Battery box question

[yoraish]

So I was thinking, I have 2 receivers, 2 battery boxes and 2 XL motors. I want to power those motors with all the power possible and still leave one receive for other functions(like gearbox). So what should I do?

Right now I connect each receiver to a battery box and an XL motor to each receiver. It leaves no receiver free.

Will adding a some extension wires and connecting the 2 battery boxes help? Like, when the batteries are attached connect the 2 receivers to them (on one input) so the 2 receivers will get 100% power?

Thanks,

yoraish

[rien]

Hi

people wil awnser youre question no doubt about that rgbrown knows alot about this and more so.

Until here is some info where you can find youre awnser aswel i think anyway lots of learning stuf to read there:power funktions

goodluck

If you want real extra power look at my topic powerfunktions on 11,1 volt powerd by a li-po

Edited January 3, 2011 by rien

[quilkin]

So I was thinking, I have 2 receivers, 2 battery boxes and 2 XL motors. I want to power those motors with all the power possible and still leave one receive for other functions(like gearbox). So what should I do?

Right now I connect each receiver to a battery box and an XL motor to each receiver. It leaves no receiver free.

Will adding a some extension wires and connecting the 2 battery boxes help? Like, when the batteries are attached connect the 2 receivers to them (on one input) so the 2 receivers will get 100% power?

Thanks,

yoraish

Don't connect two battery boxes together! At best the batteries will go flat faster, at worst they could leak and ruin your boxes.

If you want more power use good rechargeables (lower in voltage but better current supply - see the other thread earlier today)- but only use one battery box at a time!

[rgbrown]

So I was thinking, I have 2 receivers, 2 battery boxes and 2 XL motors. I want to power those motors with all the power possible and still leave one receive for other functions(like gearbox). So what should I do?

Right now I connect each receiver to a battery box and an XL motor to each receiver. It leaves no receiver free.

Will adding a some extension wires and connecting the 2 battery boxes help? Like, when the batteries are attached connect the 2 receivers to them (on one input) so the 2 receivers will get 100% power?

Thanks,

yoraish

First, as has been said - don't connect the battery boxes together - a small difference in voltage could cause current to flow backward through some of the cells which can cause a nasty mess, depending on what you are using.

Let me briefly explain. You may well understand this, but others might not.

What you want to achieve is to have each motor running on the maximum voltage that the battery can supply (e.g. 9V). The other limitation of a battery is current (amps). Ideally a battery would serve up the same voltage, and hence have everything connected to it running the same, no matter how much current was being drawn. More current gets drawn by loading the motors, or connecting more things.

But in reality, the more current gets drawn, the lower that the voltage coming out of the battery is. This is due to the internal resistance of the battery. Different types of cells are better or worse - this is being discussed in a parallel thread at the moment. So running two motors off the same battery box will be worse than running one off each, although if you are using some types of power source the difference will be pretty small / negligible.

What you should do depends on how heavily you are loading the motors. If the motors aren't working hard (revs near the no-load speed), then you may be fine to put them on the same receiver. If the motors are very heavily loaded and you have two on the same circuit, then you might hit the current limit on either the receiver or the battery box. You'll notice this because the power will just intermittently drop out. In that case you'll need to use two circuits, there isn't any other option. Lots of information on motors here: http://www.philohome...s/motorcomp.htm

Things to try if you want to increase performance and use only 1 box/receiver - use NiMh cells, or if you have plenty of money, the 8878. If you want to get adventurous and don't mind wielding a soldering iron, you could try a 11.1V LiPo as Rien has done, but there are quite a few precautions to take, and I would strongly recommend connecting some diodes in series with it to lower the voltage to within recommended limits.

edit: typo

Edited January 3, 2011 by rgbrown

[DLuders]

On the Powerfunctions.Lego.com website, there is a "Frequently Asked Questions" (FAQ) page. As pictured below, there is excess capacity on the one Power Functions (PF) Receiver shown for other stuff. The FAQ #2 answer says,

"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."

FAQ #12 answer: "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."

Edited January 4, 2011 by DLuders

[yoraish]

Thank you very much! I think I'll just get another receiver And maybe sometime the rechargeable batteries.