I’m installing a backup system for some critical loads using a victron phoenix 24/500.
The original circuit takes a dedicated phase and there is a small 300W grid inverter feeding that circuit to offset the normal consumption.
I was thinking that in the likelly event of a prolonged grid failure, it would be very convenient for the grid tie inverter to feed into the phoenix as that would have the bonus of both charging the battery and increasing the capacity. The enphase IQ8M’s support frequency shifting. But I can’t see a feature on the phoenix to enable this. In fact, I can’t even see a programmable high voltage cut out on the settings!
Does anyone have some insigts on how this could be implemented?
I’m not quite sure if I understand correctly how your setup is built and I’m not sure I even want to understand it.
Protecting a critical load: OK, that’s usually done with a Multi.
You’re using a Phoenix inverter ?
How is your load switched from Grid to Phoenix in case of a grid failure ? Please don’t tell me you’ve connected the output of your Phoenix inverter in parallel with the grid phase towards your critical load ?
In any case: even though a Phoenix is an inverter and thus the charger settings usually are irrelevant, with the aid of certain assistants a Phoenix can be instructed to charge.
So yeah, it can be done.
That doesn’t mean it’s a good idea !
Since this really is very advanced usage territory, I’d like to make sure that you really understand very well what you’re doing and trying to do, before I disclose more on how to do this.
I do not want to be held accountable for telling you where you can find a flamethrower and then you setting your house on fire with it.
(The flamethrower is a metaphor, you setting your house on fire due to bad cabling or config is not.)
I’m not quite sure if you have no idea if the phoenix supports frequency shifting or you are sure it doesn’t. Can you elaborate on that?
My setup consists of a 3 way transfer switch which isolates the grid in case of a power failure and diverts the circuit to the victron inverter or a generator. The enphase inverter has it’s own isolator switch, the enphase IQ-Relay (A legal requirement) so it can be setup to isolate from the inverter, in fact this is a necessity with the generator.
The multiplus of course has it’s own transfer switch built in and also has frequency shifting by standard. But I don’t need a charger (can’t use it when there is no AC Grid) and I already have a transfer switch in place. I’m looking to find an official victron statment on whenever the Phoenix also supports frequency shifting and how to program the correct voltage at which this will happen to see whenever I can ask the installer to make sure the grid tie syncs with it.
I could find here and here - threads where people seem to indicate this is possible, but I didn’t find an official victron statment on this matter.
There’s little advantage in having an AC charger as on the multiplus on my setup. There is already an AC charger for grid / generator use, but this doesn’t cover the situation where I can’t physically start the generator or the grid is down. I also don’t want to go with a dedicated MPPT charger as this would not be able to share the same circuit as the grid tie under normal operating conditions - Doing so would invalidate any warranties or insurance claims. But I can ask my installer to program the grid tie to sync on the inverter which is “VDE-4105” compliant.
So really, I’m just looking for a confirmation statment that frequency shifting is indeed supported on the phoenix before evaluating other options. Can you help me with this?
The answer to -does it support frequency shifting is going to largely depend on which phoenix inverter you are referring to. Ve direct this one?
If it is that one, then no it does not.
If the inverter supports frequency shifting it is clearly stated in the manual. For Example here for the inverter RS.
So check the product page for the model you are looking at
Over here I have a VE Bus Phoenix Inverter 48/5000 which supports frequency shifting.
Its internals are almost the same as a Multi, takes the same firmware even.
As @lxonline stated: the smaller (VE.Direct) inverters don’t support frequency shifting, so then you’re out of luck.
I have reviewed these products and have a few more questions.
Let’s suppose I go with the multiplus 2. As I understand I have AC charging, PowerAssist and I can work offline from the batteries, which includes grid forming and frequency shifting.
From what I can see, when connected to mains power, where frequency shifting doesn’t apply, the device will try to use it’s battery charger to charge the battery with any surplus energy and send the rest to the grid as an export.
