Hello, Some electronic motor controllers have a power port for the radio receiver to get power from. I think it labeled B.E.S.

Also you could check with the maker of the receiver to see what they have. Its best if you can keep such parts compatible. It makes your life a lot easer.

Good luck

Charles

metalSmith's

I can also suggest you, if you really would like to make it your own, a DC-DC converter using a LM7803 zener diode or such. It's really tough, and based on your higher input voltage, would give you plenty of regulated power to the receiver. Check out in the net. There are several examples of circuit using it. The total hardware cost would be something around 3 USD in most of the known world.

Maxim has several switching step-down regulators, it can be more efficient.

Bondy111,

Is there a reason that you can't use a separate rechargeable Li-Ion cell for the receiver?

If this is possible, when the motor battery pack is dieing the receiver will still operate even through several motor pack changes or recharges depending on the cell capacity and the load of the receiver.

Jon

I don't think I could use a seperate battery pack for the reciever because the power for the motors is got through the rc PCB.

Bondy,

You asked: "Could it be wired up so the receiver has 3volts and then the two motors get their power from the lithium battery pack?"

I have one of those simple 49.86 mHz receivers in front of me.

I say yes. It only requires one Li-Ion cell, not another battery pack. I assume that the Receiver originally ran on a couple of series connected 1.5 Volt cells that ran it and passed power to the motor and any other devices. So to use the 3 Volt PCB you may need to use its outputs to drive separate relays or switching transistors to pass the higher Voltage and current to the motors. (and servos if any.)

If you want to use the 11 Volt motor power for the receiver the LM317 circuit described will do that.

The extra Li-Ion cell is not very big.

The regulator circuit is also not very big.

I assume a lot of things due to the lack of specific details about the receiver and associated control circuitry.

The quality of the answer is as good as the info provided by the question.

Jon

" ... the power for the motors is got through the rc PCB ... "

Bondy111, can we assume that the 'rc PCB' has connections for receiver supply power & ground (3V) and motor supply power & ground (11V)?

If so, then any two DC supplies in the appropriate voltage & current range can be used - be they separate cells or batteries, supplies derived via a transformer/rectifier etc from an AC service, one supply generated from the other or anything conceivable combination. It may or may not be necessary to common the ground side of the two supplies - if in doubt, common them - it won't do any harm.

If not, please explain a bit more .

The 3V goes into the PCB, and then there is the positive and negative terminals on the PCB for the motor. I presume they are also 3V

OK, you need to get from the 11V battery pack to the rc board at 3V, with enough current to drive the motors at maximum demand (plus a bit in hand). A simple linear regulator (e.g. LM317) will do this for you, but it will waste a lot of power.

For example, if you were running at 5A, you'd have 3 x 5 = 15W usefully supplied to the rc board & motor, but there'd be (11-3) x 5 = 40W lost heating up the regulator!

A better method would be a DC/DC converter such as I suggested in #2, which is ok up to 3A, and over 80% efficient.

If you need more current, here's one that's good for 10A. It's about £10, and quoted as being 93% efficient.

what about the battery pack is there a way to re configure the connections & have an output closer to 3v? at least to run the controller. I didn't quite catch the rating on the motor[s] bondy plans to use. What kind of overvolt tolerance would the controller board have? Of course this would add a bit of complication to replacing the battery pack & a 2nd pair of wires, couple of diodes....

Good idea, but there are too many unknowns. Don't know the no. of cells in the pack, or the pack construction. Don't know the overvolt tol. of the rc board ... Bondy111?

In the end you would probably need a driver circuit for the motors....

it also depends on the power requirements for the controller, you might be able to use a hand full of diodes for the 3v. The controller probably already has a regulator, these things tend to be bullet proof.

JohnDG,

"Don't know the no. of cells in the pack, or the pack construction."

He said 11 Volt rechargeable Li-Ion pack. Each cell in the pack is about 3.6 Volts with no load. That would be 3 cells per pack.

One small cell would satisfy the power to the RC Receiver PCB as would two Alkalines in series.

