LEGO Train 12 Volts

Single lithium batteries for Power Function trains

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Posted (edited)

Hello everyone,

if you are tired of depending on normal non-rechargeable batteries :angry:

...or...

if you are not fan of the 1,2 Volt rechargeable batteries (that in the 6-piece battery pack deliver the paltry 7.2 volts) :hmpf_bad:

...but...

on the contrary you want trains that run fast for hours

...then read on! :wink:

 

The Columbus' egg

The easy solution is the use of only one lithium battery of the type you prefer (the classic AAA 10440, the big sister AA 14500 or the very strong 18650)

mt3608-003.jpg

combined with a voltage regulator such as the MT3608.

mt3608-001.jpg

mt3608-006.jpg

The MT3608 allows you to adjust the output voltage bringing it exactly to 9 Volts (with the appropriate trim screw and the use of a multimeter).

mt3608-002.jpg

 

Advantages

The advantages are basically 4:

1) The life of lithium batteries is significantly higher

2) The regulator supplies 9 volts constant so if the battery starts to run down you will not notice it until towards the end

3) The locomotive is lighter and therefore faster

4) The batteries can be recharged

 

The circuit

The circuit is very simple (and cheap :laugh:), you will need a single housing (or double if you want to exaggerate :excited:) for the battery, a switch, an MT3608 (the screw must be turned counterclockwise to increase the voltage) and a PF connector (which must be connected to the PF receiver).

Here you can find some pictures that explain more than many words.

mt3608-004.jpg

mt3608-005.jpg

mt3608-007.jpg

mt3608-009.jpg

That's all folks! :classic:

Edited by LEGO Train 12 Volts

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25 minutes ago, LEGO Train 12 Volts said:

 

3) The locomotive is lighter and therefore faster

Less weight is a disadvantage because traction is lost. 

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Posted (edited)
32 minutes ago, legotownlinz said:

Less weight is a disadvantage because traction is lost. 

I assure you that with this solution the loss of traction is not appreciable ...in any case if you want you can always add a fishing lead, surely with this solution you will save space! :wink:

Edited by LEGO Train 12 Volts

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I think your solution is great when the battery box doesn't fit.

If the goal is only to avoid the loss of voltage of the 1.2 V rechargeable batteries, then there is an easier solution that requires less technical skills: Using 1.6 V AAA NiZn rechargable batteries instead.

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1 minute ago, legotownlinz said:

I think your solution is great when the battery box doesn't fit.

Correct!

But I'm currently working on a PCB of my own design to replace the one inside the original battery box to incorporate this solution on the standard Lego battery pack.

I hope to show my progress soon. :classic:

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Posted (edited)

What fascinating modern times we live in :bonaparte:

The multiturn pot is the biggest component! When I first started making DC2DC converters I couldn't even get the right coils so I had to wind them myself

And now I can get this marvel for just a few EUR. What is the input range? Can I use two 18650 in series?

I don't have any trains anymore but a lot of monorail :wink:

Edit : it's 2-24V for 9V out

Edited by 1974

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Posted (edited)
11 hours ago, 1974 said:

What is the input range? Can I use two 18650 in series?

The input range is from 2V to 24V and the output can be set between the input voltage and 28V.

...and yes you can use two 18650 in series (personally I've put two 18650 in my Railjet and now the train has the right speed for that name! :wink:)

Edited by LEGO Train 12 Volts

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50 minutes ago, legotownlinz said:

Whats the benefit of using them in series?

With two batteries in series, you get twice the voltage of a single battery .

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2 hours ago, LEGO Train 12 Volts said:

...and in this case you double the duration

Forgive my ignorance but wouldn't that require connecting in parallel to get extra runtime? Connecting in series increases the voltage by 1x the original for each battery added to the series and connecting in parallel adds 1x the original power, right? I haven't searched for this to confirm my understanding, just blindly posting, so please feel free to correct. I would certainly be interested in adding more voltage and runtime with a  decreased footprint. Presently my EN MOC is running a tender containing the AA battery box filled with NiZn batteries. That's a pretty good performer, but if the tender could be a bit lighter that would be good. I could probably drop the height of the tender by a couple of plates too if I could remove the need for the AA battery box for the extra capacity. 

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1 hour ago, Toxic43 said:

Forgive my ignorance but wouldn't that require connecting in parallel to get extra runtime? Connecting in series increases the voltage by 1x the original for each battery added to the series and connecting in parallel adds 1x the original power, right? I haven't searched for this to confirm my understanding, just blindly posting, so please feel free to correct. I would certainly be interested in adding more voltage and runtime with a  decreased footprint. Presently my EN MOC is running a tender containing the AA battery box filled with NiZn batteries. That's a pretty good performer, but if the tender could be a bit lighter that would be good. I could probably drop the height of the tender by a couple of plates too if I could remove the need for the AA battery box for the extra capacity. 

