Finally getting around to doing my yearly capacity testing on my 400Ah bank.
Last year I capacity tested this 400Ah bank consisting of 4X 400Ah Winston cells and took out 425Ah's at a load of 102-105A. I shut that test down at close to 2.8V for the lowest cell
This year, I completed 208 cycles, with most to 80% DOD. During this time there was no balancing, no BMS/shunt balancing and only charging to 13.8V and 5A accepted current
, or close to that current
level before shutting off charge sources and using the bank to 80% DOD per a calibrated Link-Pro using Ah consumption
. Battery monitor
was manually reset each time the bank hit 13.8V/5A net accepted current.
for this capacity test I first charged the bank to 13.8V and 8A of accepted current. I got impatient and did not want to wait a few more minutes for it to drop to 5A. The pack had been charged using my 50A bench top power supply. Top finishing voltage was 13.82V as measured with my Fluke 179. charging was discontinued at 8A of current flowing into the bank at 13.82V.
I ran this test at the same load as last year, using the same equipment
, to keep everything as A/B as possible. Load was 102-105A continuous for a approx 4 hours. (load changes slightly with voltage)
Ampere Hours: To track Ah consumption
I used a Victron BMV-602 with the Peukert set to 1.03. The Victron was programmed then manually synched after charging to 13.82V @ 8A net accepted current.
Voltage: I used a calibrated Fluke 179 to track pack voltage and a calibrated Cell Log 8S to track cell voltage. Periodically cell voltage was double checked with the Fluke. I also have a Smart Gauge and the voltage on the Victron BMV.
I also have a Bogart Engineering PentaMetric with computer interface which was giving me fits today. Don't even get me going on the Log View software
for the Cell Log 8.
I could not get the USB interface to cooperate on the Pentametric and finally gave up and did the test using the Fluke, Victron BMV-602 and Cell Log....
I fired up the inverter
which was driving a ceramic disc heater and also a smaller inverter
driving a large light bulb to push the current where I wanted it.
It ran at 102-105A load (approx .25C) for the duration.
I stopped the test when I hit 425Ah the same exact performance I had 208 cycles ago. When I stopped the test the lowest cell was at 2.872V.
After I shut off the large load and the voltage crept back up I turned on the small inverter and a 15A load. As I type this the lowest cell is at 3.008V and the Ah consumption just surpassed 431Ah's..
Cell & pack voltages measured at -432Ah's (400Ah bank) under a 15A load:
Cell #1 = 2.993V
Cell #2 = 2.966V
Cell #3 = 3.043V
Cell #4 = 2.956V
Pack Voltage 12.045V
Keep in mind that these cells have not been balanced for 208 DEEP cycles. When they were balanced, they were top balanced not bottom balanced so the 0.087V variance or cell drift, while loaded, 32Ah's beyond "rated" capacity is pretty darn good and to be expected IMHO....
From where I sit these cells never need to be charged beyond 13.8V. If you let the current tail to 5A at 13.8V you are going to get the vast majority of the capacity in the bank. As your charge source gets larger the tail acceptance time gets a tad longer and that is the only down side. The upside is the cells don't seem to need balancing and you keep yourself out of the danger
Why charge to a voltage beyond 13.8V when 13.8V yields more Ah capacity than the bank is rated for while pulling a constant 25% of capacity in load? Boat house banks rarely pull .25C and when they do it is not for very long. Perhaps a windlass
, thruster, inverter etc. but these are short in duration not 4+ hours on a 400Ah bank pulling 105A continuously.......
I have come to believe that pushing your cells into either the upper or lower knee is where the cells become unbalanced.
I completed my .25C capacity test and the bank actually matched and has now exceeded last years numbers. This after 208 cycles most to 80% DOD. The problem is this test is grossly unrealistic for my boat.
I plan to do a 10A capacity test next. They say these cells have minimal Peukert effect but I suspect that under a 10A load I can easily exceed 450Ah of capacity. I even suspect I might hit 500Ah.
Lead Acid Musing:
A 400Ah lead acid bank would be subjected to just a 20A load to earn its 400Ah
rating. I applied 102-105A load and hit 425Ah's. I then shut down the heater and kept pulling a 15A load after I'd hit -425Ah's. As I type this my lowest cell is hoovering at 2.856V and I've removed -438Ah's of capacity from the bank...
At house loads when only charged to 13.8V and 5A net current these cells GREATLY exceed the 400Ah rating. There is no need to worry that you are short changing yourself if you choose to charge to 13.8V..
I just terminated the capacity test and removed -440Ah's of capacity. I stopped the test when my lowest cell hit 2.800V.
The resting voltage has not yet stabilized but at -440Ah's it is hoovering at about 11.71V
No load Voltages -440Ah's
Cell #1 2.965V
Cell #2 2.898V
Cell #3 2.966V
Cell #4 2.899V
Pack Voltage = 11.73V
Cell Drift = 0.067V
Note: I don't feel this is very accurate as the cells have only been resting for a few minutes. Will update again if I remember..