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Weird idle readings in my new system


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Hi and thanks for letting me join in.

I just finished last week installing th following system:

- 16 x 310Wp solar panels, in 2 channels of 8 ea.

- 7.2 kW Axpert MAX inverter (hybrid)

- 2 x 3.2 kWh Pylontech US3000

This on top of a one-phase 220V/50Hz grid (utility) installation (Chile).

I have a lot of issues!

1. In SUB priority the inverter never quite shuts down the grid. Even when there is enough solar power, it draws about 0.5kW from grid (utility). If I switch to SBU priority it then draws properly. This even if for both modes I just disconnect the battery to take it out of the equation.

2. I'm disappointed of the idle draw power of the inverter. I test the power with 2 efergy sensors, one before the grid (utility) input at the inverter, and another at the output. There are situations where if I'm drawing 2kW at the house, the inverter is consuming 3 - 3.5! It doesn't make any sense.

3. If I install the Pylontech batteries using the default settings on the Inverter (of course, setting the battery mode to PYLON), it drains them too low. The default is set at 46V to go back to utility, and this means that at night the BMS has to use grid to charge the batteries a bit, I get grid spikes of 3-4kW for about 10 minutes (maybe the batteries asks for an emergency charge?).

Anyone with similar issues? The information on how the inverter works is not very big...

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Welcome.

Yes we've had similar problems. Coloumb is the guru here so can correct me where I'm wrong.

The Max is designed as an off grid inverter rather than a true hybrid so it prefers to power it's electronics from the grid rather than from solar even when solar is available whilst in SUB. This is the constant 50W load.

On point 2 I'm not sure exactly what's happening to your load. One thing to be careful about is if your load is not purely resistive i.e. you are running motors you should really be comparing your kVA in and out not kW.

I'm not a fan of the direct connection between the inverter and lithoum batteries. The settings are set up such that you see best power supply from the battery but this drives them hard. I prefer to use an external monitor such as ICC or Solar Assistant that can more accurately be set to control the behavior of the inverter. The spike you see at night is yes the battery being topped up. My suggestion, and it depends on your load and usage, is to actually use the batteries at night so that you get maximum charging possible from your panels during the day. If your load is close to your generation during the day don't push this. Plus weather and utility reliability will also affect this. Again ICC or Solar Assistant can help manage how low you discharge the batteries and at what time.

Edited by Shadders
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Thanks a lot! Guess for now I'll set the back to grid to 47 or 48, even if that doesn't translate well to %, and start working on a ICC update with a PI.

Funny how this world is. I'm thinking on the wasted energy and equipment going to hell due to companies doing installations and users not getting involved in the tuning of the system. I thought this was going to be a a set it and forget it thing. Well, at least there's nice support thanks to you guys! Plus it's entertaining...

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5 hours ago, Shadders said:

On point 2 I'm not sure exactly what's happening to your load. One thing to be careful about is if your load is not purely resistive i.e. you are running motors you should really be comparing your kVA in and out not kW.

Here's an example. I'm more and more thinking that a clamp current sensor is not good in this case. Looks like the Inverter phase is not near enough 1 so it's as you say, kW doesn't translate well. Because it doesn't make absolutely no sense... (Device is just another clamp for a heat pump water heater I installed and wanted to check performance. Totally recommended!).

Screenshot from 2021-04-22 20-57-49.png

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On 2021/04/23 at 3:35 AM, geprieto said:

1. In SUB priority the inverter never quite shuts down the grid. Even when there is enough solar power, it draws about 0.5kW from grid (utility).

I think you'll find it's about 0.5 kVA, but nearly zero real power. The output filter of the inverter is an LC network, with the C across the utility in SUB mode. So there will be considerable apparent power, but little real power. So nothing to worry about, it doesn't cost you anything to have power shuttling to and from the capacitor.

Quote

2. I'm disappointed of the idle draw power of the inverter. I test the power with 2 efergy sensors, one before the grid (utility) input at the inverter, and another at the output. There are situations where if I'm drawing 2kW at the house, the inverter is consuming 3 - 3.5!

Some of that would be reactive power to the capacitor as above, but that's too much of a difference. I'd say it must be charging the battery with the difference. Check settings.

Quote

3. If I install the Pylontech batteries using the default settings on the Inverter (of course, setting the battery mode to PYLON), it drains them too low. The default is set at 46V to go back to utility, and this means that at night the BMS has to use grid to charge the batteries a bit, I get grid spikes of 3-4kW for about 10 minutes (maybe the batteries asks for an emergency charge?).

Any utility charging should be limited by the maximum utility charge current setting (setting 11).

I believe that the Pylontech or other BMS will not override the back to utility voltage setting (setting 12). You should change that to your liking, or have ICC or other monitoring software control the switch to utility power. But I'm no expert on SUB mode.

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14 hours ago, Coulomb said:

I think you'll find it's about 0.5 kVA, but nearly zero real power. The output filter of the inverter is an LC network, with the C across the utility in SUB mode. So there will be considerable apparent power, but little real power. So nothing to worry about, it doesn't cost you anything to have power shuttling to and from the capacitor.

Some of that would be reactive power to the capacitor as above, but that's too much of a difference. I'd say it must be charging the battery with the difference. Check settings.

Now that I'm reading it with Solar Assistant I get more reasonable readings. The Efergy sensors seem like the culprit here, and they were not exactly designed for this anyway. Thanks for all the clarifications!!!!

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16 hours ago, geprieto said:

Now that I'm reading it with Solar Assistant I get more reasonable readings.

The Axpert inverters actually go to the trouble of calculating real power (the average of instantaneous voltage times instantaneous current, or similar). For a purely reactive (capacitive or inductive) load, this will be zero, but something like the Efergy units will merely report the product of voltage and current, ignoring phase (i.e. apparent power, in Volt·Amps).

Edited by Coulomb
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