Futaba RX/BEC supply voltage & load current limits

[Dreamscape]

Heya,

Picked up a Futaba 2ch RX with BEC function (model FP-R122JE). A
pretty common RX if I'm not mistaken. Info on these things (wiring
them, in particilar) is stunningly hard to find. :-/ Ok, got it
running - eventually (was supplied with NO info whatsoever). That's
wiring out of the way. Now for the tech data. ;)

Would anyone familiar with these beasts please be able to let me know
what its maximum input voltage (ie drive battery voltage) is, and what
current it can supply to servos and misc devices at that maximum input
voltage?

I suspect 8.4V (ie 7 cells) though i just tested it (briefly!) on an 8
cell pack showing an O/C voltage of 10 volts... didnt seem to complain
(though i wasnt exactly drawing a lot of current with servos etc), and
was regulating to just over 6 volts. Running off a 4 cell pack
showing 4.4 volts O/C, BEC output basically followed battery voltage.

I'd love to be able to run this off a small 12V gel battery... not
liking my chances of having it handle that sort of input voltage
though. :-(

Any wisdom would be much appreciated. :)

MTIA

*DS*


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[Kevin Russell]

try http://www.futaba-rc.com/ for Futaba manuals
the below link is for you reciever
http://www.futaba-rc.com/manuals/2er-manual.pdf
If you read this manual it states 4.8 to 8.4 but you can always run the
receiver off of a 5 volt regulator
Kevin
"Dreamscape" <none@nothanks.com> wrote in message
news:h2ivivce37sbsrn8k77nu4d1tsreja9nvg@4ax.com...

Heya,

Picked up a Futaba 2ch RX with BEC function (model FP-R122JE). A
pretty common RX if I'm not mistaken. Info on these things (wiring
them, in particilar) is stunningly hard to find. :-/ Ok, got it
running - eventually (was supplied with NO info whatsoever). That's
wiring out of the way. Now for the tech data. ;)

Would anyone familiar with these beasts please be able to let me know
what its maximum input voltage (ie drive battery voltage) is, and what
current it can supply to servos and misc devices at that maximum input
voltage?

I suspect 8.4V (ie 7 cells) though i just tested it (briefly!) on an 8
cell pack showing an O/C voltage of 10 volts... didnt seem to complain
(though i wasnt exactly drawing a lot of current with servos etc), and
was regulating to just over 6 volts. Running off a 4 cell pack
showing 4.4 volts O/C, BEC output basically followed battery voltage.

I'd love to be able to run this off a small 12V gel battery... not
liking my chances of having it handle that sort of input voltage
though. :-(

Any wisdom would be much appreciated. :)

MTIA

*DS*


---
standard anti-spam measures taken
email sundevil ... at ... iprimus , com , au
to contact me privately
sorry for the inconvenience
---

[Dreamscape]

Many thanks, Kevin - and anyone else who may have replied... thanks
iPrimus for dropping up to 75% of posts. :(

I dl'ed manual after manual from Futaba's site - gave up not long
before I'd have gotten to the Attack2 ER manual... :(

You're right, a 7805 regulator (boosted to 6 volts, of course:) would
be the simplest way to supply the BEC from a 12 volt battery. I'm not
questioning that advice, and will prolly go with it for sake of
convenience, but as a concept it begs the question: why bother with
BEC? :(

Tempting it is to use an LM317 in place of a 7805 - easier to adjust
to a specific voltage, higher regulation stability, etc. Trap: 78xx
regulators have a 2-volt minimum input-to-output differential, LM317's
have a 5-volt minimum... drop below (output voltage + 5volts) and the
317 loses regulation. a low drop-out regulator would be ideal... i
know i have a handful here somewhere, cant remember the name, most
importantly im not sure if theyre A) variable and B) support external
pass transistors to boost current at the regulated voltage. 78xx
support both (the variability by the simple act of raising the voltage
on the ground/common pin to x volts above ground, where x =3D desired
regulated voltage minus the device's preset reg voltage ... in my case
(6 volts from a 7805, the ground/common pin needs to be raised by 1
volt). by also using a bypass transistor (or a high-current
regulator), servo drain becomes irrelevant.

short version: i bought a BEC receiver because...? ;-/

thanks for the info - i appreciate your effort :))

cheers,

DS

On Tue, 5 Aug 2003 19:01:09 +0100, "Kevin Russell"
<kevin_russell@ntlworld.com> wrote:

>try http://www.futaba-rc.com/ for Futaba manuals
>the below link is for you reciever
>http://www.futaba-rc.com/manuals/2er-manual.pdf
>If you read this manual it states 4.8 to 8.4 but you can always run the
>receiver off of a 5 volt regulator
>Kevin

---
standard anti-spam measures taken
email sundevil ... at ... iprimus , com , au
to contact me privately
sorry for the inconvenience
---

[Kevin Russell]

Bec is ok for all the cars modellers which use mainly 7.2-8.4volt nicads but
as you say its useless for boats with a 12v lead acid and the Futaba web
site is ok until you need any info on a receiver then you have to guess
which set it came from
Kevin
"Dreamscape" <none@nothanks.com> wrote in message
news:21n4jvgoqsdmqs2aut0h980r7nmqcmqfep@4ax.com...

Many thanks, Kevin - and anyone else who may have replied... thanks
iPrimus for dropping up to 75% of posts. :(

I dl'ed manual after manual from Futaba's site - gave up not long
before I'd have gotten to the Attack2 ER manual... :(

You're right, a 7805 regulator (boosted to 6 volts, of course:) would
be the simplest way to supply the BEC from a 12 volt battery. I'm not
questioning that advice, and will prolly go with it for sake of
convenience, but as a concept it begs the question: why bother with
BEC? :(

Tempting it is to use an LM317 in place of a 7805 - easier to adjust
to a specific voltage, higher regulation stability, etc. Trap: 78xx
regulators have a 2-volt minimum input-to-output differential, LM317's
have a 5-volt minimum... drop below (output voltage + 5volts) and the
317 loses regulation. a low drop-out regulator would be ideal... i
know i have a handful here somewhere, cant remember the name, most
importantly im not sure if theyre A) variable and B) support external
pass transistors to boost current at the regulated voltage. 78xx
support both (the variability by the simple act of raising the voltage
on the ground/common pin to x volts above ground, where x = desired
regulated voltage minus the device's preset reg voltage ... in my case
(6 volts from a 7805, the ground/common pin needs to be raised by 1
volt). by also using a bypass transistor (or a high-current
regulator), servo drain becomes irrelevant.

short version: i bought a BEC receiver because...? ;-/

thanks for the info - i appreciate your effort :))

cheers,

DS

On Tue, 5 Aug 2003 19:01:09 +0100, "Kevin Russell"
<kevin_russell@ntlworld.com> wrote:

>try http://www.futaba-rc.com/ for Futaba manuals
>the below link is for you reciever
>http://www.futaba-rc.com/manuals/2er-manual.pdf
>If you read this manual it states 4.8 to 8.4 but you can always run the
>receiver off of a 5 volt regulator
>Kevin

---
standard anti-spam measures taken
email sundevil ... at ... iprimus , com , au
to contact me privately
sorry for the inconvenience
---