Portable Mini 12V/300W "Powerwall" Project

TomTinkerDIY

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Howdy DIY Powerwall-ers! I am taking inspiration of building a DIY powerwall and scaling it down into a more beginner friendly project that isaffordable andhasa useful purpose. The goal of this project is to DIY a 12V power system which will run an 300W inverter which is intended to be used for light loads over many hours, or can take a modest load for a shorter period of time. I am starting a YouTube channel and build series for this project, so be sure to check back for updates as it all comes together.

 
Droid126 said:
I am actually thinking along the same lines. probably 1000w tho. I rent so whatever I build needs to be portable.

This is the mini project as a stepping stone to learn from before I tackle a 2000W system that runs off of a24V battery packand will have almost three kilowatt hours of power. The 2000W system will still be portable, but of course not nearly as compact as this 300W system I am building.
 
I've got roughly 600 cells that are 2000+ mah, I'm going to build 3 packs of 200, probably will use a plastic Stanley, rolling 50 gallon tool box to house it. I may or may not get some sort of solar charge controller. I'd like to be able to maybe run my fridge for a day or 2 if the power goes out.
 
Here is episode two, which tears into a (new) laptop battery to harvest its nine cells and start the process of capacity testing them:

 
12 volt is a great place to start!
 
Here is episode three, which breaks down the 36V eBay batteries and capacity tests them:

 
Here is episode four which looks at how well the used Dell laptop batteries tested, how well some Ultrafire Red batteries tested, how well some Ultrafire Yellow batteries tested, how well the eBay 36V pack batteries tested, and how well the no-name Chinese laptop pack batteries tested.

 
Droid126 said:
I've got roughly 600 cells that are 2000+ mah, I'm going to build 3 packs of 200, probably will use a plastic Stanley, rolling 50 gallon tool box to house it. I may or may not get some sort of solar charge controller. I'd like to be able to maybe run my fridge for a day or 2 if the power goes out.

I would go with 4S vs 3S for 12V, 14.8V for 4S and 11.1V for 3S nominal, 4S will result in lower current draw. Efficienciesacross the board should be better. Itwould also allow for a pack to fail and the system to continue to function with 3S for a limited time.
 
Also, the 3s pack has a limited Ah capacity compared to the 4s. The cut out for a 12V battery is about 10.8-11V. If you build a pack at 11.1V, you're not far from cutout voltage. Whereas at 14.8V, you have a lot longer run time well within the safety margin of the cells.
Remember, your car battery is charged up to 13.8V and the alternator puts out a charging voltage of about 14.2 - 14.8V. So most devices designed for 12V use can handle up to 14V input without issues. Usually they are designed for 16V max as they have a regulator to drop the voltage down (or resistors to kick it down; though not as efficient)
 
Scepterr said:
Droid126 said:
I've got roughly 600 cells that are 2000+ mah, I'm going to build 3 packs of 200, probably will use a plastic Stanley, rolling 50 gallon tool box to house it. I may or may not get some sort of solar charge controller. I'd like to be able to maybe run my fridge for a day or 2 if the power goes out.

I would go with 4S vs 3S for 12V, 14.8V for 4S and 11.1V for 3S nominal, 4S will result in lower current draw. Efficienciesacross the board should be better. Itwould also allow for a pack to fail and the system to continue to function with 3S for a limited time.
Hey guys been reading all the comments on this idea. I am most likely going to have to do the same due to where I live we have a lot of flooding. sometimes it can get to 10 feet in our yard. and since our house is on stilts I have no garage and no where to store a power wall. I am most likely going to convert a enclosed trailer into a portable power wall unit with solar panels and a wind generator on top.

As far as the 14.8 volt and the 11.1 volt goes I tried this with one 450 watt inverter I had and at 14.8 volt it would give me a voltage error. it was too high. I knocked it down to 12 volt +/- and it worked fine. only down side was it did not last long. I have not tried my 1500 watt or my 2000 watt yet. I am debating on making bigger packs or smaller packs in case something goes wrong. I know its a lot more work but I would rather destroy a 40 cell pack than a 200 cell or more. even though I am going to fuse it how everyone does I guess it still worries me that something will go wrong.
 
For those instances, it may be needed to use a buck converter to drop the output voltage closer to 12V. However, you need to make sure the buck converter can handle the amperage draw. You might need to make one.
You just dont want to run a battery pack at 11.1V as this is already lower than what the devices really need and will pull a higher amperage to compensate for the loss of voltage.

Remember, Voltage/Amperage is related to water flow. As the diameter of the pipe gets smaller, the higher the PSI needs to be to keep the same water flow. Increasing PSI puts a heavier load on the motor/pump shortening its life. Similar with batteries, lower the voltage the higher the amp draw, shortening the cells life.

So 4s is the highly recommended layout as it dramatically reduces the amp draw needed. As stated earlier, you may need a buck converter (or you can use resistors) to drop the voltage down.
 
I agree that a 4S configuration may be more ideal, but the real limit to how you configure a power system in based on the operating range of the inverter you're going to be using. In the case of this system, the inverter has a upper limit of 15V and a low cut off of 10V. A 4S battery pack is too much voltage when fully charged and may not allow the inverter to start up; also the low volt cut off drains the batteries to 2.5V which is a bit too low for my comfort. So the specifications of the inverter I chose decided how the batteries were going to be setup.

Using a voltage regulator to bring down a 4S battery pack to the inverters upper limit wastes power as heat and would reduce the over all efficiency of this system.

Here is episode five where I talk in more detail about the inverter and some of the numbers around how I planned for it to operate:

 
Here is episode six, which takes a look at the three battery chargers I use and the pros/cons of each:

 
Episode seven is here, and in it is a montage of half of the build process with some stress testing at the end. In the next video I will discuss some challenges I had in the build process and the results of that first stress test.

 
Here is a more detailed look at the battery pack for the Portable Mini Powerwall Project. It also talks about the build process, risks, and lessons learned:

 
1958 greyhound said:
How many amp are your fuses ?

Some of the cells look double fused ?

I used 20 AWG tinner copper wire for the fuse between the batteries and bus bars. This wire -should- be able to sustain 1.5 amps of current from each battery and will break between three and five amps of current.

Both the positive and negative side of the batteries were fused to the bus bars, but each side uses only one strand of the fuse wire.
 
20 awg is a bit too heavy. It'll hand 1.5 amps just fine. In fact, it'll handle close to 15 amps. Fuse wire at the cell-ular level should be no bigger than 30 awg, as this will blow around 7 amps.

Pos and Neg fusing is a good idea. Though, I haven't heard of both blowing, but I suppose it's just for the extra added safety :) Several of the big guys here are using dbl fusing
 
As Korishan said about the thicknes. 20AWG is high current :)

i dont "fuse" double sides in sense of using same wire. I have 20AWG or thicker on one side and then i have 35AWG on the other side for actual fuse. Just to make sure that the resistance is kept as low as possible.
 
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