Using two PF (Rechargeable) Battery Boxes with one IR Receiver?

[Paperballpark]

Hi all,

I'm wondering if anyone knows whether this is possible? I need to power a long train, which will need two train motors to pull it. The only problem with this is that it'll probably drain the battery box in about half the normal time, so I'm wondering if it's possible to connect both motors to an IR Receiver, then connect that to one battery box, and connect that battery box to a second one (using an extension cable mounted between the first battery box and the cable from the IR Receiver)?

I assume it would work, as it would then be drawing power from both battery boxes, but I'm not an electrical engineer, so can't be certain.

Thanks!

[Hemlock Falls]

I'm actually wondering the same sort of thing

[Dutchiedoughnut]

Well. In theory it might work, but things go bad when the two battery boxes don't drain evenly.

I think the IR receiver will limit your output power. So why not use two IR receivers and have two independant systems?

[Covenant84]

Noob question I think is related... If you have multiple ir recievers are they operated by separate controllers? Do you have to program them with a channel number or something?

[TF Twitch]

Noob question I think is related... If you have multiple ir recievers are they operated by separate controllers? Do you have to program them with a channel number or something?

Set both of the IR Receivers on the same channel and they can be controlled by the same remote.

For the original topic, I would have both motors on separate systems if you want it to run for longer with less up front power drain.

Hi all,

I'm wondering if anyone knows whether this is possible? I need to power a long train, which will need two train motors to pull it. The only problem with this is that it'll probably drain the battery box in about half the normal time, so I'm wondering if it's possible to connect both motors to an IR Receiver, then connect that to one battery box, and connect that battery box to a second one (using an extension cable mounted between the first battery box and the cable from the IR Receiver)?

I assume it would work, as it would then be drawing power from both battery boxes, but I'm not an electrical engineer, so can't be certain.

Thanks!

To add to my previous answer, you may want to have an extension cable run from each battery box to the IR Receiver. That will give you more initial power up front, but as someone else said your output is ultimately limited by the IR Receiver. So I would suggest for maximum power potential to run two separate systems.

[jtlan]

Set both of the IR Receivers on the same channel and they can be controlled by the same remote.

In theory. More likely, one of the receivers will miss a command, causing the two to run at different speeds, draining your batteries and generally being bad for the motors.

@Paperballpark, If you have room, I would try to use the AA battery box; Using this battery box with good rechargeable AA batteries should provide about twice the capacity of the Lithium PF battery.

[dr_spock]

You may have to make your own PF cable to connect two battery boxes in parallel. The new PF extension cables look like they don't allow you to connect two battery boxes in parallel. I don't know if the old 9V cables will allow it since I don't have one to check out.

Edited November 9, 2015 by dr_spock

[jtlan]

You may have to make your own PF cable to connect two battery boxes in parallel. The new PF extension cables look like they don't allow you to connect two battery boxes in parallel. I don't know if the old 9V cables will allow it since I don't have one to check out.

The non-connectivity seems to be a sign that you probably shouldn't do this. Also, the 9V cables won't work for this because they connect the C1/C2 wires and not the +9V/GND wires.

[zephyr1934]

In general I believe you are not supposed to connect batteries in parallel, otherwise any uneven voltage level will result in one battery attempting to charge the other one. If instead you tried to connect the batteries serially (e.g., in the AAA battery pack you get 9v by summing 6*1.5v) when serially connecting two PF battery boxes you would instead get 2*9v=18v which is too much for the PF motors. So as others have said, make two separate systems.

I would think that putting the motors in separate engines with one on red and the other on blue but both on the same numbered channel would be the way to go. As per earlier posts, both on the same color output will wind up with them being out of sync if one misses a "increase speed" command. You can match it by hand though if you have one on red and the other on blue, you just have to listen and watch to make sure they are not too far out of coordination (I suspect it would be okay if they were off by one speed step since either unit would already be overwhelmed without the help of the other). Alternatively if you had a large locomotive you could use an SBrick that allows you to set multiple outputs (potentially on multiple SBricks) to the same level, but that can get expensive really quickly.

Getting back to your original question, pulling a long train, have you thought about using XL motors instead? You might have to hide them in a boxcar, but that shouldn't be too hard to do. I've pulled 50+ cars with this unit (plus a few weights to help for traction). It will pull the magnets apart first, then pull the cars off the rails on the curves before it runs out of pulling power. The battery lasts for at least two hours... probably more. The train does run very slow though.

[dr_spock]

The non-connectivity seems to be a sign that you probably shouldn't do this. Also, the 9V cables won't work for this because they connect the C1/C2 wires and not the +9V/GND wires.

Thanks for the 9V wire information. Connecting 9V battery boxes in parallel would provide more current. Probably should have intelligent circuitry to monitor voltage and current and shutdown cells to avoid bad outcomes.

