Running several motors on a single battery

[Pedro Antunes]

Hello EB community

I'm planning for a new MOC and I'm going to need 2 XL-Motors and 5 M-Motors.

From the LEGO website I can read:

As a rule of thumb, you can drive 2 Power Functions XL-Motors, 3 Power Functions Train Motors or 4 Power Functions M-Motors at the same time from one Power Functions Battery Box.

Ok, so this is my question, can I connect the 7 motors all to the same battery assuming I'm only going to use (at most) 2 of them at the same time?

Or does the LEGO sentence actually refers to only connect 2 XL (for instance) and nothing more to a single battery?

I think that I can connect all the motors I want to the same battery as longs as I dont use them all at the same time, so if dont use them simultaneously there should be no problem as they only use the battery when they are running (right?)

Sorry if my question sounds confusing

Edited May 24, 2012 by Pedro Antunes

[timslegos]

My Towtruck MOC ran over 8 functions on only a single battery pack. The truck worked fine as long as I used only a couple of motors at a time.

tim

Edited May 24, 2012 by timr

[Pedro Antunes]

Thanks tim

[dhc6twinotter]

I think that I can connect all the motors I want to the same battery as longs as I dont use them all at the same time, so if dont use them simultaneously there should be no problem as they only use the battery when they are running (right?)

That's correct.

The Technic bulldozer from a few years ago had 2XL and 2M motors in it, and all motors were connected to one battery box.

My tractor ran 2XL motors and 2 or 3 M motors simultaneously off one AA battery box. I had the 2XL motors for drive, the M motor for steering, the M motor for the compressor, and, sometimes, the M motor for the PTO all running at once. Never had any issues, but none of the motors were stressed much.

BTW, welcome to the forum!

Edited May 24, 2012 by dhc6twinotter

[cavegod]

I can run 4 xl's off 1 batt and 1 receiver thought this was a no no?

[Crtlego]

I can run 4 xl's off 1 batt and 1 receiver thought this was a no no?

I believe the problem there is having four XL's on one receiver..

[kieran]

Back emf keeps the current low on a running motor, the real issue is when it stalls, this is the point of max current draw, if you have a few stalled motors then you can draw more current than some components are designed to deal with. The type of battery used will also have an impact, NiCads for example can supply many amps of current when called upon where as alkaline the max current they will supply will be lower

[AndyCW]

This a question that has been rolling through my head recently. We know how much current the motors draw because of Philo's research and we know the rule of thumb given us by lego, but do we know what the current limits are on the recievers and batteries. It seems that torque is a function of current draw and knowing available current draw before encountering the safety mechanisms will alow us to determine available torque in any given motor application.

Prime example, we all know that the RC buggy motors are hobbled by utilizing PF architechture. The question is by how much.

I aplogize if this is viewed as a highjack, but these questions may shed some illumination on the OPs questions.

v/r

Andy

[DLuders]

@ AndyCW: You should read this prior Eurobricks topic about the Power Function Infrared Receiver's current limitation. Other related topics can be seen here.

Here is a Eurobricks topic about the "Maximum Number of Components on PF Battery Box."

[AndyCW]

Thank You Dluders. That makes everything pretty clear for me and hopefully the OP.