Max Voltage for Power functions

[Xargon321]

Well i just got the excavator set 8043 and love it so far just wondering what the max voltage that the power functions can take without frying? i was thinking about putting a 3 cell lipo that at full charge is 12.6v or 11.1 nominal this should provide some extra power for the motor so they wont bog as bad this site Here has tested the motors at 12v just really wondering about the IR receivers thanks in advance!

[JopieK]

Well i just got the excavator set 8043 and love it so far just wondering what the max voltage that the power functions can take without frying? i was thinking about putting a 3 cell lipo that at full charge is 12.6v or 11.1 nominal this should provide some extra power for the motor so they wont bog as bad this site Here has tested the motors at 12v just really wondering about the IR receivers thanks in advance!

My idea was also to check philohome, but anyway. Logic normally works on 5V. It will be able to take 12V I guess but then a built-in convertor like an 7805 voltage regulator will still regulate it down to 5V. Some power will be converted to (essentially) heat, so be sure it will not overheat your PF logic. Maybe use a lab power supply and try it in small steps.

[Xargon321]

That makes sense im going to assume that it can take at least 10v because i saw someone on here with a 9.6v battery. anyone have some good pics of the inside of the receiver?

[Mortymore]

Try here for some pictures (though I think they are not valuable for what you need)

http://www.brickshelf.com/cgi-bin/gallery.cgi?f=402995

See if you can find useful info here:

http://www.philohome.com/pf/LEGO_Power_Functions_RC_v110.pdf

I believe though, that the 8884 IR receiver has to have an internal power regulator, that despite the power supply (in acceptable levels), can keep the data signals on a desired level.

But if you intend to use a voltage regulator, use a low dropout one to avoid run out the batteries fast, rather than the usual 7805.

Now you have to consider the current need to supply the receiver, and I guess that will depend on what you have connected to it.

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EDIT: Conchas brought to my attention that there's an earlier version of LEGO PF document, v1.20

Edited August 18, 2010 by Mortymore

[JopieK]

Try here for some pictures (though I think they are not valuable for what you need)

http://www.brickshelf.com/cgi-bin/gallery.cgi?f=402995

See if you can find useful info here:

http://www.philohome.com/pf/LEGO_Power_Functions_RC_v110.pdf

I believe though, that the 8884 IR receiver has to have an internal power regulator, that despite the power supply (in acceptable levels), can keep the data signals on a desired level.

But if you intend to use a voltage regulator, use a low dropout one to avoid run out the batteries fast, rather than the usual 7805.

Now you have to consider the current need to supply the receiver, and I guess that will depend on what you have connected to it.

cumps

Of course it has a regulator. standard IC's don't work on higher voltages than 5V (or even 3.3V). It has nothing to do with data signals however. I have made a bunch of PF receivers of my own. Either the uC (microcontroller) that processes the IR messages works or not. The capacitors and diodes seen in the brickshelf photos are just there for making it work even better but strictly speaking not necessary (although for toy purposes they are of course).

And Xargon321 can't get away with using a voltage regulator be it a low dropout or not, he needs an H-bridge etc on it's own, since if he uses the regulator the motors are also regulated and that is what he doesn't want. I was just saying that probably the voltage regulator will be the problem when giving it more than 10V.

[rgbrown]

My idea was also to check philohome, but anyway. Logic normally works on 5V. It will be able to take 12V I guess but then a built-in convertor like an 7805 voltage regulator will still regulate it down to 5V. Some power will be converted to (essentially) heat, so be sure it will not overheat your PF logic. Maybe use a lab power supply and try it in small steps.

Agree with the last piece of advice (experiment in small steps), but I seriously doubt PF uses a linear regulator (e.g. a 7805) to power the control logic, as that would be highly wasteful of battery power. It probably uses a small buck converter. There will be some nominal input voltage range that the receiver has been designed to work with, going above that is probably not a good idea. That range may well be quite high, but who knows. Anyone got technical (electronic) specs for the 8884?

