upgrading to lipo tx batteries
 

About 3 years ago I picked up a lipo battery for my JR max 66 Tx to replace the nicad it came with. The OE battery would only hold a charge for very limited amount of time, so I ignored all the warnings a tried a Tx specific lipo from Himodels. 3 years down the track, and it still holds its' charge far better than the original one, with no problems encountered. Encouraged, I went one step further. Having basically changed over to 2.4 for everything, I decided to pull apart one of my budget priced "Radiolink" Tx's that I bought from Lowpricerc. This entry level futaba clone ( or a re-badged one, I'm not sure:confused:) uses 8 AA batteries, and actually works quite well. I stupidly left it outside one evening, turned on, to retrieve a plane out of a tree, and it subsequently rained all night:eek: To cut a long story short, I dried it all out, and while pulled apart, I removed the power wires with a soldering iron, and put on a two pin jack compatible with the battery from the JR. The Battery won't fit inside the original battery compartment, so I drilled a hole for the wires to run through, and mounted the lipo externally, using gorilla tape. A little ugly, but practical, and showing a charge of over 11 volts after many hours of use:ws:. The AA's lose their charge much more quickly. I'm only using it on one of my electric sailplanes that doubles as a trainer, until I'm convinced it won't cause any glitches. Lets see how it goes[popcorn]....cheers..

You won't get any glitches...
It will either work fine or at some time, with no warning, you won't have a working transmitter.

The issue that can come up is if the TX maker used a marginal voltage regulator, expecting 8 cell NiCd / NiMh. (8 AA alkaline cells usually means the regulator will handle 3S LiPo)

Peak charge of a 3S LiPo is higher than peak for 8 cell NiCd / NiMh.

If the regulator is marginal then it could work for a long time before failing or it might fail the first time you turn it on with a full charged 3 S LiPo in.
If the regulator fails it can either fail open (turn off power to everything after the regulator) or it can fail shorted sending full LiPo voltage to the components rated for lower voltage, burning up the chips.

Even for the JR 2.4 ghz radios that are known to have marginal regulators, 3S LiPo can work for years then suddenly the transmitter quits working.

There is about 50-50 chance of the regulator failing open or shorted.

Yep that's right. It wont cause glitches because the voltage regulator only feeds the correct voltage forward to the Tx circuitry regardless of the battery voltage. The problem comes if/when the voltage regulator fails, and you wont get any warning if/when it does.

And, just to add to the other posts a MUCH better option IMHO is a 3s LiFe pack with an operating voltage of 9.9v. Very easy on the regulator and has the good qualities of the LiPo without as much fire risk too boot.

:)

Mike

Thanks for all the feedback everyone:). I charged the Tx lipo to about 11.6 v, instead of the 12.65 that is full capacity ( according to the what the charger is telling me), and left it on for about 6 hours to see what it would do. Voltage barely dropped, and all the functions appear to work on the trainer plane. I'm unfamiliar with the LIFe packs; I'll have to look into them. The Lipo worked without a hitch in the JR for ages, and the technology in that is at least 6 years old, so we'll see what pans out. Hate to have to post back saying my Tx burst into flames while instructing a novice:eek:.......

Most people get away with it. They are VERY happy and VERY smug.
A few do not. They are VERY unhappy.
With the new low discharge capability of some newer NiMh and LiFe packs the stampede from old lousy low capacity NiCad packs to lipo has slowed significantly.

I used to use a 3S Rhino TX pack, I think it was a very low 3C discharge pack rated at 2650mAh. Hobby King sells (or sold) them. Fit perfectly in my battery tray on my JR XP9303.

Then twice I had left the TX on and ran the battery flat. The middle cell wound up not wanting to recharge properly, so instead of risking my TX in a lipo fire, I went and got an 8-pack of Eneloops from Costco. I put them in an 8-cell AA holder and soldered my TX battery connector to it.

The Eneloops hold charge for a VERY long time. They fully charge to 11.1v, but quickly rest at 10.3v. Then they will hold 10.3v steady for about 2 months. As soon as it hits 10.0v I pull them out and recharge.

