That does seem more convenient. I wonder how well voltage-based SoC monitoring works with LiFePO. I'm so used to it being supper crappy with the SLAs in the Ryobi that I thought measuring actual current would be a much better way. But I suppose we can always calibrate as needed against the...
I thought your situation was different in that you just never top-balanced them in parallel. The procedures outlined by Will Prowse and Filter Guy both recommend to pre-charge them in series (if SoC is not already close to 100%) as long as it is followed by a parallel top-balance. So I will...
Did you end up pulling the trigger on these? I'm looking at these same cells to make a 48V 100Ah battery pack. At this point I have 2 concerns:
1) Just by looking at the product images, those ring terminals seem kinda small for their rated 100A continuous / 200A peak, no? They say the rings are...
I tried with mine to keep it over 50%, but wasn't always disciplined enough and a few times got far below. But, the percentage displayed in the stock gauge is based on voltage, not on true SoC, so it's kinda meaningless to begin with.
2 years in, I was only getting about 20 minutes per charge...
Cool! I hope to get my batteries ordered soon so I can catch up with you guys. This is all very exciting.
Once you have the charger stuff all figured out, do you plan to keep it plugged in through the winter?
Thanks @Hedges. Yes, I will use the BMS for this step. I will do this on a bench top so not worried about assembly/disassembly (considering the ~160 hours it would take to set them up in parallel at their current 40% SOC).
Very interesting idea!
58.8 V? That would make the average cell voltage 3.675, which is no good. What are the voltages according to the overkill app? Hopefully this is a typo or you have a very bad multimeter. Can you share a screenshot of the app? Are you confident that you installed all the balance leads correctly...
Thanks for the tip. So you don't think hitting the original torque spec using a torque wrench is sufficient? I suppose that might make it slightly under-torqued on the threads which I thought would be a safe bet.
Nice, Jack. That looks great! Those are some serious drawings. I love the power distribution block coming through the box and how you are including the original tie-down clamp.
What happened to your mower?
That's amazing. Is that an acrylic mount for your shunt? Did it come with it or did you make it? I'll wait to see what @AMDPower says about his new monitor and I might just get the 100A version as well. It's nice to be lagging behind you guys, haha!
Do you guys have any thoughts about...
Here's another question (or 2): Once the current starts dropping when top balancing in parallel, does the current drop to zero at any specific time rate? Mine left the 3A limit about an hour ago and is now at 2.5A. Will the current eventually plummet as the cell voltage rises sharply?
If it's...
Yeah good point. Yes, fuse is on main positive lead.
I would also check that all the lug nuts are tightened. I can't imagine how the relay would suddenly go bad. You said you drilled through the panel without removing it. A metal shaving could be creating a short somewhere. Or like USJ...
@Nizadar Good luck with your conversion. Regarding your first two questions, I'm not sure what is the correct protocol when top-balancing pre-fabricated batteries vs individual cells but I assume it's the same as you describe. You will probably get more responses asking those specific questions...
Good luck! For what it's worth, I've been using the original Ryobi charger with my LiFePO without issues so far. The key thing is whether you can trust your BMS to cut off the charge beyond a certain individual cell voltage. The Overkill BMS has an app where I can see (and modify) this cutoff...
From the measurements I took the vertical clearance is just under 9". The inside of the tray footprint is 13 3/4 x 26 3/4.
I considered building the box out of 1/4" acrylic or polycarb instead of wood which would have been a bit pricier, but just as easy to make.
If you have access to a welder...
Opened my box back up to inspect everything and found a couple strange things. My box is not fully enclosed; there is an opening of about 10 sq in. that the power cables go through. Plenty large for stuff to get in, for sure. I expected to find some grass clippings, but not this:
I'm not...
Thanks @FilterGuy,
That's very helpful. So is it not a good idea to set the BMS overvoltage protection below the charger's charge voltage?
So for example the charger that you linked to has a charge voltage of 58.4V (3.65V per cell). This is pretty much the default charge voltage that I've seen...
It's down to 1.6A and still slowly dropping. From what I've read, I should let it get down to zero or near zero from them to be considered top-balanced. Cell voltage right now reads 3.45V (and still slowly rising). Just not sure if it's a good idea to leave them unattended overnight. The...