I just bought a Futaba 7CAP. I notice the TX battery and the RX battery are both 9V 600mAh and 4.8V 600mAh respectively. The current drain for the TX is 250mA and the RX is 16mA. Can anyone explain how I can find out approximately how long the battery will last. Is there an easy calculation or do I need to know physics?

Any recommendations on battery upgrade so they may last longer. I was able to find plenty of 1000, 1500, 2000 mAh batteries for the RX but I cannot find any for the TX. Are there any that will fit my TX or am I going to just have to live with it and buy another 9V 600mAh .The battery in the TX is 1.125" x 1.125 x 4".

The basic calculation is very simple.

A 1000mAh battery will deliver a current of 1000mA (1000mA = 1 Amp) for 1 hour

So mA X time in hours = mAh capacity.

Couple of things to remember though:-

1. You cannot assume to use the full capacity from your battery

2. Your receiver may draw only 16mA, but most of the load on the flight battery is applied by the servos. Just what this is depends on how many servos you have, what type they are, and how much you use them in flight.

3. The good news is that your Tx load should be pretty much constant, as the Tx is always transmitting when it is turned on and most of the power goes to the rf stage. Your Tx will have a meter anyway so you should be able to keep an eye on it. Surprised you cannot find larger Tx batteries, I use an 1100mAh in my JR.

For flying with 4 or 5 standard servos I normally use 800mAh batteries and find them sufficient. I normally take two planes out with me and find that I can get as much flying as I want (it is not my usual habit to spend a day flying in gentle circles either[>:][>:][>:]

Hope this helps


Terry

Thanks Redback for your explanation.

I would like to know if any Futaba 7CAP users have a larger TX battery than the standard one which comes in the box? Does not look promising.[&o][&o][&o]

Agree with the advice above. The Tx is generally not an issue, and will last for quite a few flights. The Rx will generally allow 3 or 4 10 to 15 minute flights before recharging, but I ALWAYS check mine with an ESV after the 3rd flight.

You could purchase a second Tx pack and keep it charged.
Dennis-

If you get the AA 2000+ Mah batteries your TX can last to almost a month on one charge. Mine is only a 700Mah but has lasted me for over 1.5 years despite flying/driving everyday. I believe in slow chargers!

For RX I run 5 cells but I hear this is not recommended for JR RXs. If I run my 600Mah 4 cells I do not push it for more than 4 flights of 8-10 mins. With my 5 cell 1,500 Mah I am confortable enough to take it up to 8 flights.

Want to fly all day without recharging? Want to forget about cycling NiCd batteries and quick charging at the field.? you could try NiMH battery packs. A great place to get them at which is highly recommended here at RCU is Radical RC from Ohio.

I replaced my 600mah packs with : Tx- 1650 mah NiMH $30.00
Rx- 2100mah NiMH $18.00
these are Sanyo-the best brand.

Quality is terrific.

[link]http://radicalrc.com[/link]


NiMH have NO memeory effect problems and can be charged just as easily with the same equipment you would use for NiCd IF you don't use fast chargers at a high rate. You will never need to do this anyways with these. I'm not trying to start a discussion over which battery type is better but after myself and many others have used them we would never buy smaller capacity NiCd again.

Last month, I wanted to practice my taking off and landing. Believe it or not, I flew the plane, non stop, taking off and flying around and landing, FOR 4 HOURS STRAIGHT!! With the NIMH they were only down to 4.9V on the Rx and 9.8 on the Tx. In other words, I could have flown even longer! I for one am completely sold on these. The main selling point I think is that for anly a FEW dollars more, you can have higher capacity NiMH instead of lower capacity NiCd.

Why use a lower capacity battery on the TX?

That's because like one of the guys said, the Tx has a constant, slow drain on its battery so it wears down at a slower rate than the Rx.

What charger would YOU use?

Well, the one that came with your Tx system is probably too weak for higher capacity batteries. You could buy a field charger which will charge both packs at once and allow you to vary the charge rate to suit the capacity of the packs OR you could do what I did and buy another wall charger like the one you now have but which puts out a higher rate for higher capacity packs. This charger can be plugged in and left on without worry about frying the packs etc. etc.

Where do I find one of these?

The best place is Hangtimes Hobbies

[link]http://hangtimeshobbies.com[/link]

The one I bought puts out a rate of 180 mah on the Rx and 120 mah on the Tx.
It will charge BOTH packs at once.

Check this stuff out and you won't be sorry if you buy these. It has been the best thing I've done for my enjoyment of flying.

Matt

One other option is to simply purchase a field charger and recharge your packs at the field when they need a charge. You could easily fly all day that way.

That's a good idea too. However, if you only fly one or two planes then field charging would cost about as much as new higher, capacity battery packs. If you have more planes then obviously it would cost a bit to buy all new packs. Then a field charger would be handy and economical. If you're like me, you couldn't be bothered with having to hook up my batteries to a field charger, field battery (which also needs some maintenance) or car battery, and have to time them etc. etc. AND cycle them periodically to get the most from them. It sounds like you just want more flying time. Higher capacity packs are the easiest way to go.

I personally would go with a field charger. I do not like nickel hydride batterys. I have heard too many horror stories of failed nmhi batterys. Nicads will be fine and work well for you. Just get a field charger. Mine is a Hobbico unit.

Mark Shuman

How exactly have they failed in ways that NiCads won't?

Mark, have to disagree with you on this. I have soldered up many nimh packs. These are flight batteries powering the motor/rx on electric
planes. I have had drains up to 30 amps and more on these packs without nary a problemo. I've also soldered up 4 cell 1600 mah nimh batts for rx use in my glow planes. Never had a failure. For what ya pay for a futaba transmitter pack, I can make 3 nimh packs that last 3 times longer at the same voltage.

Dave...