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kai avatar image
kai asked

How to deal with high grid voltage

Hi all


My installation consists of shorepower going to a Victron iso transformer then into a multiplus. I found that today the multiplus wasn't working as a charger due to high grid voltage.


I've inferred that the winding ratio is around 1.06 (which also matches a similar post of another user having issues with high voltage trip) from measurements. Assuming that the 1.06 ratio is within manufacturing tolerances (can someone from Victron confirm?), what can be done to deal with high grid voltages in Australia.


In aus, the 230v nominal can swing up to +10% and comply with standards (so, 253v is permissible, and was what I measured today from the grid). When this happens, the iso output is at 253*1.06 = 268-269v. The multiplus charger subsystem does not turn on, I believe due to the AC high connect limit of 265v. The inverter subsystem appears to work fine off the battery, and I can talk to the multiplus through VEC3.


If I lift the AC high connect to 270v (assuming VEC3 lets me....) there will be no hysteresis for the AC high trip. I could also try to lift the AC high disconnect to 275v (again, if VEC3 lets me) but I don't know what internal margins are there in the multiplus before magic smoke comes out due to component overvoltage. Can Victron or someone whose been through this advise?


Specifically, while AS limits the positive swing to +10%, it is quite possible for the localised voltage to swing even higher due to local influences (including ppl feeding to grid...) I would like the configuration to be robust against these scenarios - the charger doesn't need to function if the swing is > +10% but the AC-in should be disconnected before internal damage occurs.


Thanks

Kai



Isolation Tranformer
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5 Answers
kai avatar image
kai answered ·

Updating for future reference:

I'm going with a portable stepdown unit (so I can remove and pack away as required) just before the shorepower input. There is at least one vendor in Australia that provides such a 240-220v stepdown (please don't get the variac units, they're the wrong choice for this problem).

240-220v seems to be a common need for some voltage sensitive / overseas equipment so there's a market to make these things. If you wanted to roll your own, look at the "buck transformer" topology. You don't need a full size isolated or even a conventional auto-transformer for this fix.

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tilo avatar image
tilo answered ·

Hi,

Just an idea (not tested): As you say the ratio is 1,06, then you might change the input with the output side, and thus lower the output voltage.

According to the diagram of the datasheet, there are three points to consider:

1) You would have to remove your earth of the boat from the (removable) N to Earth connection on the (official) output side and connect to the N of the other side, maybe do this outside the transformer.

2) The soft start circuit is on the official input side. Maybe you just could try without the soft start, of your shore power breaker does not trip, otherwise try to add a soft start circuit somehow (or move the internal soft start circuit to the other side). I don´t know if the internal soft start circuit on the (new) output side will affect somehow the output, in this case find a way to deactivate it.

3) If you have sometimes also low voltage shore power, you might want to keep it "reversible", which might it more difficult to implement to have an easy "switchover".

As I said, this is just a thought. Maybe somebody else can comment if that might work or not (hopefully with explanations).


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boekel avatar image
boekel answered ·

If it's always on the high side it might be an idea to use the IT in reverse...

I haven't dealt much with Victron IT's, but I know others often have multiple in/outputs for + or - 5% to adjust to local voltage.

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kai avatar image kai ♦ commented ·

re: voltage taps on the victron IT that I have, the only access is to the two windings on primary & secondary (configure in series/parallel to suit 240/120v). No taps available for local adjustments unfortunately.


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kai avatar image
kai answered ·

Thanks tilo & Boekel


Its a brand new transformer, I'd rather not use it outside of intended use and void warranty; and inserting 240V circuit elements (e.g. making a softstart cct) without suitable certification can present as legal & insurance issue here in australia.


Re: using the transformer in reverse, as tilo alluded to there is more to the transformer than just the windings. The number of components on the circuit board indicates there may be some self test and protection functions in addition to the soft start circuit.


I think unless Victron says the 1.06 is outside of tolerances, the solution has to rest with the multiplus configuration. I did find a note that the AC high trigger has a max range of 270v. So a temporary workaround might be to set trigger to 270v.


This workaround would have the issue of no hysteresis and operating above the nominal max of 265v without official confirmation from Victron. Would still like a Victron tick of approval or at least experience from someone who has configured it this way and has a substantial up-time after the mod.


Cheers


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tilo avatar image
tilo answered ·

If you think your IT might be a case for warranty, contact your dealer.

Here some tips for workarounds in the meantime (which shouldn´t cause warranty or insurance issues):

VEC3 will not let you raise the high voltage disconnect above 270V, those 270V are the limit. And the (re)connect high voltage limit can only be raised to 269V, that leaves you with 1V of hysteresis. This 1V sounds little, but if you really have consumption, for example to charge the batteries, then this consumption will produce a voltage drop, and thus has the effect of an additional hysteresis. The higher your consumption, the more "stable" it will be.

If your system doesn´t connect because you have the high voltage, you might connect a big consumer (water or air heater) before the Multiplus to lower the voltage below the 265V (or 269V), till the Multiplus starts consuming and thus lowers the incoming voltage itself, and then you can remove your "starter" consumption. You also can leave the additional consumer there if you need it, or if you don´t mind that it increases your electricity bill but stabilizes your system at this moment.

Additionally you can use a longer shore power cable with a low cross section to keep the incoming voltage a little lower once there is a current flow (with your "starter" consumer). But beware, don´t leave the "surplus" cable on a roll, because it can get hot and melt (as it happens with any power cable extension left on the roll). And use cables only up to their maximum current specification.


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kai avatar image kai ♦ commented ·

Thanks tilo, good info on workarounds while I look for a permanent solution.

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