A. J. Clark

What's every one using for a receiver battery in there 1/2A planes? I have a couple that I would like to fly this season that have been setting for a while and need batteries. There still on 72Mhz receivers. In the past I used nicd 270Mah. There doesn't seem to be any around now. I seen 2 cell 500Mah cordless phone batteries. Has anyone put a couple of these together and used them. Would this be something practical to do? What other options is there?

Andrew

You can still get NiMH packs in the 260 to 400 mah range from sources like Radical RC and CheapBatteryPacks.com .

However, as my NiCad and NiMH packs age, I've been tossing them and replacing them with 2s LiPo batteries and a 3A to 3.5A UBEC. A 500mah 2s LiPo will weigh about an ounce; A decent 3A switch mode UBEC will weigh about a 1/4 ounce -- many of these UBEC's have the option of being set for 5v or 6v output. This combination will give you all the power you need in a 1/2A setup and generally flight times beyond anything you would get with NiCd's or NiMH batts.

The downside is that you will need a charger capable of handling and balancing LiPo's. However, since you've listed AXE and Century heli's in your sig, you likely are already setup to charge LiPo's.

andrew

John C

I'm trying something different for my small models. It's a 200 mah LiFe batt, 6.6V full charge. It's only 15.3 grams. I've plugged it in to my .074 powered GP Chipmunk conversion with wattmeter in line and I'm not seeing any significant voltage drop when moving all the servos simultaneously (HS65). Obviously, I'll need to watch the charge state closely with the low capacity and only a 1C rating, but it's lighter by at least half vs. the 300 mah NiMH I was using previously. I got mine from Radical RC along with an 1100 mah for a larger plane I'm finishing.

John C

Boomerang1

I used a 450 mAh 2 cell Hobbyking lipo & a home made voltage regulator for my
020 powered Roaring 20. The build thread is here detailing the regulator.

http://www.rcuniverse.com/forum/1-2-...ange-pace.html

Or, use a single cell lipo with this voltage booster to raise the single cell voltage to
5 volts to power your radio.

http://hobbyking.com.au/hobbyking/st...to_5v_1A_.html

Interestingly, I converted the Roaring 20 from Pee Wee power to electric with a tiny
brushless motor & the battery I originally used to power the radio only now runs the
radio AND the motor for about 3 flights of good duration with more performance than
the Pee Wee.

John.

049flyer

My Feedback: (18)

Here are the batteries I use.

049flyer

My Feedback: (18)

I've tried the 6.6v 200ma LIFE batteries from Tower Hobbies but they are rated for only 1c which is a little shy for me as I use HS81 servos in my 1/2A planes. Dynamite sells a 200ma LIFE battery rated for a higher current draw but after taking a pack a part I have decided against using them as the quality is VERY POOR. So I am back to Nicad and Nimh batteries.

Polou has STEP UP regulators as well as STEP DOWN regulators. With a step up regulator you could run a single LIPO and get a 6v output or 5v if you prefer to your receiver. The step down will allow you to run a 2 cell lipo. However all this regulator stuff just increases the number of possible failure points so I am still using Nicad or Nimh batteries.

BrightGarden

Yes, this is the part that concerns me, especially using cheap Chinese regulators.
But I am going to give this setup a shakedown and see what the reliability is.

A. J. Clark

Thanks for all the replies. I look at the Pololu site. I think the 2/3AAA 350mah they have will suit my needs.
They have the packs made up with a JR connecter. Which will make it easy to install in what I have.

Thanks Everyone.

Pond Skipper

I have the new SANIK 2/3 AAA 400 mah they peak out on my smart charger at 470 mah.

Andrew

The pack in question looks to be just the ticket for you.

