Best power supply?

[Tobaganner]

So I want to use stuff like the powerfunctions and rc system, but the voltage drops with regular batteries and rechargeable batteries only offer 7.2 volts instead of 9 volts, and rechargable lego pf battery is super expensive. So, is there a rechargeable AA size battery with 1.5 volts that maintains steady voltage?

[mocbuild101]

8 hours ago, Tobaganner said:

So, is there a rechargeable AA size battery with 1.5 volts that maintains steady voltage?

Short answer: No

Long answer:

There are Ni-Zi batteries, which have about 1.6v-1.8v when charged, but that small increase in voltage (0.3v x 6 = 1.8v = 10.8v) can damage Lego PF/RC - so they are best avoided. (unless you modify the battery box to limit the voltage)

I personally would recommend the 1.2v Ni-MH Panasonic Eneloops - they outperform all other types of Ni-MH batteries, and are actually much better than normal alkaline batteries. I've found that they come very close to alkaline, because they maintain a more consistent voltage - and therefor end up having a higher voltage than alkaline batteries after very little use.

Here are the comparisons:

• Alkaline:  + has perfect 1.5v  - not rechargeable, don't last very long, voltage very drops quickly, and are prone to leaking
• Ni-MH:  + lasts much longer than alkaline, can be recharged many times (up to 2100x for Eneloops)  - has lower 1.2v starting voltage (but is more consistent)
• Lego PF Lipo:  + higher voltage than Ni-MH (8.4 volts when fully charged)  - VERY expensive

[Jurss]

You can use 9V battery, just buy 

and solder to some LEGO battery wire. Yes, You will need to sacrifice some battery box, to get LEGO connector.

[mocbuild101]

21 minutes ago, Jurss said:

You can use 9V battery

Except that it's not rechargeable, and isn't AA size...  (not to metion that it doesn't last very long)

10 hours ago, Tobaganner said:

is there a rechargeable AA size battery

 

[Jurss]

OK

https://www.amazon.com/Rechargeable-li-battery-LEDflashlight-4SlotsUSB-SmartCharger/dp/B00SXV9Z4U/?tag=metaefficient-20

but in LEGO case we will need to buy two, and it is allready close or even more expensive than LEGO li-po box.

Edited October 2, 2017 by Jurss

[Tobaganner]

On October 2, 2017 at 12:09 AM, mocbuild101 said:

Short answer: No

Long answer:

There are Ni-Zi batteries, which have about 1.6v-1.8v when charged, but that small increase in voltage (0.3v x 6 = 1.8v = 10.8v) can damage Lego PF/RC - so they are best avoided. (unless you modify the battery box to limit the voltage)

I personally would recommend the 1.2v Ni-MH Panasonic Eneloops - they outperform all other types of Ni-MH batteries, and are actually much better than normal alkaline batteries. I've found that they come very close to alkaline, because they maintain a more consistent voltage - and therefor end up having a higher voltage than alkaline batteries after very little use.

Here are the comparisons:

• Alkaline:  + has perfect 1.5v  - not rechargeable, don't last very long, voltage very drops quickly, and are prone to leaking
• Ni-MH:  + lasts much longer than alkaline, can be recharged many times (up to 2100x for Eneloops)  - has lower 1.2v starting voltage (but is more consistent)
• Lego PF Lipo:  + higher voltage than Ni-MH (8.4 volts when fully charged)  - VERY expensive

What is the lowest voltage that the eneloops get to

[Tobaganner]

Would this 2 cell lipo work? https://www.hobbyzone.com/batteries/lipo/2-cell/DYN1422.html

[Toastie]

3 minutes ago, Tobaganner said:

Would this 2 cell lipo work? https://www.hobbyzone.com/batteries/lipo/2-cell/DYN1422.html

They would work perfectly well - in fact the >cells< in the LEGO rechargeable LiPo box are less powerful. BUT: The thing is to charge them "intelligently". And this is very important - otherwise you may destroy the cell pack easily. The charging electronics is somewhat fancy. You can get that for relatively small money as well. But then you need to build your charging "infrastructure".

To be quite honest: The LEGO LiPo is really expensive. But it is a beautiful piece of engineering. I have tested that thing extensively and simply could not break it; here are some of the results 

If I were you, I'd save some money, go on BrickLink and get the LEGO rechargeable battery for a decent amount of money. Did that a couple of weeks ago ...

Best
Thorsten 

[mocbuild101]

19 hours ago, Tobaganner said:

What is the lowest voltage that the eneloops get to

If you look at the discharge curve, you can see that it will stay above 1.2v for most of it's discharge, however - to answer you question - it will go down to about 0.9v.

