xphasor

Hi All,

I'm building an 0.020 powered 2 channel plane and am trying to work out what battery to use as a flight pack. Man it is tougher to nut out than I expected. I would prefer to use NiMH for capacity reasons, but can not find small enough cells.

What do you reccomend I use? The plans call for a '270', and I don't want to buy an mega light pack just to have to add noseweight and suffer unnecessarily reduced flight time.

Thanks guys,

Julian.

Bipe Flyer

I got 120 mAh and 280 mAh packs from http://www.batterystation.com/nicads.htm that weigh about 1/2 oz and 1 oz respectively.

I use the 120 packs for .010 and .020 stuff and the 280 packs for .049 to .074 planes. I have used 110 mAh packs in 1 lb .061 4 channel planes before which gave about 3 flights of about 15 mins before needing to be recharged.

I'd go with the 120 pack and move things around until it balances. When it comes to weight; less is more.

xphasor

Awhhh Nice one man!
Should have asked 3 days ago!
I've got me one of those LED fangled voltage indicators, so I'll do as you have, and let ya know!
Cheers.

Dukester

My Feedback: (31)

FYI, for a receiver pack, I also use a little bit of electric flight equipment. I use a set of lithium polymer batteries for light weight coupled with one of the cheap GWS speed controls with 1A BEC circuit. You get 1A at 5V to the RX and enjoy the benefit of lighter weight from the lithium polymer batteries. The most common setup I use like this is a set of kokam 1020 mah lipo cells with the IC50 speed control for a total weight of 1.3 oz. Just make sure you blank off the motor leads for the speed control to prevent any possible problems.

Duke

Andrew

BF --

Are your making up your own packs or did you get them pre-assembled?? What is the cell size in your 280 mAH pack --- 2/3 AAA or AAA?

Thanks,

the "other" Andrew

PsychTeacher

Not to contradict the other suggestions posted but merely to tell you what works for me:

I fly an .020-powered plane with 3 channels. I use a 110 mah 4.8V pack bought from Hobby-Lobby. I tested it by plugging everything together: a Hitec Electron 6 rcvr. and three HS55 servos. Then I "diddled" the transmitter sticks continuously until my thumbs got tired (I was watching TV to pass the time). After 45 minutes of continuous (3)servo action everything was still working fine. I do take a second rcvr. pack to the field for back-up, but have never had to use it.

I am sure the NiMH batteries are better but the nicads work just fine for me.

Regards

onecb

My Feedback: (5)

I solder my own together. The ones I currently use are 160 mil nmh cells that are 1/3 of AAA in size, very small. I also have some 240 mil that are 1/3 AA size. The 160 lasted good through 5 10 min flights. I bought the cells on Eb** they are new unused and very cheep. I so make sure that I test cycle them three or four times before I put them in a Plane.
Alvin

Bipe Flyer

Andrew,

The packs were made by Battery Station as yo see them. The 280 mAh pack is 2/3 AAA.

PsychTeacher,
THe NiMh aren't better per-se, just lighter for the same capacity. At $1.50 per cell they're cheap enough too.

Ragwing

My Feedback: (2)

How are you guys charging these little packs. From what I heard NiMH need to be charged at C/10, but my wall wart only goes down to 50ma, where a little 170mah pack would need 17. Maybe I'm just confused [] Thanks!

Derek

Bipe Flyer

NiMH should be charged at C/10 for the first charge, then they can be charged at 1C. Many people will actually charge them at 2C, although it is supposedly bad for them

For the first charge I Charge NiMH on my Accu-Cycle at 25 mA (that's as low as it will go). For the 280 mAh packs I let them go through a complete cycle. I charge the 120 mAh packs for 5 or 6 hours. After that I just put them on charge the night before I go fly and if I have to I charge them at 1C on my Supernova at the field. If the pack doesn't get too warm during charging then I'm happy.

