Batteries and Battery Packs

[Philo]

All you ever wanted to know about batteries and battery boxes to power your Technic or MINDSTORMS creations - discharge curves, capacity, voltage under load, current limitations...!

The results of an extensive test campaign are summarized here.

Here's the kind of data you'll find:

Enjoy!

[Tomahawker]

Philo, thanks for compiling this information and placing it alongside your very helpful information on Lego motors and sensors.

Aside from the value of having this information readily available for Technic and Mindstorms applications, it's great information on a purely academic level.

[clarkdef]

This info is always a huge help, in my understanding of how all this works. Cheers. Now time to study it.

[Hey Joe]

Hey, that's quite useful. Many thanks.

Maybe a mod could cross-post this over in Train Tech?

Joe

[Blakbird]

I am surprised to see that the capacity of the PF Li-Po is so low (~1000 mAh). Considering the size, you can get R/C 2 cell Li-Po's that size with 3 times the capacity. Do have any idea if the actual lithium cells are flat cells or round cells?

I am also surprised to see that the starting potential of the alkalines is not closer to 9V.

[Someonenamedjon]

You can also use a 9v battery for your nxt easily, you just have to attach the wires to the right spots of it will short.

[Alasdair Ryan]

Philo have you done any detailed tests on a geared up buggy motor connected to a PF li-po?

My buggy motor seams to get overloaded and slow down when I connect it to a centrifugal regulator and gradually up the speed....

[GuiliuG]

Thanks for these helpful informations. Seeing the alkaline curve (beginning at 8V), I'm wondering if your measure appliance doesn't own a 'systematic error' ?

[Philo]

I am surprised to see that the capacity of the PF Li-Po is so low (~1000 mAh). Considering the size, you can get R/C 2 cell Li-Po's that size with 3 times the capacity. Do have any idea if the actual lithium cells are flat cells or round cells?

Nonetheless, result is pretty close to rated capacity (1100mAH). Maybe cell choice was more oriented towards safety than capacity? Cells are flat, see photos at the end of page.

I am also surprised to see that the starting potential of the alkalines is not closer to 9V.

Thanks for these helpful informations. Seeing the alkaline curve (beginning at 8V), I'm wondering if your measure appliance doesn't own a 'systematic error' ?

I was kind of surprised too... But no systematic error, or it would affect all cell technologies! The problem is that I used a pretty high current (750mA), typical of what we use in heavy duty applications (eg. trial truck) but actually above "normal" usage for alkaline cells. See for example this Energizer datasheet, their constant current performance test is done at 250mA. Higher current test (eg. 1A for photoflash) is done using low duty cycle intermittent discharge (10s/minute). Look at my 250mA discarge curve, it does start at 9V and is very similar to datasheet discharge curve.

So many parameters to test... and with non-rechargeable cells it's kind of expensive ;)

Philo have you done any detailed tests on a geared up buggy motor connected to a PF li-po?

My buggy motor seams to get overloaded and slow down when I connect it to a centrifugal regulator and gradually up the speed....

No detailed tests, but buggy motor is a real power hog. If you gear it up, friction in gears may well make it consume more current than what PF battery is able to provide (about 1A)

[chorlton]

Perfect timing. I was just looking at buying Ni-Mh AAs esterday and trying to decide on energizers over unbranded.

Thank you Philo!

[sunnykoomos]

Thank you for this useful information.But I have a request,can you test the max current output of the rc unit?

[Philo]

Thank you for this useful information.But I have a request,can you test the max current output of the rc unit?

Sorry, I don't have one!

[Blakbird]

Nonetheless, result is pretty close to rated capacity (1100mAH). Maybe cell choice was more oriented towards safety than capacity? Cells are flat, see photos at the end of page.

Thanks, I hadn't noticed those photos. I can see now that the cells occupy only a very small portion of the internal volume, so that explains the relatively low capacity for the size.

[clarkdef]

Thank you for this useful information.But I have a request,can you test the max current output of the rc unit?

I am curious of this too.

Has anyone tried hooking 3 or 4 buggy motors to it? It may not be the unit that says no to the extra current demand, it would most likely be the batteries.

I have hooked my buggy unit up to a DC power supply and 9 volts from that, destroys 9 volts from any battery, as it can have up to 25amps drained.

Wouldn't hook more than two motors up to the unit when being powered by the DCPS though! Might burn out the transistors!!!