You can also see that the curve of the alkaline batteries is much steeper, and they drop down below 1.2v much quicker than the Eneloops - even though the captivity is similar.

In this example, RED = Duracell Ultra AA (alkaline), and BLUE = Eneloop AA (Ni-MH)

 

19 hours ago, Tobaganner said:

Would this 2 cell lipo work? https://www.hobbyzone.com/batteries/lipo/2-cell/DYN1422.html

Yes (I have previously had successes using something similar), but like @Toastie said you have to charge them very carefully. And another thing, they should NEVER be discharged below 3v/cell - as they will be damaged, and possibly destroyed.

Edited October 5, 2017 by mocbuild101

[MangaNOID]

6 hours ago, Tobaganner said:

Would this 2 cell lipo work? https://www.hobbyzone.com/batteries/lipo/2-cell/DYN1422.html

thanks to @Attika and his youtube how to video, I have been converted into using these batteries. great if you dont mind a small bit of non-purism.

for $30 ish AUD i got 6x1200mah batteries including smart charger. 

great for sbrick/buwizz where its easy to monitor voltage in batteries.

I have pretty much ditched 24 rechargeable aa Ni-Mh batteries (well i'll still keep them for when purism is required) as the power difference (lack of dropping output voltage) was very noticeable.

[mocbuild101]

Just now, MangaNOID said:

I have pretty much ditched 24 rechargeable aa Ni-Mh batteries (well i'll still keep them for when purism is required) as the power difference (lack of dropping output voltage) was very noticeable.

I bet you weren't using Eneloops... I did once have duracell rechargeables, and I also found that they were lacking in power - but that all changed when I got some Eneloops.

And yes, I'm a big fan of Eneloops

[MangaNOID]

You are correct! No eneloops,  energizer.

there is a similar chart to voltage drop off on philohome.com of energizer that looks like the chart you posted. 

When using 8 motors on my 42042 these li-po hold the torque up till the last drop...3-3.5v or so anyway as you mentioned.

[Toastie]

OK, I guess we need to get this a little more into the clear.

The discharge curve of the "eneloop" vs "alkaline" batteries as shown above is simply not true - with regard to the Alkalien curve. You can google "alkaline discharge curve" and you will see a rather flat profile for all alkalines - it is in their (chemistry) nature. Of course it depends on model and make and most importantly on their nominal capacity. There are so many different manufacturers. Some are reliable, some are not. The same holds true for NiMH cells. It does nor get any flatter on the sustained current drawing curve - provided you adapt your power draw to the cell capacity (or the other way around). Drawing current into 8 motors with poorly matched overall cell capacity will just - cause pain. I am using some China 2200 mAh NiMH cells - and believe me, they are doing very well. I guess I was lucky ... 

All the best
Thorsten 

   

[mocbuild101]

Just now, Toastie said:

The discharge curve of the "eneloop" vs "alkaline" batteries as shown above is simply not true - with regard to the Alkalien curve.

Maybe that wasn't the best example... (rather a example of me using the first image I found )

I have changed the image in my post above - are the curves more realistic now?

 

[Toastie]

1 hour ago, mocbuild101 said:

Maybe that wasn't the best example... (rather a example of me using the first image I found )

I have changed the image in my post above - are the curves more realistic now?

Hey, nothing is wrong! And I did not want to be rude (!), I guess this is because I am sometimes teaching electrochemistry classes and alkaline vs NiMH chemistry is usually on the final exam.    

Both images are perfectly fine - with appropriate information, they entirely make sense and are reliable. Just look at this data sheet this data sheet provided by Duracell. You can find your original image (high constant current) as well as the one you updated (lower constant current). It just depends on how you would plot the data. And this is what people sometimes simply overlook. Or some people accidentally plot ...

All is good. And you are right: The chemistry in NiMH does allow to draw higher sustained currents without significant voltage drop, provided current and cell capacity match. And yes, you are right: It appears as if the folks at Eneloop do very carefully design their products. Quality should always win, but then there is marketing.

Best regards,
Thorsten

   

[mocbuild101]

Just now, Toastie said:

And I did not want to be rude

You weren't, you just (helpfully) corrected me. 

Just now, Toastie said:

It just depends on how you would plot the data.

Agreed, and also, it's important to compare them using the same discharge rate, which I doubt my original image did - which would explain the huge difference between Ni-MH and alkaline.

Just now, Toastie said:

Quality should always win, but then there is marketing.

Yeah, and it's all that marketing that makes it so hard to compare!

[aminnich]

If you can fit a car battery, go for it!! They might a little heavy, but you can power all then motors you want!! Just take it out of your neighbors car and you have a power source!! :D 

Of course I'm kidding,  never do that!!! 2 car batteries is really the way to go.... JK JK