[Paperballpark]

Hi all, thanks for all your answers.

So if I'm reading everything right, all that connecting two battery boxes would do is increase available power? Rather than prolong battery life. Plus there's the possibility that one box would try to charge the other if they drained slightly differently. Is that correct?

A couple of comments on other solutions proposed:

Regarding the AA battery box, extra battery life sounds good, but the real draw of the rechargeable box is that I van build it into my trains, and only need to leave a small opening for the plug, rather than needing to take it out completely every couple of hours.

For the XL motor, pulling a large train would be good, but it'll be a 'high speed' passenger train, so it running slow wouldn't be good.

I don't want to use two IR receivers for the precise reason that one might not pick up the signal, even if I arranged them 'back to back'. Equally, I don't want to use sbrick because it seems like a lot of hassle, and it's pretty expensive!

I think what I'll probably end up doing is running one rechargeable battery box with two train motors, and just built another identical driving train to swap over when the first dies after a couple of hours.

[jtlan]

So if I'm reading everything right, all that connecting two battery boxes would do is increase available power? Rather than prolong battery life. Plus there's the possibility that one box would try to charge the other if they drained slightly differently. Is that correct?

No; for the situation you described, you would be connecting the batteries in parallel. Two batteries in parallel would provide the same voltage as one battery, but would last twice as long for a given load because each is being drained half as much. Connecting them in series (as described in zephyr1934's post) would provide twice the voltage of one battery, which is probably not what you're looking for.

Connecting two batteries in parallel forces the positive terminals of the batteries to be at the same voltage, measured relative to the negative terminal (this is Kirchhoff's Voltage Law applied). If the batteries are not at exactly the same voltage, current will flow through the loop, resulting in one battery trying to charge the other one. However, the Lego PF battery contains some complex circuitry, so it's not exactly clear what would happen with those.

I think what I'll probably end up doing is running one rechargeable battery box with two train motors, and just built another identical driving train to swap over when the first dies after a couple of hours.

This seems like the most straightforward scenario for your use case, although if it's possible to design the locomotive so the battery box can be easily removed you can avoid having to build an entire other locomotive. See some of Commander Wolf's PF models for inspiration.

[andythenorth]

Unless you're in sunlight, or at the limit of the remote, IR receiver command 'misses' are pretty rare for two receivers placed very close together.

I have PF technic MOCs with the receivers adjacent, and there's no problem. Unless you run one motor reversed against the other, there's no harm. Two motors at slightly different speeds is no problem, you'll just get inconsistent battery drain between the two. Even one motor stopped and the other running is not likely harmful, most DC motors can be run as generators, and there is protection (thermal, current?) which would prevent damage to the powered motor.

My kids run trains with mixed PF / RC trains on the point, or with rear pushers, and they run Horizon Express with the receivers separated by 4 coaches. The worst that happens is stacking up the train on curves when the rear engine is pushing harder/faster.

[legoman666]

I connect the AAA battery boxes with NiMh batteries in them in parallel all the time. My horizon express has 3 battery packs in parallel. Seems to work fine.

[zephyr1934]

For the XL motor, pulling a large train would be good, but it'll be a 'high speed' passenger train, so it running slow wouldn't be good.

I don't want to use two IR receivers for the precise reason that one might not pick up the signal, even if I arranged them 'back to back'. Equally, I don't want to use sbrick because it seems like a lot of hassle, and it's pretty expensive!

I think what I'll probably end up doing is running one rechargeable battery box with two train motors, and just built another identical driving train to swap over when the first dies after a couple of hours.

Ah, okay, I have two heavy passenger trains that are probably like yours in terms of weight and drag if not heavier, e.g., my North Coast Limited. Those trains are both powered with two PF train motors and a single LiPo PF battery. They are heavy enough that even with a pair of rare earth magnets behind the engine that the train will sometimes pull off if I am not really careful with the speed. I believe I can get at least two hours of run time out of them without recharging... maybe even 3 hours.

In this case I found the IR receiver to be the most limiting factor, it cannot deliver enough current. So if I pushed too much power by running too fast the train would stall for a second or two until the receiver cooled down and then come back on at the same power level. So the engine would rocket off without the train, hit the very next curve and take off like a kite. I went with an SBrick because it can deliver at least twice the current of the IR receiver without problems. Compared to two IR receivers it is only about twice the price.

It sounds like you'll need to do some experimenting to find the solution you like. Assuming you are able to move the train all the way around your layout with two PF train motors and one IR receiver you should be good to start, the rest would be fine tuning. To this end, probably start with a single battery box and a single IR receiver and only augment as needed.

