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!?: Charge a “Slave” solar system from a “Master” solar system, how to do grounding/bonding!?


Azz

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Hi,

Sorry for my English, I am from Sweden living in Tenerife, Canary islands.

I am a newbie here and grateful to have found lots of relevant information as well as patched firmwares to my inverters!!!

It feels like a well working & sharing community!

 

We have a farm here with several cottages with tenants.

 

We have two separate off-grid solar systems providing power.

One “Master” with:

2 x Axpert 48v, pf 1.0, connected in parallel (patched fw72.20e)

1 x Genergy 6 kW generator (autostart)

24 x AmeriSolar 275w panels

24 x 2v Cynetic batteries (750Ah)

1 x Victron BMV 702

1 x Raspberry Pi with ICC

 

One “Slave” with:

1 x Axpert 48v, pf 0.8 (patched fw73.00e)

9 x AmeriSolar 340w panels

8 x 6v Trojan T105 batteries ( 250Ah)

1 x Victron BMV 702

1 x Raspberry Pi with ICC

 

Lately the “Slave” hasn’t been able to provide enough power during cloudy days and my plan is to connect the “Master” and “Slave” together to be able to charge the “Slave” from the “Master”. “Master” acting like a grid-provider ;-). Occasionally the Generator will be kicking in to provide extra power needed.

 

Now to the challenging question:

How should the grounding/bonding be made to keep all the inverters & generator “happy”?

 

Thanks for your input in advance!

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3 hours ago, Azz said:

How should the grounding/bonding be made

Welcome to the forum.

It depends on your Axpert PF0.8; did it come with 73.00 from the factory, or with an earlier version?

That decides whether or not there is a relay that shorts neutral to ground.

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10 hours ago, Azz said:

No, it is an older one!

Ok. What I do with mine is, I connect neutral out to neutral in. Neutral in should be earthed back at your switchboard (depending on your country's earthing system), so then your neutral out is earthed at all times.

That does bypass one half of the "safety relay" (both live and neutral are switched between AC-in and AC-out), but I see no need to switch a neutral ever. It's been working fine since 2016.

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Correction:

Everything works perfectly except for when both the Master system inverter and the Slave system inverter are in utility mode and at the same time needs charging from the Generator.

Generator is connected to AC-In on Master system inverter, Slave system inverter is connected to AC-Out on Master system inverter.

Then following occurs:

either
When generator start the initial “negotiation” of power it doesn’t stop (fluctuates between 200 - 270 volts) until one of the Master system inverters shuts off with an ICC mail alert “Fault : Inverter negative power” (I believe it is fault Code 60 - Current feedback into the inverter is detected).
Typically it happens on the slave (2) inverter and the master (1) is still on.

or
The initial “negotiation” of power succeeds but the voltage stabilises at high 270 volts (still 50Hz).

 

In both cases the voltage between ground and neutral is at more or less zero volts (between 0.02 - 0.12 volts).

I have checked & refitted the parallel cables between the Master systems inverters.

It feels like the Master system inverter and the Slave system inverter are competing for the power ;-).

Any ideas!?

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11 hours ago, Azz said:

When generator start the initial “negotiation” of power it doesn’t stop (fluctuates between 200 - 270 volts)

That sounds like either your generator can't handle the load (I think Voltronics recommends a generator rating at least 50% higher than the expected load, though I can't quickly find that figure now), or more likely, it's an unfortunate timing issue between the speed with which the AC-in charging power ramps up, and the speed at which the generator's automatic throttle and/or automatic voltage control works.

I can't imagine why your generator is ever settling at 270 VAC, for example. Maybe the generator control mechanism could use a service, or at least a few squirts of oil from a spray can?

It might help to have a moderate (very roughly 200 W) load that you can switch temporarily across the generator, so that the minimum required power isn't ever zero. Then when it's all settled down, disconnect that temporary load.

11 hours ago, Azz said:

It feels like the Master system inverter and the Slave system inverter are competing for the power ;-).

They are, in a way, since the power that the generator can stably produce is limited.

Another thing to try, though I understand you don't want to leave it that way, is to connect the slave system's inverter's AC-in directly to the generator. If that works, maybe have a big changeover switch that allows you to choose between generator directly, and via the master system's inverters.

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Thanks for reply and your time,
it is not a load issue since I get the same result when setting the inverters to 5 amp charge each and the 7 kW generator have no issues to charge the batteries at 60 amp normally with about 3 kW in household load at the same time.
The generator works perfectly when charging the systems individually, but normal days there is no need for generator power at all. The Masters battery bank just charges the Slaves battery bank.
The stragen 270 volt issue only occurs when the Master and the Slave systems inverters are eager to get charge at the same time (in Utility mode when battery banks are lower than 55% SOC). It can charge Master inverter battery bank while the Slave system inverter is connected to the Master as long as the Slave system inverter isn't in Utility mode.

I will probably install a dry-contact controlled relay/contactor that disconnects the Master to Slave system connection while the generator is charging and reconnects it when it isn't.
That way it will be a more automated solution where the generator only charges the Master system (when needed) and the Master system charges the Slave system (when needed).

 

 

Edited by Azz
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