One thing that is often overlooked is formation charging of NiMH packs. The difficulty many of us have had is finding a charger that can be set low enough to charge the low capacity packs since formation charging is usually done at C/10, or in your case, 35ma. Rather than go into detail about formation charging, I've attached a FAQ from NoBSBatteries that covers the subject quite well. I built a simple constant current charger that could be set to a low charge rate just for managing packs of this type. There are likely other solutions that are available, however.

http://www.hangtimes.com/rcbattery_faq.html

andrew

Pond Skipper

My smart charger will go down to 10mah at that level the peak voltage during charge is unable to exceed 5.86v yet it will pack in over a 100mah over nominal. If I charge at 30mah It will push the voltage up to 6.2v and pack in an additional 70mah over the 400mah nominal rating. The additional cell density seems to be real and not a phantom condition of charge rate.

049flyer

My Feedback: (18)

How much energy you can put into a battery with a peak charger often has no relationship to how much energy the battery can actually deliver under load. The only way to know the condition and capacity of a battery is by a measured discharge. Therefore if you were to discharge the battery at a rate of 300 ma or so or even 1c, then you would know exactly what it can deliver to your receiver under a typical flight load.

Pond Skipper

Yes really need to do a load test or a discharge cycle and see how it performs. So far these Sanik's have been able to hold their charge well I have to get some more use out of them once the weather improves.

aspeed

I guess the 2/3 AAA would be ok. I have had only two seasons out of NiMh batteries, so I try to just use NiCd mostly. I just get the AAA dollar store ones for the 1/2A and little gliders. I am starting to go with the LiFe, but am afraid of the higher voltage on the older servos. I do have a step up regulator to try still for a single cell LiFe that should be light, but only good on low drain servos.

aspeed

double post

MJD

My Feedback: (1)

Agreed - I thought most or all of that so called extra charge was just slowly shed as waste heat. Capacity test will tell of course.

You can trickle 10mA into a 300mAh pack for four days.. the area under the output curve would be huge. But the amount of charge taken up by the battery wouldn't be any different (well, unless it started venting). But you would have been shedding 30 milliwatts of heat into your workshop all that time.

Using electric baseboard heat rules of thumb (500w per 100 sq ft up here), that's enough for a 2-3/16" square area of your home.

ffkiwi

I fully endorse Andrew's comment-I use very small NiCd and NiMH packs in my F1A free flight gliders (well half of my fleet-the other half are still using multifunction clockwork timers)-of 100 or 160 mAh capacity. I have two packs per model-and with periodic replacement over the years, a mix of NiCd and NiMH-the NiMH have been sourced from Radical RC. With these very small packs I think it is essential to give them the appropriate forming charge then cycle a few times before use. I have Jr Triton and Imax B6 chargers for mundane use in general battery charging (field battery, glowplug battery, 'normal' RC battery packs)-but for the very small stuff I wouldn't dream of using anything but the trusty Sirius chargers shown here-durable-and very reliable. I even carry a 12V 1100mAh NiCd pack to run the charger in my glider flightbox for field charging of the small on board packs. This in turn gets recharged on the Triton or Imax at home. No doubt over the next few years I will replace the NiCD/NiMH packs with 2S Lipos and a 6V regulator-though with the airlines being 'difficult' with carriage of Lipos it might be just as wise to stick with NiMH....

You can see the Sirius forming charger handles packs as small as 100mAh

MJD

My Feedback: (1)

I bread-boarded up an adjustable current regulator for form and trickle charging, 10-50mA output. It worked well actually, the main troubles I had were packs suddenly not accepting charge or going flat on me, despite what I thought* was reasonable care. I made a few 220 and 300 4 cell packs from those Tower batteries everyone was using, and had some fun with them before starting to have problems. Plus.. I was late in that game so didn't have to wait too long for viable Lithium based Rx packs to come along. My main problem was likely impatience and indifference.. with lithium batteries the smart chargers handle everything just fine with minimum effort on my part.

smallrc

I still prefer Ni-Cad's. NiMH's don't seem to last and have a higher internal resistance. My favorite pack through the years is the 2/3 AA, which was 270 mAh years ago and is now 350 mAh. Batteries America makes this pack with Sanyo N-350AAC cells and sells them for $15 w/o connector and $18 with connector ($18 & $21 for 6.0 volt packs).