@FilterGuyI would think either would work (assuming your SCC has an accessible on-off switch)
Your SCC is being effectively 'disconnected' every night when the sun goes down, so this is natural for it.
If your SCC has an on-off switch, then it is designed to be turned on and off... so it should be fine.
Of course the need for either is up for debate. A lot of people say disconnecting the battery while the panels are generating power will damage the SCC. Other people say it does not damage the batteries. I'll stick with Victron SCCs. They say they are designed for handling BMS disconnects.
@FilterGuyThe SSRs typically get in trouble with large inrush currents. Since the SCC is not a highly inductive or capacitive load, it should not have much of an inrush current. (Even if it did, the panels will limit the inrush). Consequently, this should not be a problem for a properly sized DC SCC. Size the SCC for something well over the Isc and worst case Voc of the array. Be sure to take into account low-temperature rise of the rated Voc.
Theoretically, if they are identical BMS's it would work but in practice it could be problematic. No matter how good the tolerance on the BMS design and manufacture is, they won't be identical. The best way to explain is by an example. One of the BMS's might read a cell as 3.51V and the other at 3.54 volts. The two of them might then 'fight' with each other to balance the cell.@FilterGuy
Thanks filterguy. While you are on, do you know if there is any issues with having two BMS's hooked up to one battery pack(parallel like)?
Different entirely. Only one BMS handling balance. Two totally different BMS's to be used. First one simply as a disconnect mechanism on the SCC only. The second BMS has the overall contol of the safety aspect/balancing. Simply using the first one as a diconnect on the SCC at a targeted voltage limit. If it failed, the second BMS provides the redundancy/insurance, being set just a little bit higher threshold.Theoretically, if they are identical BMS's it would work but in practice it could be problematic. No matter how good the tolerance on the BMS design and manufacture is, they won't be identical. The best way to explain is by an example. One of the BMS's might read a cell as 3.51V and the other at 3.54 volts. The two of them might then 'fight' with each other to balance the cell.
I assume you are thinking of this in order to handle a higher current than the BMS is designed for. If the battery is under load and the BMS decides to shut off (low temp or under-voltage), it is unlikely the other BMS will shut off at the same instant. This means the 2nd BMS will suddenly be faced with handling the full load. Hopefully the over-current built into the BMS will shut it down before any damage....but you never know.
Bottom line: I would not advise doing it.
SureIf you were interested, i could provide a sketch and outline of my idea later?
@FilterGuyWow. That strategy is the exact opposite of what most people do. The SCC is designed with multi-stage charge profiles and makes decisions on what to do based on where the battery voltage is. In this design, that is pretty much bypassed and all of the charging comes down to the voltage the BMS is set at.
The generally accepted strategy is to make the BMS disconnect the exception and let the charging be done by the SCC.
Yes, but im terminating before the current reduces to zero, ie only wanting a 90% charge.I have to think about it some, but I suspect it might not fully charge the battery because it will disconnect as soon as it gets to the CV stage of the charge cycle.
When the battery is 'empty' the charging is limited by the amount of current the battery can safely take (or the charger can provide). As the battery charges the voltage will rise. Once it hits the charge voltage, you control the charge by limiting the voltage. At this point the current will eventually start going down till near zero. At that point the charge is complete and the voltage should be removed.
yes exactly....what i was aiming for.By letting the BMS control the charging, the charging stops as soon as it hits the charge voltage so you never get the 2nd stage of charging.
Ok thanksI would use the charge profile of the SCC as the primary driver of the charge cycle. If you don;t like the relay of the Chargery, use the charge relay output to turn the SCC on or off as a fail-safe. Not as the primary.