Testing grid-tied inverter with battery

Jordi

Solar Enthusiast
Joined
Oct 13, 2020
Messages
193
I have just received a 600W MPPT grid-tied inverter from Aliexpress [22-60VDC, 220V AC] (see link) and I would like to test it without solar panels.

In order to do that I have thought of using a 8S 2P 18650 battery in combination with a DC-DC buck [Input: 8-36V ; Output: 1,25-32V] with current regulation (max. 5 A) (see link).

1638527965407.jpeg

The battery could be connected directly into the inverter, but this would inquire the max. load 600W at which the cells would most likely be unable to deliver (insufficient voltage) and If possible, the current through the cells would be so high that they would overheat and easily get damaged. My expectation is that the buck current regulation is the same as a limit and therefore the cells never operate at more than 1C, doable for 18650.

In between the buck and the grid tied inverter I will place a wattmeter [working voltage: 0-60V] (see link) to monitor the discharge and know how far I can go with the test given that the battery will have no BMS. To mitigate battery damage I will use cells from the same batch all top charged recently to full capacity; meaning at 1 single discharge voltage differences should not be too big.

I wonder only what the MPPT function can do to the buck converter or else, what the buck can do to the MPPT function of the inverter. I would like to run this test for at 50% of the battery capacity.

Hope you enjoy this explanation and please point me red flags If you see something wrong.
 

Jordi

Solar Enthusiast
Joined
Oct 13, 2020
Messages
193
I could not perform the test; the brand new DC-DC buck converter from Aliexpress acts weird. It only allows voltage regulation when no load is attached to it. As soon as a load is connected; this shows signs to receive some little current but then the voltage gets crazy and starts fluctuating all over the output range. Regulating current does nothing to this, for which I think I am not really regulating anything.

The wattmeter LED screen (1W) blinks a few seconds and does not turn on.
The 12V LED bulb (5W) that I easy regulate with another USB voltage regulator barely turns on.

As I have seen in other youtube videos, I could just connect the battery directly into the inverter. I would not mind doing that for a few minutes If it wasn't for the size of the battery. 600W from 8S2P 18650 is like 10Amps current from each cell. I think that is too much; 5Amp would have been acceptable. Maybe I could try 20 seconds....?
 

kundip

New Member
Joined
Jun 27, 2021
Messages
10
I have just received a 600W MPPT grid-tied inverter from Aliexpress [22-60VDC, 220V AC] (see link) and I would like to test it without solar panels.

In order to do that I have thought of using a 8S 2P 18650 battery in combination with a DC-DC buck [Input: 8-36V ; Output: 1,25-32V] with current regulation (max. 5 A) (see link).

View attachment 74285

The battery could be connected directly into the inverter, but this would inquire the max. load 600W at which the cells would most likely be unable to deliver (insufficient voltage) and If possible, the current through the cells would be so high that they would overheat and easily get damaged. My expectation is that the buck current regulation is the same as a limit and therefore the cells never operate at more than 1C, doable for 18650.

In between the buck and the grid tied inverter I will place a wattmeter [working voltage: 0-60V] (see link) to monitor the discharge and know how far I can go with the test given that the battery will have no BMS. To mitigate battery damage I will use cells from the same batch all top charged recently to full capacity; meaning at 1 single discharge voltage differences should not be too big.

I wonder only what the MPPT function can do to the buck converter or else, what the buck can do to the MPPT function of the inverter. I would like to run this test for at 50% of the battery capacity.

Hope you enjoy this explanation and please point me red flags If you see something wrong.
According to
I have just received a 600W MPPT grid-tied inverter from Aliexpress [22-60VDC, 220V AC] (see link) and I would like to test it without solar panels.

In order to do that I have thought of using a 8S 2P 18650 battery in combination with a DC-DC buck [Input: 8-36V ; Output: 1,25-32V] with current regulation (max. 5 A) (see link).

View attachment 74285

The battery could be connected directly into the inverter, but this would inquire the max. load 600W at which the cells would most likely be unable to deliver (insufficient voltage) and If possible, the current through the cells would be so high that they would overheat and easily get damaged. My expectation is that the buck current regulation is the same as a limit and therefore the cells never operate at more than 1C, doable for 18650.

In between the buck and the grid tied inverter I will place a wattmeter [working voltage: 0-60V] (see link) to monitor the discharge and know how far I can go with the test given that the battery will have no BMS. To mitigate battery damage I will use cells from the same batch all top charged recently to full capacity; meaning at 1 single discharge voltage differences should not be too big.

I wonder only what the MPPT function can do to the buck converter or else, what the buck can do to the MPPT function of the inverter. I would like to run this test for at 50% of the battery capacity.

Hope you enjoy this explanation and please point me red flags If you see something wrong.
I have an Enphase M215-60-230-S22 inverter.
Recommended maximum input power W 310 MPPT voltage range V 27-39 Operating range V 16-48
Looking at Doctorbass on Youtube Watch?v=GxSafeeUWB4&t=525s
The battery input voltage has to be above the maximum MPPT voltage (39 Volts).
...But below the maximum operating range (48 Volts). So I am thinking say 42 volts.
This switches off the MPPT which Doctorbass says causes problems for this use.
Others in this forum have these Enphase inverters running at 52 Volts.
I am thinking the Inverter you have may have similar characteristics.
 

Jordi

Solar Enthusiast
Joined
Oct 13, 2020
Messages
193
I very much think you are right. MPPT range is smaller than VDC range and so you can feed the inverter with the MPPT function off. The small C-DC buck I have or the new one does not reach such voltage, so I guess the test will happen in the MPPT range instead. I will try.
 
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