MR Flyer57

Hi Bipe and the rest of the gang,
This is my weak point, and I am looking for any help I can get. Bipe which battery's are you holding (by part number) and which cells did they use to make them? (also by part number) I have just gotten into the NiMH with no success, been some plane loss and I hit a guy with one due to bad battery charging. That is how the Chicken Hawk got it's name.

I have no Idea which charger to get and have ordered a Great planes Triton, because it has been used here and seems to work.

My questions are probably going to sound simple but please try to talk down to me, because I really don't have a handle on this stuff.
First, the initial charging. I am a old nicad user and NiMH seem to be charged very differently from what I have always known. I have read about the problems of overcharging the NiMH batteries and ruining them with the extra heat the is generated by continuing to charge a fully charged NiMH battery. How do you know when full is really full?

Initially what do you have to do to the NiMH batteries to get them to the point of full capacity and ready for use? And then what do you do to maintain them, first at home and then at the field to recharge them?

You use the term C/10, and I don't know what that is.

Next can you cycle them? And if you do, to what voltage do you drain them down to? 1.1 volts, .09volts or something else.
What charger are you using, and what would I look for or avoid in a charger. I want a field charger that will run from my 12 volt car battery and recharge my planes at the field, are NiMH batteries able to be fast charged with no problem? I know there is a heat problem that must be kept in check. What about the do's and don't's when charging overnight at home with a wall wart?
Do NiMH packs develop memories? and if not why would you need to cycle the packs?

Maybe it would be easier to take the prospective of a new battery pack and walk through the steps needed to set up and use the NiMH pack.

Between the battery packs and the charger I'm going to be into this for about $200 and I just hate going down the wrong road spending money, just to find out that what I got was the wrong thing, and now I have to discard it and buy something different. The weight and capacity of the NiMH batteries are such a draw that I would really like to take advantage of them.
Thanks for your help folks,
And don't be afraid to include all the baby steps, because I really need to get this stuff cleared up.
Thanks again,
MR Flyer57

ZAGNUT

My Feedback: (1)

[link=http://www.gpbatteries.com/industrial/batteries/NiMH/NiMHspecs.htm]GP Battery[/link] has a nice list to choose from. i use the 2/3AAA cells for most of my .15 and smaller planes. a 4 cell pack is a tad over an ounce.

and for under $1 you can wire up an LM317 in current limiting mode and adjust it for any value you want to charge at. works good for tiny cells.


dave

Bipe Flyer

Hi Marshall,

The cells I bought were GP-12AAAM for the 120 mAh pack and GP-28AAAM for the 280 mAh pack.

The only real difference between charging NiMh packs and NiCads is when using a fast peak charger. If a peak charger is used then you must use one designed for NiMH, like the Triton, Supernova etc.

"How do you know when it is full?" I use a loaded digital volt meter to check my packs before each flight. A peak charger will stop charging when the battery is fully charged. If you are charging on a constant rate non-peak charger, like the standard wall charger that comes with your radio, you charge based on time like you do with NiCads. For example if you have a 50 mA wall charger you would charge a 500 mAh pack for 10 hours, regardless of whether it is NiMH or NiCad. That would be a C/10 charge. Capacity = 500 divided by 10 = 50. 500/10 = 50 so 50 mA is a C/10 charge for a 500 mAh pack. 50 mA on a 250 mAh pack would be C/5 (250/5 =50) and would charge in 5 hours.

Simplified, capacity divided by the number of hours to be charged will tell you the desired charge rate.

Yes you can cycle them, but NiMH do not have a memory effect, so ther is no point.

I just bought a Hobbico Quick field charger MKII. It can charge NiCads, NiMh packs of 1 to 8 cells and Lithium packs of 1 to 3 cells. It has charge rates of 200mA to 2A and can charge 2 packs at the same time. The best part is that Tower has them for $50.
http://www2.towerhobbies.com/cgi-bin...?&I=LXCTZ5&P=7

Japanman

Hi Bipe,
I have read in many faq`s about charging nicads that they need to be charged up 1.4times their capacity- thats why most 50ma wall chargers for 550mah nicads state you should charge for 16hours (a total of 800mah)
This is i believe to compensate for the ineffeciencys of the cells.

