Can I use three rechargeable batteries for train motor?

[mikezang]

I have three rechargeable batteries All are 3.7v from phones as below, can I use the for train motor?

[Bojan Pavsic]

Short answer: No.

Long answer: First of all you'd need to connect two batteries in serial, so you'd get enough voltage, but that's usually done with same type/capacity/age batteries. From your picture, i can see you have 800 mAh, 860 mAh and 940 mAh batteries, so that's the big "no-no".

[mikezang]

Short answer: No.

Long answer: First of all you'd need to connect two batteries in serial, so you'd get enough voltage, but that's usually done with same type/capacity/age batteries. From your picture, i can see you have 800 mAh, 860 mAh and 940 mAh batteries, so that's the big "no-no".

Can you explain why they have be the same type? Is it ok if they are different type but with the same current?

[Bojan Pavsic]

Because of the internal resistance. Different types have different resistances, which means in 2S configuration (2 cells serial), that one of the cells will take more load then the other and that leads to cell failure. That's why good packs have cell balancing (which makes the cells have the same voltage while charging them). Even same type of cells, same capacity different age is not recommended. If you have the old NiMH, NiCd or newer LiFePO4 cells, it's not that big of a problem (it's still not good for the cells and not recommended), but LiIon and especially LiPolymer are dangerous. They can catch fire, explode etc.. if they're not handled correctly.

And btw, it's not current, it's capacity (mAh).

[Barduck]

Short answer: No.

Long answer: First of all you'd need to connect two batteries in serial, so you'd get enough voltage, but that's usually done with same type/capacity/age batteries. From your picture, i can see you have 800 mAh, 860 mAh and 940 mAh batteries, so that's the big "no-no".

that's not enterily correct. If you use rechargeable batteries in the LEGO battery holder, having batteries with different power outage won't affect overall performance, it'll just last shorter as the power each battery holds is different and it'll "flatten" out so to speak (to make it easier to comprehend) The biggest no is that these sort of batteries aren't made to be used like that, you shouldn't try to put them in serial. Secondly, they won't last as long as ordanary rechargeable batteries (be it regular or those Lithium) as these batteries are made to power a celphone, which doesn't require as much power constantly as a LEGO train motor would

[Garrcomm]

it'll "flatten" out so to speak (to make it easier to comprehend)

But isn't that a problem as well? I mean, if you have a fully charged battery with a capacity of 2000mAh and a fully charged battery of 400mAh, it'll be impossible to flatten it out; 2400mAh devided by two batteries would be 1400mAh per battery. But the 2nd battery can't be charged that much.

Edited December 2, 2013 by Garrcomm

[mikezang]

So what is the conclusion ? Can or can't I use them? What the lowest capacity if I can use them?

By the way, I got two more batteries as below

[Bojan Pavsic]

Acording to Philo's research, a train motor (RC, PF) uses about 400 mA but in stall condition, PF pulls out 1.3A. That's somewhere between 1.5C and 2C (for your batteries). Since we don't know what max current they can take, i'd say it's unsafe to use them. Another thing i don't know is the presence of PCM (protection circuit) or lack of it inside the batteries.

IF there is one (in each cell ofc), then it probably has max current and overdischarge protection. That means that u can combine any of the 2 batteries and the pack will last as long as the smallest of the batteries will last.

!!BUT!! if there is no PCM inside the cells, you'll probably end up with cell failure (the smallest one) or if u're gonna use it in an "emerald night" type of train, with a smoke (not really high probability since we're dealing with not that much current here, but it can happen) :D

http://diydrones.com/profiles/blogs/complete-guide-on-lipo-batteries]And a little guide on LiPo's[/url]

Edited December 2, 2013 by Bojan Pavsic