12V 2KW DC battery

smunx

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Apr 14, 2018
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Hi All,

I am working a distributed computing platform, and most of my devices require a 12V power supply. I want to build a battery pack with 12V DC output and close to 2KW and I want to stick to Lithium-ion batteries. Most of the time I work with low power devices and embedded systems.

Here is my list of questions.

  • Since I am going to connect 4 units in series with output will be higher than 12V. What is the best way to get a 12V DC regulated output from the battery system?
  • Everything in my computing system runs of DC voltage. I will be charging the battery system using solar panels, but I also want to have a provision to charge the battery system using wall power. What is the best way to do that? Can a solar charge control do the job?

Thanks
 
1) Welcome to the forum
2) Buck regulator
3) Either get a hybrid charger/inverter, use a contactor or manual rotator switch to select charging method

These have been answered several times in the forums. If you browse and do a search you will see loads of information about 12V setup and the requirements to use such a poor configuration. Pros/Cons/Costs involved.
 
2kW for how long? 24hrs a day would just kill batteries unless you've got serious sized packs & equally serious charging source(s).
2kW is high current for 12V.
Voltages of packs of Li-ion also don't line up well with 12.0V
You should probably look at a 24V pack & decent stepdown converters to get more accurate 12V.
 
Yes, I am aware of the problem with creating 12V it's more like close to 15V I will see how hard it can be to design a buck converter for each of my load. Because each load will draw at most 5A at 12V. The reason I don't want to use a converter is due to the power loss. But I am still in an experimental phase I finalized nothing yet.And coming to usage I might just need it for 12-18 hrs/day.
Please check the attachmentfor my setup. The 40AH modules are readily available so I just want to go with it for now.

I would like to know what is the best way to charge these modules. What charger should I use? it would be helpful if you can share some links. I cannot take these modules apart there are 20 cells in parallel in each of the module.

Thanks

image_owmexz.jpg
 
If you want to find an efficient converter, look for ones saying "synchronous rectification", these can be 90%+ efficient.
If you put 15V+ into 12V computer kit, I'd reckon there'll be magic smoke & tears ...

You're doing some numbers there right?
1x 5A current will empty a 20 cell pack battery bank like the drawing in ~ 9.2 hrs (= 2.3AHrs/cell x 20 cells/5A)
ie might need a lot more of the 20 cell packs in parallel.
 
You can use the LM2596S Buck Converter that is found on eBay to do the conversion. If your input voltage is over 20V and output is 12V, you'll get close to 90% or better on efficiency. Altho, it's max output current is 3A. But you could always put 2 in parallel (with a couple of diodes to negate possible back-feeding) to get higher amps. They are relatively cheap and there are at least 2 variants to choose from. The base does voltage output adjustment, the others have current clamping to set the max output current.

When you are needing 12V power supply and using LiIons to store your power, it's not about efficiency. It's about protecting your devices and the cells and getting the most power of them. If you take LiIons and set them for 3s, you loose a lot of run time due to voltage drop under load. If 4s, you loose a lot of capacity because you can't fully charge the cells (if you do, as Redpacket said, you can get magic smoke). But going with 24V setup you gain back most of that lost capacity and if you use buck converters, you can actually gain all of it back as you can charge to fully capacity and discharge down to 3.2V/cell safely.
 
Just some thoughts

Your distribution will be more efficient at 24v
You can use a step down DC-DC at each load vs one big converter
Your load might not like voltage fluctuations, you might need a buck or buck/boost converter stabilizer regardless.

Not sure if this is possible, but can you connect two of the loads in series creating a more compatible 24V voltage requirement?
 
If you must go 12v, you can use buck or boost converters. The best option would be to source LiFe cells. 4s, a far better match for a 12v system. Also LiFe cells have a nice flat discharge curve, so they maintain their voltage until they almost completely discharged.

Personally if I were looking at 12v from Li-Ion, I would build a 6s battery and use a 24v to 12v buck, as they are readily available.
 
What is the best charger for charging 20 Li-ion batteries at a time?
I will post my updated design soon.
 
There isn't any single charger that can do 20 cells at once. The most I've seen is 4. If you go custom built, then that'd be with TP4056 style boards that people have built whole arrays out of and using a computer power supply for the current. Other than that, there isn't any, non-industrial/commercial anyways.
 
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