Putting 2 batteries in series increases the Voltage (V). Putting two batteries in parallel increases the Amperage (A). In BOTH cases the Power increases, because Power = Voltage x Amperage.

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Does the PU hub low voltage detection cut off the power when the Li-Ion cell falls below 3.2 volts?

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Posted (edited)

I did some tests long ago with two 18650 batteries, but had problems fitting it in my Maersk engine with the PU hub. My plan was to 3D print a custom bottom battery box that attaches the PU hub white top with electronics. This would have been a much better solution.
Even if you have just a single 4,2 V battery with 3300 mAh and you double the voltage with a voltage regulator, you get 1650 mAh which compared to 900 mAh of Ikea Ladda batteries is a lot better, (and at higher voltage). Hmm, I think I will order some mt3608, and maybe even try to get a 21700 ... :drool:

Edited by Wabbajack

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Nice one, Emanuele!

Now with regard to @dr_spock's comment: Is this of concern? The mt3608 will hold the output constant as long as it can (which is excellent of course!). But will it do so even when the input voltage drops below the critical value of about 3V? Or is there some unvervoltage protection, as in all the devices running on LiPo/Li-Ion rechargeable batteries? If not, then you need to install such undervoltage protection circuit as well, as you won't notice too low volatges, because the output is always 9V - even with 2 V input. Which in turn may severely damage the batteries.

Best
Thorsten 

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Posted (edited)
10 minutes ago, Toastie said:

Nice one, Emanuele!

Now with regard to @dr_spock's comment: Is this of concern? The mt3608 will hold the output constant as long as it can (which is excellent of course!). But will it do so even when the input voltage drops below the critical value of about 3V? Or is there some unvervoltage protection, as in all the devices running on LiPo/Li-Ion rechargeable batteries? If not, then you need to install such undervoltage protection circuit as well, as you won't notice too low volatges, because the output is always 9V - even with 2 V input. Which in turn may severely damage the batteries.

Best
Thorsten 

Li-Ion are very sensitive to low discharge (not sure about LiPo, but its better to be safe than sorry) and it is strongly recommended to use a battery protection circuit between the battery and the regulator.

I think a battery charging circuit with these protections built-in would be perfect.

Edited by Wabbajack
Grammar

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Posted (edited)
1 hour ago, dr_spock said:

Does the PU hub low voltage detection cut off the power when the Li-Ion cell falls below 3.2 volts?

Don't know - but don't think so - with LEGO devices running on LiPos (there are only very few, I believe) this circuit is usually built into the "battery pack" replacing the batteries or the compartment, isn't it? At least the NXT LiPo battery had that protection built into the battery pack but there is no such circuitry in the NXT. Nor RCX, etc. pp. 8878 certainly had that - but that is just a battery pack ...

I believe you need to tell the hub that you are using a rechargeable battery set, which may explode when running below a certain level. OK, maybe not explode, but calling it quits :pir-skel:. Wasn't there a mirco switch thing in the Technic hub? Don't remember.

Also in case of @LEGO Train 12 Volts's solution, the hub would not know that the battery is operated below damage threshold, as the output is held constant as long as possible but the input not as long as healthy ;)

Best
Thorsten 

 

11 minutes ago, Wabbajack said:

Li-Ion are very sensitive to low discharge (not sure about LiPo, but its better to be safe than sorry) and it is strongly recommended to use a battery protection circuit between the battery and the regulator.

LiPos are as well a bit diva-ish - at least when it comes to operating range. They also do tend to go into flames when not treated as such:pir-skel:.

TLGs answer to all these challenges was the 8878 LiPo box: Input: Charging while operating, wide charging range, overload protection. Output: Overcurrent protection, under-voltage protection (9V/0), on/off switch (9V/0), adjustable output (C1/C2) ...

Too expensive and ... retired. For whatever reason. Maybe LiPos are too much for a toy company.

Best
Thorsten 

Edited by Toastie

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Posted (edited)
16 minutes ago, Toastie said:

Don't know - but don't think so - with LEGO devices running on LiPos (there are only very few, I believe) this circuit is usually built into the "battery pack" replacing the batteries or the compartment, isn't it? At least the NXT LiPo battery had that protection built into the battery pack but there is no such circuitry in the NXT. Nor RCX, etc. pp. 8878 certainly had that - but that is just a battery pack ...

I believe you need to tell the hub that you are using a rechargeable battery set, which may explode when running below a certain level. OK, maybe not explode, but calling it quits :pir-skel:. Wasn't there a mirco switch thing in the Technic hub? Don't remember.