At that charge level your sacrificing over half the capacity.LiFe packs are a good option but you lose the ability to wall wart charge.Low voltage alarm is probably not at the correct level.
LiPo at higher voltages hammers the regulator.That all there is to that.

Eneloop(LSD) type NiMh thumbs up.Best option IMO.You dont lose the ability to wall wart charge it without having to pull it out and smart charge it.It runs the same voltage range the radio was designed to use.Low voltage alarm is at the right place without a change(if possible).They have a better chance of recovering from overdischarge at low rates like a Tx does.Plus you can leave it sitting for months and it will at the same charge level as when you parked it.LiFe will do the same.

On the subject of spring loaded battery holders for packs.
Please rethink.IMO a very bad idea.Dont bump your radio on the side.The inertia of the cells will compress the spring and contact will be momentarily lost.Radios dont like being turned off by pulling the power supply while the switch is still on.You can mitigate this issue a bit by stuffing some bits of a dense foam on the spring end to help the spring pressure.Or an extra spring in there to help.The other issue over time especially if you dont remove each one from the holder to charge is the marginal corrosion that will creep onto the ends of the cells and contacts.This can be hideous and cause all kinds of weird things to happen.
In a pinch to get you by for awhile yeah maybe.With extra precautions.A hard connected pack is the only way to go.
The Eneloops and an assembled pack is going to be the priciest.

With good skills its not hard to make your own packs.

My 25 cents worth.

My 8-cell holder springs are very very stiff. I have no worries about momentary loss of contact.

Same here. Very tight fit on my 9x. Still planning on upgrading to LiPo though. http://www.hobbyking.com/hobbyking/s...poly_Pack.html

[QUOTE=aerocal;904594]"At that charge level your sacrificing over half the capacity.LiFe packs are a good option but you lose the ability to wall wart charge.Low voltage alarm is probably not at the correct level.
LiPo at higher voltages hammers the regulator.That all there is to that".

I simply charged the Lipo to @11.3v because that is the usual charge indicated on the screen. Just erring on the side of caution, as the full capacity of 12.65 might be tempting fate. Even at the reduced capacity, it still holds its charge far longer than the nicad. Checked the radiolink again this morning, and still at the same voltage after nearly a week. The nimh would have have dropped about about .3v by now.....What ever the opinions, the Lipo appears to be superior in every way, including being able to use my Hyperion charger. With a solar panel and auto battery, I'm not limited to finding a wall socket to plug in the slow tedious OE charger ( I live and fly in fairly remote areas ). Replacement price is less than a nicad, or AA nimh batteries too:).

LiPo should be perfectly fine at a partial state of charge.Self discharge is almost non existent.If you have enough runtime between charges then it should be good for your use.
We have in a way become spoiled to the amount of time our radios will run on a charge now.I remember when a full charge would barely last a full day of flying.And you almost had to charge the night before or self discharge would let it fall enough in a day that you wouldnt get a day of flying and had to charge at the field.

very true:rolleyes: It wasn't that long ago either:<:. The last couple of years have seen us all get used to leaps in technology very quickly. It does seem like only yesterday that nicads and brushed motors with 36 mhz tx's seemed like cutting edge. Now you can buy the latest and greatest for a fraction of the price as well. You can only wonder what the next few years will bring.....unless the authorities ban R/C under national security regulations or something:eek:

I put a HK lipo in my DX7 many yrs ago with a diode in the + line to drop the voltage a bit. Couple of times I left it on while doing bench work and killed it deader than a doorknob. Used the nimh starter charge to get it going again and worked fine. Did that twice. I put an LED in the top of the trans to remind me that it was turned on:oops: Sold it a few yrs ago when I bought the DX8. Changed hands a few times in the club and still going strong. I bought the HK 2 cell lipo for the DX8 when the nimh that came with it only lasted a few months, and never looked back:D Runs for a month and a half conservatively with the lipo.

so far so good....
 

All is well with the conversion so far. The Gorilla tape on the external lipo is holding up too. Only dropped about .3v since being charged, which is light years ahead of the nimh OE. Time will tell, but it is all very encouraging:D........