Hi everyone!
I've been doing a whole lot of research and have come to the conclusion that the KID best fits my offgrid setup, mainly because of how it can simplify my system - with its LOAD control functionality (other controllers can only supply 12V @ 200mA and need a relay) and Solar U-Set VOC% manual mode (which allows connecting to a constant voltage power supply). I may expand the system in the future, but my current setup involves:
- 2x 345W panels
- ~5KWhr of 6s74p NCR18650 Li Ion cells, 24V system (https://engineering.tamu.edu/media/4247819/ds-battery-panasonic-18650ncr.pdf (https://engineering.tamu.edu/media/4247819/ds-battery-panasonic-18650ncr.pdf))
However, I have several questions about the KID:
- I presume the voltage of the LOAD terminal is same as the battery. What about the AUX terminal? Is it rated at 12V 200mA instead? I can't seem to find this info in the KID datasheet.
- I plan to charge/discharge my battery bank from 3.4Vpc to 4.05Vpc, which does not reach the cell's absorption/CV phase according to its datasheet. Is there a way to disable the ABSORB & FLOAT phases, and only bulk charge to 4.05Vpc?
- I'm planning on incorporating a BMS (http://electrodacus.com/ (http://electrodacus.com/)) to protect the bank from overcharging & overly unbalanced cells. I see that the AUX terminal can act as an input, but it doesn't seem like it can function as a "Stop Charging!" signal input? A way around this is to have the output of the KID connected to the BMS, then the BMS to the bank. However, how can the voltage drop due to the insertion loss of the BMS solid state relays be compensated? Also, the charging algorithm of the BMS might conflict with that of the KID?
Thanks! Looking forward to hearing your comments and inputs!
BEFORE you rely on a BMS to manage things, can it shunt enough current around a "full" cell to prevent overcharging it?
If you are charging with 20 amps, and the BMS can only shunt/divert/bypass 5 amps, you are still hitting a full cell with 15 amps. And if a cell is that far out from the rest of the pack, you have Trouble.
Finally, are those LFP (LiPo4) cells, or some other flavor of Li ? Many are NOT stable enough. And your data sheet shows only a 500 cycle count. You may get more, but with reduced capacity.
Connections ? Do you have a spot welder to tie those together with ? 6s74p is a LOT to ask of spring load terminals
I personally think you are using too many tiny cells for this.
Thanks for your reply mike90045!
That's actually a great idea to have the BMS divert power from the bank. It seems like the Electrodacus SBMS can do an external shunt, but I can't seem to find out whether it's able to do it internally from the datasheet, though. I'd really like to keep the system as simple and safe as possible.
Those are NCA (nickel cobalt aluminum) cells. The pack came already assembled with cell level fuses! So no messing around with the cells :)
Hi unlimited, welcome to the Forum.
Do you have a diagram of the configuration that you are considering?
In general, it is not a good idea to connect the input of an MPPT Charge Controller to a constant voltage power supply ... this can work, but can be a risk to the health of the CC.
It is not clear just what the Load control of the KID is doing, but there is no current limiting on this output, and so on.
Thanks for any diagram that you have. Vic
Thanks for your reply Vic!
QuoteDo you have a diagram of the configuration that you are considering?
Sure! I can draw a simplified one here:
Solar------\
|-select----->KID charge controller---->battery (have not yet decided the placement of BMS)
CV supply-/
Quote
In general, it is not a good idea to connect the input of an MPPT Charge Controller to a constant voltage power supply ... this can work, but can be a risk to the health of the CC.
Yeah I was concerned about that, but the KID's manual page 34 states that the U-set VOC% mode is useful for testing or constant voltage sources, so that gave me a piece of mind.
Quote
It is not clear just what the Load control of the KID is doing, but there is no current limiting on this output, and so on.
Hmm however the KID's manual page 29 says that the load current can be set by the user?
Hi unlimited,
Thanks (I think) for the detailed diagram ...
To me, the current limit on the Load output of the KID is an overcurrent protect mechanism, but you do seem quite certain in what you want to do, so will not try further to dissuade you. Good that you can handle the duty-cycle of the current limiting of the Load output.
Good Luck! Vic
Why can't you just set the absorb and float to the same voltages ? It will bulk until it gets to absorb for absorb time and then go to float.
If you can figure out at what current your batteries are full you can use ending amps to terminate the absorb and go to a different float voltage. You need a Whizbang to do this but would want one anyway for SOC too.
You might want to consider the Classic instead. That has a feature where you can limit the battery charge current but it won't effect what the other higher currents that can be delivered to loads if available.
The Classic also has the Ending Amps feature , but load control would be via AUX 1 - Aux 2 is taken up by Whizbang .
Larry