Design of 24v battery pack need some advice

Greetings all !

I just found the forums the other day and have already learned so much ! ! !

I have a question about setting up a 24v system with the 18650s.... I have a project that is a work in progress. Company that I work for is getting into the ISP business. We want a way to be able to power some APs that can be powered with a POE. We found a TP-SCPOE-2424from Tycon systems however there are some issues that I discovered with what was ordered. The original plan was to do a 7s7p setup which would give us the 24v and 42Ah ( batteries are rated at 6000mAh ) total for the setup. The charge controller is not adjustable really, it will do a charge voltage of 24v.

I have read the threads and realize that there are a lot of considerations to take into account with charging to make sure that you don't get a premature 4th of July or at minimum cause issues with the cells. Is there a way with the charge controller that we purchased to be able to safely charge our battery setup ? What additional protection could/should be put in place with this sort of setup ?

Thank you all in advance ! ! !

Welcome...

If the charge voltage of the charger is not adjustable, you can not use a 7s setup...to charge the cellsfully,you need voltagebetween 28,7v and29,4v(4,1- 4,2v/cell) and somekind of CC to get there.

Maybe you can post the specs of the chargecontroller so we can have a look.
We do like that stuff

Beside the charger, you gonne need a bms also.....

Looking at the TP-SCPOE-2424-HP datasheet it appears that it will charge to 27.3v +/-.5v overcharge protection 28.6v +/-.3v The PoE 24v output is regulated to 24v The secondary output is 20-25v. the user manual states a different number
The charger would charge the cells to 3.9v-4.13v per cell (26.8v-27.8v)
over discharge protection is at 20v +/- .3v 2.8- 2.9v per cell (19.7v-20.3)
I would contact Tyconsystems.com and find out if the model ordered is compatible with lithium batteries

The 6000 mah 18650's are most likely fake I once bought some 5800 mah 18650 before I knew better they tested out at 400 mah to 600 mah

The top end seems good. The lower end seems a little low, but doable. If it only gets to a max of 4.13V per cell, then that'd be fine. At that point, you don't really need to switch from CC to CV mode while charging.
The low end of 2.8V is a bit too low, imho. You could add a little extra circuitry that would shut down before the cells get that low, say around 3.1V

Really curious about the cells that are rated at 6000mAh. Please post what they are and where/whom you got them from.

Korishan said:

The top end seems good. The lower end seems a little low, but doable. If it only gets to a max of 4.13V per cell, then that'd be fine. At that point, you don't really need to switch from CC to CV mode while charging.
The low end of 2.8V is a bit too low, imho. You could add a little extra circuitry that would shut down before the cells get that low, say around 3.1V

Really curious about the cells that are rated at 6000mAh. Please post what they are and where/whom you got them from.

Click to expand...

I wasn't the one that got them but can post a pic of the cells.... As I wasn't the one that ordered no idea but from all that I have absorbed from finding the forum have concerns if legit etc about the cells...

Iam in the caribbean and we got whacked by back to back superstorms, the office we have projects for but for me personally taking the idea of this for new solution. Powergrid in VIrgin Islands is still a mess and when up kwh is about .38c-.40c ..... really interested in this but want to do in baby steps for my personal rig.

Can post more details if needed with regaards to this project....

Here is a pic of 18650 that we got for office, do not know where we got them from, still trying to find out

I know where you got them from. These are from your nearest friendly chinese merchant (or local merchant who imports and resells these cells) and are a scam. There are no 18650s with 6Ah capacity, it is not possible with todays technology. 3.5Ah is the maximum for 18650s. The cells you got may be as bad as ~500mAh, depending on what is actually inside them and how much current you want to draw. It could be a smaller lithium cell, maybe some sand to add weight, a used and rewrapped 18650 or a homebrew chemistry made from chinesium and magic.
The best you can hope for is one of the latter, a rewrapped cell, maybe rejected due to QA, or a homemade cell. In this case the cell might have around 2Ah@1A.

Whatever it is though, it isn't a proper 18650 cell. The only thing these cells and proper 18650s have in common is the size.

Garbage, rubbish, trash, refuse, detritus, and any other synonym you can think of.

I hope you guys didnt buy a very many of them

Korishan said:

Garbage, rubbish, trash, refuse, detritus, and any other synonym you can think of.

I hope you guys didnt buy a very many of them

Click to expand...

Sadly 100 of these were purchased...... Haven't got a chance to test them yet because haven't got/designed the proper initial charger system. Then again from what you guys are saying it sounds like a waste of time to put a lot of effort into these

lol FAKE

Well, 100 is better than a 1000. I wouldn't waste the time testing the so-called 6000mAh cells. They will most likely test under 1000mAh. Then look out for more realistic values of around 3000mAh new, or some lesser value. Unless you go with LiFePO4, then those can be higher.

Always cross reference with the part number of the cell before purchasing.

LiFePo4 will be lower in 18650 form

You could try your luck and test them. The problem is they will probably not be the same (they aren't made according to a specsheet as proper cells are) and the differences can potentially be huge, so you'd have to test them all or none at all. Just testing a few to get a reference is probably not enough.

And also, have a look at this for proper cells: https://eu.nkon.nl/rechargeable/186...op/brand/lg-panasonic-sony-samsung-sanyo.html
Now, this is NKON, the only proper wholesaler for 18650s in Europe as far as I know, and you probably can't buy there if you live overseas. But all of these cells a legitimate 18650s that are sold by the big five manufacturers LG, Sony, Samsung, Sanyo and Panasonic basically worldwide. And while you probably can't buy at NKON you can use this list as a reference, many of these models will probably be available in your part of the world. You will get a feeling for what is a realistic claim for a 186550 and what isn't. If a particular cell isn't listed there it doesn't mean it's a fake obviously, not all of them are on offer at NKON. As long as they are made by the big five and sold by a reputable seller you won't have any issues with any model of cell as long as it meets your requirements.

The absolute maximum as of now is 3500mAh of capacity OR 30A continuous discharge. Not both, this is important. If you need high capacity AND high current you are probably looking at around 3000mAh/20A as the best compromise. Cells with higher capacity will have lower continuous current and vice versa.