As has been mentioned though, only the switching logic works at low voltage; the PF supply and control pins will always be at 0/9V (or whatever you're running it at)

[hoeij]

As has been mentioned though, only the switching logic works at low voltage; the PF supply and control pins will always be at 0/9V (or whatever you're running it at)

Before increasing the voltage, I would first measure what the actual output voltage is that you get right now.

Six AA batteries produce about 9.6 Volt, so that voltage will be the input for the PF receiver. I have

some doubts that the output will be 9.6 Volt as well (I've read that the Emerald Night train, which uses PF

and an XL motor, runs the same speed regardless of whether you're using 6 AA batteries (9.6 volt) or

the rechargeable battery which produces 7.4 Volt).

A quick way to check it is this way: connect an XL motor straight to the 6 AA battery pack, and see how

fast it spins. Then connect it to the PF receiver (powered by the same 6 AA battery pack) and see if it

turns at the same rpm.

[Buffalo]

That makes sense im going to assume that it can take at least 10v because i saw someone on here with a 9.6v battery. anyone have some good pics of the inside of the receiver?

I'm running a 9.6v NiMH battery in my 8043 and have had no problems with it so far. It provides a lot more grunt to run the motors than a PF battery box with fresh alkalines, and it's rechargeable. Not knowing the specific details of the receiver's innards, I wouldn't run them on much more than that for fear of letting the smoke out.

Whatever you decide to do, I've got a tutorial for making a battery adapter in my 8043 mods thread.

[Xargon321]

Buffalo can you test the output on your 9.6v battery pack? fully charged it should be putting out more then 9.6 should be closer to 12v at full charge if the 9.6v pack i have here is not faulty

[CP5670]

Philo tested all the motors on his motor page at 12V and they apparently worked fine, although he has a warning about it at the bottom. I tried out a few of fine at 12V just to see if they work, but haven't used them in actual models.

9.6V should be fine for motors. My guess is that the actual motor cores TLG uses are designed for 12V operation anyway. You probably need to be more careful with the IR receivers or lights though.

[rgbrown]

A quick way to check it is this way: connect an XL motor straight to the 6 AA battery pack, and see how

fast it spins. Then connect it to the PF receiver (powered by the same 6 AA battery pack) and see if it

turns at the same rpm.

I'd be interested to hear the outcome of this. I can't check it until I get home (in September), but judging from all the comments about how the 8043 works less well on rechargeable batteries, I'd expect that the voltage is passed straight through ...

[Xargon321]

Well i just got down to it and did it. i have a 3 cell lipo battery that i use on my r/c cars it was at 11.5v when i used it and it made a huge difference in performance. much faster lifting and lowering of the boom and dont seem to load down as much. it what it should have been in the first place.

Just fully charged the battery at 12.6v and it runs just fine so far going to have to get a smaller batter to fit into the battery box i think i can get a 950mah 3 cell to fit into the stock battery box just fine so it will not look out of place

Edited August 16, 2010 by Xargon321

[Blakbird]

Well i just got down to it and did it. i have a 3 cell lipo battery that i use on my r/c cars it was at 11.5v when i used it and it made a huge difference in performance. much faster lifting and lowering of the boom and dont seem to load down as much. it what it should have been in the first place.

Just fully charged the battery at 12.6v and it runs just fine so far going to have to get a smaller batter to fit into the battery box i think i can get a 950mah 3 cell to fit into the stock battery box just fine so it will not look out of place

Seems like a good enough plan. Do you intend to just hook up the battery to the +/- battery terminals inside the battery box and still use the same external connection and switch on the battery box? This should work except for the fact that there is no protection circuitry for the Li-Po. Make sure not to run it too low on voltage before recharging or it will explode.

