Cheap way to charge 28.8v, 8s4p battery pack

[PfloydBham]

I bought some 28.8v, 7.8 ah modules from battery hookup to experiment with. (https://batteryhookup.com/products/samsung-8s) . I am likely going to connect 5 to 10 in parallel via bus bars and charge then with solar panels. but, all test at right at 32.1 volts with one a 27.9v. I want to hook up some type of cheap/versatile way of charging the single pack so they are balanced. Then once assembled I want to be able to slow charge them from my home power source when I want. I am relatively new to the lithium world so I want to try to make something cheap and effective --- mostly for the fun of it. Right now my only chargers are little lead acid motorcycle chargers and Milwaukee 18v power tool chargers
Does anybody have any suggestions that might shorten my learning curve?
Thanks in advance,
Pink Floyd

 

[snoobler]

Keep in mind that theses are explodey-burny Lithium cells. Over-charging can result in damage and fire. These are among the worst possible ways to introduce yourself to the Lithium world.

I can't emphasize this enough. These are HORRIBLE in this configuration. They are useless and dangerous. The ONLY good thing about them is they are pretty cheap for 24 quality cells.

They did a good job marketing them and planting ideas that using them would be a good idea.

Until you absolutely understand these cells intimately and know how they work and the risks involved, AND understand how the existing BMS works, I wouldn't even consider trying to charge them.

 

[PfloydBham]

Thanks for your concern and warning. I am pretty cautious and am aware of the cobalt drawbacks. These particular packs all have a BMS built in. I have been running a tesla "S" pack in a travel trailer for over a year and it is all sunshine for me. I am not an expert but I understand their weak points and limitations. I am not trying to convince anybody to endorse what I am doing because it is not for everybody. I really do not mean to seem curt.
What I am trying to accomplish is basically some kind of inexpensive way to push a little under 33.6v in at about 1 to 3 amps. Most devices I see seem to work at under 30v. I am looking for lighting in a feral hog camp and I am going to be using under 200 watts per hour, and if it works out like I think it will, I may add an inverter or a converter to watch tv, charge devises, chase women, etc. I'll probably charge it with a used Santana 250 and an Epever SCC. I do not have a charger that will put out 33.6 volts so I can bench test my "little Frankenstein" other than hooking up solar panels for a temporary source. I do not know how to cheaply build a suitable charger so I am asking for suggestions

 

[Ampster]

I do not know how to cheaply build a suitable charger so I am asking for suggestions

The least expensive options for chargers are power supplies. They are a good tool to have if you get one of the $50 ones in the voltage range of your batteries. That way you can adjust your charging rate to suit your purposes. On this type you can adjust current and voltage.

An even less expensive option is a fixed power supply. Meanwell is an example of a good Brand but there are plenty of clones. These don;t come with fancy digital meters and knobs and you get a limited range of voltage which you have to adjust with a philips screwdriver. I have a 3.3 volt one that I can adjust to 3.65 for parallel top balancing and some others of difference ranges that I have accumulated for other batteries. They are essentially CC/CV two stage devices. the current is usually fixed and the price goes up by the Amperage that they can produce. Most are 120/240 AC volt input capable.

 

[PfloydBham]

Thank you. ----I have a little knowledge and, as you know, that is dangerous. ----
I have some devises I ordered form "china" that are cheap "buck converters". they step-down,---- and volts and amps are adjustable, with screws. I am thinking I can get a power supply out of an old computer (or something else) and run it thru this converter to set the voltage at the limit for charging these 8s packs. I think they run between 22.4v (2.4v/cell) and 33.6v (4.2/cell). I think I can use a multi meter to set the voltage coming out of the devise.
Anyway, I do not know all the stats for these components but it seems like there are cheap power supplies out there, somewhere, that will work for conditioning this electricity for sweet diet.
I don't mind standing around and monitoring the SOC to make sure it is safe, if I can learn how this fits together.
Does it seem like this can work? If not, what do I need to modify?

 

[Ampster]

I agree with @snoobler that eventually you will want to access the included BMS or add an external one so you can see if one cell group is a runner at the top or bottom. You can be the BMS with a good mulitimeter. My experience with Lithium is when a cell hits the knee of the curve it rapidly jumps up or down in voltage depending on which knee you are at. These packs may have been abused more than your Tesla pack and it does not have the individual fuses that your Tesla pack has. Enjoy. At least you are familiar with the NMC charge parameters from your earlier experience.

 

[PfloydBham]

I see what you are saying and respect your point. I just do not care if they burn up. Either way, I am going to learn something and its going to be where it really doesn't matter. If it works like the Israeli engineers designed it to work, I will have a workable unit. if not, it is toast. I might kill a fence post, but I still need to bring all my cells up to the common voltage to put them in parallel. I think I need a charge devise to do that.
Pink Floyd