Questions about my first 14s4p battery. Pics Inside

[turbodsm21]

So two months ago, I wouldn't have known what an 18650 battery was. Yesterday, I used one pack I built to power a vacuum and leaf blower just to see if I could. I was pulling 1200 Watts from the battery as measured by my plug-in meter (belkin power monitor).

I'm using Panasonic NCR18650B cells. Each one tested to nameplate capacity. So they give me 56 * 3.4 A = 190.4 AH. And around 700 watt hours.

I soldered 12awg leads on and connected to to an 48v inverter through a 50amp fuse just to test this out.

How I built the pack:
6mm X 0.15MM pure nickel stripes.
Sunkko 709A
Hot Glued together
High Temp tape to prevent shorts.
Will wrap in SBR sheet before heat shrink wrap a a final step.
BMS not installed yet.

Here's what I was able to measure.
Pack voltage was 58.3. It did not drop any voltage in over a week since I built it.

After running the devices, I think I would have measure 48V on the pack. This was after running a vacuum and leak blower for a good 30 mins.
I say I think because I did not get a chance. Individual cells were around 3.42.

So I have some thermal imagery of my pack. I was concerned about the temperatures reached. I wanted to cool down the batteries so I started to poke holes in the tape between the cells to increase convection. I screwed up and hit a cell. It hissed and released a gas and I nearly shit myself.I thought i was about to watch the whole battery go up in flames in my drive way.

Lucky, It did not go any further but as a precaution I ripped apart the battery right there to isolate that cell. The cell still reads 3.4V but I will not be using it obviously.

So was I trying to pull too much power from my pack?
Do I need another row in parallel?
Thermal images show the cells were about 170F. Is this a problem?
Are the welds ok?

I think some of the hot spots in the thermal images are from the tape. The nickel strips show up cold because they are shiny essentially. Metal usually needs to be painted to get an accurate temperature off it.

Here's an Album of more thermo pics and pack.

 

[redilast]

You are pulling too much power from those NCR18650B’s for regular use. Those cells have a max discharge current of 2C, but are ideal for <1C. They are laptop grade cells, not power tool grade cells.

For a 14s4p pack probably want to keep total power draw below ~650W, which would be about 1C. If you were pulling 1200W AC power from the inverter, then you were likely consuming 1400W or so from the pack itself, which is greater than 2C discharge, and not recommended for these cells especially without good cooling.
170F is far too hot for normal use as well. Ideally I wouldn’t be comfortable with a pack that exceeds 50C/120F on a regular daily use.
Also those are some wild looking welds, how’d you pull that off? Home made welder?

 

[turbodsm21]

I have a sunkko 709a. When you say wild, do you mean bad?

I picked the cells for capacity. I will consider going towards ones with a higher discharge rating. However, this was a stress test.

Here's another shot of my welds. https://imgur.com/jXiLlTX

 

[redilast]

I have a sunkko 709a. When you say wild, do you mean bad?

I picked the cells for capacity. I will consider going towards ones with a higher discharge rating. However, this was a stress test.

Here's another shot of my welds. https://imgur.com/jXiLlTX

I see way more welds than needed and also maybe its turned up too high, as it appears that excessive power/heat is discoloring the metal. Looks like the metal has turned blue around some of the spot welds in this picture: http://i.imgur.com/NafS8g9.jpg

I'd stick with like 6 welds per cell IMO. More welds are not really going to help.

What's your planned continuous load for this pack? Might want to add more cells in parallel if you can so you can stay at or around a 1C discharge for normal use for this type of cell.