PF Power

[cavegod]

hi all,

i am thinking that 4 large motors on one battery box will be a big drain, so is there a way to connect 2 or more battery boxes together to get more amps but still have 9v? or are there better ways?

[Zerobricks]

Use 2 battery boxes with 2 receivers, each for 2 motors? Two independnet systems.

[cavegod]

but recievers are expensive and that will limit the number of functions i can have as i presume there is a maximum of 4 recievers i can use due to 4 channels on the reciever. if i have more than 5 recievers then some will operate when other functions areoperated?

[Dutch_EE]

No,

if you want 2 functions that each use 2 XL-motors, you can use this system.

Batterybox -> receiver -> 1 XL-motor on each output

and dubble them up, so again the hole thing stated above.

The 2 receivers are on the same channel and thus will operate from the same signal. You can easily have more than 4 receivers, there is just a limitation on 8 possible functions.

Edited February 16, 2011 by Dutch_EE

[cavegod]

has anybody connected two battery boxes to one motor and is the voltage 9v or 18v?my only other option would be using a 9v nicad and just soldering a connecting plug to a pf battery box, that way i could have as many 1.5 cells as i want in parallel but, it's not the lego way.

[Dutch_EE]

That sadly doesn't work because of 2 reasons

1. If you want more voltage you will be foiled by the voltage regulators in the receivers that get too hot at 18 Volt. Also, the motors are not made for such a high voltage. The thread at which the motors were tested went up to 12 Volts, but with this you'll loose all guaranties.

2. If you want more amps you will be foiled by the current limiters inside the receivers. They are set at around 800 mA, which isn't even enough to supply 2 XL-motors at full power (stalled)

If you want to parallel 2 batteryboxes for more mAh (more capacaty), that is possible. You're limitations are in the receivers.

[cavegod]

so i could then have a battery box per motor and use the PF reciever to power a motor to switch all the battery boxes on and off to control the motors, thus giving each motor full amps. I can sort the problem out when i know whether it will drive with 4 XL motors on 1 reciever.

[DLuders]

If your goal is MORE ACCELERATION, then perhaps you should consider what Mahjqa did -- use TWIN PF RECEIVERS to power a single motor. See his video on Flickr, where he wrote,

"This is in response to Sunskytechnic's idea to put two receivers to a single motor: .

"I made two identical cars, where an XL motor is geared up 1:9 to the wheels. The right car has a single receiver, the left one has two. Weight has been added to both cars. Both cars use fully-charged PF batteries. I did additional runs with the batteries switched, with the same results.

"It seems like the car with two receivers has a tiny advantage when accelerating, but the top speed remains the same."

Here is Sunmint1's

and photo. They show how "Multiple receiver outputs are connected to one point and fed to a motor. The benefits are 1) more power 2) enhanced signal acceptance. Two sample vehicles are presented (4WD MOC and 8043 mod).

"Since the LB1836 (that's responsible on 8884 for running the motors) has a 1A current limit, and a XL motor may draw instantly more than that at start-up, giving the motor 2 channels, each from 2 receivers. [it] is allowing it to draw a maximum current of 2A.

"Then, when the motor is running normally (lets say if it draws 200mA...600mA...), there's no difference if its power is provided through 1 or 2 receivers, because only one was perfectly capable of keep him running at that speed."

The white 2x8 plate that was used is the 4758 "Electric, Plate 2 x 8 with Contacts."

Edited February 17, 2011 by DLuders

[cavegod]

thanks for that very interesting, but i don't need accelaration it just needs to move at about 1 mph. having never used PF before i'm just worried that there will not be enough go in the battery box for 4 large motors to move 10kg of lego.

[Ape Fight]

thanks for that very interesting, but i don't need accelaration it just needs to move at about 1 mph. having never used PF before i'm just worried that there will not be enough go in the battery box for 4 large motors to move 10kg of lego.

I'm facing the same challange - I think the only way, as people have stated above, is to have two whole systems on the same channel. I'm running 2 XLs and a Medium motor from one battery box currently, and that's more that Lego says you should.

I'll be getting another battery box and 2 more XLs to cope with the weight, but my issue is will I actually need yet another battery box to ensure the Medium motor doesn't drain the power from one battery box quicker than the other, which has no Medium motor attached? I.e. Battery Box no.1 will have 2 XLs and 1 M, Battery Box no.2 wil have 2 XLs only.

Can anyone help with this? I don't want 2 XLs to be on lower power than the other 2, as all 4 are for drive

Edited April 24, 2011 by Ape Fight

[DLuders]

@ Ape Fight: From the PowerFunctions.Lego.com Frequently-Asked Questions (FAQ):

Question #2: "How many Power Functions Motors can I drive from one Power Functions Battery Box?"

Answer #2: "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. If you wish to run a combination of motors, you can e.g. have 1 XL and 2 M running together. The XL-Motor requires about twice as much power as the M-Motor. The Battery Boxes and the IR Receiver have overload protection, so attempting to drive too many motors will not damage anything. The power a motor consumes depends on what function the motor is performing. Motors will operate best when driving a small load."

Question #11: "What is the battery lifetime for the Power Functions system elements?"

Answer #11: "In general battery lifetime will strongly depend on use.

In heavy loaded models with more XL Motors and M Motors (e.g. the 8275 – Motorized Bulldozer) you will have around 4 hours drive time with the 8881 Power Functions AA Battery Box.

The Power Functions AAA Battery Box is used for less demanding tasks. With a Train Motor or 2 M Motors the drive time will be around 4 hours.

For a good rechargeable solution we suggest 8878 Power Functions Rechargeable Battery Box. This rechargeable battery box has the exact same size as the Power Functions AAA Battery Box and they can be interchanged directly."

Question #12: "What happens when the Power Functions overload protection kicks in?"

Answer #12: "Overload protection is activated when too much power is consumed from either a Power Functions Battery Box or the IR Receiver. This can happen when a motor is blocked or when too many motors are running at the same time. If overload protection is activated, the Battery Box or the IR Receiver will cut off power to the output until power consumption has dropped under the allowed value. To regain power, unblock the motor or disconnect motors from the output – then turn the Battery Box OFF and ON again. Under overload protection, the green light on the Power Functions Battery Box will still be ON."

Philo's "LEGO 9V Technic Motor Comparised Characteristics" webpage shows how many amps the Power Functions (PF) XL and FP Medium Motors draw when loaded.

Edited April 25, 2011 by DLuders