bring extra packs and my Triton 2 to the field and can charge them if I run them down, which never seems to happen.

I can get very distracted at the flying field and I would probably start a fire if I tried to use lipos.

David

That's why LiFePO4 are better they don't go *bang* in the same way as LiPos and if you inadvertently run them flat you can just charge them back up again without trauma or risk.

That does sound interesting, XJet. I will read up on them. I have always felt that lipos were simply a stopgap until a better technology became available. They are far, far from being the ideal power source.

David

The A123 cells are big and heavy and small capacity (for the size/weight). Other than charge shelf life and charge rate why not use a AA 2400-2600 pack?
The main benefit of these cells is the discharge rate, but isn't that wasted on a rx[:-]

I use the A123 in 4s2p to power my sullivan heavy duty starter motor.

You have to watch the ultra-hi capacity NiMH packs, some of them have a *very* high internal resistance.

It also pays to remember that the A123s can be recharged in a very short space of time (typically 10 minutes if you're flying them down to half) so you don't need the same capacity as you do with NiMH. When I want to fly the whole day I just throw mine on charge while I have a coffee or bite to eat at lunch-time and then I'm good to go again.

And two 1350mAH LiFePO4 cells weight a *lot* less than five AA cells.

In my 40 size planes I use a 2s A123 1100mah packs and they only weigh 90grams and my 5 cell nimh pack weighs 155grams. I can fly most of the day on the 1100 with one charge during sandwich time.

Kevin

Oh yeah and if it is dead it only takes 15 minutes to charge. Gotta love them....they are the future.

I use AAA nimh 720's for my glow .40 & 1/2A stuff.
I also have the AA rx pack that came with the radioset.... no, I dont put that anchor in my DNU

The AAA last for a few flights on the .40 or lots of 1/2A flights.
But I dont do extreme or speed .40 flying with high torque pulls on the $9 std servos (3 + a lil 5g on Throt).

A couple of years ago I tried AAA packs on a 40-sized 3D plane in an attempt to keep the weight as low as possible.

All went well for a while then, on the third flight (about 20 minutes total flight-time) I was taxiing back after landing and lost all control. The plane continued taxiing until it hit a big piece of concrete. No damage, just a broken prop but the receiver battery was *flat*.

I also noticed that the AAA cells would sag really badly when I wiggled both sticks at once (free linkages, no binding). They just have too much internal resistance to keep me happy and I wouldn't dare fly 2.4GHz with them.

But, if they're working for you then I'm pleased to hear it.

Curious about your experience with these batteries. I've got a pair of these as well but have not been able to get them to hold anywhere near 370 mah, at least not according to my Hobbico Accu-Cycle. The Radical site "blames" the Accu-cycle for this, but I've never had any issues with my 270 or 600 mah NiCds - they always charge and discharge over the rated MAH.

EG

where are you buying the LiFePO4 batteries?

I've looked at those 1100 MAH A123's, also - they look like a pretty good battery for the weight, for sure.