Connecting one reciver to two batteries

[piterx]

is it possible? im planning my next supercar and i want to use 2RC motors....in the fiesta i had two batteries and two recivers....what if i want to use a single reciver? is it possible?

[JM1971]

Connect two battery boxes with a extention and attach the receiver to any one of the batteries, that might bypass the lego limiter too, but I'm not sure it will work 100%.

[Hrafn]

It should be easy enough to test, right? You'll still hit the current limit of the battery boxes unless you modify them, though - Philo shows the peak mechanical power of the RC motors happening when they draw 1.4 A each, and the PF motors can only supply about 1A for any length of time. 3 battery boxes would supply enough current, if linking them works. If you're using the LiPo batteries that will get expensive at $50 each....

[DrJB]

If I recall, the current limitation is built-in the receiver (maybe also the battery box). If true, then no matter how many battery boxes you hook up in parallel ... the receiver will draw whatever max current is limited by its internals, not a milli-amp more.

Edited April 18, 2014 by DrJB

[Philo]

Well... More or less. First IR receiver V2 current limit is about the same for one channel as two battery packs in parallel. And it's actually more a power dissipation limit in the receiver than a current one, for a short time it can provide significantly more...

[Hrafn]

I just tested this and ran into a snag relating to the extension/converter cables. Each cable has two ends; the light bluish gray (LBG) end has a PF connector on top and a 9V on the bottom, while the dark bluish gray (DBG) end has PF on top and bottom. Only the DBG end will attach to the top of the battery boxes. This means that each battery box has a wire connected to it, with the LBG end of the wire free. There is no way I can see to connect the two LBG ends exclusively through their PF sides. This is critical, because it appears that the receiver can only be powered through the PF side.

Can anyone else verify that this is a real problem? Am I just missing something?

There is an alternative, if you have a switch (PF or 9V; 9V is easier) and a spare PF-M motor. Use extension cables on the two battery boxes to connect them to one side of the switch, and more cables on the other side to connect the motors. Then operate the switch with a PF-M motor connected normally to a receiver. I just tested this and it works. For a real vehicle you'd also need to add in something (a hockey spring or rubber bands) to make the switch return to center when the PF-M motor turns off, and stops to keep the motor from moving the switch too far in either direction.

Schematically:

battery box -> DBG end of PF cable -> LBG end of PF cable -> [9V cable] -> 9V switch -> 9V cable -> RC motor

The 9V cable in brackets is only needed for the 2nd (and 3rd, etc.) battery box. 9V electrical plates would also work in place of any of the 9V cables.

Edited April 18, 2014 by Hrafn

[piterx]

:P thanks everyone...

so at the end of the day it's better just using two recivers... :\

[Philo]

@Hrafn: you are right with the cables, this is done on purpose to avoid any mistakes such as injecting current in a battery pack. Of course it is annoying for people who know what they do.... You have to do some cable surgery.

[kieran]

Yes, the good old days of 9v cables are long gone. Not a big deal to splice the cables though. Good luck

[Lakop]

And why don't we have a 9V battery box that takes a 9V battery? That would be much lighter and more compact.

H

[MrNumbskull13]

And why don't we have a 9V battery box that takes a 9V battery? That would be much lighter and more compact.

H

I've tried that, 9V batteries last about 10 mins...

[KirTech LAB]

I coupled IR receivers and battery boxes by using electric plates. it is working and this system is a bit more compact than with 9V switch.

[Hrafn]

I coupled IR receivers and battery boxes by using electric plates. it is working and this system is a bit more compact than with 9V switch.

Could you expand on that? How did you use the plates to connect them, since the 9V system only has 2 wires and the PF has 4?

[KirTech LAB]

Could you expand on that? How did you use the plates to connect them, since the 9V system only has 2 wires and the PF has 4?

The idea isn't my - i've took it at this video:

[Boxerlego]

I tested out several variations on how you can connect the receivers up with motors and batteries awhile back when I posted the Guide on how to connect two battery boxes in series for 18V.

Could you expand on that? How did you use the plates to connect them, since the 9V system only has 2 wires and the PF has 4?

The two inner wires on the pf cable connect to the motor. The White Plate is a parallel connection for the pf extension cable which increases the amount current can be supplied to the motor at 9V but this all depends on the battery capacity and the ability to reach that potential discharge.

[Hrafn]

I tested out several variations on how you can connect the receivers up with motors and batteries awhile back when I posted the Guide on how to connect two battery boxes in series for 18V.

The two inner wires on the pf cable connect to the motor. The White Plate is a parallel connection for the pf extension cable which increases the amount current can be supplied to the motor at 9V but this all depends on the battery capacity and the ability to reach that potential discharge.

Thanks for the link! I'll have to peruse that carefully and try a few experiments.