I have a Futaba transmitter that I bought from a friend at work. It has a battery adapter in it with separate 1.2v nicad batteries in it. I don't think the batteries are holding a charge for very long anymore and I was wondering if it would be a bad idea to use NiMh batteries instead of nicad? NiMh are easy to get at Wal-Mart but I would likely have to order nicads to replace the ones I have now.

Personally I would see if it would be possible to replace the seperate cells with a proper NiCd or NiMH pack. Check to see if there is a plug in battery compartment for a battery pack to plug in.

I don't see why replacing the cells would be a bad thing - NiMH cells should work better than the original NiCds, seeing as they have probably died by now.

Graeme</p>

Yeah, good advice. Go to www.radicalrc.com and go through the battery packs (they have pictures with dimensions) and see what will work. Just remember to total up the number of discrete cells you would use, probably 8 for a 9.6 volts (nominal) and get a pack that matches what you would use as single cells. This, of course, is if the transmitter is set up for a pack.

If it is not set up for a pack, then switching over to NiMh packs will be just fine. I assume they are AA cells.. Get the highest capacity you can find, though.

CGr.

Some of the lower channel Futaba TX (4C, 6EX etc) come with the battery section built for 1.2v AA size batteries. If this is the case, traditionally you were stuck with the AA type. That is because the thickness of the battery compartment is only one AA battery thick. The battery packs mentioned above are also built from the same AA batteries but the batteries are stacked in two layers and wired together. That is why the cross-section of the packs will be thicker than the space available in the battery compartment, so you cant use them. However, recently I saw NiMh packs from Hydrimax on Tower that have the batteries arranged in a flat pack, you could use these if you have the Futaba J-plug in the TX or could solder in the plug yourself.

Personally, I dont think the 8 seperate AA batteries option is bad. It means you can use any reliable and cheap rechargable AA cells set available locally instead of the expensive ones from the hobby shop and you can use lower mAh capacity (meaning they will have more usable life). Also, you can keep two sets so that when the voltage on the first set drops to 9V (which you can see on the TX LCD) you and swap out and continue flying. Just remember to replace the cells between flights, buy all 8 Nos of the same make and capacity and stay away from the cheap chinese stuff. Also, keep an eye on the amount of time they last as even if one cell in the pack goes bad, you will get a reduction in the time they hold charge and you will have to replace the entire set

Ameyam

Thanks guys. The transmitter is a Futaba T8UAFS. It originally had a battery pack with 8 cells stacked in two layers. The guy that originally had it wired in one of those battery adapters that accepts individual cells. He said he did that so he could use off the shelf batteries from wherever he wanted to get them. Right now it has Sanyo Cadnica 1.2V 700mAh Ni-Cd cells in it. I have not flown in about 2-3 years but I charged them yesterday. After a full charge they showed almost 11 volts on the transmitter digital display but dropped to 9.8V in a matter of minutes after I started my plane and let the engine run awhile. I wasn't even exercising any of the servos besides the throttle. I don't know how to test these batteries to see if they are any good but I know they are fairly old. I thought maybe I could run to Wal-Mart for the time being and pick up some Ni-Mh cells to replace them. Of course the brands I would be able to get would be Energizer or other normal brand. If I did do that, what mAh would be best to get? I noticed a couple of people said get the lower mAh ones.

Since you have not used them for a couple of years, I wouldnt trust them. A simple way to test them would be to leave the TX on for some time and note how long it is before you get a voltage alarm. Keep the airplane off of-course.

While most cant tell you what mAh you would get from Walmart, there are two ways you can go- either buy the high mAh ones i.e 1500mAh or above or buy the lower mAh ones i.e. 1000mAh or below. mAh basically current draw multiplied by number of hours for which it is drawn. So a 1500mAh battery will theoretically deliver 1500miliamperes for an hour. Since the TX doesnt draw that much current, the battery will last longer. The higher mAH ones will hold charge for longer. Obviously anything that is higher performance will go bad (i.e will lose charge holding capacity over time and usage) faster.

Ameyam

Okay, thanks. I will try to pick some up in the next day or two. I guess my next question then would be, can I use the charger that came with the radio if I use the NiMh batteries? I would assume not. I have NiMh cell chargers so I am guessing I would have to remove them from the radio and charge them in one of those wall chargers?

You will find out testing your cells without a cycling type charger is time consuming and not very practical. If they are three years old and especially if they were purchased at Walmart then I would pitch them just as far as you can, no ifs ands or buts.

Another problem if it was modified with some sort of spring contact holder for the individual cells then that is another liability that can and will fail at some point. I would never use that kind of cell holder in any kind of airplane. They can corrode and cause problems and lessening tension as the box cracks or bends is another failure mode that is common.

