Not sure whether this is the right place since the real build is in progress, but here is the initial proof-of-concept (needed testing against thick concrete walls, etc.)…
Thank you - yes, noted. There are neither generators nor grid(s) involved here. I still am considering ATS for idiosyncratic reasons though; curious what you might recommend given the setup or where to read up on the different options that play well with the MultiPluses. Victron’s own transfer switches seem a bit odd or deficient.
I also wish Victron would make their own racks, rather than having them custom made.
Still pending, finalizing the 48V DC busbar, instrumenting Cerbo/Touch/etc., possible ATS, comprehensive metering end to end.
Some questions:
Curious whether anyone would advise for or against more [identical] batteries given the above combined parallel 45kVA setup, including the rest of the equipment like the BMS 1000A NG - I’ve read up to 16 would make sense, while Victron supports up to 25 of the same (note fwiw that it’s 50 max if presumably you went with the 25.6Vs or 12.8Vs).
The busbar will almost certainly sit vertically (on concrete) in between the MPs to the right and the batteries and MPPTs to the left; any thoughts on that welcome. (In fact everything will be wall mounted on concrete except the racks, on the ground.)
The room will be dedicated for this, and has two fully independent HVACs that can maintain constant temperature and humidity and any level of ventilation all year around; it’s not clear whether e.g. 16C will help prolong battery lifespan versus say 19C, or what humidity is optimal irrespective. All sunlight and ambient saline air can be fully shut out.
Thanks!
OGPS
(Ed @ Off-Grid Power Systems - offgridps.com)
10
That is a large system, potentially pulling lots of current since you are using low-voltage (48V) batteries. The Lynx buss, despite the marketing, is not sufficient to pull all that current unless you actively cool the buss bars. I would suggest you use at least two Lynx BMS NG in parallel to reduce the amount of current flowing at any given time across the buss bars. You would put half the batteries on one BMS and the other half on the other BMS, with each BMS, Multi, and MPPT distributed across the buss to localize the currents. See here for a better explanation: Bus Bar Ampacity
Thank you! Curiously, my initial instinct had been to do use BMSes, but was strongly advised against it because of collisions on the control surface.
[The other extreme, one BMS per MP (each running independently) each with its own Cerbo/etc and batteries (say I had 9, so 3x evenly split), seems nuts to me - you’d lose most benefits.] But it’s never been clear how a hybrid unified multi-BMS system would work. I’ll check out your link.
OGPS
(Ed @ Off-Grid Power Systems - offgridps.com)
12
This isn’t Ethernet; it’s a dc buss. There aren’t collisions Just make sure all the equipment knows what everyone is doing and you won’t have any voltage mismatches. Your equipment will certainly do that. Now you just need to make sure your DC buss can handle your design choices. Using a single Lynx BMS with that much current is not a good design choice if you ask me.
Thanks again. So, I’ve gotten two takes on this: that a single BMS will make life much easier/simpler, in wiring and instrumentation (Cerbo, etc), and two BMSes will indeed contend in at least some situations and require careful configuration; the other is that two identical BMSes, split exactly down equal battery banks, will allow for greater margins and redundancy/resilience due to cells dying or surges or whatever.
(One correction: the 1000A shunt listed above is a Lynx Shunt VE.Can 1000A, not an older SmartShunt like the other two; there is not 2000A VE.Can version afaict, and fwiw I don’t think the 500A will be used in the end. And it appears that the VE.Can Lynx Shunt can make the contention complexity and configuration problems moot, or much more manageable.)
Anyway, anyone have concrete real-world experience with both approaches for similar systems who can compare the pros & cons?
Much appreciated.
OGPS
(Ed @ Off-Grid Power Systems - offgridps.com)
14
I would not use a Lynx Shunt for anything more than a paperweight. You can search the forum if you’re interested. Did you watch the video on buss bar ampacity I linked to? I’m guessing not, or you wouldn’t be asking about using one Victron Lynx BMS. Three 15kVA inverters - 45kVA total - divided by 51.2V is nearly 880A. The Lynx buss bars can’t handle that on a continuous basis, despite the marketing. You could point the output of one air conditioner on to the buss bars and they might not melt the plastic enclosures that way.
For the ng batteries you need the ng lynx bms units. The ve.can lynx shunt doesnt support victron bms comms and doesn’t have a contactor like the lynx bms units either.
Multiple banks are supported with the lynx bms units and the cerbo will co-ordinate the multiple banks.
The issue is the current draw of three 15kVA at full tilt can be beyond what a single 1000A lynx busbar system can provide. Generally for larger installs you’ll see custom busbars in use that can easily handle more than 1000A.
Just make sure all the equipment knows what everyone is doing and you won’t have any voltage mismatches. Your equipment will certainly do that. Now you just need to make sure your DC buss can handle your design choices. Using a single Lynx BMS with that much current is not a good design choice if you ask me.