That’s all fine for the multiplus 2, but I can’t find any details whenever the multiplus also supports this. It would be fairly convenient to have a feature to use excess PV to charge the batteries, and still be able to charge them during an outage, but the MP2 is only available in fairly large output variants, mostly 48V and I need 24V.
The main differences between regular Multiplus and Multiplus 2 is a) slight difference in Power Electronics and b) Multiplus 2 having two relays in series on AC In.
The latter is a requirement in many countries to be allowed to feed in.
Thanks. In that case, I assume I can use the VE.BUS port to program it as needed, correct?
My country requires G98 type aproval as far as feed-in is required.
I Think the availability of a G98 certificate on the multiplus would therefore confirm whenever it conforms or not, with the signle relay.
Does Victron provide a G98 certificate for the multiplus? I Could only find one for the Multiplus 2.
In my Multiplus 12/1600/70-16 , I can select “UK: G98/1 Amendment 6 (16A max)” as grid code, which would make it compliant.
No idea for other Multi’s.
G98 should be included as of firmware 460, with updates in 498 and 510.
Both, but this one will be installed in Poland. I actually checked their register and it seems only the multiplus 2 is approved. Not the greatest Victron move if they are both G98 compliant. But then, people were complaining on foruns for years about their inverters not being able to be registered here.
I think it will be easier and cheaper to run the critical loads from my phoenix through the transfer switch and trow in a few panels just for offgrid use to top up the batteries. It’s a shame as the solution with the multiplus seemed quite robust, but having to invest in a 3KW multiplus 2 just to be compliant is a bit too much.
Considering the low power consumption of the loads you’re protecting, investing in a Multiplus II doesn’t seem to be to the best choice.
You could buy a seperate anti-islanding box for the regular Multi, but that box costs more than the Multiplus II
In your case, I would buy an (automatic) transfer switch to transfer loads from AC to Phoenix inverter.
If the transfer speed isn’t very critical, this could be as simple as a plain relay switching the COM connection from NO to NC when the coil (connected to grid) isn’t powered anymore.
With a double-pole relay you can switch both neutral and phase that way.
The Enphase IQ8M micro-inverter I would leave on the grid side but would connect a Victron MPPT between the solar panel(s) and the battery.
This will ensure the battery gets charged (on grid or off grid) and you never have an overloaded battery or need to fuss with frequency shifting.
My guess is that this will be your best solution with the lowest investment.
I shoudn’t need anti islanding. Once power goes out, I have protection relays that isolate the house from incoming supply and wait 30 seconds upon power being re-applied before connecting. We had far too many problems last year when broken trees damaged overhead wiring downstram our house and the power pulsated many times as they tried to re-connect. The overhead lines run for kilometers here. That caused havoc with some of our appliances and even tripped breakers, on ocasion. This year has been challenging in terms of weather related events…
The backup loads are again connected through a transfer switch, so another layer of isolation. But for the batteries and the panel I’m aware the failure of an MPPT could cause some serious safety complications, for example in case of lightning. That’s why the multiplus seemed a good idea. The microinverters are transformer isolated and the multiplus further isolates the battery through it’s own transformer… Can’t get any safer than that!
When a lightning bolt strikes the solar panel, both an MPPT or your microinverter will be toast and I’m pretty sure the overvoltage will blow straight through any transformer and kill any sensitive equipment downstream.
If that’s what you fear for, you could add overvoltage protectors (the serious stuff like Dehn Guard, ABB 2CTB803973R1100 style) everywhere, but even then.
Lightning is like water: if it hits you, it will find a way, no matter what you try to keep it out.
The best protection against lightning is to unplug everything.
I still stand by my advise in my previous post.
In theory unless the devices are grounded or referenced to the (grounded) grid, they should simply be floating. The chances of lightning striking a floating object would be minuscule, there would be no path or a very high impedance path to ground through the electronics. The grounded panel frames would much likelly be hit.
