Let's design our own UPS

wingnut771 said:
How long does it take to test one battery.
Click to expand...
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
 
RaptorSA said:
@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
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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
 
Pineapple Smurf said:
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
Click to expand...

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



My bad. But actually worse than LiPo from a flammability perspective afaik.
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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
 
Park@82 said:
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
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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
 
Jarrod said:
Throw in one of these and it can function as a ups

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It will impact cost tho. I kinda have the same small setup but with a victron inverter. So i can set at what volts the inverter must switch off to prolong battery life.
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Great find, pity they out of stock, cant find anywhere else,.....
 
leutwein said:
Great find, pity they out of stock, cant find anywhere else,.....
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Search outomatic transfer switch or automatic change over switch on takealot or geewiz. Not sure how to wire them but with enough time I'm sure you will figure the wiring out :)
 
Pineapple Smurf said:
I am adding a fuse to each cell so no I am going to be using Peter Matthews method (Youtuber)
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I would not recommend soldering 2nd life batteries. For 999 out of a 1,000 I'm sure it will be fine... but it just takes one to really mess up your day. Have a safety protocol in place while you build your pack, Lithium fires are difficult to put out if it starts with a cell in the middle of a 100P battery. Etc, etc

Consider spot-welding with fusable nickel
1676543727412.png

Question: when you where testing your cells, did you cycle them at 0.5A or 1A and did you track and remove cells that started to overheat ?
 
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kidcolt said:
I would not recommend soldering 2nd life batteries. For 999 out of a 1,000 I'm sure it will be fine... but it just takes one to really mess up your day. Have a safety protocol in place while you build you place.

Consider spot-welding with fusable nickel
View attachment 1477079

Question: when you where testing your cells, did you cycle them at 0.5A or 1A and did you track and remove cells that started to overheat ?
Click to expand...
500mA test
No heat issues
Very good cells
 
Pineapple Smurf said:
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

View attachment 1476677


Li-ion Voltage Analysis
Click to expand...

Let us know how this works out.
I want to build a custom battery for my electric dirt bike one day and this is the kind of skills needed.
It would basically end up looking something like this:

1676546844488.png

I'm s**t scared of building one though, seems like one neesd to really know what you're doing.
 
Düber said:
That fit on the trolley is perfect and looks nicely balanced too. :thumbsup:

That is going to work so nicely.
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Yeah, still blows my mind that all the components line up like this.
I even ordered my own battery terminal crimp tool and some cables and lugs so I can create custom cables so the build can be as clean as possible.

It's starting to make sense at this point to maybe build one or two more of these and see if people would be interested in buying them. No idea if there's a market though.
The closest competitor in terms of price/performance that I've seem would be something like this:

1676547210254.png

But honestly, those things are ugly and the batteries seem to be made using second life cells.
I think the Growatt inverter is also nicer if someone wanted to disassemble the trolley in future and turn the components into a wall-mounted home hybrid solution with a decent sized solar array and WiFi monitoring included.
 
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