The business end of the PCB is where it's value is seen. The receiver doesn't take much power to operate. It can provide input to separate high power control devices that can start your coffee pot, open the garage door and start your car or fly a jet airliner from a distance or operate 11 Volt fan motors on an RC Car to bring your cup of coffee.

Using power from the 11 Volt pack to run an LM317 circuit to drop 11 volts down to 3 volts uses only the small power required to operate the regulator and the receiver. An LM317 regulator circuit uses only the small demand of its internal workings (between 50 and 100 micro Amps) added to the draw of the divider (5 milli Amps) to set the output Voltage.

Vout = Vref X (1+ R2/R1). Vref is typically about 1.25 Volts, R1 is 240 ohms, R2 is 336 Ohms so Vout would be about 3 Volts.

Jon

Hi Jon,

I tried to get to the bottom of this in my #10 - Bondy111 replied in #11 indicating that the PCB has input connections for a 3V supply, and output connections for the motor (presumably a PWM drive supplied from the 3V - there is no mention of any other connections).

If it is possible to get at the motor supply connections, then there's no problem (as I indicated in #10). I would still say it would be better to go for e.g. the LE30ABZ regulator, which drops only 0.5V (handy if you're starting from a low (3.6V?) input supply), and doesn't need the resistors to set Vout.

3 cells per pack? That's what I thought was most likely (^{_{BTW - he actually said "a 11.1v lithium battery pack"}}). The pack construction, however, is still unknown. Is it all sealed up in heatshrink (or whatever), so it has to be hacked into to find the intermediate connections?

POSTING IN HASTE - BATTERY Dying....

Hi JohnDG

Saying 11 Volts was easier to say or type and for a Li-Ion pack it is a nominal Voltage.

You never want to unseal a Li-Ion Cell or Battery pack as a little moisture can cause a big fire.

One version of the LE30ABZ has a convenient inhibit control.

Yes "the PCB has input connections for a 3V supply, and output connections for the motor (presumably a PWM drive supplied from the 3V - there is no mention of any other connections)."

I would want some variable steering, forward and reverse and PWM speed control.

Mine is not very sophisticated at all. All mine can do is forward and reverse. They can't get much simpler. (Kangaroos and Emus cant go backward.)

The 3 Volts supplies the Receiver and the motor power.

It would be nice if we had more info about his PCB.

Pi$$ing into the wind sucks.

Jon

Cheers everyone.

Yes, of course.

Bondy111, couldn't get to sleep leaving this - laptop batteries dead - mains adapter left at the factory - had to drag myself out of bed & up to the office PC.

Can you please give us links to the specs of the rc board and the battery pack? Until we get some firm details, we're all pi$$ing in the wind.

Cheers & good night,

John.

I don't know about the PCB, it was pulled from an old rc car. I also have an old 7.2v one (I don't know if that would be better. That is pulled from a RC helicopter. The battery is this: http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&ssPageName=STRK:MEWAX:IT&item=350210969704 That one is an ended listing.

Right, there's a board that needs 3V in, has an rc receiver and has an output for a motor.

1. Any other inputs/outputs?
2. Did the car just have speed control?
3. Any chance of a photo of the board?
4. What are the EDFs rated at (volts/amps)? Do you have a link to a spec?
5. Do you still have the carcass of the old rc car - and if so, can you find any details about the motor?

This is getting interesting!

_{^{(Work is getting very boring - testing a bit of kit that needs attention every 30-40 minutes, & writing manuals in between times. Dull, dull, dull.)}}

The 3V PCB is only one channel, but the 7.2V is 2 channel.

Feature :
- The up thrust up to
110g (MAX 130g) with a
11.1V 350mAh 15C LiPo battery

N60 Brushed Motor
Size : 30.5mm(L) x Dia. 12mm
Rpm(Kv) : 9600Rpm/V
Loading Current : 5.5A
Shaft Dia. : 1.5mm
Weight : 16g (Motor only)
Input Voltage : 6 - 12V

I don't still have the carcass, and since yesterday, it seems some water has got to the 3V PCB

I will attach a picture od the 7.2v board instead - Do that tonight - gotta dash