But even if I were to be super unlucky, I’m counting on the grid tie being destroyed, not anything downstream
Transformerless inverters on the other hand, at least when operating, provide a direct connection from the panel to either neutral or live. The chances of lightning striking a DC connector on those are significantly higher and anything with a direct non isolated path could in theory be equaly as bad.
Granted one could never be fully protected, one can only mitigate the risks significantly by playing it safe, on the understanding that probably no aproach will be 100% safe.
On another subject, I was playing with the demo section on the victron connect software and I don’t see a setting to limit the charger current based on detected export, when AC tied. There are some settings to limit the input current to a fixed value but I can’t see anything that would dinamically limit export on both the multiplus or the MP2, or how to customize the frequency shifting profile when operating off grid. Where would I find these settings? Thanks!
Since the panel frames are (or should be) grounded and the solar cells themselves (and thus also the transformerless inverters) are galvanically isolated from the frame, I’d say the odds of lightning striking the DC part instead of the grounded frame are low.
But true: not impossible.
My brother recently had a lightning strike on his PV setup, blowing up one SMA inverter completely, the overvoltage protection circuits from another SMA and multiple appliances inside the house.
These were older (>10 years) SMA Sunny Boy inverters, so probably with a transformer.
And that didn’t protect just one bit.
Pretty much the only real protection is to install decently sized overvoltage protectors on AC and DC side.
Not sure what you mean with “charger current based on export”.
What matters is the maximum input current for load + battery charger so it doesn’t trip a fuse.
In case of export there is an excess of energy so the charger can take all it wants (up to it’s configured limit in order to not damage the battery).
The Multi itself will not limit any export current, your grid tied PV inverter should be sized so it can’t overload the circuit it is connected to.
Some PV inverters (like Fronius) can be configured to limit the export power independently from the grid frequency (since we can’t control the grid frequency), using a grid meter and/or a GX device.
Every PV inverter will start limiting when the grid frequency gets above a certain treshold but as those are heavily regulated and mandated by grid operators, there’s no way to tinker with them inside a Victron device.
Using frequency shifting to limit a PV inverter’s output only works in off grid setups, not when grid tied.
That’s interesting. We have a large inverter with surge arrestors installed, as well on as the AC incoming supply - but on the microinverters, since they operate at low voltage, I’m not aware of anything that could be installed on the DC side. Do you have any recomendations?
With the high voltage surge arrestors I wonder how effective they are in real life. They are meant to clamp dangerous voltages to earth. But that’s assuming both the earthing and cabling are low enough impedance. When they are not I can see that using the remaining lines, either AC or DC to dissipate the strike, effectivelly reducing the extend of damage, but not eliminating it.
It’s hard to win with lightning, that’s for sure. I’m also surpised the SMA blew up, because I know those toroidal transformers inside are shielded to earth between primary and secondary. Could it be that the strike came through the earth wire? That would explain how it managed to propagate.
With “charger current based on export” I would immagine the victron sees that there is a current flowing from the house to the grid and tries to charge the battery up to the maximun output of the charger. For example, if I set a maximun limit of 35A (@24V = 840W) and the export is 250W, I would expect the charger to limit charge to 10A or so, whereas if the export is 1000W, I would expect it to cap at the maximun 35A with the remaining 160W being fed into the grid. It’s not about the grid tie overloading the source, it’s prioritizing the generation to charge batteries, before exporting to the grid. At least that is how I understand most AC coupled hybrid inverters work.
This is of course different from the power assist feature, that tries to not overload the AC source and would be better utilized to prioritize battery power over utility import. Maybe the victron can’t do what I need?
I see there is an option to use an auxiliary input to determine the charger output when using VE configure. I guess that’s usefull to integrate with a meter or a current transducer, but my original expectation was that the victron would be able to do it internally.
I guess this conversation is proving really usefull. Many thanks for your support here!