[Xargon321]

Thats the plan have a lipo cell checker that i can use to see what level it is when i go to use it. im going to get a second battery box to modify so i have a regular box to use in case of a dead battery or another model to power etc. do lego stores sell just the battery box or is it all in a set?

[Blakbird]

Thats the plan have a lipo cell checker that i can use to see what level it is when i go to use it. im going to get a second battery box to modify so i have a regular box to use in case of a dead battery or another model to power etc. do lego stores sell just the battery box or is it all in a set?

You can only buy it in the Power Functions expansion set which also comes with a bunch of other stuff including an M-motor, LED lights, and a pole reverser. You can get just the battery box from LEGO Education or from Bricklink.

[dhc6twinotter]

Great thread!

The battery box is also available on LEGO's website:

http://shop.lego.com/ByTheme/Product.aspx?p=8881&cn=587&d=70

[rgbrown]

If any TLG employees are watching, we'd love to know the design limits of PF ... :)

Edited August 17, 2010 by rgbrown

[Mortymore]

Well... my curiosity was awaken, and I didn't sleep much.

So far I manage to take some photos to the IR receiver 8884 board.

http://www.brickshelf.com/cgi-bin/gallery.cgi?f=442112

It has a hidden controller under a drop of black epoxy

And on the other side, has a dual channel H-bridge motor driver LB1836

I can´t find the datasheet for the exact reference LB1836. So far I only found the datasheet for LB1836M.

Though they may work the same way, there's probably a slight difference on some specification, because the "M" should stand for something and I didn't find so far what it is, so be aware.

One note for now. The LB1836M has max voltage supply of 10.5v and since some people here has applied more than that to the 8884 receiver, or the LB1836 has higher specs on this, or I still have work to do on finding what is the Vcc voltage for it at different supply voltages for the 8884, because is has to be somehow lowered by some of the extra components seen on board. Maybe I'll try to sketch a partial schematic, if I find the time and mood.

Made also a video where some measurements can be seen. Devices attached to the 8884 receiver, and controlled by the 8879 remote, are regulated by PWM signals at a frequency of 1150Hz, and 7 forward, and 7 reverse, levels are provided, plus stop.

Duty cycles of the PWM control signal are: 0%, 26.6, 38.9, 51.2, 63.0, 75.0, 87.2 and 100%. The corresponding DC level output, depends on the voltage supplied by the battery box, and at a level of 100% the output of the receiver 8884 has the same voltage level as the voltage supplied to him by the 8881 battery box.

For now, that's all I could find. Suggestions or corrections are welcome, since part of the time spent on this I was probably more asleep than awaken.

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PS: Square voltage AC from the PWM output of the 8884 receiver was measured accurately, because a TrueRMS meter with a passband of 20KHz was used. A traditional multimeter wasn't able to measure it correctly.

Edited August 17, 2010 by Mortymore

[rgbrown]

A couple of questions.

That plane of track on the top side of the board, is that connected to the power functions 9V line? If so then it appears that the VCC and VS pins on the motor controller follow a rectifier diode of some sort (1N4002 perhaps?), but I can't quite tell.

That would mean that the output voltage to the motors at 100% duty cycle should be about 0.5-0.7V lower than the supply, which would also be the same as the VCC pin on the the motor controller. Which would also mean that applying a voltage higher than about 11V would be outside the recommended operation range of the motor controller. By the way, I think the LB1836M and LB1836 are the same thing -- if you do an image search for LB1836M, you never find a picture of one with the M printed on it.

So I think that's probably our answer. If you're applying more than 11V or more, you are probably working outside the operating limits of the motor controller, and are asking for trouble ... It will probably work, but you may be shortening the life of the controller.

Forgot to say: Thanks! You are awesome for dismantling your IR receiver

Edit: OK, watched the video properly. There definitely is no voltage drop. VS and VCC are definitely connected together on the PCB, so the output voltage is the voltage that you are applying to the LB1836. Even more reason not to stick higher voltages on it.

Edited August 17, 2010 by rgbrown

[Mortymore]

...

