Simultaneous measurement of charging current and cell voltage during charging.

[sirhc]

I think I've figured out a simple way to simultaneously measure the charging current and cell voltage while charging a Lithium cell. I searched the forum for clues and came up with this design which may be obvious to some but it wasn't to me.

I cut some 1/4 inch strips of thick aluminium foil from an old take-away food container and a 3/8 inch strip of thick plastic film from some old plastic packaging and sandwiched the plastic film insulator between the aluminium contact strips with double sided adhesive tape. I used mini-alligator clips to connect two multimeters to the aluminium strips. Seems to work OK.

 

[Kremer]

yep, that looks perfect.

 

[Light Sabre]

I had already thought of that idea, but didn't have a way to draw it in such an excellent manner. I have some DVM's that have an RS-232 output and could collect the voltage and current data and plot the result with Excel.

 

[Norm]

:welcome: I think you'll find double sided circuit board to be a tidier solution for the positive contacts.
Cheers Norm

 

[sirhc]

Light Sabre, I created that diagram in Excel. It's a very useful program. I now wish I had a data logging DMM.

Norm, I agree the double sided circuit board would be a much tidier solution and would also allow for soldered contact leads for a more permanent setup, and that will probably be the next step. Having read so many posts referring to current and voltage measurements, I was stumped on how to measure the current until I read a post which referred to the d.s.c.b. but since I don't have any d.s.c.b. yet, this was just a quick solution so I could test my recently purchased DX sku.13820 charger and sku.20392 cells to see if they were behaving themselves during charging.

After reading so many threads here about Lithium cell explosions, I'm a bit nervous about playing around with these things. My new sku.17401 flashlight should arrive in the next few days and it will be with trembling, sweaty hands that I insert the 18650 cell and push the on-switch! I built numerous rockets, cannons and bombs when I was a kid and survived my pyrotechnical phase unscathed and with all fingers intact, but I have now lost the desire to see things disassemble themselves spectacularly and am still wondering if I shouldn't stick to my pathetic old Eveready 2D-cell torch.

Cheers Chris

 

[Light Sabre]

Light Sabre, I created that diagram in Excel. It's a very useful program. I now wish I had a data logging DMM.

The logging DMMs that I use are Radio Shack cat# 22-812. It's only $70 and comes with leads, RS-232 cable, and logging software. The software is OK, not the greatest, but gets the job done. The only thing I really don't like about the software is that you can't import a saved data file to view it again. You just have to do all the analyzing, zooming, etc before you save it. You can print out whatever is on the screen. Screen capture is another way to save the graphed data. The saved data is in ASCII, but the data from the DMM to the computer is in a proprietary format, so you have to use their software. Anything the DMM can read by itself, can be saved on your computer.

I found another data logging DMM at a local electronics store, but by the time you purchase the DMM, then the cable, then the software separately it costs something like $150-170. Their software might be better tho.

 

[Mr Happy]

The logging DMMs that I use are Radio Shack cat# 22-812.

Yeah, that meter is pretty neat. I kick myself that I didn't buy it when I saw it on sale at $49.99 or something like that.

I think better logging DMMs might be available on the web, but for something available in a B&M that meter is hard to beat.

For data analysis you might want to just dump out the raw data and do your graphing in Excel.

The data stream from the meter is not too hard to decode; you can find information out there on the data format if you look. I've been toying with writing my own program to collect data from the meter instead of using the provided MeterView software, but honestly, programming can be something of a chore when someone else has already written the program for you. Putting my programmer's hat on, I have discovered that the data protocol does not allow a reliable and fault tolerant way of handling the input stream, so there is always a risk of missed samples. Sometimes it just doesn't pay to look under the covers and peek at things that are not meant to be seen...