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My Lithium Ion power bank
#1
Hi all

Attached are some pictures of my Lithium Ion power solution for my WeatherDuino station. The batteries are 2400mAh 18650's in a 3s5p solution, giving me 12.6v and 10Ah. The solar panel is currently 50W but I may down size that to 25 or so if the batteries are working well. 

The solar charger is designed for Li-ion batteries (and others of course) but all the voltages for charge, low voltage cut-off and restore are configureable over a wide range. Not bad for a $12USD unit! It is only PWM but I will keep an eye out for an MPPT controller at some stage in the future.

I still need to do some work on the mounting in the box, it's a bit cramped. A job for another day  Big Grin 

Cheers from NZ

Colin


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41south.net.nz powered by WeatherDuino and Weewx
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#2
Nice job!
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#3
Very nice.  Smile

But, should't acupack have a balancer or other protective electronics?
Best Regards
Zdenek

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#4
Hi Colin,

great job, you have a nice battery assembled.
The good 18650 Molicells  Wink 

As hornychz I would recommend to add some protective devices. State of the art, as posted for example in the IEC 62133:2017, contains the following:
  • Overcharge and overdischarge protection of the whole battery - should be active under 3*2,5V and above 3*4,20V in your case.
  • Overcharge and overdischarge protection of each parallel branch, otherwise in case of a disbalancing one parallel string could be overcharged or overdischarged
  • Overcurrent protection in charging and discharging protection
  • Temperature protection, in your case at least two temperature sensors on the cells would be appropriate
  • Balancing circuit to ensure long lasting performance, otherwise the usable capacity will be reduced very quickly
Idea This is only a basic information and guideline - the whole standard demands much more. Idea

If you need additional advice, just let me know.

And be careful, flying and red glowing cell cans can be nasty - I'm not joking in this case  Exclamation 

Best regards,
engolling
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#5
Hello gentlemen

Yes indeed I should mention the protection mechanisms already built in.

The solar charger unit provides charge over voltage protection which is set at 12.6v for these batteries. It also provides over-discharge protection set at 9.2v as per the recommendations of my battery supplier. The unit disconnects the load at that level. It will not reconnect until 10.5v currently - this is all automatic and well tested by me. There is also over current protection for both charge and discharge. 
What is not here (but will be very shortly) is the balancing board. I have these ordered and will fit them shortly. Temperature wise the solar controller has an internal temp sensor but I will look at something for the batteries perhaps as well - thanks for that suggestion!

And indeed flying red cans are not a good sight, I will avoid them at all cost  Big Grin

Thanks again for the feedback and comments

Colin
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#6
Perfect.  Heart
Please, inform us. Good luck.
Best Regards
Zdenek

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