Let's design our own UPS

Getting there on my project
Free salvaged 18650's
My 7S100P is almost complete
Taken over 3 months to test each cell
Average 2200mA each
This will be a 24v array (4.2v x 7 = 29.4 volts actually)
1540 amps @4.2volts
= busload
But the curve drops quickly to settle at 3.7v nominal so on this number we can calculate my power wall will be 5698Wh on average

Basically a 5killowatt battery bank

How do you test them?
 
With my Opus BT-C3100 charger
I measured the mA value
As well as the resistance, the lower the number the better, mine averages out at around 120 milli ohms
Nice. I didn't see them locally when I looked about 2 years ago. I have a Liitokala Lii-500.
 
Nice. I didn't see them locally when I looked about 2 years ago. I have a Liitokala Lii-500.
Bought mine here, not the best reviews on the power forums but at least it gives you a guideline
And that's all I needed
Are the cells good or phucked?

 
Bought mine here, not the best reviews on the power forums but at least it gives you a guideline
And that's all I needed
Are the cells good or phucked?

How long does 2200mAh take?
 
How long does it take to test one battery.
Aaaaah gotcha
Yeah pretty long
On average about 12hours per test
I test 4 batteries at a time
It will charge up to 4.2v
Then discharge to whatever
And then recharge to 4.2v
And then give a final reading
I just left mine on default settings
 
@Düber

Jirre I have the worst post Valentines hangover ever but I finally just got my inverter delivered after a month's delay.
The stock sizing of components for this thing couldn't be more perfect.... it looks like I'll actually be able to mount it to the trolley frame without having to mount wood or aluminium slats first, just straight up drill and bolt.

Can't wait to start the final build this weekend.

View attachment 1476433View attachment 1476435


View attachment 1476437View attachment 1476439
That fit on the trolley is perfect and looks nicely balanced too. :thumbsup:

That is going to work so nicely.
 
I still haven't bought my BMS yet.
Cannot find anything decent in this country
Thought about getting the Batrium from Australia but it is so damn expensive
 
I still haven't bought my BMS yet.
Cannot find anything decent in this country
Thought about getting the Batrium from Australia but it is so damn expensive

Could be fun to build you own BMS. But that's a lot of combustible LiPo. Edit: lithium.
 
Last edited:
Isn't there going to be a TON of soldering regardless?



My bad. But actually worse than LiPo from a flammability perspective afaik.
Oh for sure there is gonna be a ton of soldering.
700 cells
But why fabricate a PCB and then solder all the components onto it when you can just buy a BMS?
Ive never heard of anyone building a BMS before

I am not the tiniest bit afraid of the Li Ions, Ive been working with these 700 cells for between 3 and 8 years on a weekly basis.
I too this day of working with 18650 batteries have never seen 1 go up in flames in 14 years I have been here.
 
All 700 cells are Samsung, Sony, LG, Panasonic and Sanyo
None are the cheap ebay kak
I also weigh each battery
None are below 45 grams

Ive encountered a few fakes weighing 30 grams before with the cheap solar lights I buy on Takealot. Pure rubbish, I toss them out and replace it with a genuine 2nd hand one
 
Yeah I saw that. 7a seems kinda slow. But I can understand that you are trying to cut costs. I can imagine that your cost ex labour is close to 8K. Inverters, LFP batteries and LFP chargers are insanely expensive now.

A small pure sine inverter build in LFP charger would have been ideal for your build but I only see them without pure sine and only support for lead acid. e.g. this one https://leroymerlin.co.za/800w-inve...64&sfdr_hash=653c61a14bd5e2747653a47f1c7a0c0c
Correct, I target people that want to power small loads, and want the system to have decent components that will last long, not a easy thing to achieve if you try to keep the price low
 
Back
Top