Rather than building a second motor car, why not design it so that the battery box can be easily swapped out? That way if you are not happy with the battery life you can do a quick battery change and probably do so for less than any other two-battery solution. If you then find the IR receiver is limiting (which should only happen in extreme cases) then potentially add a second IR receiver to the same battery to see if that solves the problem. If so, either stay there or consider an SBrick.

In any event, just be careful that you can reach all parts of your layout (otherwise, you know that the batteries will decide to die under that mountain in the far corner that you cannot reach).

Now here is another complication about heavy trains. My aforementioned trains slow down A LOT in standard lego curves. The motors can only deliver so much power (and that is with a lot of extra weight on the engine to improve traction). When using R44 curves the trains will only run well on layouts that are close to square. So the train is always in roughly the same number of curves. Otherwise, if it can sometimes run straight and sometimes be in two curves that will cause a lot of problems- slows greatly for the curves so you need a lot of power to get through them, then the train speeds up way to fast when it straightens out, and then derails as it enters the next curve due to the speed from the power that was necessary for the previous curve. If you run into this situation, then you'd probably want 4 PF train motors powering your train so that you can maintain a more constant speed in and out of curves (you'll have a lot more power at a given speed so the train will slow less in the curves). But here you'll need either the SBrick or two IR receivers... and quite possibly two batteries.

Of course large radius curves are another story. Both of my heavy trains are quite happy to run at full speed in ME R88 and R104 curves with the IR receivers. When running on the PennLUG extremely large radius curves built out of straight track segments the IR receivers did not like all of the extra drag caused by all of the trucks constantly changing directions at each rail joint and so the IR receivers would stall.

[Paperballpark]

^ I hate Lego's r44 curved track, and will be getting the ME models track sometime soon so that I don't have the exact problem you describe, of having to find the right balance of speed. One of my trains in particular is a right pain to do that with.

Also, my trains tend to be so tightly packaged that it'd be difficult to design it to easily remove the battery box. I'm also looking at doing the same thing with my Horizon Express, although I'm aware there may not be space for two boxes in the one car.

One final thing to note, I don't have a layout at home, because my house is too small. My layouts are at shows, so I'd rather decide beforehand how to run them, rather than playing around rebuilding stuff at shows :)

Edited November 11, 2015 by Paperballpark

[zephyr1934]

Oh, yes, I know what you mean about not being able to set everything up at home. And I must say, "Doh!" that's right, I remember that you have some insanely detailed trains (e.g., your Flying Scotsman)... yeah, that makes it a lot more difficult to simply swap batteries in and out.... Could you do a temporary loop at home for R&D and test the endurance to avoid unpleasant surprises at a show?

In any event, looking forward to seeing your new trains.

[Paperballpark]

Oh yes, I could do a small loop at home just to test that it actually works. I just wanted to ask in advance, in case connecting two battery boxes ruined them both - the rechargeable ones are too expensive to ruin by doing that!

[marook]

Running separate engines in each end of the train, is where SBricks come in handy!

They also allow 3Amp current, compared to the 1.5A in the IR system ...

[Paperballpark]

I bought a PF extension cable today, and there's no way to use it to connect two battery boxes, so it looks like I'll either build an identical loco with another battery box etc, to swap over, or use two IR receivers and run two motors on separate systems.

[Ashi Valkoinen]

I'm wondering that you are experiencing battery draining problems with using two of the wonderful PF-train motors. I run heavy trains with two or more PF-train motors for 5-6 years by now, without any battery problem.

As I remember, the output voltage of the rechargeable battery box is 7.2V, which is maybe not enough for the two motors.

For start I advise to make the bigger (AA batteries) PF-battery box fit into your loco. It has the advantage that it won't turn off after two hours, and putting 6 of AA batteries inside (rechargeable of course) will prove you enough capacity to run your train. For more power try to use PF IR Receiver V2, or if the current limitation still bothering you, maybe SBrick.

Currently I'm running my Siemens Taurus locomotive with the old RC-train base, using two PF-train motors connected to it and my Stadler FLIRT EMU from SBrick, using two motors as well. The train pulled by Taurus locomotive is around 4 kg-s, the EMU is around 3 kg-s, 6 of AA batteries prove around 3-4 hours of runtime.

[Paperballpark]

What I like about the rechargeable box is that you can recharge it! You don't have to take the train apart to get the box out, or unscrew anything. I tend to build the boxes into the train, so it's impossible to get them out without dismantling half the train.

[Ashi Valkoinen]

Depends on the locomotive, the width you use, etc, etc.

with couple of clever solutions (hinges, tiles under roof, technic solutions) it is not impossible to create a train body which can be easily opened to reach the battery box. Of course, in some cases the battery box holds all the train together, but it is not that usual.

What I like about the rechargeable box is that you can recharge it! You don't have to take the train apart to get the box out, or unscrew anything. I tend to build the boxes into the train, so it's impossible to get them out without dismantling half the train.