Power Functions - PP3 Battery

[Hod Carrier]

Just a quick question. Is it possible to use something more compact than the various official LEGO battery boxes to provide power to a PF model?

I was thinking something along the lines of a 9V PP3 battery. I appreciate that there's probably going to be a trade-off in terms of power output and battery life, but I simply don't have the space to fit anything bigger.

[JopieK]

Of course it is possible. I have some trains that run on non-LEGO LiPo's because they fit better in the tenders.

[JopieK]

Hi Andy,

no problem, first remember: LiPo batteries are potentially dangerous! Shorting them will make a kind of welder out of them and will probably cause a flame or your battery to explode. Believe me, I'm a tech teacher and have seen it happen ;)

That should not spoil the fun of course. I think other safety regards are somewhat over exaggerated but one should officially always stay near to the battery when charging. Li-Ion seems to be a little more safe. LEGO built so many safety features around their LiPo, makes it costly but also very safe (students shorting the LEGO LiPo had more luck: inserting the power adapter resets the internal protection and the battery functions like nothing happened).

When using LiPo cells, you will find that there is a difference in the amount of cells used. 1s stands for one cell (at least one series cell) and will typically provide 3.7 volts. A 2s battery will have 2 3.7 cell in series and so the voltage is now about 7.4 volts (and so on for 3s being 11.1 volts, etc). There will be a red wire that provides you with the positive voltage (so for 2s 7.4 volts) and a black wire with being the ground (0V or minus) lead.

Reversing the -/+ on a motor will make the motor turn the other way around. When using the LEGO IR receiver, there is a regulator and switch inside that will let you regulate the output and direction:

http://www.philohome...pfrec/pfrec.htm

Here is a cable setup of the PF cables:

http://www.philohome.com/pf/pf.htm

Make sure that you don't deplete the LiPo too much and also make sure you use a good charger (I buy them at hobby king).

Some general advice:

- make sure if you strip the cable that you use (from the LiPo and the PF) a good wire stripper (there are alternatives but for beginners I think they are an important tool).

- make sure if you attach the wires to the remote that you make sure you have the correct leads and also make sure you use shrink tube and/or hot glue so that you make it virtually impossible to get a short.

I use PF extension cables to accomplish this: cutting a cable will get you two of the adapter one's:

[Hod Carrier]

Thanks ever so much for that excellent guide. Since PM-ing you I did spend several hours reading and absorbing some of the gathered wisdom on the internet.

The outcome of my reading was that I'd decided on a 7.4 volt two cell battery rather than taking the risk of going for the larger 11.1 volt three cell battery and over-stressing the PF components. The capacity will largely be dependent on the size, but the space is very restricted so it's likely to be in the 250mAh range.

But you have gone on to answer my next question before I'd even asked it, about how to connect it all together. Thank you so much for the excellent advice.

[bonox]

1s stands for one cell (at least one parallel cell) and will typically provide 3.7 volts. A 2s battery will have 2 3.7 cell in parallel and so the voltage is now about 7.4 volts (and so on for 3s being 11.1 volts, etc).

Useful writeup, but for general education if people start looking elsewhere, 1s and 2s are cells in series, not parallel.

(+ -) (+ -) is two cells in series, which adds the voltages together

Two cells side by side (parallel) or both + together and both - together has the same voltage as only one cell.

Edited November 1, 2015 by bonox

[JopieK]

Useful writeup, but for general education if people start looking elsewhere, 1s and 2s are cells in series, not parallel.

(+ -) (+ -) is two cells in series, which adds the voltages together

Two cells side by side (parallel) or both + together and both - together has the same voltage as only one cell.

Important notice! I fixed it in my text.