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I want to 'off grid' a client in the sense of isolating his domestic supplies from the grid supply because of very poor quality of electric and erratic supply. I have previously used a Skylla/ Titan 48/50 and solar to achieve this but I wanted something that was smarter and would show up on the Cerbo touch screen.
Could I use a second Multiplus in charger only mode and put the first in Invertor only mode. Cost wise its pretty similar to the cost of a Skylla anyway.?
I am assuming that there isn't an GX compatible charge in the Victron range hence the question...
As far as I am aware there isn't a way to add a second MP to an existing 'system' because the GX device will expect too to either define the system as split phase or a parallel pair, I tried it once which is why I think that. The problem with that is that both units, which must be identical, will operate in the same mode. There was a discussion a couple of days ago about running only one charge in a multi-phase setup, which is apparently possible, but the long and short of it is that you cant separate charging from passthrough, because of the physical architecture, unless you turn off the output.
I have 3 suggestions, all way outside the 'normal' box...
1. Do what I have done... install a second MP with it own GX device and battery. arrange the two systems electrically so that you have Grid > Sys1 > Sys2 > Loads. this gives loads of room for flexibility and redundancy but has drawbacks that will likely make it a poor choice in your case.
The worst being the extra battery and the fact that shunting power from bat 1 to bat 2 by inverting and then charging will be very inefficient. Given your goal to keep the Loads from being directly connected to the grid this probably isn't a good choice.
So with the box way off in the distance now...
2 & 3. Use a PV charger/inverter but feed it with DC from an industrial supply, bear with me, I have done this several times... Meanwell units I have used ... CSP Hi voltage, RSP low Voltage.
I am assuming you have PV on site, so you could use CSP/RSP series, depending on string voltage, PSU to leverage the existing PV charger into service when there is little/no sun. Basically the PSU, or a stack of them, gets set up as a voltage capped current limited supply that will augment or replace the PV array. this solution will also work if you added an additional supported PV charger/inverter AC or DC coupled. I have a couple of systems in the wild that have been running for years, one is a bank of 9 low voltage supplies that take wayward AC and and charge a huge 48 V pack in an off grid estate and the second is 4 separate DC links, 16kW each, that shunt power from two remote grid connections up to the main house where standard PV inverters combine the three supplies. All three grid connections have hydro installations connected, in case you were wondering why, the system allows the house to use hydro power from both remote systems, 700m away, without needing silly sized cables.
Both the CSP and RSP ranges of PSU can be set at a max voltage and then controlled with an analogue signal that drive the current limit between about 8% and 100%. The units are rated for continual current limit, not just overload protected. The 48V units will adjust up to about 62V max.
You absolutely could just charge the battery with that but you wouldn't have an integrated system and I am not recommending you go charging the battery with some dumb thing that the Victron system isn't aware of, hence the PV charger/inverter connection.
If you select a PV unit that Victron is aware of and feed it with DC derived from the dodgy grid via a PSU which you can control you get a GX compatible charger that you can enable/disable/throttle however you need to.
The PSU's are about £120 / kW. The units will parallel and have inbuilt current sharing but if you configure them that way you you cant then manage the current, just the voltage.
In this application, if you wanted more than 3000W, you would be better with separate supplies with individual current setpoints and diodes to prevent backfield between them. (which is what I did with the big charger I built.)
Interestingly you can also stack them vertically, my DC links use two 250V CSP's giving a maximum of 500V DC. I use an external PWM signal to drive the stack via opto-isolators because the control signal is referenced to the DC Neg which the top supply has its control ground floating at 250V, which is a flash waiting to happen.
Give me a shout if you want further details, I would manage the thing from NodeRed running on the GX bhut there are many options there, including just turning the PSU on and off with a relay and letting Victron control the PV device.
Hope that gives you food for thought, and helps.