Yes, in this application Nimh is a better choice now and you can get high capacitys up to about 1600 mah. There is no reason you cannot get good ready made packs to fit that tranny in many capacitys. Please get rid of that Spring box.

Your Tx and Rx flight packs are the very last place to start scrimping a buck, some of the home brew battery packs that I have seen are simply horrifiying and most have failed in some way.

John

John, you are probably right. It would be no problem to solder the original connector back on and order the battery pack. They are available. I wasn't trying to be cheap on the batteries, but thought since it was setup the way it was it would be convenient to be able to stop by the store to pick up new batteries if needed rather than ordering replacement packs. You are right on the reliability of the spring contact holder though. Thanks for the advice.

Excellent YH, reliability always trumps convenience.

On your chargers for the Nimh over Nicd you can use the same wall chargers if they are of similar capacitys.

The problem is if the Nimh is a considerably higher capcity then it takes much longer to receive a full charge from that same wall charger. Now what can happen although not neccessairly a safety problem it can result in the Nimh not ever really getting a full charge and therefore not suppling the full rated capacity. For example if you fly everyday there may not be enough hours in the day to sufficiently recharge using the wallcharger intended for Nicd's.

A more capable charger that has adjustable currents for higher capacity packs is a good idea in this case.

John

If I really wanted to do things right, what charger would be suitable for charging the packs for my transmitter and receiver? One that would charge, recycle, and let me know when I have a full charge?

Right now I have no real way of knowing if my batteries are fully charged, other than a cheap multimeter. The only charger I have is the little wall transformer unit that came with the setup I have.

I would love to go fly right now but I just don't have enough confidence in the batteries I have for the transmitter or receiver. They have been sitting in the units for a couple of years now, unused, and uncharged. My other issue is, I plug them in, let them sit for however many hours...don't know if I am over charging, under charging or just right.

Sorry for the barrage of questions...just trying to get a better understanding of what I need.

There are several places that sell ready made battery packs. Get rid of the individual cells. The batteries are OK, but the holder will cause you grief one day. Hangtimes.com, Radicalrc.com, Electrodynamics, E.h. Yost, RCaccessory.com to name a few. Then get a good charger. I have some(Turnigy brand) from HobbyKing USA that work well for about $20-40. I have also seen them with other brand name stickers on them on other websites. If you insist on using the holder, just get regular lead acid batteries and throw them out when they go low. You can buy a 32 pack that will last quite a while at most stores. Never have to charge that way. I have done it on my glider radios. One set of batteries will last better than two months of Sunday flying on a Hitec 3 channel transmitter.

John is correct. And normally the Futaba wall chargers will have the output printed somewhere on them. Somewhere around 75 ma is common, so divide the capacity of the battery, for instance a 750MaH pack, by the output to get the time required to charge it. In this case it would be 750 divided by 75 or ten hours. And what he was saying by not having enough hours in the day to charge them is that if you have a 2100MaH pack, it would take 28 hours to charge so if you fly every day, you will never get it fully charged with a 75ma charger.

If you're wanting to keep costs down, I see new transmitter packs on ebay fairly often that go for under $10. They are from guys buying new radios who want a high capacity pack so they replace them without even using them. Otherwise, the www.hangtimes.com packs are a good buy.

As for a charger, there are many on the market that will take care of all your NiCh/Nimh needs. Any of the Triton series (Electrifly brand), any Hyperion that has the cycling capability (very easy interface on the Hyperions too), Thunder Power, and the list goes on. Keep in mind that many chargers run on DC 12v power only, so if you buy one of those you will also need a power supply. A standard lead acid battery will work fine if you have one for your field box, or there are a number of AC power supplies for them. I bought a Triton EQ which was more expensive but it has an AC adapter in addition to being able to use DC, and it also has a balance board built it to take care of all the lithium batteries.

I have had excellent results and service from www.radicalrc.com Dave Thacker, the owner, is both very helpful and friendly. He will answer any of your questions, sometimes referring to his FAQ section, which has a pretty good library of questions and answers for most battery issues that come up.

His battery selection shows the battery as well as the dimensions, weights, and so on. He will also do custom connectors based on your needs. Best of all, he guarantee's everything he sells. For example, I bought a LiPo pack from him about a year or so ago, it came in ok, but as soon as I put it on the charger, it puffed up. I stopped the charge and sent him an Email. He said "return it to me and I will replace it" no questions asked, even though I may have caused the problem.

He sells all sorts of packs, and individual cells, and, his prices are very competitive.

As far as a charger is concerned, well, I have a Duratrack Intepeak ICE charger/discharger, as well as a new Triton II EQ. I use them both and get outstanding results from both of them on all sorts of batteries and battery packs. The ICE is DC input only where the Triton II EQ is both AC and DC input.

CGr.