What damages cells is overcharging- then the cell has to reject the charge, which causes crystal growth between the plates, and lots of heat !
At 1/10C there is little chance of damage to the cell if overcharged a bit- but at 1C you want to be careful- I have never had a bad experience stopping at 1C or 1.2C as the cells are actually almost completely charged then anyway (they do not take charge in a totally linear way- a lot to start with and less as time goes on)

I am no electronics expert though!

J.M

jboy381-RCU

i use a wall wart to charge my 120 mah packs...i let them charge for 2.5 hours per pack...it seams to work out pretty good...


john

Bipe Flyer

I know, but I didn't want to confuse the issue.

That's the beauty of a peak charger. It shuts off when the battery is fully charged without overcharging.
If you just use an appropriate peak charger and don't charge at more than 1C you shouldn't have any problems. The Supernova, for example, wont allow you to charge a 250 mAh NiMH pack at more than 250MA.

I'm not sure that the maximum charge rate is for Lithium. I've heard that it is C/3, but I don't know for sure.

onecb

My Feedback: (5)

I also lost a couple of planes two years ago when I first started flying again. I was using the wall chargers and trying to time the charge. After I had the dead battery crashes I did a lot of reading about nimh bats. I decided the best way for me to keep them in good condition. I already had from racing electric cars the fast chargers. The ones I use are Tekin BC112A. they are totally adjustable charge rates and are designed to charge nimh cells. All you do is take the capacity of the pack multiply that by 1.5 or 2. set the charge rate at that and start it. The bats don't get hot and they don't get over charged. I would recommend the charger I use except they are no longer made. The one described above sounds like it works the same and there are probably several available. Just be sure that it is designed for the type of bats you want to use and that the rate is adjustable for the size cells you want to charge. I have some nimh bats that have two to three hundred cycles on them now. and they are still holding a charge well.
Alvin

Bipe Flyer

I never take for granted that the charger has done it's job. Even if the charger charged for the correct amount of time or detected a peak, the pack could have a bad cell, be down on capacity or who knows what else. That is why I check before every flight with a loaded volt meter.
http://www2.towerhobbies.com/cgi-bin...?&I=LXWW16&P=7

xphasor

It is funny - I've been asking a few questions in the Battery forum, and no one is really interested in discussing it too much! I guess you all over here see it as an interesting topic change. Thankyou all for your ideas and scenarious.

I haved asked Dave in Israel to elaborate on this current tuning method as it sounds as though a few of us could make use of something to lower the output of a plug in power pack transformer to allow optimal charge rate of small packs. Certainly I can't see any other way to perform the initial slow charge required to get the thing going.

I've ordered a NiMH pack (too scared to solder or weld yet - will likely do so in the future) based on your experiences.

Looking forward to putting some pics of the plane up in a month or so (have to source more things yet)

Julian.

jboy381-RCU

here is the one i use...http://www2.towerhobbies.com/cgi-bin...?&I=LXNK81&P=7

the small packs work well on it...

john

Dukester

My Feedback: (31)

For what its worth, I second the Hobbico field charger MkII as a good all around charger. Not quite as good as some of the more expensive (ex Triton) for making sure things are 100% topped off, but the price plus ability to charge two packs at once makes it a bargain in my book. I have one too and find its all I need.

Duke

MR Flyer57

Thanks for all the info so far.
I needed a tach and a battery load tester a while back and got this one (picture 1). I wanted to tach some of the little engines and find out just what they were doing, a little like combatpigg with his thrust o meter. So I wrapped it all into one.

