Once my installation is complete I will be using 27.2v as a charge controller starting point. Like you, I don't think it is wise to use the internal BMS cutoff - especially if (like me) the batteries are connected in parallel (one BMS shuts off and then the current rises on the other two - and then they all suddenly shut off). For me, better to adjust the top end to a lower voltage, at just the beginning of the upper slope - I will observe that effect - and then vary that voltage up or down according to the results. My feeling is not to push these BYDs too hard - they are already compromised by age and possibly by overcharge/discharge. Let me know how they are working for you. Good luck and best to you.
your running LA batts with lithium together in parallel?GV,
Curious as to what you ended up using for the charge limit on your charge controller. Was it 28v? I have mine set for 28.4, but right around there the internal BMS cuts out. The ammeter shows 28.5, but it's pretty cheap, and with the LA bank in parallel, it's probably not 100% accurate.
My goal is for the internal BMS to not disconnect the load. I have an older lead acid bank in parallel, so when the lithium bank disconnects, the charge controller still functions off that bank, but I hate having to trust the internal BMS to kill power to the battery.
your running LA batts with lithium together in parallel?
StevieP - Probably a good idea to run an A/B switch and top off the LA bank from time to time... if you haven't done so already. Set the CC's for LFP - they'll take a lot more damage from a LA charging profile than LA will from an LFP charging regimen.
Clever fellow, that Steviep19...
Hey GV,Did my first charge/discharge cycle with 3 paralleled pre-assembled TechDirect/BYD units: They were fully charged to the internal BMS cutoff of 28v. Using a 500w heater @ approx 18amp discharge the batteries lasted for 17 hours 12 minutes - using a cut-off voltage of 24.0v.
Didn't want to press the voltage any lower on my first discharge cycle. At 24.v my meter read: 8.14Kwh, 315Ah.
That would represent 2.71kwh/105ah per battery. It's not 4Kwh per battery, but it's a start, and there may be some operator error in there.
I've started the recharge cycle and will be more rigorous in my measurements next time - we'll see if the capacity increases with each "wake up" cycle. I will also push the discharge voltage a little more aggressively - perhaps as low as 23volts. Best to all.
Finally found this, THANKS GV!
8S LFP LifoPo4 BMS Detail Min Standard Max Single cell overcharge protection voltage 3.72 V 3.75 V 3.78 V Single cell overcharge protection delay time 0.6S 1.0S 1.5S Single cell overcharge recovery voltage 3.50 A 3.60 A 3.60 A Recharge current / / 130A Single-section equalization voltage 3.55 V 3.60 V 3.65 V Single-section equalization current 35 mA 40 mA 45 mA Single cell over-discharge protection voltage 2.15 V 2.70 V 2.80 V Single cell over-discharge protection delay time 0.6S 1.0S 1.5S Single cell over-discharge release voltage / / 130A Discharge protection current 350 A 370 A 390 A Charging high temperature protection 85'C 90'C 95'C
FYI: These are the TechDirect specs listed for the built-in BMS unit.
Hi Matt,Hey GV,
What kind of meter are you using to give these details? Shunts, connectors etc.. with pics and links for the ignorant like me would be nice.?
Thanks GV!Hi Matt,
I've posted this picture before - it's how I took my original measurements. A cheap eBay 200a ammeter w/shunt -
attached to two 3/8" battery posts (carefully separated). I bought the custom TechDirect anderson SB75 connectors with 3/8" lugs to connect - and alternated between 23amp battery charger (for recharge measurements) and a cheap 24v inverter/500w heater (for discharge measurements). There are detailed instructions for that meter (and others) if you search by model number or eBay listing.DC 0-200V Solar Power Multimeter Ammeter Voltmeter Battery Tester Monitor T6U4 | eBay
Type 3: Tester + 100A shunt. Type 4: Tester + 200A shunt. Type 5: Tester + 300A shunt. 1 Battery Tester Monitor. Internal Resistance Minimum resolution: 1mΩ. 9 datas shown in the one screen, allows you catch the information you want at a glance.www.ebay.com
Nothing tricky - you just have to make sure not to overcharge or over-discharge. My measurements were from 23.5v (low) to 27.5 high (BMS disconnects right around 28v).
In my actual working installation I am using Schneider Conext charge controllers and inverter - and they have built in monitoring which goes by xanbus to my Mac or my iPad. Best of luck...
I have a Schneider XW4024 inverter and am using the Schneider, System Control Panel, for Conext XW... for battery charging from the grid to my 3-parallel wired 24v BYD power walls. Can you show a close up of your wiring? Does the context scp work well with the BYD? I still need Anderson connectors. How do you get the positive and negative post to opposite ends of the battery? |
Very nice job GV!Hi totalicf:
You can get Anderson connectors with #6 wiring (for both parallel and series) made at TechDirectClub - with custom lugs. I did so. Or try BatteryCablesUSA for larger wire sizes. I have 4 BYD pre-built units so my net charge/discharge amperage per unit is appropriate for a #6 cable.
As to wiring: I used negative and positive busbars (see photos) and 200 amp type T fuses. I wired my SW4024 using Schneider switchgear components - my battery room is located directly behind the wall of that Conext installation. The unit lying on top of the batteries is a temporary test bed for a Moe's automatic transfer switch.
The Conext SCP works very well - but it is designed to be used with the SW4024 inverter (and any Conext charge controllers or AGS). It does not interface directly with the BYD units - it simply sees them as a "battery" - reporting their relative voltage and amperage in/out. However, if you integrate a Conext Combox with your system you can access robust system realtime monitoring & graphs and easily set system parameters for your Conext charge controllers and inverter (via iPad or phone as well). This really helps to keep on top of the day to day management of the system.
There is a sticky thread for Wiring Unlimited on the forum should you want to consult any wiring diagrams.
Best of luck and good thoughts.