Running your rx on 9v?

[xx29l9]

In his build thread "Elliot Bay Steam launch", Kmot mentions that he is running his rx on a 9v alkaline battery, instead of the 4 pack of AA batteries, he mentions it as a FE trick.

I was curious, how many people have run their rx on a 9v alkaline? Any issues? I haven't looked at the specs yet for rx's, do any support 9v? I'm guessing they don't have a built in voltage regulator....

bob

[Tachikaze]

Did he mention if he is using a voltage regulator?
I run all of my ships on the drive battery, which in most cases is 12V, with a voltage regulator that drops down to 5.8v.

[patmat2350]

Many Rx's have BEC, which allows them to run off higher voltages. Check your docs.

[mxz70017]

Its not the reciever that regulates the voltage.But the speed control does.If the BEC Is disarmed on the ESC.You will burn the reciever out at 9v's.

[steamboatmodel]

Back in the beginning of fast electric before BECs some of the guys used to run off the small 9 volt transistor batteries. They claimed that the voltage dropped down on the battery very fast. Most of the receivers would handle 6 Volts, I used to take apart the rechargeable ones and use 5 cells.
Regards,
Gerald

[xx29l9]

This is on Kmot's steam boat, so no ESC would be involved. He mentions the FE guys do it to save room and weight when you compare a single 9v cell to the typical 4 AA cell radio pack.

[mxz70017]

Yes most all of them would run. At 4.8v cad1.2v cells.Or 6v alkaline at 1.5v.But personally I have never seen a reciever with a voltage regulator built In!!

[Kmot]

I was curious, how many people have run their rx on 9v? Any issues?

1) Me
2) None
:p

[cyclops2]

What is the voltage fresh off of a charger ?

[AndyKunz]

The reason they can get away with it is because the high internal resistance of the 9V batteries causes their voltage to drop to a "reasonable" voltage. It also means that the batteries have a very short life in a boat. With a steering servo drawing 1A or more, the voltage drops to almost nothing. Spektrum receivers (http://www.horizonhobby.com/Products/Default.aspx?ProdID=SPMAR6200) are rated for up to 9.6V.

If you were to use a high-capacity 9V source (say 8 x 1200mAH NiMH or 2S LiPo), you would likely fry the servos quickly. There's a reason that JR makes these High Voltage servos (http://search.horizonhobby.com/index.jsp?N=0&Ntt=hv+servo) for use with 2S directly!

Andy

[Kmot]

What is the voltage fresh off of a charger ?
You don't recharge alkaline batteries.

[mfr02]

You don't recharge alkaline batteries.
Apart from the NiCads, which are alkaline, and available as a rechargeable PP3 package.
Some RXs were sold labelled "BEC" but the manufacturers were always reluctant to say just what the BEC in the RX was actually capable of. Looking at the chips, and googling for the part numbers to get data sheets shows that they are fairly uniformly rated for a maximum of 7.5 volts. I would suspect that the FE-ers were getting away with dumb luck.

[mxz70017]

Well me personally If a servo draws one Amp.An not sure If Andy was refering to a standard or 1/4 scale.I would not trust a 9v alkaline battery. That drops voltage that fast.You guys willing to risk a say $1500 boat to save 2 Inchs square roughly of space?I personally would rather make room.Then run a 1200Mah reciever pack or larger in my 55" Shockwave hull or my 48"hydro!!!

[xx29l9]

I emailed Futaba tech support just to see what they would say if the rx can run on 9v...no big surprise-

Thank you for your recent e-mail.

No, the receivers can use a 4.8 or 6.0 volt battery. If you use a higher voltage battery, you will need to regulate the voltage down to 6.0 volts.

Sincerely,
John G.- PS9004
Product Support Lead Technician
Futaba Programming Technician
Great Planes Model Distributors
www.futabarc.com
NO AUTORESPONDER

[AndyKunz]

Well me personally If a servo draws one Amp.An not sure If Andy was refering to a standard or 1/4 scale.I would not trust a 9v alkaline battery. That drops voltage that fast.You guys willing to risk a say $1500 boat to save 2 Inchs square roughly of space?I personally would rather make room.Then run a 1200Mah reciever pack or larger in my 55" Shockwave hull or my 48"hydro!!!

Most guys ran HS225MG's. Check them out sometime with a good ammeter :)

These were not in big boats - they were small, fast race boats. Check out Jay Turner's articles for some more info.

Andy

[Kmot]

Been running a 9V battery in several boats with never an issue. In my Wave Shark, I have been using a 9V battery since it was built which is around 4, maybe 5 years now. A 9V battery lasts a long time too, probably all year for me as I only take it out about six times a year.

[steveciambrone]

Your typical RX draws only about 10ma all the time no change in current draw. This would not cause any voltage drop on any battery. A servo any servo draws next to nothing when under no load, which should be the case most of the time if installed correctly. For a sport or scale boat at low speeds I would expect the Servo loads to maybe peak for short periods at 200ma or so. A 1 amp draw on a battery from a servo would be under severe load and may be a peak load only. If a boat is just sitting in the water then the rudder servo should be drawing almost no power. For scale boats I would expect the load to be quite minimal. FE and other performance boats would be expected to draw higher currents, there is usually a big separator when it comes to sport/scale boating and flying compared to racing boats and planes.

I have used the smaller NICAD and NIMHD packs of 110ma, 225ma, 250ma, or 350ma for planes and boats and they are also good for weight and space savings.

Thanks
Steve

[cyclops2]

I agree with Steve on The very light intermittant servo loads. I use HS-55's a lot. Forget current drains in small sport stuff.