When using the load meter what would you be looking for, to tell if a battery is good? I could tell if a cell was dead, but is there more to the story?
I know that they can't be too low when your looking at the voltage but where do you draw the line?

I have these batteries (picture 2), some I have made from cells that I got at the LHS and one pack came prebuilt. I don't really know what I am buying, I have been just watching to see what has worked at the field, and then do the monkey see - monkey do, kind of a thing!!

I am looking over your formulas and trying to get a handle on the whole picture, but I have one question. What do you do to find out a packs capacity if you don't all ready know it? Is there a test or a way to tell what kind of real life power comes from a unknown pack?

Thanks again, the fog is lifting but the sun doesn't shine just yet!!
MR Flyer57

Bipe Flyer

The Hangar 9 meter/tach should do just fine. I've been thinking about buying one myself the next time the batteries in my tach need replacing.

The meter just tells you if the pack is charged and will hold that charge under load. There should be a chart that came with the meter telling you at what voltage it is unsafe to fly. I don't fly if the RX pack is under 4.9V.

To find the capacity of an unknown pack you need to cycle it. In fact that's about all cycling is really good for. You should get a feel for how many flights you get on a pack and over time you might notice that the pack isn't holding a charge as well as it used to.

I've read that a pack should thrown out if it is not at least 70% of it's rated capacity. I'm not sure cyclers show 100% of the battery's capacity or not. I would think that they don't because they only discharge the cells to .9V, or whatever, insted of draining them dead. Maybe someone here knows the answer.

Check out Red's Battery Clinic. http://www.rcbatteryclinic.com/ It has lots of good information and reviews on some chargers.

flyinrog

My Feedback: (1)

I got a ? too.. Nimh batteries dont discharge at a linear rate do they.....?can you measure Mah on a pak? on my parkflyer the esc has a bec so that when the battery drops from 7.2 volts to ~3.8 volts the motor cuts off that way you have power to the servos so you have time to glide in under control..interesting from Pysch teacher, I thought of doing that too but in your living room with the servos under no load wouldnt quite match a plane doing say 40mph with air pushing back on the control surface....A good idea though so maybe half that time would be more realistic... and I have heard (long ago) chargers that run off car batteries can damage the car battery? I, like Jboy charge my rx paks with my radio charger at 50mah/hour my 120 at 2.5 hours my 270 at 5 hours and it works fine, I'd rather get/take extra paks than hook up a charger to my car,, Mr Flyer... your paks are,,50Mah is made up of 4 1/3 AA cells of 50 Mah at 1.2 volts each so you have 50Mah at 4.8 volts per pak....if you take the covering off or peel it back you unknown pak should say what the Mah is on each cell......well its 08:30 and past my bedtime, are you all thoroughly confused yet?...Rog

ZAGNUT

My Feedback: (1)

the LM317 is an adjustable regulator IC that can be wired to limit current or voltage, all that is needed is the IC and a resistor of the correct value. the current limiting mode is VERY helpful in battery maintenence. it can be used to charge, discharge or load test at a precise current regardless of the number of cells or voltage (within the IC's limits of course!!). many people use a simple dropping resistor or light bulb for the same purposes but they will never get a precise value this way as just a slight change in voltage will change the current. the best thing about the LM317 is that it is as comman as dirt and can be found in any electronics shop.

i have a bunch of these set up for different currents and purposes. my most common use is in load testing where i use a rotary switch to select different resistor values for each load. i have this wired to a cable that can plug into my digital multi-meter or my TX's battery tester. with circuits designed for anything over 300 mA i use a heat sink.

here be some links to get you started:

[link=http://62.236.156.23/ideaport/d/lm317.pdf]ST data sheet[/link]

[link=http://www.ncws.com/rcrock/charger.htm]schematics and help in calculating resistor values[/link]

[link=http://www.rcuniverse.com/forum/m_579946/mpage_1/key_317/tm.htm]old thread on same subject[/link]


dave