
Kurt
Yes, a little confusing. I think inverters are often quoted at a power factor of 0.8, so the headline number (in this case 5000 VA or 5.0 kVA) is more impressive than the actual power output (4000 W or 4.0 kW). I suppose it's nice to know that the IGBTs or MOSFETs will circulate the current required for an 0.8 power factor load, such as an induction motor. But you can only draw 4 kW plus losses from the battery side. (the extra kVA just circulates from the DC bus capacitors to the motor and back to the capacitors again 100 times per second, with some losses of course).Adverse Effects wrote: its the 4048 4000W BUT it seems that its also listed at 5KVA
PlanB wrote: Just curious which graph you got the 76%=3.32v balancing point from a few pages back weber?
PlanB wrote: So for a cell cycled between 20% & 80% SOC only about 0.1v difference? Or just 1.6v for a 16 cell pack. That's less than the voltage drop typical of 1C discharge.
"This entry was posted on April 1, 2013 at 11:14"weber wrote: Reports of a fault in a 24 V model
https://brandon314.wordpress.com/2013/0 ... er-review/
weber wrote:PlanB wrote: So for a cell cycled between 20% & 80% SOC only about 0.1v difference? Or just 1.6v for a 16 cell pack. That's less than the voltage drop typical of 1C discharge.
Right. But when floating/balancing at 76% SoC using our BMS, the charge current will be throttled back to the balance current of 800 mA which is around 0.005C for a 180 Ah cell. So voltage rise due to internal resistance will be around a millivolt per cell and can be ignored.
The low end of the cycle can be determined by coulomb counting. The capacity of the smallest cell, and hence the battery, could be determined by an occasional excursion all the way down to 2.8 volts, which can safely be considered empty, even at 1.2C (the peak load of the PIP-4048MS on a 180 Ah battery) and at temperatures as low as 15°C. This might be done annually, or every 365 cycles.
PlanB wrote: Good point, I never did the sum to realise 1C is pretty unlikely for this. Makes the performance of battery management systems in EVs, where 1C or 2C is likely, look good.
Our BMS has 0.8 A bypass and will be used with 180 Ah cells. I assume you're thinking of BMSs that don't control the charge current (except OFF or ON). Ours will attempt to throttle the charge controller back to the bypass current when the first cell is full, by using the serial input to the PIP-4048MS to send commands that reduce the absorb and float voltages.T1 Terry wrote:Battery management for house battery has very different requirements to EV battery management. These cells behave differently under light discharge and the cell capacity makes a huge difference to cell balancing using the discharge method or shuffle transfer. 0.5 amps will balance a 40Ah or 60Ah cell, but useless for a 400Ah to 1,000Ah cell. This requires a completely different management method, combine that with solar charging that can be any where from a trickle to over 100 amps yet only available for around 3hr in winter yet up to 10 hrs in summer and the EV battery management system would not even close to being up to the task.
offgridQLD wrote: The cells just don't drift much under light C loads and modest DOD levels.
Bzzzt. Factor of 10 error. 0.1% difference would be 0.18 Ah and take 15 minutes to correct. But no-one cares about a 0.1% imbalance, so I'll just take your point as still applying to a 1% imbalance (which we barely care about).T1 Terry wrote: The trick is reducing the current down to 0.8 amps yet charging all the other cells, at the same time. Even a 0.1% out of balance equals a difference at that time of 1.8Ah between the highest and lowest cells and that will take a continuous 2 1/2 hrs to correct with a 0.8a discharge balancer.
Sort of. The present plan is to use the modified CMU that we call an IMU, for this. It lives on top of the current-shunt rather than on top of any cell. We would put it last in the comms daisy chain, instead of first as it is in Mexy. It would run a PI control loop on the maximum cell voltage, to keep it down to 3.32 V (76% SoC).PlanB wrote: Dave is it one of your cell top modules that will throttle the absorb & float voltages?
If I took your cmds in on an RPi serial port & echoed them to the 4048 (so we can maintain our serial connection) then echoed the 4048 response back at you would your wait for ACK timing be generous enough to allow this to happen transparently?