Also in case of @LEGO Train 12 Volts's solution, the hub would not know that the battery is operated below damage threshold, as the output is held constant as long as possible but the inout not as long as healthy ;)

Best
Thorsten 

 

Yes, but if you connect a Li-Ion battery to a charging board, for example one with TP4056 and connect the regulator to its output, you will have overcharge and overdischarge protection. The regulator will keep the Hub at 9V, so it will think the battery is always full.
The charging board however will simply stop outputting power once battery voltage drops too low.

Best regard,

Martin

Edited by Wabbajack
Changed link to a better source

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Posted (edited)
5 minutes ago, Wabbajack said:

The charging board however will simply stop outputting power once battery voltage drops too low.

Oh yes, that is what I was aiming for, Martin! I just don't know, what mt3608 has in its brain ;)

So let's do the math: mt3608 + tp4056 = 8878?

Best
Thorsten

Edited by Toastie

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1 minute ago, Toastie said:

Oh yes, that is what I was aiming for, Martin! I just don't know, what mt3608 has in its brain ;)

So let's do the math: mt3608 + tp4056 = 8878?

Best
Thorsten

Also I used tp4056 as an example for Li-Ion, but it seem it can be also used with LiPo. I have done a little googling, but am not sure. Maybe someone can help?

I think the equation mt3608 + tp4056 = 8878 is true, but I think the charging circuit was in the wall adapter 45517. You can use the charging circuit with tp4056 to charge with USB, so maybe mt3608 + tp4056 >= 8878.

Martin

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35 minutes ago, Toastie said:

Don't know - but don't think so - with LEGO devices running on LiPos (there are only very few, I believe) this circuit is usually built into the "battery pack" replacing the batteries or the compartment, isn't it? At least the NXT LiPo battery had that protection built into the battery pack but there is no such circuitry in the NXT. Nor RCX, etc. pp. 8878 certainly had that - but that is just a battery pack ...

I believe you need to tell the hub that you are using a rechargeable battery set, which may explode when running below a certain level. OK, maybe not explode, but calling it quits :pir-skel:. Wasn't there a mirco switch thing in the Technic hub? Don't remember.

Also in case of @LEGO Train 12 Volts's solution, the hub would not know that the battery is operated below damage threshold, as the output is held constant as long as possible but the input not as long as healthy ;)

Best
Thorsten 

 

My PU Hub blinks and stops working when my NiMH batteries fall below a certain level.  I assume it'll do the same when the output from the step up converter drops to it.  If it corresponds to 3.2V on the Li-Ion battery, then it is good.
I bought some of these 18650 battery protection when I tried to salvage some from an old laptop battery pack.  You shrink wrap them to the battery after wiring them up.  They make the battery a bit taller too.

bms.jpg

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4 hours ago, dr_spock said:

I assume it'll do the same when the output from the step up converter drops to it.

But the input voltage range of mt3608 is 2 - 20V - doesn't that mean it'll drown the battery to 2 V before it gives up?

4 hours ago, Wabbajack said:

You can use the charging circuit with tp4056 to charge with USB, so maybe mt3608 + tp4056 >= 8878.

Hmm. The charging voltage range of 8878 is (was) 9 - 18V, the power supply required is (was) a dead cheap unregulated wall wart.

Spoiler



 

 

However, with a 5V regulator as input, one could achieve the same or even better performance of 8878 so yes, your equation holds true!

Most importantly: $/€(LiPo battery + mt3608 + tp4056 + 5V regulator) << $/€(8878)! Wow, I guess I need to order some stuff :pir-huzzah2:

Thanks Emanuele and Martin!!!

Best wishes,
Thorsten

 

 

 

 

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6 hours ago, Toastie said:

Oh yes, that is what I was aiming for, Martin! I just don't know, what mt3608 has in its brain ;)

On the MT3608 datasheet that I found online, it says that the minimum operating input voltage is 2V and that the under voltage lockout is 1.98V.
However, I installed this module in a casio calculator (3.7V -> 6V) and it stopped working when the battery voltage dropped to 3.2V. This needs further testing, but this first empirical test was successful.

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12 hours ago, LEGO Train 12 Volts said:

On the MT3608 datasheet that I found online, it says that the minimum operating input voltage is 2V and that the under voltage lockout is 1.98V.
However, I installed this module in a casio calculator (3.7V -> 6V) and it stopped working when the battery voltage dropped to 3.2V. This needs further testing, but this first empirical test was successful. 

That could be because Li-Ion batteries cut off at around 3.2V/3.3V (wiki link).

13 hours ago, Toastie said:

Most importantly: $/€(LiPo battery + mt3608 + tp4056 + 5V regulator) << $/€(8878)! Wow, I guess I need to order some stuff :pir-huzzah2:

Thanks Emanuele and Martin!!! 

You are welcome and I am glad to be of help. I already have the parts ordered and will hopefully show some prototype here soon.

Martin

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