That would mean that the output voltage to the motors at 100% duty cycle should be about 0.5-0.7V lower than the supply, ...

That was one thing that I checked and they are the same.

The voltage provided by 100% duty cycle to the motor, is equal to the voltage provided by the battery box. No drop-out.

I know it's best to put some notes on the video, but I hadn't find time to do it so far, but can be seen on it.

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PS: About the LB1836, you may be right, but I found somewhere that there's a LB1836 listed as been made by Fugitsu, and the LM1836M always appears as being made by Sanyo.

Edited August 17, 2010 by Mortymore

[rgbrown]

That was one thing that I checked and they are the same.

The voltage provided by 100% duty cycle to the motor, is equal to the voltage provided by the battery box. No drop-out.

I know it's best to put some notes on the video, but I hadn't find time to do it so far, but can be seen on it.

cumps

PS: About the LB1836, you may be right, but I found somewhere that there's a LB1836 listed as been made by Fugitsu, and the LM1836M always appears as being made by Sanyo.

This page http://www.icver.com/html/pro/13/25395.htm claims to sell both, and the image appears to match the one on your board (same font, similar batch number, etc ...). But, frustratingly, the datasheets for both are for LB1836M. (I downloaded lb1836m.pdf and lb1836.pdf). I'm now pretty convinced that they're the same thing ... I think it would be more obvious if they were not ... happy to be proven wrong though. The one sanity check left to do is to probe the voltage on the VCC pin (pin 1) of the motor controller

[Xargon321]

if im reading the chips schematic correctly then the motors Voltage input is separate from the control that would enable us to keep the control part of the chip below 10.5v while allowing full voltage to the motors?

[Mortymore]

if im reading the chips schematic correctly then the motors Voltage input is separate from the control that would enable us to keep the control part of the chip below 10.5v while allowing full voltage to the motors?

Yes, the chip allow you to have separate voltages for control (Vcc), and for H-bridges (Vs1 and Vs2), i.e, for motors if that's what you plug at the output.

Trouble is that chip allow 10.5v max, for all kind of voltage supplys, Vcc or Vs.

...The one sanity check left to do is to probe the voltage on the VCC pin (pin 1) of the motor controller

I'll do my homework as soon as possible.

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EDIT: Vcc pins 1, 4 and 11 of the LB1863 are directly connected to Vcc line of the battery box, and GND pins 7 and 14 of the LB1863 are similarly connected to GND of the battery box, so the Vcc line on the motor controller IC has the same voltage as the battery box.

Edited August 17, 2010 by Mortymore

[Xargon321]

was just thinking that the controller side would be the one we need to protect because the motors can pull some good current threw those and i figure that they are over built just in case.

in any case it seems to work find as it is with buffalo and me so i might just let it go and if it poofs just chalk to experience and get some more they are cheap to replace so its not too bad

[Mortymore]

Speaking of current...

Fresh work.

The setup

The load for the 8884 receiver are 2 motors (8882 and 8883) in parallel, connected to just one output.

With the 2 motors running freely, no more than 150mA was pulled.

With the M motor 8883 stalled, the current went up at around 600mA.

With the XL motor 8882 stalled, was around 800mA.

With the 2 motor stalled, about 950mA.

The maximum input current measured was 1A, and for the output 980mA.

The batteries used were regular alkaline ones, and they're not fresh as can be seen from the voltage measured by meter at the left, so higher values for current may be achieved with fresh batteries, though the maximum current that the motor controller LB1863, allow through GND pin is 1A, so we are close here.

I could do some tests with a regulated power supply instead of the batteries, but that wouldn't be a real scenario, and if unproper limit to current would be set at high level voltages, I might kill my receiver and it would be the end of the fun.

Or maybe it could be a test for the thermal protection of LB1863 if done smoothly.

I have something else left to do, but it will take some time. The partial (possible) schematic of the receiver.

Cumps.