Delta Sierra
New Member
- Joined
- Aug 22, 2021
- Messages
- 26
Im posting here and deleting my previous post. I initially ordered 8 of the new style LF280K cells from Docan Power but emailed Jenny Wu @ Docan before purchase making sure the cells I was to receive were not going to be bloated. She advised the cells do have a slight bulge to them and recommended I take delivery on the older style LF280DK (EVE 280N I believe, as the LF280DK is just their internal naming for these cells.) as these cells have no bulge and satisfy a few of my other concerns.
I received them via ups promptly and they were in great physical shape. Barcodes show the oldest one manufactured on 12/1/2020 and newest one on 2/26/2021 so looks like they have been sitting around for about a year before I got them. I assembled them into two separate 12.8v packs with an overkill BMS on each of them. I ended up using .125" thick aluminum plate cut just wider than width of cells and just shorter than their height, one plate onto each end of the group, with 8 hose clamps banding them together tightly. Also used some 2mm thick rubber sheet in between each cell and the plates on the end for protection.
Wanting to go with a flexible connection between each cell rather than a rigid bus bar, I chose to arrange them physically in parallel and built my own 'bus bars' with 2/0 AWG cable and tinned copper lugs, hydraulically crimped. They actually have about 33% more cross sectional area than the 2mm x 20mm bus bars that came with the cells, can move slightly to account for cell expansion / contraction as well as have excellent contact area when tightened- unlike solid bus bars.
I initially connected in parallel with bus bars and top balanced them at 3.65 volts with a cv/cc charger until amps went to near zero. I then used my cables to series connect the cells for each pack, attached the bms and torqued each nut to 3 Nm.
For the capacity test, I put the assembled pack into my RV and connected my Victron BMV-712 smart monitor shunt in line between inverter neg / trailer neg & C- lead from bms so the shunt measures everything, without anything else bypassing shunt. I then reset history of smart monitor, connected 1000w heater to inverter and started logging data into excel every 5 minutes for the 3 hours it took to run the battery to the 2.5v per cell cutoff. Average amp draw through the tests were around 92 amps.
Ended up getting only 275.8 AH out of battery #1 (one test) and 272.9 AH out of battery #2 (ran two tests, exactly same result). These AH numbers are from the Victron app where it says "Consumed AH". Under history tab, discharged energy shows 3.5Kw for all the tests. In excel, I ran a formula that added up all the wattage drawn from the pack from each sample point and got 3514 watts for battery #1 and between 3477 (test 1) and 3487 (test 2) for battery #2.
I'm assuming the watts I would be expecting from these packs would be approximately 3.2v * 4 * 280 AH = 3584 watts correct? So- bottom line question here- did I get screwed on buying these cells or no?
I do realize that there is energy loss on the battery side of the bms that the shunt is not measuring, for instance the battery and bms temps raise approximately 6 and 12 degrees respectively and of course all the connections are not zero resistance either and get slightly warm to the touch (never hot). I'm assuming over the course of a 3 hour test it would be fair to expect 50 to 100 watts of energy loss from this?
So, perhaps I got a fair deal? Please let me know if my methodology for capacity testing these cells is correct and what your thoughts are as to my purchase from Docan I emailed Jenny Wu, will see what kind of resolution if any at all she may have for my situation.
Attached a few pics, they will eventually both be in a plano box wired in parallel for 7 kw of power and eventually in series for 24 v
I received them via ups promptly and they were in great physical shape. Barcodes show the oldest one manufactured on 12/1/2020 and newest one on 2/26/2021 so looks like they have been sitting around for about a year before I got them. I assembled them into two separate 12.8v packs with an overkill BMS on each of them. I ended up using .125" thick aluminum plate cut just wider than width of cells and just shorter than their height, one plate onto each end of the group, with 8 hose clamps banding them together tightly. Also used some 2mm thick rubber sheet in between each cell and the plates on the end for protection.
Wanting to go with a flexible connection between each cell rather than a rigid bus bar, I chose to arrange them physically in parallel and built my own 'bus bars' with 2/0 AWG cable and tinned copper lugs, hydraulically crimped. They actually have about 33% more cross sectional area than the 2mm x 20mm bus bars that came with the cells, can move slightly to account for cell expansion / contraction as well as have excellent contact area when tightened- unlike solid bus bars.
I initially connected in parallel with bus bars and top balanced them at 3.65 volts with a cv/cc charger until amps went to near zero. I then used my cables to series connect the cells for each pack, attached the bms and torqued each nut to 3 Nm.
For the capacity test, I put the assembled pack into my RV and connected my Victron BMV-712 smart monitor shunt in line between inverter neg / trailer neg & C- lead from bms so the shunt measures everything, without anything else bypassing shunt. I then reset history of smart monitor, connected 1000w heater to inverter and started logging data into excel every 5 minutes for the 3 hours it took to run the battery to the 2.5v per cell cutoff. Average amp draw through the tests were around 92 amps.
Ended up getting only 275.8 AH out of battery #1 (one test) and 272.9 AH out of battery #2 (ran two tests, exactly same result). These AH numbers are from the Victron app where it says "Consumed AH". Under history tab, discharged energy shows 3.5Kw for all the tests. In excel, I ran a formula that added up all the wattage drawn from the pack from each sample point and got 3514 watts for battery #1 and between 3477 (test 1) and 3487 (test 2) for battery #2.
I'm assuming the watts I would be expecting from these packs would be approximately 3.2v * 4 * 280 AH = 3584 watts correct? So- bottom line question here- did I get screwed on buying these cells or no?
I do realize that there is energy loss on the battery side of the bms that the shunt is not measuring, for instance the battery and bms temps raise approximately 6 and 12 degrees respectively and of course all the connections are not zero resistance either and get slightly warm to the touch (never hot). I'm assuming over the course of a 3 hour test it would be fair to expect 50 to 100 watts of energy loss from this?
So, perhaps I got a fair deal? Please let me know if my methodology for capacity testing these cells is correct and what your thoughts are as to my purchase from Docan I emailed Jenny Wu, will see what kind of resolution if any at all she may have for my situation.
Attached a few pics, they will eventually both be in a plano box wired in parallel for 7 kw of power and eventually in series for 24 v
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